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Phosphorus Requirement of St. Augustinegrass

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Title:
Phosphorus Requirement of St. Augustinegrass
Creator:
LIU, MIN
Copyright Date:
2008

Subjects

Subjects / Keywords:
Fertilizers ( jstor )
Greenhouses ( jstor )
Leaching ( jstor )
Oxides ( jstor )
Phosphorus ( jstor )
Plants ( jstor )
Soil samples ( jstor )
Soil science ( jstor )
Soils ( jstor )
Turf grasses ( jstor )
City of Madison ( local )

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Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright Min Liu. Permission granted to University of Florida to digitize and display this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Embargo Date:
7/12/2007
Resource Identifier:
660034152 ( OCLC )

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Full Text





PHOSPHORUS REQUIREMENT OF ST. AUGUSTINEGRASS


By

MIN LIU


















A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2007





























2007 Min Liu

































To my wife Ma, Kehong, my father, Liu, Dinghong and my mother, He, Wanmei









ACKNOWLEDGMENTS

I give my sincere thanks and appreciation to the chair of my supervisory committee, Dr.

Jerry Sartain. It is his continuous support, guidance, and encouragement that made this degree

possible. I would also like to thank the other committee members: Dr. Laurie Trenholm for her

expertise in turfgrass, Dr. Grady Miller for his knowledge of turfgrass research methodology, Dr.

Peter Nkedi-Kizza for his suggestion for the leaching data analysis, Dr. Willie Harris for his

knowledge in soil mineralogy, Dr. Rongling Wu for his guidance in Statistics.

Thanks go to the Florida Department of Environment Protection who sponsored this

research project. Special thanks go to lab personnel, Ed Hopwood Jr., Nahid Varshovi, Martin

Sandquist, who helped me throughout my research. Specially, I would like to thank my dear wife,

Kehong Ma, our incoming baby, both sets of parents and family members for their ongoing

support.









TABLE OF CONTENTS

page

A CK N O W LED G M EN T S ................................................................. ........... ............. .....

LIST OF TA BLES ............... ........................................................... 7

LIST OF FIGURES .................................. .. ..... ..... ................. .8

A B S T R A C T ............ ................... ............................................................ 1 1

CHAPTER

1 INTRODUCTION ............... ................. ........... .............................. 13

2 L IT E R A TU R E R E V IE W ........................................................................ .. ....................... 15

Phosphorus in the Soil-Plant Environm ent.................................... .......................... ......... 15
Phosphorus R actions in Soil ................................................ .............................. 15
O rg anic Soil P ............................................................................ 16
Leached P in Turfgrass Environm ent........................................................... ... .......... 17
M management Practices to Reduce P Leaching ....................................... ............... 18
Conventional Soil and Tissue P Tests ............................................................................. 19
Soil P Extractants ............... ... .... .................................................19
Suitability of Different Extracting Procedures..... .......... .......................................20
Soil P Extracting Procedures and Geographical Regions............................. .............21
T issue e P test ................................................................... ......... .............. 22
Response of Turfgrass to P Fertilizers and Fertilizer Recommendations..............................22
P hosphoru s T oxicity T rial ....................................................................... ..................22
Phosphorus Requirem ents by Turfgrasses.................................... ....................... 23
Critical M minimum Soil P Concentrations ............................................. ............... 25
Effects of P Application on Soil Test P Levels .................................... ............... 27
Critical Tissue P Concentrations .............................................................................. 28
Interaction w ith other N utrients....... ......................................................... ............... 30
Phosphorus and N .......... ........................................ .. .............. ........ 30
Phosphorus and K C a and M g .......................................................................... .... ...31
Phosphorus and Zn .................. .......... ... ............ ............ ... .......... 32
Effect of N, P, K, and their Interactions on Water Use Efficiency...............................32

3 M A TER IA L S A N D M ETH O D S ........................................ .............................................37

G lasshouse H ydroponic Study........ ......... ......... .......... ........................ ................ 37
G lasshouse Soil Study 1 .......................... ......... .. .. .. ...... .. ............39
Glasshouse Soil Study 2 .................................. .. .. ........ .. ............40
G lasshouse Soil Study 3 .......................... ......... .. .. .. ...... .. ............42









4 RESULTS AND D ISCU SSION .................................................. ............................... 46

G lasshouse H ydroponic Study....... ................ ........................................... ...............46
T u rf Q u a lity .......................................................................................................4 6
Tissue P and Root P............................................ ......... .............. .. 46
Tissue Growth Rate and Root Growth Rate ...........................................................47
Critical Tissue P level ........... ...... .... ........ .. ................ ..... ...... 48
Glasshouse Soil Study 1 ................................... .. .. ........ .. ............49
T u rf Q u a lity .......................................................................................................4 9
T op G row th R ate ....................................................... 49
Tissue P Concentration.......................................... 50
The Critical Minimum Tissue P concentration ........................................ .....51
Soil T est P ............... ................ ... ....... ........ ......................51
The Critical Minimum Soil Test P Concentrations ................................... ....52
P Downward M movement ......... .. ............................................. .......... .... 53
Leached P M ass and Concentration ................................................. .... .. ... 54
G lasshouse Soil Study 2 ................................................................... 55
Turf Quality ................................................................ 55
T op G row th R ate .............................................................................................. 55
T issue P C oncentration............................................... ............... ...... ............... 56
The Critical Minimum Tissue P concentration ........................................ .....57
Soil P Tests ........................ ................... .................... ...... ..... .. ... 57
The Critical Minimum Soil Test P Concentrations ................................... ....58
P Downward M movement ......... .. ............................................. .......... ... 59
Leached P M ass and Concentration ................................................. .... .. ... 60
G lasshouse Soil Study 3 ................................................................... 6 1
T u rf Q u a lity .......................................................................................................6 1
T op G row th R ate ....................................................... 62
Tissue P Concentration........................................ 62
Critical Minimum Tissue P Concentration ...................... ............ ....... 63
Soil P Tests ......... .... ............. ......... .. ...... .......................63
The Critical Minimum Mehlich-1 P Concentration ...................................... 65
P D ow nw ard M ovem ent........................................... .......................... ............... 65
L reached P M ass and C concentration ........................................ ........... ...............66

5 CONCLUSIONS ...................... ......... .. ... ... ................. 108

G lasshouse H ydroponic Study ........ .. ........ .. ........ .. ............ .... ............ .. 108
Turf Quality in Glasshouse Soil Studies.............................................................. 108
Top Growth Rate in Glasshouse Soil Studies.............................................. 10
Tissue P Concentration and Critical Tissue P Concentration ..................... .............. 109
Soil P Tests and Critical Soil Test P Concentrations......... ............................................ 109
P Downward M movement and Leached P ......... ........................................................... 110

L IST O F R E FE R E N C E S ......... ......... ............................................................................. 111

B IO G R A PH IC A L SK E T C H ....................................................................................................... 120



6










LIST OF TABLES


Table page

2-1 Common soil test extractants used for available P. ........................................ ................35

2-2 Critical P concentration in some subtropical and tropical grasses (Kamprath and
W atson 19 80) ................................36............................

3-1 Selected chemical properties used in the glasshouse soil study 1, 2, and 3.....................45

4-1 Visual quality rating of St. Augustinegrass as influenced by P application rate in
2005-2006 glasshouse soil study 1.................... ........ .. .................................... 73

4-2 Top growth rate of St. Augustinegrass as influenced by P application rate in 2005-
2006 glasshou se soil study 1.......................................................... .............................. 74

4-3 Tissue P concentration of St. Augustinegrass as influenced by P application rate in
2005-2006 glasshouse soil study 1........................................... ............................. 74

4-4 Visual quality rating of St. Augustinegrass as influenced by P application rate in
2005-2006 glasshouse soil study 2............................................... ............... 84

4-5 Top growth rate of St. Augustinegrass as influenced by P application rate and soils in
2005-2006 glasshouse soil study 2............................................... ............... 85

4-6 Tissue P concentration of St. Augustinegrass as influenced by P application rate and
soils in 2005-2006 glasshouse soil study 2. ........................................... ............... 85

4-7 Visual quality rating of St. Augustinegrass as influenced by P application rate in
2005-2006 glasshouse soil study 3.................................. ......................................99

4-8 Top growth rate of St. Augustinegrass as influenced by P application rate in 2005-
2006 glasshou se soil study 3...................................................................... .................. 99

4-9 Tissue P concentration of St. Augustinegrass as influenced by P application rate in
2005-2006 glasshouse soil study 3.............................................................................. 100









LIST OF FIGURES


Figure page

2 -1 T h e P cy cle in so il........................................................................................................ 3 4

3-1 Glasshouse solution culture P study layout. ........................................... ............... 44

3-2 G lasshouse soil P study 1 layout................. ..................... ................... ............... 44

4-1 Turf quality response to solution P concentration. Turf quality is the mean of five
replications over time after treatments were applied. Means marked by the same
letter are not significantly differently at P = 0.05 according to Duncan's Multiple
R ange T est. ............................................................................... 68

4-2 Tissue P response to solution P concentration and time ..................................................68

4-3 Relationship of solution P and tissue P concentration on day 148. Means marked by
the same letter are not significantly differently at P = 0.05 according to Duncan's
Multiple Range Test .................... ........ ......... ............ 69

4-4 Relationship of solution P and root P concentration on day 148. Means marked by
the same letter are not significantly differently at P = 0.05 according to Duncan's
M multiple Range Test ........ .... ........ ........ ....... .... .... .. .... ............ 69

4-5 St. Augustinegrass tissue growth rate relative to solution P concentration .....................70

4-6 Root growth rate relative to solution P concentration. Means marked by the same
letter are not significantly differently at P = 0.05 according to Duncan's Multiple
R ange T est. ............................................................................... 7 1

4-7 St. Augustinegrass tissue growth rate relative to tissue P concentration.........................72

4-8 St. Augustinegrass tissue growth rate relative to tissue P concentration in the
glasshouse soil study 1.................................... .. .. .. ...... .. ............75

4-9 Soil Mehlich-1 P, Fe Oxide P, and WEP concentration as influenced by P application
rate (soil sampling depth of 0-2 cm) in the glasshouse soil study 1. ................................76

4-10 Relationships among Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils
sampling depth of 0-2 cm) in the glasshouse soil study 1. .........................................77

4-11 Relationships between tissue P concentration and Mehlich-1 P, Fe Oxide P, and
WEP concentrations (soils sampling depth of 0-2 cm) in the glasshouse soil study 1......78

4-12 St. Augustinegrass tissue growth rate relative to soil Mehlich-1 P concentration in
the glasshouse soil study 1............... ..... .... ....................... .. ......79









4-13 St. Augustinegrass tissue growth rate relative to soil Fe Oxide P concentration in the
glasshouse soil study 1............ .......................................... ..... ........ 80

4-14 St. Augustinegrass tissue growth rate relative to soil WEP concentration in the
glasshouse soil study 1............ .......................................... ..... ........ 81

4-15 Soil Mehlich-1 P concentration as influenced by P application rate and soil sampling
depth in the glasshouse soil study 1..............................................................................82

4-16 Leached SRP mass as influenced by P application rate and leaching event in
glasshouse soil study 1............ .......................................... ..... ........ 82

4-17 Leached SRP concentration as influenced by P application rate and leaching event in
glasshouse soil study 1............ .......................................... ..... ........ 83

4-18 St. Augustinegrass tissue growth rate relative to tissue P concentration in the
glasshouse soil study 2 ..................................... ................... ....... ........ ..... 86

4-19 Soil Mehlich-1 P, FeO P, and WEP concentration as influenced by P application rate
(soil sampling depth of 0-2 cm) in the glasshouse soil study 2 (soil No. 2)....................87

4-20 Soil Mehlich-1 P, FeO P, and WEP concentration as influenced by P application rate
(soil sampling depth of 0-2 cm) in the glasshouse soil study 2 (soil No. 3)....................87

4-21 Relationships among Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils
sampling depth of 0-2 cm) in the glasshouse soil study 2 (soil No. 2). ............................88

4-22 Relationships among Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils
sampling depth of 0-2 cm) in the glasshouse soil study 2 (soil No. 3). ............................89

4-23 Relationships between tissue P concentration and Mehlich-1 P, Fe Oxide P, and
WEP concentrations (soils sampling depth of 0-2 cm) in the glasshouse soil study 2
(soil N o 2). ............................................................................... 90

4-24 Relationships between tissue P concentration and Mehlich-1 P, Fe Oxide P, and
WEP concentrations (soils sampling depth of 0-2 cm) in the glasshouse soil study 2
(soil N o 3). ................................................................................ 9 1

4-25 St. Augustinegrass tissue growth rate relative to soil Mehlich-1 P concentration in
the glasshouse soil study 2 (soil N o. 2)...................................... ........................... 92

4-26 St. Augustinegrass tissue growth rate relative to soil Mehlich-1 P concentration in
the glasshouse soil study 2 (soil N o. 3)...................................... ........................... 93

4-27 St. Augustinegrass tissue growth rate relative to soil Fe Oxide P concentration in the
glasshouse soil study 2 (soil N o.2). ............................................................................. 94









4-28 St. Augustinegrass tissue growth rate relative to soil WEP concentration in the
glasshouse soil study 2 (soil N o.2). ............................................................................. 95

4-29 Soil Mehlich-1 P concentration as influenced by P application rate and soil sampling
depth in the glasshouse study 2 (soil No. 2). ........................................ ............... 96

4-30 Soil Mehlich-1 P concentration as influenced by P application rate and soil sampling
depth in the glasshouse study 2 (soil No. 3). ........................................ ............... 96

4-31 Leached SRP mass as influenced by P application rate and leaching event in
glasshouse soil study 2 (soil N o.2). ............................................................................. 97

4-32 Leached SRP concentration as influenced by P application rate and leaching event in
glasshouse soil study 2 (soil N o.2). ............................................................................. 97

4-33 Leached SRP mass as influenced by P application rate and leaching event in
glasshouse soil study 2 (soil N o.3). ............................................................................. 98

4-34 Leached SRP concentration as influenced by P application rate and leaching event in
glasshouse soil study 2 (soil N o.3). ............................................................................. 98

4-35 St. Augustinegrass tissue growth rate relative to tissue P concentration in the
glass ou se soil stu dy 3 ...................................................................... ... .... ......... 10 1

4-36 Soil Mehlich-1 P, FeO P, and WEP concentration as influenced by P application rate
(soil sampling depth of 0-2 cm) in the glasshouse soil study 3. Within columns for
each soil, means followed by the same letter are not significantly different according
to D uncan's m multiple range test (0.05)....................................... .......................... 102

4-37 Relationships among Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils
sampling depth of 0-2 cm) in the glasshouse soil study 3...........................................103

4-38 Relationships between tissue P concentration and Mehlich-1 P, Fe Oxide P, and
WEP concentrations (soils sampling depth of 0-2 cm) in the glasshouse soil study 3...104

4-39 St. Augustinegrass tissue growth rate relative to soil Mehlich-1 P concentration in
the glasshou se soil study 3 ............................................................................... .... .......105

4-40 Soil Mehlich-1 P concentration as influenced by P application rate and soil sampling
depth in the glasshouse soil study 3.............................................................................106

4-41 Leached SRP mass as influenced by P application rate and leaching event in the
glasshouse soil study 3 .......... .. .................................. ....... ...... .. ....... .... 107

4-42 Leached SRP concentration as influenced by P application rate and leaching event in
the glasshouse soil study 3 ............................................. ...................................... 107









Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

PHOSPHORUS REQUIREMENT OF ST. AUGUSTINEGRASS

By

Min Liu

May 2007

Chair: Jerry B. Sartain
Major: Soil and Water Science

St. Augustinegrass [Stenotaphrum secondatum (Walt.) Kuntze] is widely used for Florida

lawn grass. At present phosphorus (P) fertilization of Florida lawn grasses is based on soil tests

which were designed for agronomic crops in a production culture. Little information exits

relative to the exact P requirement of St. Augustinegrass. The objective of this research was to

determine the critical P requirement of St. Augustinegrass. Four individual studies were

conducted in a glasshouse including one solution culture study and three soil studies. Data

collected in the solution culture study included visual quality rating, top growth rate, tissue P

concentration. From the solution culture study, the critical solution P concentration and critical

minimum tissue P concentration were determined to be 111 ppb and 1.6 g kg-1, respectively.

Data collected in soil studies included visual quality rating, top growth rate, tissue P

concentration, soil test P concentrations, and leachate volume and soluble reactive P

concentration. From the soil studies, the minimum P application rate to achieve the maximum

growth rate was 0.31 g P205 m-2 4-wk-1; the critical minimum tissue P concentration were

determined to be 1.8 g kg-1. Mehlich-1 P, Fe Oxide Strip P, and WEP were highly correlated to

each other and they were also highly correlated to tissue P concentration and top growth rate.

Mehlich-1 was the best soil P extractant for St. Augustinegrass. The critical soil Mehlich-1 P









levels were in the range from 5 to 9 mg kg-1 depending on soil properties. Most of the applied

concentrated superphosphate did not leach below the top 2 cm of soil. Approximately 1% of P

applied leached in the 10 cm of soil profile. Larger quantity and higher concentration of P

leached in the first leaching event. Application of 0.31 g P205 m-2 4-wk-1 did not result in either a

larger leached P quantity or a higher concentration. Based upon these research findings, 0.31 g

P205 m-2 4-wk-1 is recommended for St. Augustinegrass only if the soil Melich-1 P concentration

is below 10 mg kg-1. Otherwise, no P application would be recommended. Multiple applications

with small quantity each time is suggested and do not apply P fertilizer before a rain event.









CHAPTER 1
INTRODUCTION

In the recent past, more attention has been directed towards phosphorus (P) fertilization of

Florida lawn grasses, because P is recognized as an element of impairment of water bodies and

streams, which is called eutrophicaiton. Eutrophication of surface waters, the proliferation of

aquatic plants, is caused by a surplus of available nutrients (such as P and N). Eutrophication can

cause a decrease in dissolved oxygen in waterways, a situation that can kill fish. Compared with

the other major nutrients, phosphorus (P) is by far the least mobile and available to plants in most

soil conditions. The poor mobility of soil inorganic phosphorus is due to the strong reactivity of

phosphate ions relative to numerous soil components and to the consequent strong retention of

most soil phosphorus onto those components. However, a typical Florida soil is sandy and acidic,

and the potential for P leaching exists. Ballard and Fiskell (1974) reported that most of the sandy

soils of the Southeastern Coastal Plains have a very small retention capacity for water soluble P

against leaching, but that the surface horizons of Spodosols had the lowest retention capacities.

In a lysimeter study, Neller (1946) reported that in 4 months 72.4 cm of rainfall leached more

than 70% of applied superphosphate-P from the surface of 20 cm of a Leon fine sand. Therefore,

P applied to Florida lawn grasses have potential to cause eutrophication if not managed properly.

At present P fertilization of Florida lawn grasses is based on soil tests with were basically

designed for agronomic crops in a production culture. Little information exists relative to the

exact P requirement of Florida lawn grasses and fertilization levels required to produce the

required levels in the soil. The objectives for this study are to identify the critical P tissue P

concentration of the St. Augustinegrass using solution culture techniques; to determine the

minimum P fertilization level on four types of soils (three with low in Mehlich-1 P and one with

medium level of Mehlich-1 P) required to achieve the optimum growth; to select the best soil P









test procedure for recommendation on St. Augustinegrass; and to identify the critical minimum

soil test P level to achieve the optimum growth.









CHAPTER 2
LITERATURE REVIEW

Phosphorus in the Soil-Plant Environment

Phosphorus is a macro nutrient used by plant. The most essential function of P in plants is

in energy storage and transfer. Phosphorus is also an important structural component of nucleic

acids, coenzymes, nucleotides, phosphoproteins, phospholipids, and sugar phosphates. Plant

tissue P concentration ranges between 1 to 5 g kg-1. Plants absorb either H2P04- or HP042-

orthophosphate ions (Havlin et al., 1999). Phosphorus ion concentration in soil solution ranges

between 0.03 and 0.5 mg kg-1 in most soils (Ozanne, 1980; Mengel and Kirkby, 1987;

Raghothama, 1999; Frossard et al., 2000). In general, it is believed that a soil solution P

concentration of 0.2 mg kg-1 is adequate for most crops. Phosphorus exists in the soil solution

primarily in anionic forms and the distribution among various species (H3P04, H2P04-, HP042-

and P043-) in solution is governed by solution pH. In the pH domain of most soils the dominant

orthophosphate ions are H2P04- and HP042-, the latter being the major species at pH above 7.2

(Lindsay, 1979). In order to ensure adequate P availability to plants and limit the environmental

impact of P fertilization, one must thoroughly understand the P-cycle (Figure 2-1) and the

dynamics of P transformations in soils.

Phosphorus Reactions in Soil

Phosphorus ions have a strong tendency to form ion pairs or complex species with several

metal cations, most frequently with Ca and Mg in alkaline soils, and with Fe and Al in acid soils

(Lindsay, 1979). Ruiz (1992) reported that 9 and 20% of soluble P occurred as Mg-P and Ca-P

complexes for a hydroxyapatite in equilibrium with a simplified nutrient solution (NH4N03

2 mM, KNO3 3.5 mM, and MgSO4 0.5 mM) at pH values of 7 and 8.5, respectively. Phosphorus

ions also readily precipitate with metal cations to form a range of P minerals in case of external









concentrations. In acidic conditions P ions will precipitate as Fe and Al phosphates such as

strengite, vivianite, variscite and various minerals of the plumbogummite group (Norrish and

Rosser, 1983; Lindsay et al., 1989). With pH increasing to neutral or alkaline conditions, P ions

will precipitate as Ca phosphates such as octacalcium or dicalcium phosphates, hydroxylapatite

and eventually least soluble apatites (Lindsay et al., 1989). P availability in most soils is at a

maximum near pH 6.5.

Many soil physical and chemical properties influence the P solubility and adsorption

reactions in soils. Consequently, these soil properties also affect solution P concentration, P

availability to plants, and recovery of P fertilizer by crops. Sanchez and Uehara (1980) reported

the influence of clay mineralogy on P adsorption. For three soil orders with >70% clay content,

they found that the P adsorption occurred in the order: Mollisol soils composed mainly of

montmorillonite < Oxisoil soils containing some Fe/Al oxides < the Andept soils composed

principally of Fe/Al oxides and other minerals. Soils containing large quantities of clay will fix

more P than soils with low clay content. Coleman et al. (1960) reported a strong positive linear

relationship between exchangeable Al and P adsorption.

Organic Soil P

Organic soil P represents about 50% of the total P in soil and varies between 15 and 80%

in most soils (Havlin et al., 1999). Havlin et al. (1999) also reported that soil organic P decreases

with depth and the distribution with depth varies among soils. The average C/N/P/S ratio in soils

is 140:10:1.3:1.3 (Havlin et al., 1999). Many of the organic P compounds in soils have not been

characterized. Most organic P compounds are esters of orthophosphoric acid and have been

identified primarily as inositol phosphates with approximate proportion of 10-50%,

Phospholipids with proportion of 1-5% and nucleic acids with proportion of 0.2-2.5% (Havlin et

al., 1999). In general, P mineralization is similar to N. Dormaar (1972) reported that organic P









content decreases with crop growth and increases again after harvest, which suggests P

mineralization and immobilization. Tiessen et al. (1982) reported that organic P decreased an

average of 21% after 60 and 70 years of cultivation. Sharpley (1985) reported that with an

increase of total organic P content, the organic P mineralization rate increased. Tabatabai and

Dick (1979) found that P mineralization increases with increasing total organic C. The C/P ratio

of the decomposing residues regulates the predominance of P mineralization over immobilization

as suggested by the following guidelines. Net mineralization of organic P occurs in case the C/P

ratio is less than 200 and net immobilization of inorganic P would occur for a >300 C/P ratio.

Leached P in Turfgrass Environment

Phosphorus is an essential macronutrient required by turfgrass for proper growth and

function. Accordingly, P is often included in fertilizer regime used to maintain aesthetic lawns.

Although P enters into many inorganic forms in natural setting, which renders it sparingly

soluble by precipitation and adsorption in most cases and not prone to leaching, a typical Florida

soil is sandy and acidic, and the potential for P leaching exists. Many of Florida's soils have low

P-retention capacities, which allow significant P leaching. Additionally, shallow groundwater

intercepted by drains allows leached P to join surface water bodies. From 20 to 80% of P and

other fertilizers which were applied to Florida sandy soil may be leached (Champbell et al., 1985;

Sims et al., 1998). Shuman (2001) investigated P leaching from a simulated USGA putting green

in an environmentally controlled greenhouse and reported 27% of applied P was lost via leaching.

Studies addressing N leaching from turfgrass environment are quite extensive (Snyder et

al., 1980; Broschat, 1995; Erickson et al., 2001). Relatively few studies have addressed the P

leaching under turfgrass environment. Erickson et al. (2005) examined fertilizer P leaching loss

from contrasting residential landscape models (St. Augustinegrass vs. a mixed-species landscape)

established on a sandy soil. They reported that during the 45 month study, cumulative mean P









leached was 23 kg ha-1 from approximate 1400 kg ha-1 application on the St. Augustinegrass

model. Leaching losses were high during establishment and following intense precipitation.

Leaching losses of P were high enough to raise concern over ecological impacts on neighboring

hydrologically linked systems. Chung et al. (1999) evaluated the influence of a number of

different P sources in a glasshouse study simulating the USGA putting green root-zone mixes on

bermuda (Cynodon dactylon (L.) Pers. C. transvaalensis Burtt Davy) growth, plant uptake and

leaching characteristics. They reported differences in P leaching characteristics among the P

sources, with monopotassium phosphate contributing the largest quantity of P to the leachate,

accounting for approximately 28% P applied, and concentrated superphosphate (CSP) the least,

accounting for 13% of P applied. Brown and Sartain (1999) studied the P retention in United

States Golf Association Greens by looking at the influence of sand type (clay coated vs.

uncoated), amendment sources (peat and iron humate), and P fertilizer materials (MKP, 0-20-20,

and CSP). They reported that more P leached during establishment. Coated sand retained more

Mehlich-1 extractable P, which resulted in more P uptake and less P leaching. Iron humate

reduced leachate P and experiment units receiving CSP leached least P. Snyder et al. (2000)

investigated coated sands for use in putting green construction and concluded that naturally-

coated sand retained more P than uncoated and artificially-coated sand with approximately 1%

leached for naturally-coated sand.

Management Practices to Reduce P Leaching

Different management practices have been proposed to minimize P leaching in sandy soils.

In recent years, water treatment residuals have been studied extensively to improve the P holding

capacity of sandy soils. O'Connor et al. (2002) evaluated WRTs P retention capacities and found

that all three WRTs tested could reduce P solubility by either adsorption, precipitation, or both

mechanisms and the Al-WTR had an especially large P-sorption capacity of at least 5000 mg P









kg1. Decreasing P fertilizer rates or application of calcite or dolomitic limestone to increase soil

adsorption capacity are the traditional ways for reducing P leaching (Sims et al., 1998). However,

both procedures may lead to insufficient P availability to plants because liming promotes

transformation of plant-available P into unavailable forms (Lindsay, 1979). Silicon fertilizers

have a high adsorption capacity and positively influence soil physical properties. As a result of P

adsorption onto a surface of Si fertilizer, P leaching is reduced. At the same time, Si fertilizers

can induce transformation of slightly soluble phosphates into plant available forms (Matichkov

and Ammosova, 1996). Therefore, Si fertilizers can improve P nutrition in plants and keep P in

the upper soil layers. Matichenkov et al. (2001) found that Si-rich substances or Si fertilizers

increased bahiagrass biomass and reduced P leaching by 40 to 70%.


Conventional Soil and Tissue P Tests

Soil P Extractants

Most soil P extractants were developed to estimate the capacity of the soil to supply P.

They were designed to extract some fraction of the labile P and thus provide an index of the

availability of P to plants over the growing season. Soil P test extractants can be placed into

various categories related to the chemical nature of the extracting solutions. A list of the

commonly used soil test extractants is given in Table 2-1.

Extractants Troug and Mehlich-I contain dilute concentrations of strong acids normally

with a pH of 2 to 3. This provides sufficient H ion activity to dissolve the Ca-P and some of the

Al-P and Fe-P as well. Mehlich III, Bray I and Bray II contain both diluted strong acids and a

completing agent, fluoride ion. Fluoride ions are very effective in completing Al ions from Al-P

and also precipitate Ca ions to release P form Ca-P into solution. With the double effects of P









extraction mechanism Mehlich-III, Bray-I and II tend to extract more P from the same soils than

Mehlich-I and Troug would. On coarse textured Georgia Coastal Plain soils, Gascho et al. (1990)

found that Mehlich-III extracts about 1.46 times more P than Mehlich-I. Also, on finer textured

soils Mehlich-III extractant removes about 1.6 times more P than Mehlich-I. Olsen-P extractant

is so called buffered alkaline solution containing 0.5N NaHCO3 with pH 8.5, which originally

was developed for calcareous soils. The HC03- is quite effective in replacing adsorbed P.

Because of high pH Olsen-P extractant is also very effective in extracting P from Al-P and Fe-P

due to the hydrolysis of the Al and Fe. The extractant citric acid, Egner and Morgan, consist of

diluted weak acids, which were developed based upon the idea of mimicking the root

environment. The organic anions associated with the weak acids tend to affect the extraction in

two ways. The organic anions form complexes with Ca, Al or Fe ions to release P and can also

replace adsorbed P and prevent its readsorption. Modified Morgan extractant was modified from

Morgan extractant by substituting NH4 for Na and adding NH4F to provide a 0.03 N F solution.

NH4 is more effective in removing K from clay soils than is Na. NH4F would give a measure of a

greater portion of P reserve by forming Al-F or Fe-F complexes. FeO strip P test is the so-called

chemical sink-based test, which has been proposed to rely on P sorption-desorption reactions

instead of dissolving soil P with chemicals. It extracts P using Fe-oxide impregnated filter paper

strips or discs (Chardon et al, 1996).

Suitability of Different Extracting Procedures

The suitability of the extracting methods can be evaluated by correlating the P extracted

with plant growth parameters such as yield, P uptake and P concentration (Fitts and Nelson,

1956). The Olsen and Bray I methods are quite satisfactory across a wide range of soil conditions

and the Mehlich I appeared to be very good when used for soils with a pH of 7 or less (Fitts,

1956). The soil testing laboratory at the University of Florida is currently using the Mehlich-I









procedure. The Egner method was as effective as Olsen and Bray-I methods while the Morgan

method is least satisfactory across a wide range of soils (Van Diest, 1963). In a study that related

turfgrass growth response to extractable soil P concentration in sand greens, Guillard and Dest

(2003) reported that extractable P was highly correlated among Mehlich-I, Bray-I and modified-

Morgan procedures with r value of around 0.9. Mehlich-I and Bray-I extractable P extracted four

to six times more P than modified Morgan. Extractable P with Bray-I P was 1.3 times greater

than Mehlich-I extractable P. A better correlation was observed between Bray P and Mehlich-I P

than with modified Morgan P.

Soil P Extracting Procedures and Geographical Regions

The compounds that control the availability of P differ with soil conditions in different

geographical regions of the country and different extractants have been developed and used for

these situations. For example, P chemistry of soils in the southeast primarily involves factors

affecting the availability of aluminum and iron phosphates. Therefore, most commonly used

extractants in these regions are the Mehlich I and the Mehlich III. The Morgan extractant, which

is used by some states in the northeast and Pacific northwest and contains acetic acid, is a

buffered weak acid extractant. Both of the Mehlich solutions extract more P from soils than the

Morgan extractant. The Mehlich III extractant removes about 10 times more P from soils than

the weak acid-based Morgan extractant (Wolf and Beegle, 1995). The extractant used

predominantly in the Midwest is the Bray-Kurtz, commonly referred to as Bray I. The extraction

of P by this procedure is based upon the solubilization effect of the H on soil P and the ability of

the F to lower the activity of Al and to a lesser extent that of Ca and Fe by forming complexes in

the extraction system. Clay soils with moderately high base saturation or silty clay loam soils

that are calcareous or have a very high base saturation will lessen the ability of the extractant to

solubilize P. Consequently, the method should normally be limited to soils with pHw (soil pH









determined in water) values less than 6.8 when the texture is silty clay loam or finer. Calcareous

soils, or high pH, fine textured soils may be tested by this method provided the soil:solution ratio

is changed from 1:10 to 1:50. However, it should be noted that the Olsen extractant is used most

extensively for calcareous soils (Anonymous, 1992, Knudsen and Beegle, 1988). The Olsen

extractant is quite effective for soils with medium to high CEC, high percent base saturation,

moderate to high amounts of calcium phosphates, and containing free calcium carbonates

(Thomas and Peaslee, 1973). It is used extensively in states such as Arizona, California, Utah,

Wyoming, and Oregon. Research also indicates that the procedure works reasonably well on

moderately acid soils. However, not many laboratories testing moderately acid soils use the

procedure. The fact that it is not used more widely on these soils is probably due to the lack of

correlation data.

Tissue P test

Plant tissue analysis is an indicator of attaining or maintaining maximum yield or quality.

Therefore, the good correlation between the concentration of P in plant tissue and in the soil as

well as between the concentration in plant tissue and yield, plant growth or quality normally

exists. Ballard and Pritchett (1975) reported that the relationship between the concentrations of P

extracted from the soil by different extractants correlated highly with the concentration of P in

the tissue of pine seedlings.

Response of Turfgrass to P Fertilizers and Fertilizer Recommendations

Phosphorus Toxicity Trial

Accumulations ofP in soils growing turf, citrus, vegetable crops and field crops are

common when heavy application of fertilizers containing a high proportion of P are usually

applied frequently. Since only a portion of P added in fertilizers is recovered by plants, the

continuous use of P fertilizers on turfgrass would be expected to raise soil P level well above the









optimum level. In most states, soils contain substantial portion of clay and P leaches very little.

Scientists question whether or not these high levels are detrimental to plant growth. Juska et al.

(1965) looked at the effects of P on the development of Red Fescue (Festuca rubra ssp.

commutata), Merion, and Common Kentucky Bluegrass (Poapratensis). The P application rates

were: 0, 244, 488, 734, 978, 1222, 1466 and 1710 kg ha-1. The largest increase in weight of both

tops and roots of Merion and common Kentucky bluegrass resulted from the first increment of P.

Differences among remaining increments were small. It is conceivable that P application as high

as 1710 kg ha-1 did not depress top growth and P application rate of 244 kg ha-l supplied

sufficient P already. These results suggest that grasses can tolerate very high levels of P and may

require low rate of P application for optimum growth.

Phosphorus Requirements by Turfgrasses

Grasses exhibit marked species difference in response to P supply. Robinson et al. (1976)

found no influence of P applications to a New Zealand browntop-New Zealand chewings fescue

(Festuca rubra var. commutate) lawn mixture for verdure, root weights, or tiller numbers. Jones

et al. (1970) grew Italian ryegrass (Lolium multiflorum), hardinggrass (Phalaris tuberosa var.

stenoptera ), tall fescue (Festuca arundinace), orchardgrass (Dactylus glomerata), and tall

oatgrass (Arrhenatherum elatius (L.) P. Beauv.) with 0, 100, 200, 300, and 400 kg P ha-l. Tall

fescue, ryegrass, and tall oatgrass produced the highest yields without P, but tall fescue and

ryegrass also showed the greatest response to P fertilization. Christians et al. (1979) investigated

the N, P and K effects on quality and growth of Kentucky bluegrass and creeping bentgrass

(Agrostispalustris) using solution culture. No response to P levels in solution was observed,

which indicated that the requirements of these two species for P, under the conditions established,

were met at or below the lowest P level of 2 mg L-1 in solution. Fry et al. (1989) conducted a

field study over 8 years on a sand medium to determine creeping bentgrass quality response to P.









They found that creeping bentgrass fertilized at 60 or 132 kg P ha-1 yr- was similar in quality. In

calcareous sand greens Johnson et al. (2003) found that creeping bentgrass plots receiving 27.5

kg P ha-1 yr- or higher rates attained the maximum quality. Allen et al. (1977) established

Pensacola bahiagrass (Paspalum notatum) on a Lexington silt loam that contained 34 mg kg-1 P

in the surface 1.5 m soil. For 5 years they applied annually 224, 336 and 448 kg N ha-1; 112, 224

and 336 kg P205 ha-1; and 112, 224 and 336 kg K20 ha-1 in a complete factorial experiment.

Rates of 224 and 336 kg P205 ha-1 accounted for increases of only 1% and 2% forage above the

49 kg P205 ha-1 level, respectively. Maximum yield response of bahiagrass to P fertilizer in south

Florida occurred on Arenic Haplaquods at 24 kg P ha-1 (Rechcigl et al., 1992). Another study on

the bahiagrass fertility requirement in south Florida on soils with a spodic horizon called forl3

kg P ha-1, and only if>1 12kg N ha-1 is applied. If less than 60 kg N ha-1 is applied, no P is

recommended (Sumner et al., 1991). Turner (1980) found little influence of P on the growth of

perennial ryegrass (Lolium perenne), Kentucky bluegrass, or creeping red fescue, despite low

soil P levels.

Robinson and Eilers (1996) obtained 90% of maximum ryegrass dry matter yield with 45

to 50 kg P ha-1 on a Tangi silt loam (Typic Fragiudult) at pH 6. Higher rates of P had little

influence on yield but significantly increased P removed by the crop. This result was consistent

with the study of irrigated annual ryegrass responses to N and P on calcareous soil by Lippke et

al. (2006), in which they concluded that increments of growth responses to levels of fertilizer

about 39 kg applied P ha-1 were relatively small. Watschke et al. (1977) looked at the effect of P

application of 0, 85, 170, 340, and 680 kg P ha-1 on soil test and tissue analyses P. Phosphorus

fertilization increased the Bray extractable P from 13 to 137 mg kg-1. Treatments P1, through P5

gave P concentration of 3.2, 3.5, 3.6, 3.8, and 4.4 g kg-1, respectively, with all differences being









significant except 3.5 and 3.6 g kg-1. When soil test P was related to yield response, the

correlation was slightly lower than those found for tissue P and yield, which was in agreement

with Hall and Miller (1974) who also found that tissue P and yield were better correlated than

soil test P and yield. Watschke et al. (1977) also investigated the zone of maximum root

absorption for 'Merion' Kentucky bluegrass as affected by P application. Results indicated that P

enhanced rooting, and the magnitude of absorption from the 1.3-cm depth exemplified the need

for P near the soil surface for optimum turf establishment. Juska (1959) reported that adequate P

was necessary for rapid establishment of zoysiagrass (Zoysia spp) on a soil extremely low in P.

St. Augustinegrass growth was affected by P most during the first 8 weeks of establishment

(Wood and Duble, 1976). On P-deficient soils, McVey (1967) reported a Kentucky bluegrass

seedling growth response to extremely low rates of P applications. Long-term benefits from P

application to the seedbed have also been observed by Turner et al. (1979). He reported that 6

years after establishment, spring greening was enhanced by the original seedbed P applications.

Critical Minimum Soil P Concentrations

The critical soil test level implies the P level above which little or no response to fertilizer

P is obtained. Woodhouse (1969) and Jordan et al. (1966) reported that about 25 mg kg-1 of

Mehlich-1 extracted soil P is adequate for coastal bermudagrass (Cynodon dactylon) in North

Carolina and Alabama. Lunt et al. (1965) indicated that about 14 mg kg-1 of Olsen extractable P

was adequate for common bermudagrass harvested frequently as turfgrass; Bruce and Bruce

(1972) indicated that 17.5 mg kg-1 of P extractable with 0.005 M H2SO4 was necessary for high

production of various tropical grasses. Vicente-Chandler et al. (1974) concluded that tropical

species such as guineagrass (Urochloa maxima), napiergrass (Pennisetum purpureum), and

stargrass (Cynodonplectostachyus) require fertilization with at least 73 kg P ha-1 annually when

cut every 40 to 60 days. Annual ryegrass (Lolium multiflorum Lam.) response to applied P









ranged from 8300 to 8600 kg ha-1 as extractable soil P increased from 3 to 55 mg kg-1 (Hillard et

al., 1992). Christians et al. (1981) did not find significant quality responses for creeping

bentgrass on calcareous sand greens when initial Bray-1 extractable P concentrations were 12 mg

kg-1. Dest and Guillard (1987) reported that on a loam soil with modified Morgan extractable P

at 10.7 mg kg-1, quality responses of creeping bentgrass were not affected by P fertilization. Fry

et al. (1989) reported that creeping bentgrass quality improved with addition of P on sand-based

media putting greens only when extractable P was <5 mg kg-1. Kuo (1993) reported that Olsen-

extractable P concentrations at 95% of maximum clipping yields was from 2.8 to 4.8 mg kg-1 for

the growth of annual bluegrass and creeping bentgrass (Agrosti stolonifera L.). In calcareous

sand greens the critical Olsen-P level of 3.0 mg kg-1 was reported for the growth of creeping

bentgrass (Johnson et al., 2003). For Pensacola bahiagrass on a virgin Clarendon loamy sand the

critical Mehlich-1 P concentration was 3 mg kg-1, which corresponded to 56 kg P205 ha-1

application (Burton et al., 1997). To locate the critical soil P concentration the plant growth rate

or turf quality are most commonly used to relate to soil test levels. Guillard and Dest (2003) used

a number of plant response variables including shoot counts, thatch thickness, relative clipping

yields, quality ratings, P deficiency ratings, tissue P concentrations, and root weights, which

resulted in different soil critical P concentrations. Selection of a particular critical extractable soil

P concentration would depend on the quality or growth variable that is the most important to the

individual manager. Among the three extractants, modified Morgan, Bray I and Mehlich I,

critical extractable P concentrations for creeping bentgrass were lowest for the modified Morgan

extractant (1.4 to 12.0 mg kg-1) and greatest for the Mehlich I extractant (14.1 to 63.6 mg kg-1).

The critical values are generally influenced by soil properties, such as texture and

temperature. A lower amount of P is generally extracted from a clayey soil than from a sandy









soil (Woodruff and Kamprath, 1965). Rouse (1968) found that an application of 5 to 6 kg P ha-1

was required to raise Mehlich-I extractable P 1 kg ha-1 with sandy loam to clay loam textured

Ultisols, but on clayey textured soils 12 kg P ha-1 were required to change the soil test values 1

kg ha-1. Finn and Mack (1964) showed that both soil moisture and soil temperature affected P

response of orchardgrass (Dactylis glomerata). Yields were higher at 75 than at 25% of the

moisture-holding capacity at each level of P applied. Under 75% moisture-holding capacity level,

at a 10 C soil temperature, maximum yield of the S-143 cultivar occurred with 35 mg kg-1 of

applied P; at 20 OC, yields were still increasing with 70 mg kg1.

Effects of P Application on Soil Test P Levels

When soil test P is below the critical level, the rate of fertilizer P recommended is

sufficient to supply adequate P for the plant and to result in some buildup of available soil P

when applied at the rate for several years. In trying to predict how much fertilizer P is needed to

change the soil test P, information is needed about the P adsorption characteristic of the soil,

which is related to soil texture, as well as the initial level of soil test P. In a Honeoye fine sandy

loam soil, Peck et al. (1975) found that continuous applications of concentrated superphosphate

over 10 yr for a total of 248 kg P ha1 increased soil test P (Morgan's method) from 10 to 186 kg

P ha 1. An application of 4 kg P ha-1 was required to raise the Bray I extractable P of medium-

textured Mollisols and Alfisols 1 kg ha-1 (Peck et al., 1971). Single applications of 22, 45, 90,

and 180 kg P ha1 raised the levels of Olsen P by 1, 2, 4, and 8 mg P kg 1 soil, respectively, on a

glacial till soil after 16 yr of P fertilization (Halvorson and Black, 1985) In a 29-yr study on

Ultisols in Alabama, Cope (1981) found that 24 and 20 kg P ha1 raised Mehlich-1 soil test P by

1 mg P kg 1 when P was applied at rates of 31 and 54 kg P ha1 yr respectively. For a corn-

soybean rotation on a Portsmouth fine sandy loam, annual rates of 19, 38, and 57 kg P ha-1

increased the soil test levels 7, 20 and 40 mg kg-1 P over a 7-year period (Kamprath, 1964). After









14 yr of annual application of P fertilizer in a Webster fine-loamy and a Canisteo fine-loamy soil

located in north central Iowa, Webb et al. (1992) reported that annual P additions required to

maintain Bray-1 P values increased from 16.8 to more than 33.6 kg P ha1 with increases in the

initial Bray-1 P value. In a Chicot sandy loam soil, an application of 14 kg P ha of net added

inorganic fertilizer P was required to increase soil Mehlich-3 P by 1.0 mg P kg 1 (Zhang et al.,

1995). Cox (1994) showed that increases in Mehlich-3 with each unit of applied P were 0.7 units

for soils with 10% clay, and it decreased exponentially to 0.2 units for soils with >50% clay.

Results obtained from a study by Randall et al. (1997) in Minnesota, showed that every 1 mg P

kg 1 increase in Bray-1 extractable P requires 35 and 20 kg P ha1 in a Webster clay loam soil

and 58 and 26 kg P ha 1 in a Aastad clay loam soil when fertilizer P was added at 24 and 49 kg P

ha1, respectively. Many studies have shown that the amount of fertilizer P required for each unit

increase of soil test P level varies with soil texture, soil test method employed, as well as the rate

of fertilizer P applied.

Critical Tissue P Concentrations

The critical tissue P concentration is normally regarded as the minimum concentration

associated with near maximum yield. The nutrient concentration in the plant at 90% of maximum

growth has often been termed the critical concentration (Ulrich and Hills, 1967). It could be

statistically determined from the shape of the yield response curve in relation to concentration of

P in the selected tissue. Knowledge of the minimum P concentrations for plant growth has been

used as a means to diagnose the P status of many plants (Hartt, 1955; Ulrich, 1952). Jones and

Eck (1973) reported that the critical concentration of P in the sweet corn leaf tissue was from

0.27 to 0.29% and the corresponding equilibrium soil solution P concentration was about 0.12 to

0.13 mg L-. A similar highly positive linear correlation between percent P in the rice tissue and









soil solution P concentration was reported by Hossner et al. (1973). The critical tissue P

concentration of 0.25% corresponds to the soil solution P of 0.1 mg L1.

Oertli (1963) reported that healthy bluegrass (Poa spp) and bermudagrass (Cynodon spp)

contain 1.2 to 2.4 g kg-1 P, respectively. Tissue P-deficiency levels were found to be 0.5 to 0.8 g

kg- respectively, for bluegrass and bermudagrass. Martin and Matocha (1973) outlined

approximate sufficient ranges for tissue P for cool-season forage grasses. For Kentucky

bluegrass, values 1.8 g kg-1 were considered deficient, from 2.4 to 3.0 g kg-1 were critical, from

2.8 to 3.6 g kg-1 were adequate, and values 4.0 g kg-1 were considered high. For annual and

perennial ryegrass values < 2.8 g kg-1 were deficient, from 2.8 to 3.4 g kg-1 were critical, from

3.6 to 4.4 g kg-1 were adequate, and > 5.0 g kg-1 were high. Jones (1980) suggested that in most

situations concentrations below about 2.0 g kg-1 indicate a deficiency for plant growth while 3.0

to 3.5 g kg-1 is usually necessary for optimum yields. Wedin (1974) reported that P concentration

in cool-season grasses range from about 1.4 to 5.0 g kg-1. Johnson et al (2003) investigated the P

requirement of creeping bentgrass on calcareous sand greens and found that tissue test of 4.0 g

kg-1 was the optimum level for maximum quality. For warm-season grasses, the P concentration

in plant tissue should be logically lower for the optimum yield compared with cool-season

grasses because the higher growth rate dilutes the P concentration in plant tissue. Burton et al.

(1997) reported that phosphorus concentration of the 1993 Pensacola bahiagrass forage receiving

56 kg P205 hal-, above which no significant yield increase occurred, averaged 1.5 g kg-1. When

P205 was increased to 112 kg ha-l, forage P concentration increased to be 1.8 g kg-1. The critical

P concentrations in some subtropical and tropic grasses were shown in Table 2-2 (Kampraph,

1980).









Some factors may modify the critical P concentration of plants such as growth rate

(Terman et al., 1972), plant tissue age (Jones et al., 1970) and cultivar effects (Terman et al.,

1975), thus making the conclusion between tissue P concentration and yield difficult. Therefore,

in many cases, the variability in the P concentration does not allow a high degree of accuracy in

the prediction of the increments of plant growth or yield. Consequently, the critical concentration

range of P in the plant is usually the criterion that is used in differentiating P deficiency from P

sufficiency and the decision to simply apply P or not is usually made.

Interaction with other Nutrients

Phosphorus and N

Increased P absorption by plants is a common consequence of adding N fertilizers (Grunes,

1959). Templeton et al. (1969) conducted a study showing the effects of N on P response of

orchardgrass. At each level of P applied, with increased N rate plant gained increased weight

increased top growth, increased root growth, altered metabolism, and increased solubility of soil

applied among three levels of N applications. In a study on response ofbahiagrass to N, P and K

on an Ultisol in North Florida, Rhoads et al. (1997) found that there were no interactions

between N and P rates with respect to bahiagrass yield. However, there were significant

interactions in 1996 between N and K rates and between P and K rates with respect to bahiagrass

yield. Hylton et al. (1965) reported that for Italian ryegrass (Lolium multiflorum Lam), as the P

supply increased from 0.16 to 0.64 mg per plant, the tissue N03-N concentration decreased from

13.2 g kg-1 with 0.16 mg of P per plant to a low of 7.6 g kg-1 with 0.64 mg. Engelstad and Allen

(1971) found that root yields and root P contents were increased by N fertilizer, with ammonium

being superior to nitrate. The addition of KNO3 to the pellet reduced the P content of the tops.

Sartain and Dudeck (1982) studied the effect of N fertilization on the P uptake of Tifway

bermudagrass and overseeded ryegrass. Tissue P content was significantly reduced by each









increasing N rate on the ryegrass. The reduction in tissue P could possibly be attributed to a

diluted effect caused by greater growth rate. Higher tissue N content was observed for Tifway

bermudagrass by excluding P, which implied a possible nutrient uptake competition between

NO3-N and H2P04-P. Sartain (personal communication) found that bermudagrass growth rate

was reduced each of three years by the application of additional P. A reduction in N uptake was

observed in conjunction with the reduction in growth rate. It was suggested that the competition

effects of the N03-N and H2P04-P anions may have been responsible for the observed reduction

in N uptake and subsequent growth rate. Watschke et al. (1977) reported that clipping yield and

rooting of Merion Kentucky bluegrass (Poapratensis L.) were enhanced by the application of

additional P. In case NH4-N was applied during cool season, NH4-N would be the major N form

available for plant uptake because of reduced nitrification of the applied NH4-N (Parker and

Larson, 1962). The increased growth rate may possibly due to the fact that additional P enhanced

N uptake for the cool season Kentucky bluegrass. Bluegrass tissue P levels were more than

sufficient (3.2 g kg-1) for all treatments, which indicate that the positive growth response to P

was not related physiologically to P. With the exclusion of P fertilization the number of H2P04-P

anions would be reduced and the quantity of NH4-N cations that can be accumulated would also

be reduced, therefore, a yield reduction was expected.

Phosphorus and K, Ca and Mg

Enhanced P utilization due to K applications was observed for stargrass (Cynodon

nlemfuensis Vanderyst var. nlemfuensis) by Pant et al. (2004). The applications of 10 and 93 kg

ha-1 yr1 of P and K, respectively, provided efficient P utilization. Phosphorus mass balance

showed that stargrass removed maximum P (161%) of the applied P by uptake from soils. This

may indicate that the supply of sufficient K appears to be crucial for efficient P utilization by

forages, reducing potential adverse effects of P over-fertilization on water quality. When the









different P:K ratios were related to the total dry matter yield, the application of 10 and 93 kg ha-1

yr-1 of P and K, respectively, achieved almost 90% of the maximum total dry matter yield, which

indicates that application of 10 kg P ha-1 yr- was critical for stargrass to achieve maximum dry

matter yield. Greenwood and Hallsworth (1960) found no direct effect of P on Ca uptake, but

found that earlier and more severe symptoms of Ca deficiency occurred where P levels were high.

Mg has been ascribed the function of P 'carrier' in plants (Truog et al., 1947), based on a

positive correlation between the Mg and P contents of plants or between fertilizer P efficiency

and the supply of available Mg.

Phosphorus and Zn

Phosphorus and Zinc nutrition in plants have often been related. In P deficient plants

additional P promoted plant growth resulting in depressed Zn concentrations in tissue and

possible Zn deficiency conditions. In P sufficient plants additional P increase concentrations to

toxic levels producing necrotic symptoms in old leaves and depressing new growth. Sartain

(1992) investigated the influence of Zn and the interaction of P an Zn on the growth of

bermudagrass. Application of Zn did not influence growth nor Zn uptake rate. Extractable soil

Zn levels over 252 mg kg-1 did not affect bermudagrass growth nor quality. In effect,

bermudagrass can tolerate high levels of soil extractable P and Zn without exhibiting toxicity

effects.

Effect of N, P, K, and their Interactions on Water Use Efficiency

When water resources become limited, it is important for turfgrass manager to use many

different cultural practices to reduce water loss through turfgrass evapotranspiration rate (ET).

Nitrogen application enhanced the ET by promoting the top growth and total leaf area. Ebdon et

al. (1999) investigated the interaction of N, P and K on ET rate of Kentucky bluegrass. The

nature of the interaction between N, P, and K on Kentucky bluegrass water use can only in part









be explained by the interaction effects of N, P and K on shoot growth response. No relationship

between clipping yield and ET rate at high P applications was found. They also discovered that

at N and P levels that are routinely applied (147 kg N and 21.5 kg P ha-1 yr-1 and lower),

increasing K levels minimized Kentucky bluegrass water use.










Plant and animal


Leaching


Figure 2-1. The P cycle in soil.









Table 2-1. Common soil test extractants used for available P.
Soil/solution
Common name Extractant ratio Reference
Troug 0.002N H2S04 buffered at 1:100 Troug (1930)
pH 3 with (NH4)2SO4


Mehlich -I
Mehlich-III


0.05N HC1 + 0.025N H2S04
0.2N CH3COOH + 0.25N NH4N03
+ 0.013N HN03 + 0.015N NH4F
+ 0.001M EDTA


1:4
1:10


Mehlich (1953)
Mehlich (1984)


Bray-I 0.025N HC1 + 0.03N NH4F
Bray-II 0. IN HC1 + 0.03N NH4F
Olsen 0.5N NaHCO3 pH 8.5
Citric acid %1 citric acid
Egner 0.02N Ca lactate + 0.02N HCI
Morgan 0.54N HOAc + 0.7N NaOAc pH 4.8
Modified Morgan 0.54N HOAc + 0.7N NH40Ac
+ 0.03N NH4F pH 4.8
FeO strip 0.02 N CaCl2 + FeO-coated filter
paper strip


1:10
1:17
1:20
1:10
1:20
1:10
1:10

1:40


Bray & Kurtz (1945)
NDSU (1980)
Olsen et al. (1954)
Dyer (1894)
Egner et al, (1960)
Morgan (1941)
McIntosh. (1969)

Chardon et al.
(1996)









Table 2-2. Critical P concentration in some subtropical and tropical g
Critical P
Age or concentration,
Grass identification stage of growth %


Bermudagrass
Midland and common
Bermudagrass
Panicum Maximum, VAR
Trichoglume, cv. Petrie


Kikuyugrass
Pearl millet
Staria spacelata, cv
Nandi


Staria anceps, cv Nandi
Dallisgrass
Pangolagrass

Buffelgrass






Buffelgrass


4-5 weeks 0.20-0.26


4-5 weeks
3-4 leaf
4-5 leaf
6-7 leaf
I.P.F. t (57days)
I.P.F.(45 days)
4-5 weeks
4-leaf
5-leaf
6-leaf
7-leaf
I.P.F.(57 days)
I.P.F.(57 days)
I.P.F.(45 days)
4 weeks
I.P.F.(57 days)
(whole plant tops
inflorescences just
appearing)
youngest expanded
leaves sampled
I.P.F.(39 days)
46 days


0.24-0.28
0.55
0.32
0.15
0.20
0.22
0.16-0.20
0.46
0.36
0.24
0.14
0.21
0.25
0.16
0.12-0.16
0.25
0.16


0.17

0.26
0.30


rasses.


Rhodesgrass, cv Pioneer I.P.F.(57 days) 0.22 Andrew and Robins, 1
Molassesgrass I.P.F.(57 days) 0.18
Johnsongrass boot stage 0.16-0.20 Martin and Matocha, 1
Sorghum-sudangrass 4-5 weeks 0.14-0.20
and sudangrass
t I.P.F. means immediate preflowering stage of growth. Most analyses apply to whole plants
unless otherwise specified.


971

973


Reference
Martin and Matocha, 1973


Smith, 1975


Andrew and Robins, 1971

Martin and Matocha, 1973
Smith, 1975



Andrew and Robins, 1971


Martin and Matocha, 1973
Andrew and Robins, 1971
Smith, 1975




Christie and Moorby, 1975









CHAPTER 3
MATERIALS AND METHODS

This research consisted of one glasshouse hydroponic study and three glasshouse soil studies.

Glasshouse Hydroponic Study

A glasshouse hydroponic study was conducted at the Turfgrass Envirotron at the

University of Florida, Gainesville, Florida. St. Augustinegrass var. Floratam was chosen as the

testing cultivar based on its greatest use among all St. Augustinegrass cultivars. Six levels of P

(0, 1.24, 6.2, 31, 155 and 775 mg m-3) with five replicates were used to test for P response.

Certified sod collected from the G.C. Horn Turfgrass Field Laboratory at the University of

Florida in Gainesville was washed to remove soil from the root system. Sod was cut to a size of

15cm x 30cm rectangle and transferred to the hydroponics system on June 27, 2004.

Nalgene tubs (31cm x 16cm x 12cm) were used as the hydroponic containers. The outside

surfaces of the containers were painted with black latex paint first and white afterwards to

prevent light penetration. A 10-mm inner diameter polynvinyl chloride (PVC) pipe was used to

make a rectangle frame (15cm x 30cm). The frame was attached with a piece of poly-hardware

cloth and fitted on the covers of opening of the container to form a grass bedding surface. Since

the frame was not fixed to the container, the frame/screen with grass could be removed to change

solution or check solution pH periodically. The grass pieces (15cm x 30cm) were placed on the

bedding surfaces. Nutrient solution level in the container was adjusted to touch the screen to

induce root growth. Roots penetrated the screen and grew into the solution after about three

weeks. Then the solution volume was reduced to approximately 1.5 cm below the frame to create

an air zone between grass stolons and solution surface to avoid water damage and algae growth

on the grass. An air compressor was used to supply air to the nutrient solution. A 5-m long with

7-mm inside diameter tygon tubing was fitted to the outlet of the air compressor at one end and









the other end was plugged. Along the 5-m plastic tube the containers were laid out on both sides

with 15 tubs on each side. Another tube of the same diameter, but shorter length was used for

each solution tub with one end fitting with a needle and the other end going to the solution. The

needle penetrated the main tube and through the short tube air was blown into each solution.

Smaller size of needles was used at the positions closer to the air compressor and larger sizes of

needles for the far positions. By doing this, the air pressure due to distance difference between

each tub and air compressor was roughly regulated and each solution achieved approximately the

same air bubbling speed. Figure 3-1 shows the experiment layout.

Nutrient solution was slightly modified from what was reported by Breeze et al. (1984) by

replacing Sequestrene Fe 138 with Sequestrene Fe 330, eliminating CaSO4 and doubling the

concentrations of nutrients they used. The nutrient solution was changed every other day to

regulate pH, maintain nutrient concentrations and minimize salt accumulation. The P treatments

were applied on October 17, 2004 at which time the turfgrass was exhibiting P deficiency. The

study was terminated on March 14, 2005. The treatments were arranged in a randomized

complete block design. Computer controlled overhead exhaust fans, a wall-length humidifier,

and an automatic roof window were used to maintain relatively constant conditions in the

glasshouse. Glasshouse temperature was maintained at an average 220C with a range of 18C to

300C. The relative humility was maintained at approximately 75%.

Top growth was clipped to 7.5 cm approximately monthly, once the dry matter production

reached harvestable quantities, for a total of seven collections. Clippings were dried at 700C for

48 h, and weighed. Root materials were clipped to 4 cm on September 8, 2004 and November

27, 2004. At root collection time the root density in the container was high. Root materials were

washed with distilled water to remove the potentially adsorbed salts, dried at 700C for 72 h and









weighed. The dry tissue and root samples were ground to 2-mm and ashed. Samples were

analyzed for P by spectrophotometry using the molybdenum-reduced molybdophosphoric

method (Hanlon et al., 1994). Turf visual quality was rated biweekly using a scale of 1 to 9

where 1 represents brown, dormant turf and 9 represents superior quality (Skogley and Sawyer,

1992).

Statistical analysis (analysis of variance) was performed by SAS (SAS Inst., 1987). Mean

separation was done using Duncan's Multiple Range test at a 0.05 significant level. The

relationship between turfgrass tissue growth rate and solution P and tissue P were determined

using linear plateau analysis (PROC NLIN).

Glasshouse Soil Study 1

With the information of the critical minimum tissue P required by St. Augustinegrass from

the hydroponic study, a study to determine the critical minimum soil test P concentration was

initiated. This glasshouse soil study was conducted at the Turfgrass Envirotron at the University

of Florida, Gainesville, Florida. The soil chosen in this study was collected from the A horizon

of a soil mapped as "Pomona sand". It contained very low levels of Mehlich-1 P (2 mg P kg-1).

The Pomona series is in the family of Sandy, Siliceous, Hyperthermic Ultic Alaquods. Selected

chemical properties for this soil (soil No. 1) are shown in Table 3-1. Nalgene tubs (53cm x 38cm

x 12cm) were used as the growth container. Outside surfaces of the containers were painted with

white latex paint first and black afterwards to prevent light penetration. Certified sod with high

initial tissue P concentration was washed to remove soil, then cut to a size of 53cm x 38cm

rectangle and transferred to the growth container on May 8, 2005.

After P deficiency was induced, P205 rate of 0, 0.31, 0.63, 1.25, and 2.5 g m-2 per four

weeks were applied initially on April 12, 2006 and reapplied 3 times during the 16-week growth

period. Treatments were arranged in a randomized complete block design with 5 replications for









each treatment. Computer controlled overhead exhaust fans, a wall-length humidifier, and an

automatic roof window were used to maintain relatively constant conditions in the glasshouse.

Glasshouse temperature was maintained at an average 24 C with a range of 180C to 30 OC. The

relative humility was maintained at approximately 75%. The experiment layout was shown in

figure 3-2.

Top growth was clipped to 7.5 cm every other week for a total of 8 collections. Clippings

were dried at 70 OC for 72 h, and weighed. Tissue growth rate was calculated by dividing tissue

dry weight by growth days. The dry tissue samples were ground to 2-mm and ashed. Samples

were analyzed for P by spectrophotometry using the molybdenum-reduced molybdophosphoric

method (Hanlon et al., 1994). Turf visual quality was rated weekly using a scale of 1 to 9 where

1 represents brown, dormant turf and 9 represents superior quality (Skogley and Sawyer, 1992).

Soil samples were taken at termination using a 3.0-cm via. soil probe. Soil samples were

separated into soil depths of 0-2 cm and 2-10 cm. Mehlich-1 extractable P was determined for

the soil samples in depth of 0-2 cm and 2-10 cm. Water extractable P and FeO-strip P were

determined for the 0-2 cm soil depth.

At one week intervals, one-half pore volume of water was applied to all growth containers

to aid in the collection of leachate. Leachate volume, pH, and EC were measured. A sub-sample

was collected and frozen until soluble reactive P was analyzed.

Statistical analysis (analysis of variance) was performed by SAS (SAS Inst., 1987).

Duncan's multiple range test with fixed variable was used for all the mean separation in this

study. Means marked by the same letter are not significantly differently at P = 0.05.

Glasshouse Soil Study 2

An attempt was made to verify the critical soil test P concentration obtained in the glass

house soil study 1. Two soils different from the one used in the previous study were chosen for









this study based on their low Mehlich-1 P concentrations (<5 mg kg-1). Samples from the A

horizons were collected from soils mapped as Tavares sand and Pottsburg sand. Classifications

of the soils were Tavares (Hyperthermic Uncoated Typic Quartzipsamments) and Pottsburg

(Sandy, Siliceous, Thermic Grossarenic Alaquods), respectively. Selected chemical properties

for soil No. 2 and 3 are shown in Table 3-1. This glasshouse soil study was conducted at the

Turfgrass Envirotron at the University of Florida, Gainesville, Florida. Nalgene tubs (53cm x

38cm x 12cm) were used as the growth containers. Outside surfaces of the containers were

painted with white latex paint first and black afterwards to prevent light penetration. Certified

sod with high initial tissue P concentration was washed to remove soil, then cut to a size of 53cm

x 38cm rectangle and transferred to the growth container on Septemer 28, 2005.

After P deficiency was induced, P205 rate of 0, 0.31, 0.63, 1.25, and 2.5 g m-2 per four

weeks were applied initially on June 20, 2006 and reapplied 2 times during the 12-week growth

period. The treatments were arranged in a 2 by 5 factorial design with 2 soils and 5 rates of P

application. Each treatment was replicated 5 times. Computer controlled overhead exhaust fans,

a wall-length humidifier, and an automatic roof window were used to maintain relatively

constant conditions in the glasshouse. Glasshouse temperature was maintained at an average 24

C with a range of 180C to 300C. The relative humility was maintained at approximately 75%.

Top growth was clipped to 7.5 cm every other week for a total of 8 collections. Clippings

were dried at 700C for 72 h, and weighed. Tissue growth rate was calculated by dividing tissue

dry weight by growth days. The dry tissue samples were ground to 2-mm and ashed. Samples

were analyzed for P by spectrophotometry using the molybdenum-reduced molybdophosphoric

method (Hanlon et al., 1994). Turf visual quality was rated weekly using a scale of 1 to 9 where

1 represents brown, dormant turf and 9 represents superior quality (Skogley and Sawyer, 1992).









Soil samples were taken at termination using a 3.0-cm dia. soil probe. Soil samples were

separated into soil depths of 0-2 cm and 2-10 cm. Mehlich-1 extractable P was determined for

the soils samples in depth of 0-2 cm and 2-10 cm. Water extractable P and FeO-strip P were

determined for the 0-2 cm soil depth.

At one week intervals, one-half pore volume of water was applied to all growth containers

to aid in the collection of leachate. Leachate volume, pH, and EC were measured. A sub-sample

was collected and frozen until soluble reactive P was analyzed.

Analysis of variance was performed by SAS (SAS Inst., 1987). Tukey's test was used for

all the mean separation in this study. Means marked by the same letter are not significantly

differently at P = 0.05.

Glasshouse Soil Study 3

Observing St. Augustinegrass growth responses on three soils low in P, a study was

undertaken to evaluate growth on a soil containing a medium level of P. This soil study was

conducted at the Turfgrass Envirotron at the University of Florida, Gainesville, Florida. The

Tavares soil used in this experiment was chosen based on it having a medium level of Mehlich-1

P (17 mg P kg-1) and was classified as Hyperthermic Uncoated Typic Quartzipsamments.

Selected chemical properties for this soil (soil No. 4) are shown in Table 3-1. Nalgene tubs

(53cm x 38cm x 12cm) were used as the growth containers. Outside surfaces of the containers

were painted with white latex paint first and black afterwards to prevent light penetration.

Certified sod with high initial tissue P concentration was washed to remove soil, then cut to a

size of 53cm x 38cm rectangle and transferred to the growth container on May 8, 2005.

After P deficiency was induced, P205 rate of 0, 0.31, 0.63, 1.25, and 2.5 g m-2 per four

weeks were applied initially on August 18, 2006 and reapplied 2 times during the 12 week

growth period. Treatments were arranged in a randomized complete block design with 5









replications for each treatment. Computer controlled overhead exhaust fans, a wall-length

humidifier, and an automatic roof window were used to maintain relatively constant conditions

in the glasshouse. Glasshouse temperature was maintained at an average 240C with a range of

180C to 300C. The relative humility was maintained at approximately 75%.

Top growth was clipped to 7.5 cm every other week for a total of 6 collections. Clippings

were dried at 700C for 72 h, and weighed. Tissue growth rate was calculated by dividing tissue

dry weight by growth days. Dry tissue samples were ground to 2-mm and ashed. Samples were

analyzed for P by spectrophotometry using the molybdenum-reduced molybdophosphoric

method (Hanlon et al., 1994). Turf visual quality was rated weekly using a scale of 1 to 9 where

1 represents brown, dormant turf and 9 represents superior quality (Skogley and Sawyer, 1992).

Soil samples were taken at termination using a 3.0-cm diameter soil probe. Soil samples

were separated into soil depths of 0-2 cm and 2-10 cm. Mehlich-1 extractable P was determined

for both depths. Water extractable P and FeO-strip P were determined for the soil samples in the

depth of top 0-2 cm.

At one week intervals, one-half pore volume of water was applied to all growth containers

to aid in the collection of leachate. Leachate volume, pH, and EC were measured. A sub-sample

was collected and frozen until soluble reactive P was analyzed.

Statistical analysis (analysis of variance) was performed by SAS (SAS Inst., 1987).

Duncan's multiple range test was used for all the mean separation in this study. Means marked

by the same letter are not significantly different at P = 0.05.













Figure 3-1. Glasshouse solution culture P study layout.


Figure 3-2. Glasshouse soil P study 1 layout.


t71












Table 3-1. Selected chemical properties of soils used in the glasshouse soil study 1, 2, and 3.
Soil Mehlich-1 P Oxalate Al Oxalate Fe
Study Soil No. Classification name Series name pH (1:2) t OM (gkg-1) (mg kg-1) (mg kg1) (mg kg1)
Sandy, Siliceous, Hyperthermic
1 1 Ultic Alaquods Pomona 4.6 9 2 32 42
Hyperthermic Uncoated Typic Tavares (a)
2 Quartzipsamments 5.1 15 3 77 60
2 Sandy, Siliceous, Thermic
3 Grossarenic Alaquods Pottsburg 4.7 9 5 49 27
Hyperthermic Uncoated Typic Tavares (b)
3 4 Quartzipsamments 4.8 13 17 173 154
t: soil pH was determined in 1:2 soil/water ratio.
: Organic Matter content was determined by ignition.









CHAPTER 4
RESULTS AND DISCUSSION

Glasshouse Hydroponic Study

Turf Quality

St. Augustinegrass visual quality increased with each incremental increase in solution P

concentration in the range from 0 to 775 mg m-3 (Figure 4-1). St. Augustinegrass treated with the

two highest P concentrations, 155 and 775 mg m-3, recovered from the P deficiency conditions

and attained mean turf quality values of 6.8 and 7.2, respectively (Figure 4-1). The turf treated

with zero P in solution suffered severely from P deficiency with a mean turf quality value of 2.5

(Figure 4-1). Turf treated with zero P declined in quality over time and by the end of the study

was dead. Solution P levels of 1.24, 6.2, and 31 mg m-3 were generally insufficient in P for turf

to recover from deficiency and promote optimum growth. Mean turf quality values from these

treatments were below 5.5, which is widely used as a minimum value for acceptable turf quality.

Tissue P and Root P

The initial tissue P concentration of the St. Augustinegrass tested was as high as 4.8 g kg1

on a dry weight basis. After three harvests prior to treatment application, P deficiency (<1.0 g kg

1 on dry weight basis) was induced. Over time, tissue P concentration changed for the six P

treatments as shown in Figure 4-2. Tissue P concentration of turfgrass receiving no P declined

over time until it reached a value of 0.48 g kg-1 after the fourth harvest. By the end of the study

most of the turfgrass was dead, but those portions which were still alive contained 0.45 g P kg1.

This could be considered the minimum P concentration to keep St. Augustinegrass alive.

The relationship between tissue P levels and solution P concentration is presented in Figure

4-3. The highest tissue P level was achieved with application of 775 mg m-3 solution followed by









P treatment of 155 mg m-3. There were no differences in P concentration among the four lowest

P treatments. One possible reason for this observation is that the turfgrasses with the four lowest

P levels remained P deficient during the experimental period.

The relationship between root P levels and solution P concentrations is shown in Figure 4-

4. Root P levels increased with increasing solution P concentration. The highest P treatment

resulted in the highest root P concentration (Figure 4-4). Root P concentration differences among

the four lowest solution P levels were noted by Duncan's Multiple Range test compared with no

significant differences among tissue P levels, which indicates that the primary use of P is for root

growth rather than top growth when P is deficient. Moreover, the root P concentration (Figure 4-

4) with the two highest P levels was lower than those in foliage tissue (Figure 4-3) when P

supplies were sufficient. But the root P concentration resulting from the four lowest P levels was

identical or even slightly higher than levels found in leaf tissue when P supplies were deficient.

This suggests that roots require less P than tissue when P is sufficient, but when P is deficient

root growth requires a higher level of P. It is possible that when P is deficient a higher quantity

ofP is required in order to produce more roots to overcome the P deficiency.

Tissue Growth Rate and Root Growth Rate

Phosphorus fertilization influence on tissue growth rate is rarely observed in St.

Augustinegrass because of the generally medium to high available P status in Florida soils and

relatively low P requirement by St. Augustinegrass. Tissue growth rate (Figure 4-5) was affected

by solution P concentration. Tissue growth rate increased with solution P levels in a quadratic

manner to a maximum value. According to linear plateau regression analysis (Figure 4-5),

solution P concentrations beyond 111 mg m-3 did not result in increased tissue growth rate (r2

0.88, p<0.0001, CV = 15.5). Asher and Loneragan (1967) reported that P at 155 mg m-3

produced maximum dry weights of clover (Trifolium subterraneum, L.), erodium (Erodium









botrys (Cav.) Bertol.) and yields of brome grass (Bromus rigidus, Roth) and cape weed

(Cryptostemma calendula (L.) Druce) were close to maximum in a similar hydroponics study.

Root growth rates (Figure 4-6) were affected by solution P concentration although the

effect was less as compared with tissue growth rates. Turfgrass receiving P at 31 mg m-3 attained

the highest root growth rate among the P levels applied according to Duncan's Multiple Range

test. Asher and Loneragan (1967) reported that P at 31 mg m-3 produced maximum top and root

growth for sliver grass (Vulpia (Festuca) myuros (L.) Gmel.). Root P concentration in the

presence of P at 31 mg m-3 was 0.7 g kg1, which indicates that roots require a smaller quantity of

P for optimum growth than tissue (Figure 4-7). Only three mean categories were separated for

root growth rates (Figure 4-6) indicating that the extent of the effect of solution P concentration

on root growth was less than that on tissue growth. Additionally, turf receiving no P produced

substantial root growth (Figure 4-6). The large reserve of P in the parent plant (approximately 5

g kg-1 P in tissue (Figure 4-1) and correspondingly high P level in stolons (not measured)) can be

a P source for root growth in case there was no P application or P supplies were not sufficient.

Critical Tissue P level

A yield response curve in relation to concentration of P in the selected tissue is commonly

used to determine the critical P concentration. Tissue growth rate was increased with tissue P

concentration in a quadratic manner to a maximum value (Figure 4-7). The slope of the

regression curve can be defined as the change of tissue growth rate over the change of tissue P

concentration. The nearly vertical portion of the regression curve shows relatively steeper slopes

and the horizontal portion has a slope of zero. The transition zone is the area of the curve where

the vertical and horizontal portions converge. With the increase of the tissue P concentration the

slope gradually decreases until it reaches zero, which is the plateau of the curve. According to









linear plateau regression analysis, the critical tissue P level was 1.6 g kg-1 on dry weight basis for

the optimum growth (R2 = 0.88, p<0.0001, CV = 15.4).

Glasshouse Soil Study 1

Turf Quality

For each week across 16 weeks, the highest P application rate of 2.5 g m-2 4-wk1 resulted

in the best turf quality (Table 4-1). There was no difference between turf quality ratings

associated with the highest P rate and the second highest P rate except for the first week (Table

4-1). The third highest P application rate also achieved best turf quality except for the first three

weeks (Table 4-1). With the P deficiency induced for St. Augustinegrass before P application, it

took some time for St. Augustinegrass to recover from the P deficiency after P application. The

higher the P rates applied, the shorter the time required for it to recover and produce the best

quality. The second lowest P application rate of 0.31 g m-2 4-wk1 resulted in the best turf quality

in 12 out of 16 weeks (Table 4-1), which provided some evidence that the minimum P

application rate was somewhat above 0.31 g m-2 4-wk- for this soil. The turf quality of the

control treatment remained above 6.0 for the first 10 weeks and started to decline afterwards. By

the last two weeks, the turf quality was below 5.5, which is widely used as a minimum value for

acceptable turf quality (Table 4-1). Overall, the turf quality ratings were above 5.5 except for the

turf with control during the last four weeks. This indicated that St. Augustinegrass could sustain

for months with very low soil P concentrations and deficient P levels in plant tissue.

Top Growth Rate

St. Augustinegrass top growth responded to P application rates (Table 4-2). Turf receiving

no P produced the lowest amount of top biomass across eight harvests (Table 4-2). The largest

increase on top growth rate was observed with the first incremental P application (Table 4-2).

Turf with three highest P application rates achieved the highest top growth rate across the eight









harvests. For six out of eight harvests, turf with the second lowest P application rate of 0.31 g m-2

4-wk-' produced the same top growth as higher P application rates (Table 4-2). The mean value

of turf top growth rate with the P application rate of 0.31 g m-2 4-wk- across eight harvests was

2.7 g m-2 day-1 and the highest mean value of top growth rate was 3.0 g m-2 day-' (Table 4-2).

The top growth rate for turf with the P application rate of 0.31 g m-2 4-wk- was reduced by 10%

from the maximum growth rate. By definition, the amount of nutrient applied that results in 10%

reduction in maximum growth is defined as the critical minimum requirement for that nutrient.

Moreover, when the overall means of top growth rate for each P application rate were compared,

turf with the P application of 0.31 g m-2 4-wk- produced tissue dry weight that was not

significant different from those with higher P application rates by Duncan's multiple range test

(Table 4-2). By either definition of critical minimum nutrient requirement or Duncan's multiple

range test, P application rate of 0.31 g m-2 4-wk- satisfied the minimum P requirement of St.

Augustinegrass in this soil.

Tissue P Concentration

The initial St. Augustinegrass tissue P concentration tested was as high as 4.9 g kg1- on a

dry weight basis. Over time before P application, tissue P concentration dropped from 4.9 g kg-1

to 1.2 g kg-1 on dry weight basis. With no P application to turf and very low soil P concentration,

it took almost one year to induce P deficiency (<1.6 g kg-1 on dry weight basis).

Tissue P concentration of St. Augustinegrass as influenced by P application rate is shown

in Table 4-3. With each incremental P application, tissue P concentration increased across the

eight harvests. The highest tissue P level was achieved with application of 2.5 g P205 m-2 4-wk-1

and was followed by application of 1.25, 0.63, and 0.31 g P205 m-2 4-wk-1 (Table 4-3). Turfgrass

receiving no P maintained a P concentration of 1.0 g kg-1, with which turfgrass showed P

deficiency symptoms, reduced turf quality (Table 4-1), and reduced growth rate (Table 4-2). In









particular, the mean value of tissue P concentration with P application rate of 0.31 g P20O m-2 4-

wk1 was 1.4 g kg1, which was slightly lower than the critical minimum tissue P concentration

according to the previous glasshouse hydroponic study. This indicated that P application of 0.31

g P205 m-2 4-wk-1 was about to achieve the critical minimum tissue P concentration in this soil.

This is consistent with the previous discussion on top growth rate concluding that P application

rate of 0.31 g P20O m-2 4-wk-1 satisfied the minimum P requirement of St. Augustinegrass in this

soil.

The Critical Minimum Tissue P concentration

A yield response curve in relation to concentration of P in the selected tissue is commonly

used to determine the critical P concentration. Tissue growth rate was increased with tissue P

concentration in a quadratic manner to a maximum value (Figure 4-8). The slope of the

regression curve can be defined as the change of tissue growth rate over the change of tissue P

concentration. The nearly vertical portion of the regression curve shows relatively steeper slopes

and the horizontal portion has a slope of zero. The transition zone is the area of the curve where

the vertical and horizontal portions converge. With the increase of the tissue P concentration the

slope gradually decreases until it reaches zero, which is the plateau of the curve. According to

linear plateau regression analysis, the critical tissue P level was 1.8 g kg-1 on dry weight basis for

the optimum growth (R2 = 0.77, p<0.0001).

Soil Test P

Mehlich-I procedure is widely used in the southeast region of US for agronomic crop soil

tests. Fe Oxide P and WEP procedures are used for environmental impact prediction. Soil

Mehlich-I P, Fe Oxide P, and WEP concentrations as affected by P application are shown in

figure 4-9. With increased P application rates, Mehlich-1 P, Fe Oxide P and WEP concentrations

increased incrementally. For each P application, the Fe Oxide procedure extracted approximately









the same quantity of P as water, which means that the labile P portion with sorption/desorption

process was soluble, suggesting there is little Al/Fe oxides in this soil. Mehlich-1 P

concentrations were all higher than the concentrations of Fe oxide P or WEP, which was

consistent with Pautler and Sims (2000).

Figure 4-11 shows the relationship among Mehlich-1 P, Fe Oxide P, and WEP

concentrations. They were pairwise linear dependent with r2 s of 0.91, 0.90, and 0.85 for WEP

vs. Fe oxide P, Mehlich-1 P vs. Fe oxide P, and Mehlich-1 P vs. WEP, respectively. All the

pairwise relationships were highly significant with p values less than 0.0001. Pautler and Sims

(2000) reported a better relationship of Fe oxide P vs. WEP than that of Mehlich-1 P vs. WEP.

This was true for this study. The explanation could be the nature of Fe oxide P procedure that it

does not dissolve water insoluble P components. While, Mehlich-1 extractant contains diluted

strong acids which could partially dissolve water insoluble P components.

In order to select the best soil test procedure for P recommendation on St. Augustinegrass,

Mehlich-1 P, Fe Oxide P, WEP concentrations were related to turf tissue P concentration (Figure

4-11). All the pairwise relationships were highly significant with p values less than 0.0001,

which means that all three soil P test methods could potentially be used as an index for P

nutrition of St. Augustinegrass. Mehlich-1 P obtained the best correlation against tissue P

concentration with r2 of 0.84 better than 0.77 and 0.79 for Fe Oxide P and WEP respectively.

The Critical Minimum Soil Test P Concentrations

Application of the various P20O rates up to 2.5 g P20O m-2 4-wk-1 resulted in a range of

extractable soil P concentration (0.5 to 16.7 mg kg- for Mehlich-1, 0.4 to 7.7 mg kg- for Fe

Oxide, and 0.4 to 7.6 mg kg- for WEP). Growth rate of St. Augustinegrass was affected by

extractable soil P concentrations (Figure 4-12; Figure 4-13; Figure 4-14). Responses were

described relatively well by the quadratic response and plateau model with the coefficients of









determination being generally high (0.71 for Mehlich-1, 0.68 for Fe Oxide, and 0.62 for WEP)

and p values of less than 0.0001. Critical concentration of the extractable P was greatest for

Mehlich-1 of 7 mg kg-1 compared 3 and 3 mg kg-1 for Fe Oxide P and WEP, respectively. This is

to be expected, because Mehlich-1 extractant contains diluted strong acids which could dissolve

water insoluble P compounds. Critical concentration of the extractable P for Fe Oxide and WEP

was the same. This indicated that P adsorbed on soil particles was soluble. CSP applied was

partially dissolved in soil solution and partially reacted with soil chemicals to form insoluble

compounds.

Previously, Mehlich-1 soil P below 16 mg kg-1 was categorized as low and below 10 mg

kg-1 as very low P. Phosphorus fertilization would be recommended in those cases. These data

showed that P levels can be kept very low for St. Augustinegrass optimum growth. Phosphorus

fertilization would not result in growth response above 7, 3, and 3 mg kg-1 for Mehlich-1, Fe

Oxide, and WEP, respectively. Mehlich-1 P had the best correlation against both tissue P

concentration and top growth rate in this soil, therefore it is the best soil P test for St.

Augustinegrass among the three used in this study.

P Downward Movement

Soil samples in depth of 0-10 cm were initially taken and analyzed for Mehlich-1 P.

However, Mehlich-1 P concentrations for the whole depth of 0-10 cm were generally very low,

and there was no difference in Mehlich-1 P concentrations among P application rates by

Duncan's multiple range test (data not shown). An attempt was made to investigate the

downward movement by separating the soil depth into 0-2 cm and 2-10 cm. Soil Mehlich-1 P

concentration as influenced by P application and soil sampling depth are shown in Figure 4-15.

Control soils contained 0.6 mg kg-1 Mehlich-1 P, which indicated extremely low soil P

availability without P application during the study. Soil Mehlich-1 P concentration in top 2 cm









depth increased with each incremental P application. Soil Mehlich-1 P concentrations in depth of

2-10 cm increased with P application, but were all very low in the range of 0.6 to 1.1 mg kg1.

Considering 0.6 mg kg-1 was the baseline of Mehlich-1 P with control, the highest P application

rate of 2.5 g P205 m-2 4-wk-1 resulted in Mehlich-1 P of 1.1 mg kg-1 in soil depth of 2-10 cm.

Moreover, for each P application other than control soil, Mehlich-1 P concentration in depth of

0-2 cm was higher than that in depth of 2-10 cm. This suggests that little to none of the CSP

applied to the turfgrass moved downward and the majority remained in the top 2 cm of soil.

Leached P Mass and Concentration

Phosphorus treatments were applied every four weeks for a total of four times. Leachates

were collected weekly. Sixteen leachates were collected during the study period. The sum of the

soluble reactive P (SRP) leached during the first, second, third and fourth leaching collections is

presented in Figure 4-16. Chung et al. (1999) has shown that a greater quantity of P leached from

sand root-zone mixture during the first two leaching events. However, a natural soil was used in

this study, for each P application a greater quantity ofP leached during the first leaching event

than those during following leachate collections. Soil receiving 2.5 g P205 m-2 4-wk-1 leached a

total of 11.8 mg P, followed by 5.9, 2, 1.3, and 0.9 mg P from application of 1.25, 0.63, 0.31 and

0 g P205 m-2 4-wk-1, respectively. The two highest P application rates resulted in larger quantities

of P leached and no differences in P leached were detected among the three lower P application

rates. In effect, soil with application rate of 0.63 g P205 m-2 4-wk-1 did not leach a larger quantity

of P than control soil. This result showed the importance of small P application rate to prevent P

leaching to ground waters. Not to mention the P requirements for certain crops could be less than

recommended, the best management practice could be to suggest multiple P applications with a

smaller quantity each time. Leached SRP concentration as affected by P application rate and

leaching event followed the same pattern as leached SRP mass (Figure 4-17). The highest P









concentration was detected in the leachates collected in the first leaching event. An application

of 0.63 g P205 m-2 4-wk-' did not result in a higher SRP concentration than control soil.

Leachates collected from soil receiving 2.5 and 1.25 g P205 m-2 4-wk-1 contained as high as 0.89

and 0.5 mg P kg-', respectively, which could cause environmental concerns. Notice that both of

these rates are commonly applied to St. Augustinegrass and application rate of 1.25 g P205 m-2 4-

wk-1 is the standard in summer months based on the 4:1:2 ratio of N: P205: K20.

Glasshouse Soil Study 2

Turf Quality

Quality ratings were influenced by P application rate for both soil No.2 and 3 (Table 4-4).

Twelve weeks of turf quality data were collected. For individual weekly evaluations across the

12 week experiment period, P application of 0.63g P205 m-2 4-wk-1 and above resulted in the best

turf quality for both soils (Table 4-4). P application of 0.31 g m-2 4-wk- achieved the best turf

quality in 11 out of 12 weeks for both soils (Table 4-4), which provided some evidence that the

minimum P application rate was somewhat above 0.31 g m-2 4-wk-1 for these two soils. For the

control turf, turf quality remained above acceptable level 5.5 for the first 4 and 3 weeks for soil

No.2 and 3, respectively, and declined afterwards. Overall, the turf quality ratings were

somewhat lower than that in the glasshouse soil study 1, which was mainly due to an incidence

of disease. Turf with no P application barely recovered from the incidence of disease, which

implied the importance of P nutrition in case of disease damage recovery.

Top Growth Rate

St. Augustinegrass top growth rate varied with P application and soil (Table 4-5). Control

turf produced the lowest quantity of top dry mass across six harvests in both soil conditions

(Table 4-5). The largest increase on top growth rate occurred in the first incremental P

application for both soils (1.6 to 2.5 and 1.6 to 2.1 g m-2 day'1 for soil No.2 and 3, respectively)









(Table 4-5). For soil No.2 the top growth rate for turf with P application rate of 0.31 g m-2 4-wk1

was reduced by approximately 10% from the optimum growth rate. Moreover, turf with P

application rates of 0.31 g m-2 4-wk- and above achieved equivalent mean top growth rates by

Tukey's test. Therefore, by either definition of critical minimum nutrient requirement or

Tukey's test, P application rate of 0.31 g m-2 4-wk- satisfied the minimum P requirement of St.

Augustinegrass in soil No.2. However, for soil No. 3 the top growth rate for turf with P

application rate of 0.31 g m-2 4-wk- was reduced by approximately 30% from the optimum

growth rate of 2.9 g m-2 day When the 6-harvest means of top growth rates were subjected to

Tukey's test, there were no differences among growth means receiving P application of 0.31 g

m2 4-wk-1 and above. This was probably due to a larger variation on top growth rate that

occurred when grown in soil No. 3. This larger variation may have resulted from more severe

disease damage in soil No. 3, which particularly influenced growth more on turf with lower P

application rates (0.63 g m-2 4-wk- and below) (Table 4-5). It has been previously shown that P

application improved recovery of turf quality from disease. These data also showed the benefits

of P application on top growth rate in case of disease incidence.

Tissue P Concentration

The initial tissue P concentration of the St. Augustinegrass was 4.1 g kg-1 on a dry weight

basis. Over 9 months before P application, tissue P concentration dropped from 4.1 g kg-1 to 1.2

g kg-1 on dry weight basis. Both soils contained very low Mehlich-1 P (< 5 mg kg-1).

Tissue P concentration of St. Augustinegrass varied with P rate and soil (Table 4-6). In

both soils, a maximum tissue P level was achieved (3.2 g kg-1) in response to P205 applied at 2.5

g m-2 4-wk- Turfgrass receiving no P maintained a value of 1.0 g kg-1, with which turfgrass

showed P deficiency symptoms, reduced turf quality (Table 4-6), and reduced growth rate

(Table 4-5). Tissue P concentration increased with each incremental P application across six









harvests for both soils. Maximum top growth rate was achieved at 0.31 g P205 m-2 4-wk-1,

suggesting that application of additional P does not enhance top growth rate but P uptake.

Greater tissue P concentrations and top growth rates were observed in soil No. 2 than No. 3,

indicating a greater P uptake occurred in soil No. 2, possibly caused by a more severe incidence

of disease in soil No.3.

The Critical Minimum Tissue P concentration

In a previous solution culture study, the critical tissue P concentration was determined to

be 1.6 g kg-1. In the glasshouse soil study 1, the critical minimum tissue P concentration was

estimated to be 1.8 g kg-1. In this study including two soils, the critical minimum tissue P

concentration was 1.9 g kg-1 (Figure 4-18), according to non-linear plateau regression analysis

(R2 = 0.70, p<0.0001). The coefficient of determination could be improved from 0.70 to 0.75 by

removing two outliers. The maximum top growth rate estimated in the quadratic relationship

was 2.8 g kg-1, which was the same as the optimum growth rates corresponding to the highest P

application rate of 2.5 g P205 m-2 4-wk-1, suggesting a reasonable plateau.

Soil P Tests

Soil Mehlich-1 P, Fe Oxide P, and WEP varied with P application for soil No. 2 (Figure 4-

19) and No. 3 (Figure 4-20). With increased P application soil test P levels increased for both

soils. For each P rate, Fe Oxide procedure extracted approximately the same quantity of P as

water, which was consistent with the findings in glasshouse soil study 1. This was possibly due

to a low bonding energy of P sorption/desorption with absence of Al/Fe oxides in these soils.

The portion adsorbed on soil particles eventually dissolved in the water extraction procedure.

Mehlich-1 P concentration was more or less double the concentration of Fe oxide P or WEP,

which was consistent with the observations in the glasshouse soil study 1. The explanation could

be the nature of Fe oxide P procedure that is based upon sorption/desorption process and does









not dissolve any water insoluble P components. However, Mehlich-1 extractant contains diluted

strong acids which could partially dissolve water insoluble P components.

Figure 4-21 showed the relationships among Mehlich-1 P, Fe Oxide P, and WEP

concentrations for soil No.2. They were pairwise linear dependent. All the pairwise relationships

were highly significant with p values less than 0.0001. In the previous glasshouse soil study 1, a

better correlation of Fe oxide P vs. WEP than that of Mehlich-1 P vs. WEP was observed. This

was true for soil No. 2 in this study with r2 s of 0.65 and 0.54 for WEP vs. Fe oxide P and

Mehlich-1 P vs. WEP, respectively. For soil No.3, an identical coefficient of determination (r2)

of 0.68 was obtained for relationships of Fe Oxide P vs. WEP and Mehlich-1 P vs. WEP. A

higher coefficient of determination was recorded for Mehlich-1 P vs. Fe Oxide P (r2=0.72)

(Figure 4-22).

In the glasshouse soil study 1, Mehlich-1 P correlated better with tissue P concentration

than Fe Oxide P and WEP (Figure 4-12). Tissue P concentration and soil test P concentrations

for soil No. 2 (Figure 4-23) and soil No. 3 (Figure 4-24) showed the same trend. For soil No. 2,

Mehlich-1 P obtained the best correlation against tissue P concentration with r2 of 0.85, which

was higher than 0.46 and 0.35 for Fe Oxide P and WEP, respectively. For soil No. 3, r2 of 0.71

was obtained for Mehlich-1 P vs. tissue P, which was higher than 0.67 and 0.63 for Fe Oxide P

and WEP vs. tissue P, respectively. Overall, the three soil P tests concentration were correlated

to tissue P concentration with Mehlich-1 P obtaining the best prediction on tissue P levels.

The Critical Minimum Soil Test P Concentrations

The growth rate of St. Augustinegrass was affected by soil Mehlich-1 P concentration

(Figure 4-25 for soil No. 2; Figure 4-26 for soil No. 3), Fe Oxide P (Figure 4-27 for soil No. 2),

and WEP concentration (Figure 4-28 for soil No. 2). Application of phosphate up to 2.5 g P205

m-2 4-wk-1 resulted in a range of extractable soil P concentrations (0.2 to 10.5 and 0.6 to 9.5 mg









kg-1 for Mehlich-1 in soil No. 2 and 3, respectively; 0.6 to 5.2 and 0.8 to 5.5 mg kg- for Fe Oxide

in soil No. 2 and 3, respectively; 0.8 to 4.0 and 0.9 to 4.6 mg kg-1 for WEP in soil No. 2 and 3,

respectively). Growth rate vs. Mehlich-1 P in both soils and growth rate vs. Fe Oxide P and

WEP in soil No.2 were described relatively well by the quadratic response and plateau model

with the coefficients of determination being generally acceptable (0.54 and 0.60 for Mehlich-1 in

soil No. 2 and 3 respectively, 0.72 for Fe Oxide in soil No. 2, and 0.41 for WEP in soil No. 2).

When top growth rate was related to Fe Oxide P and WEP in soil No. 3, top growth rate

increased with increasing Fe Oxide P or WEP concentrations and thus failed to converge to a

plateau (data not shown). This was possibly due to a low correlation between growth rate and Fe

Oxide P or WEP concentration and a large variation among replications. The critical Mehlich-1

P concentration obtained for soil No. 2 and 3 were 8 and 9 mg kg- respectively, which was

close to the critical Mehlich-1 P concentration (7 mg kg-1) determined in the previous glasshouse

soil study 1. For soil No. 2 the critical Fe Oxide P and WEP concentration was 3 mg kg-1. These

data suggest that optimum growth of St. Augustinegrass can be attained at very low soil lest P

levels. Phosphorus fertilization would not result in growth response above 8, 3, and 3 mg kg- for

Mehlich-1, Fe Oxide, and WEP, respectively for soil No. 2. Mehlich-1 P had the best correlation

against both tissue P concentration and top growth rate in both soils with exception of correlation

of top growth rate against Fe Oxide P was better than that against Mehlich-1 P. Overall,

Mehlich-1 P test was the best soil P test for St. Augustinegrass among the three extractants used.

P Downward Movement

In the glasshouse soil study 1, CSP applied to the turfgrass did not move downward and

the majority stayed in the top 2 cm in that soil. In this study soil samples were separated into 0-2

cm and 2-10 cm depths. Soil Mehlich-1 P concentration as influenced by P application rate and

soil sampling depth are shown in Figure 4-29 (soil No. 2) and Fig. 4-30 (soil No. 3). Mehlich-1 P









concentration (0-2 cm depth) with P application rate of 2.5 g P205 m-2 4-wk-1 was increased from

1 to 7.9 and 1.1 to 9.3 mg kg-1 for soil No. 2 and 3, respectively. Many studies have shown that

the amount of fertilizer P required for each unit increase of soil test P level varies with soil

texture, soil test method employed, as well as the rate of fertilizer P applied. In a 29-yr study on

Ultisols in Alabama, Cope (1981) found that 24 and 20 kg P ha1 raised Mehlich-1 soil test P by

1 mg P kg1 when P was applied at 31 and 54 kg P ha1 yr1, respectively. An application of 4 kg

P ha-1 was required to raise the Bray I extractable P of medium-textured Mollisols and Alfisols 1

kg ha-1 (Peck et al., 1971). Cox (1994) showed that increases in Mehlich-III with each unit of

applied P were 0.7 units for soils with 10% clay, and it decreased exponentially to 0.2 units for

soils with >50% clay. In this study total applications of 9.4, 18.8, 37.5, and 75 kg P205 ha1

raised the levels of soil Mehlich-1 P in top 2 cm soils by 2, 2, 4, and 7 mg P kg 1 soil,

respectively, for soil No. 2 and by 2, 3, 5, and 8 mg P kg 1 soil, respectively, for soil No. 3 after

12 week of P fertilization. Soil Mehlich-1 P concentrations in depth of 2-10 cm increased with P

application of 2.5 g P205 m-2 4-wk-1 for soil No. 2, but soils with lower P rates did not result in

increased Mehlich-1 P concentration (Fig. 4-29). For soil No. 3 P application did not influence

the Mehlich-1 P levels in soil depth of 2-10 cm (Figure 4-30). This suggests that most of CSP

applied to the turfgrass stayed in the top 2 cm soil depth and that a low application P rate would

be helpful in preventing P downward movement.

Leached P Mass and Concentration

Phosphorus treatments were applied every four weeks for a total of three times. Leachates

were collected weekly after each P application. Twelve leachates were collected during the

study period. The sum of the soluble reactive P (SRP) leached during the first, second, third and

fourth leaching collections is presented in Figure 4-31 (soil No. 2) and Figure 4-33 (soil No. 3),

respectively. In the glasshouse soil study 1, it was observed that for each P application rate a









substantial greater quantity of P leached during the first leaching event and that little P leached in

subsequent leachate collections. This was true for both soils in this study. Soil No. 2 which

receiving 2.5 g P205 m-2 4-wk-1 leached an average of 8.4 mg P, followed by 4.3, 1.6, 1.5, mg P

from application of 1.25, 0.63, 0.31 g P205 m-2 4-wk-1, respectively, among which 48%, 44%,

44%, and 34% was leached in the first leaching event. Soil No. 3 leached an average of 10.3 4.3,

3.2, 1.8, mg P from applications of 2.5, 1.25, 0.63 and 0.31 g P205 m-2 4-wk-1, respectively,

among which 42%, 47%, 47%, and 55% was leached in the first leachate collection. Not only

was there a higher percentage ofP mass leached in the first leaching event, but also the SRP

concentration was higher in the first leachate than the subsequent leachates in soil No. 2 (Figure

4-32 ) and soil No. 3 (Figure 4-34). These findings suggest the importance ofP application

timing. To avoid P application before a rain event would be beneficial in preventing P leaching

and runoff.

P application of 1.25 and 2.5 g P205 m-2 4-wk-1 resulted in larger quantities of P leached

and higher SRP concentration in soil No. 2 and there were no differences among leached P mass

and SRP concentrations resulted from the three lower P application rates. For soil No. 3, P

application of 2.5 g P205 m-2 4-wk-1 resulted in a larger quantity of P loss and higher SRP

concentration through leaching and there were no differences among leached P mass and SRP

concentrations at the lower P application rates. This suggests that P loss through leaching can be

prevented by small P application rate.

Glasshouse Soil Study 3

Turf Quality

Quantity of applied P influenced St. Augustinegrass quality (Table 4-7). A P205

application of 0.31 g m-2 4-wk- resulted in the best turf quality in 10 out of 12 weeks (Table 4-7).

Duncan's multiple range test of turf quality rating versus rate of P applied revealed differences in









mean turf quality rating up to 0.31 g P205 m-2 4-wk-'. Application of additional P beyond 0.31 g

P205 m-2 4-wk-1 did not increase turf quality. A total of 0.93 g P205 m-2 was applied, and this

equates to an N: P205 application ratio of 16:1, which is substantially higher than common used

4:1 ratio. The previous glasshouse study 1 and 2 reported the same response to P application for

St. Augustinegrass growing in course textured sandy soils. The overall turf quality including

controls was generally good, possibly because the relatively sufficient labile soil P prevented

severe P deficiency on St. Augustinegrass. The soil used in this study initially contained 17 mg

kg-1 Mehlich-1 P. By the time P treatments were applied, it was believed that this soil still

contained a substantial amount of plant available P, which was confirmed by soil analysis at the

end of the study. The soil Mehlich-1 P concentration in control soils was 2.7 mg kg-1, obviously

due to a relatively high residue soil P concentration in the beginning of the study.

Top Growth Rate

St. Augustinegrass top growth rate responded to P application (Table 4-8). Duncan's

multiple range test of top growth rate versus P application rate revealed differences in mean top

growth rate up to 0.31 g P205 m-2 4-wk-1. Application of additional P beyond 0.31 g P205 m-2 4-

wk-1 did not increase top growth (Table 4-8). Relatively smaller growth rate reduction

(approximately 25%) was observed in controls in this study compared with those in previous

studies. This was due to a higher initial soil Mehlich-1 P concentration in this soil so that P

deficiency on St. Augustinegrass was mildly developed. A CV of less than 10% suggests that

there is a small variation among replications.

Tissue P Concentration

The initial tissue P concentration of the St. Augustinegrass was 5.0 g kg-1 on a dry weight

basis. Over 15 months before P application, tissue P concentration dropped from 5.0 to 1.3 g kg-1

on dry weight basis. The soil Mehlich-1 P decreased from 17 to 4 mg kg-1 by the time P was









applied. Tissue P concentration of St. Augustinegrass responded to P application (Table 4-9).

Tissue P concentration increased with each incremental P application across six harvests. A

maximum tissue P level (3.4 g kg-1) was achieved in response to phosphate applied at 2.5 g m-2

4-wk-1. Turfgrass receiving no P maintained a value of 1.4 g kg-1, which was higher than those

found in the previous study 1 and 2 (1.0 g kg-1). This explains the smaller top growth rate

reduction in controls and only mild P deficiency symptoms observed in this study. The soil used

in this study supplied a substantial quantity of P for St. Augustinegrass growth over the entire

experiment period.

Critical Minimum Tissue P Concentration

In the previous solution culture study, the critical tissue P concentration was determined to

be 1.6 g kg-1. In the glasshouse soil study 1 and 2, the critical minimum tissue P concentration

was estimated to be 1.8 and 1.9 g kg-1, respectively. The critical minimum tissue P concentration

in study 3 was 1.8 g kg-1 (Figure 4-35), according to non-linear plateau regression analysis (r2 =

0.48, p<0.001). The coefficient of determination was lower than that found in previous soil study

1 and 2. This was possibly due to three or four outliers. The maximum top growth rate estimated

in the quadratic relationship was 2.9 g kg-1, which was consistent with the optimum growth rates

(2.9 and 2.8 g kg-1 for soil study 1 and 2, respectively), suggesting a reasonable plateau.

Soil P Tests

Soil Mehlich-1 P, Fe Oxide P, and WEP varied with P application in soil study 3 (Figure 4-

36). With each incremental increased P application soil Mehlich-1 P levels increased. Higher

soil test P values were only observed for the application of 2.5 g P20O m-2 4-wk-1 in Fe Oxide P,

1.25 and 2.5 m-2 4-wk-1 in WEP, respectively (Figure 4-36). In the glasshouse soil study 1 and 2,

Fe Oxide strip procedure and water extraction procedure extracted approximately the same

quantity of P in those soil conditions. However, in this study Fe Oxide procedure extracted









greater quantities of P than water for each P application, which suggests a higher bonding energy

ofP sorption/desorption with the Al/Fe oxides in this soil. Some portion of P ions adsorbed on

soil particles was not extracted by water extraction procedure but by Fe Oxide strip procedure.

Mehlich-1 P concentration was more or less double the concentration of WEP, which was

consistent with the observations in the glasshouse soil study 1 and 2.

Figure 4-37 shows the relationship among Mehlich-1 P, Fe Oxide P, and WEP

concentrations in glasshouse soil study 3. They were pairwise linear dependent. In the previous

glasshouse soil study 1 and 2, a better correlation of Fe oxide P vs. WEP than that of Mehlich-1

P vs. WEP was observed. This was true in this study with r2 s of 0.52 and 0.35 for WEP vs. Fe

oxide P and Melich-1 P vs. WEP, respectively. Moreover, the relationship of Fe oxide P vs.

WEP (p<0.0001) had a smaller p value than that of Mehlich-1 P vs. WEP (p<0.01). A smaller

coefficient of determination for each pairwise linear regression was obtained than those in the

glasshouse soil study 1 and 2. This was possibly due to narrower ranges of soil test P extracted in

this soil with Mehlich-1 P, Fe Oxide P and WEP mostly varied in 3, 1.5, and 1.5 mg P kg1,

respectively (Figure 4-37). These narrow ranges of soil test P revealed a strong bonding force of

P sorption/desorption and a small solubility of P compounds in water and dilute acids. These

narrow ranges of Fe Oxide P and WEP also affect the correlations against tissue P concentration.

The coefficients of determination for Fe Oxide P vs. Tissue P and WEP vs. Tissue P were 0.21

and 0.23, respectively, which were lower than those previously observed in the glasshouse study

1 and 2 (Figure 4-38). Soil Mehlich-1 P obtained the best correlation against tissue P

concentration with r2 of 0.70, higher than 0.21 and 0.23 for Fe Oxide P and WEP, respectively

(Figure 4-38). Overall, the three soil test P concentration were correlated with tissue P









concentration (p<0.05) with Mehlich-1 P obtaining the best prediction on tissue P levels, which

was consistent with observations in the previous studies.

The Critical Minimum Mehlich-1 P Concentration

Not only were the correlations of tissue P concentration against soil test P reduced by the

narrow range of soil test P concentrations, but also the relationship between top growth rate and

soil test P concentrations were reduced. Soil Fe Oxide P and WEP were poorly correlated with

top growth rate. Top growth rate continued to increase with increased Fe Oxide P or WEP

concentrations so that it did not converge to a plateau (data not shown). Therefore, it was not

possible to establish a critical minimum level for Fe Oxide P and WEP. Growth rate vs. Mehlich-

1 P was described well by the quadratic response and plateau model with the coefficients of

determination of 0.27 and p value less than 0.05. The critical Mehlich-1 P concentration obtained

was 5 mg kg-1, which was somewhat lower than the critical Mehlich-1 P concentrations of 7, 8,

and 9 mg kg-1 determined for soil No. 1, 2, and 3, respectively. This was expected because this

soil contained a larger quantity of Al/Fe oxides and has a larger P buffering capacity. For each

unit of soil test P level decrease, it supplied a larger quantity of P for plant uptake. These data

suggest that P levels can be kept very low for St. Augustinegrass optimum growth. Phosphorus

fertilization would not result in growth response above 5 mg kg-1 for Mehlich-1 P in this soil.

Mehlich-1 P had the best correlation against both tissue P concentration and top growth rate and

therefore is the best soil test method for St. Augustinegrass among the three tests used.

P Downward Movement

Soil samples were separated into 0-2 cm and 2-10 cm depths. Soil Mehlich-1 P

concentration as influenced by P application and soil sampling depth was shown in Figure 4-40.

Compared with control, Mehlich-1 P concentration (0-2 cm depth) with P application of 2.5 g

P205 m-2 4-wk-1 increased from 2.5 to 5.6 mg kg-1. Total applications of 9.4, 18.8, 37.5, and 75









kg P205 ha 1 raised the levels of soil Mehlich-1 P in top 2 cm soils by 0.6, 1, 1.6, and 3.1 mg P

kg 1 soil, respectively, after 12 weeks of P fertilization. Soil Mehlich-1 P concentration in top 2

cm soils increased with P application, however, P levels in the 2-10 cm depth was not affected

(Figure 4-40). This suggests that CSP applied to the turfgrass stayed in the top 2 cm soil depth

and downward movement of P was minimal.

Leached P Mass and Concentration

Phosphorus treatments were applied every four weeks for a total of three times. Leachates

were collected one, two, three and four weeks after each P application. Twelve leachates were

collected. The sum of the SRP quantity leached during the first, second, third and fourth leaching

collections is presented in figure 4-41. It was observed that for each non-zero P application

substantially greater quantities ofP leached during the first two leaching events than in the

following two leachate collections. This was consistent with the glasshouse soil study 1 and 2.

Soils applied with 2.5 g P205 m-2 4-wk-1 leached an average of 9.5 mg P, followed by 4.1, 3.5,

1.9 mg P from application of 1.25, 0.63, 0.31 g P205 m-2 4-wk-1, respectively, among which 71%,

68%, 74%, and 63% was leached out in the first two leaching events. Not only was there a

substantial higher percent of P mass leached in the first two leaching events, but also the SRP

concentration was higher in the first two leachates than followings (Figure 4-42). These findings

suggest timing could be an issue for P application. To avoid P application before a rain event

would be beneficial in preventing P leaching.

For each P application rate, the overall percentage of P loss due to leaching for application

of 0.31, 0.63, 1.25, and 2.5 g P205 m-2 4-wk-1 were 1.9%, 1.8%, 1.0% and 1.2%, respectively.

The percentage were relatively small, but P application of 1.25 and 2.5 g P205 m-2 4-wk-1

resulted in larger quantities of P leached and P application of 2.5 g P205 m-2 4-wk-1 led to higher

SRP concentration. P application of 0.63 g P205 m-2 4-wk-1 and below did result in neither a









greater P quantity loss nor a higher SRP concentration than control. This suggests that small P

application rate was effective in preventing P loss through leaching.































1.24


6.2 31
Solution P (mg m-3)


Figure 4-1. Turf quality response to solution P concentration. Turf quality is the mean of five
replications over time after treatments were applied. Means marked by the same letter
are not significantly differently at P = 0.05 according to Duncan's Multiple Range
Test.


P, mg m-3

- 0

-u-1.24
-- 6.2
-x- 31

-* 155
-*-775


8/18 9/17 10/17 11/16 12/16


1/15 2/14 3/16


Month/Day (2004-2005)



Figure 4-2. Tissue P response to solution P concentration and time.


6

4 5

4


3

2

1


6

5

S4

P3

H2
.C..


0


7/19


No P applied before this
pomt





















c C

E E


0 1.24


B
C C



6.2 31 155
Solution P (mg m3)


Figure 4-3. Relationship of solution P and tissue P concentration on day 148. Means marked by
the same letter are not significantly differently at P = 0.05 according to Duncan's
Multiple Range Test.


0.8

0.6

0.4

0.2


-7


0 1.24


6.2 31
Solution P (mg m3)


155 775


Figure 4-4. Relationship of solution P and root P concentration on day 148. Means marked by the
same letter are not significantly differently at P = 0.05 according to Duncan's
Multiple Range Test.


3
2 2.5
9 2
) 1.5
1


1



















U
S
0


- S


y = 0.9938 0.00004(x 110.9)2
R2 = 0.86, p< 0.0001, CV= 15.5
plateau= 1 critical x =111


0 100


200


300


600


700


Solution P (mg m3)
Figure 4-5. St. Augustinegrass tissue growth rate relative to solution P concentration.


Ct
7


800


I I I I I I I I












A
3
AB AB AB

g1 2.5 B B


2


1.5



0 1.24 6.2 31 155 775

Solution P (mg m-3)

Figure 4-6. Root growth rate relative to solution P concentration. Means marked by the same
letter are not significantly differently at P = 0.05 according to Duncan's Multiple
Range Test.


















0.

0

.0
S




S


y = 1.0456 -0.5056(x- 1.5614)2
R2 = 0.88, p<0.0001, CV= 15.4
plateau = 1 critical x = 1.6


0.0 L
0.0


Figure 4-7. St.


.5 1.0 1.5 2.0 2.5 3.0

Tissue P (g kg-')
Augustinegrass tissue growth rate relative to tissue P concentration.


T3


(N
a






o
t>










Table 4-1. Visual quality rating of St. Augustinegrass as influenced by P application rate in 2005-2006 glasshouse soil study 1.
P205 rates ------------------------------------- Week t-----------------------------
(g m-2 4-wk-1) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Mean

0 6.4c 6.5c 5.9c 7b 6.7b 6.8b 6.6b 6.9c 6.2b 6.2b 5.7c 5.4b 5.4b 6.1b 4.5b 4.6b 6.3c
0.31 7.0b 7.4ab 7.3b 7.4ab 7.3a 7.5a 7.4a 7.4bc 7.2a 7.7a 7.3b 7.6a 7.2a 7.9a 7.1a 7.4a 7.4b
0.63 6.9b 7.3b 7.2b 7.6ab 7.2a 7.7a 7.2ab 7.6ab 7.2a 7.6a 7.5ab 7.7a 7a 7.9a 7.5a 7.4a 7.4b
1.25 6.9b 7.7ab 7.7ab 7.8a 7.6a 7.8a 7.6a 7.9ab 7.6a 8a 7.8ab 7.8a 7.5a 8.1a 7.5a 7.7a 7.7ab
2.5 7.4a 8.0a 8.1a 8.0a 7.8a 8.1a 7.8a 8.1a 7.7a 8.1a 8.0a 8.0a 7.8a 8.2a 7.6a 7.9a 7.9a

CV(%) 4.3 6.3 6.4 7.4 6.1 5.6 6.3 5.5 6.2 5.9 6.1 4.8 8.7 6.9 6.0 8.8 4.7

tWithin columns, means followed by the same letter are not significantly different according to Duncan's multiple range test (0.05).









Table 4-2. Top growth rate of St. Augustinegrass as influenced by P application rate in 2005-
2006 glasshouse soil study 1.
P205 rates ----------------------Harvest t(g m-2 day) --------------------------------
(g m-2 4-wk-1) 1 2 3 4 5 6 7 8 Mean

0 2.2b 2.1b 2.1b 1.9b 2.0c 2.1c 2.1b 1.9b 2.1b
0.31 2.9ab 2.6ab 2.6a 2.3ab 2.4bc 2.5bc 2.9a 2.7a 2.7a
0.63 3.0a 2.6ab 2.9a 2.4ab 2.7ab 2.7ab 3.0a 3.0a 2.7a
1.25 3.0a 2.9a 3.0a 2.5ab 2.9a 3.0ab 3.1a 3.1a 3.0a
2.5 3.4a 3.0a 3.0a 2.5a 3.0a 3.1a 3.1a 3.1a 3.0a

CV(%) 18.8 15.4 18.5 16.9 12.7 16.6 8.5 12.9 10.6

tWithin columns, means followed by the same letter are not significantly different according to
Duncan's multiple range test (0.05).


Table 4-3. Tissue P concentration of St. Augustinegrass as influenced by P application rate in
2005-2006 glasshouse soil study 1.
P205 rates ------------------------ ------Harvest t(g kg) ---------------------------------
(g m-2 4-wk-1) 1 2 3 4 5 6 7 8 Mean

0 1.ld 1.ld 1.ld 1.0d 1.0d 1.0d 0.8d 1.0e 1.0e
0.31 1.5cd 1.5cd 1.5c 1.4c 1.5c 1.3cd 1.3d 1.5d 1.4d
0.63 1.7c 1.6c 1.7c 1.7c 1.7c 1.8c 1.8c 2.1c 1.8c
1.25 2.5b 2.3b 2.6b 2.3b 2.4b 2.4b 2.7b 3.0b 2.5b
2.5 3.5a 3.2a 3.3a 3.1a 3.5a 3.3a 3.4a 4.1a 3.4a

CV(%) 17.7 18.8 15.3 15.1 15.3 19.5 17.5 8.1 11.2

tWithin columns, means followed by the same letter are not significantly different according to
Duncan's multiple range test (0.05).












3.6




3.2-
(0
o-


E 2.8-
0)
a)


2.4 -

0
0)
0-
0o 2.0-



1.6


y
R
pi


*


* -


=2.91 1.57 (1.76-x)2
2 = 0.77, p<0.0001, CV=10.9%
ateau = 2.91 critical x = 1.8


Tissue P (g kg-1)
Figure 4-8. St. Augustinegrass tissue growth rate relative to tissue P
glasshouse soil study 1.


concentration in the


0


















S 0 0 1 WEP2

8-

Sc
4 c
cc c
d dd

0 0. 31 0.63 1.25 2.5
P205 application rate (g m 2 4-wk ')


Figure 4-9. Soil Mehlich-1 P, Fe Oxide P, and WEP concentration as influenced by P application
rate (soil sampling depth of 0-2 cm) in the glasshouse soil study 1.
































2 4 6

Fe Oxide P (mg kg 1)


4

Fe Oxide P (mg kg )


2 4 6 8 10


WEP (mg kg 1)


Figure 4-10. Relationships among Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils
sampling depth of 0-2 cm) in the glasshouse soil study 1.


20


b 16
-4

12

ia
8

-4
-s 4
(U


y 2.Ox + 0.09

r = 0.85, p<0.0001
CV 27%

.1 *


20


h 16
-4

12








0
*-

sc
0,















3


2


1


0


WEP (mg kg'1)

Figure 4-11. Relationships between tissue P concentration and Mehlich-1 P, Fe Oxide P, and
WEP concentrations (soils sampling depth of 0-2 cm) in the glasshouse soil study 1.


*^ : y = 0.17x + 0.93
r 0. 84, p<0. 0001
CV = 21%



D 4 8 12 16
Mehlich-1 P (mg kg1)



y 0.44x + 0.76
r2 0.77, p<0.0001
CV = 19.2% **









D 2 4 6
Fe Oxide P (mg kg )










y = 0.36x + 0.88
r 0.79, p<0. 0001
CV 17.4%


S4

M3

Q 2

- 1

0


4


03








0
*^













3.6 -





3.2 -
(0
co
IC

E 2.8-
0)
-^-
a)


- 2.4 -

0
0)
0-
0o 2.0-




1.6


U

* U


- 0.02(6.94 x)2
'1, p<0.0001, CV
=2.93 critical x


:20.7%
S7


I I I I I I I


0 2 4 6 8 10 12 14 16 18


Mehlich-1 P (mg kg-1)


Figure 4-12. St. Augustinegrass tissue growth rate relative to soil Mehlich-1 P concentration in
the glasshouse soil study 1.


Sy = 2.93
R2 = 0.7
/ plateau

U














3.6 -




3.2 -

(0


E 2.8-
o)

a)


2 2.4 -

0
0)
0-


o 2.0




1.6


*/ U


0


y =2.90- 0.13(3.10 -x)2
R2 = 0.68, p<0.0001, CV
plateau = 2.90 critical x =


Fe Oxide P (mg kg-1)


Figure 4-13. St. Augustinegrass tissue growth rate relative to soil Fe Oxide P concentration in the
glasshouse soil study 1.


18.9%













3.6 -





3.2 -

(0
co


E 2.8-
0)

a)


2 2.4

0
0)
0-
o 2.0




1.6


y = 2.90 -0.11(3.31 x)2
R2 = 0.62, p<0.0001, CV
plateau = 2.90 critical x =


14%


WEP (mg kg-1)



Figure 4-14. St. Augustinegrass tissue growth rate relative to soil WEP concentration in the
glasshouse soil study 1.


U

EU
U



U
U

U

U

















12


&0 8
E
C^


0 0.31 0.63 1.25 2.5
-2
P205 application rate (g m2 per 4 wks)

Figure 4-15. Soil Mehlich-1 P concentration as influenced by P application rate and soil
sampling depth in the glasshouse soil study 1.







6

E 5 -- 1st
<4 m 2nd
4
E o 3rd
(L3 4th
4th a
C,,
2-
c b



0 0.31 0.63 1.25 2.5

P205 application rate (g m"2 4-wk"1)

Figure 4-16. Leached SRP mass as influenced by P application rate and leaching event in
glasshouse soil study 1.












a
0 1st
S 0.8 m 2n
[] 3rd a
0.6 4
o L4th b
C, a
0.4 a
b

". 0.2 c
C C
C C cc

0
0 0.31 0.63 1.25 2.5

P205 application rate (g m"2 4-wk"1)

Figure 4-17. Leached SRP concentration as influenced by P application rate and leaching event
in glasshouse soil study 1.









Table 4-4. Visual quality rating of St. Augustinegrass as influenced by P application rate in 2005-2006 glasshouse soil study 2.
P205 rates ---- -----------------------------Week----------- --------------
Soil (g m-2 4-wk-1) 1 2 3 4 5 6 7 8 9 10 11 12 Mean

0 6.5a 6.7b 6.4a 5.7b 5.3b 5.5b 4.7b 4.5b 4.7c 4.5b 5.0b 4.4b 5.3b
0.31 7.3a 7.8ab 7.3a 7.6a 6.9a 7.3a 6.3a 6.8a 6.6b 7.4a 6.5a 6.8a 7.0a
2 0.63 6.9a 7.6ab 7.3a 7.4a 7.2a 7.5a 6.8a 7.1a 7.3ab 7.6a 6.6a 7.0a 7.2a
1.25 7.3a 8.1a 7.3a 7.6a 7.4a 7.7a 7.1a 7.2ab 7.3ab 8.0a 7.0a 7.1a 7.4a
2.5 7.1a 7.8a 7.5a 7.7a 7.4a 7.8a 7.4a 7.4a 7.3a 7.6a 7.1a 7.0a 7.4a

0 6.5a 6.7b 6.3b 5.4c 5.1b 5.3b 4.2b 4.2b 4.3b 4.5b 4.7b 4.5b 5.1b
0.31 6.9a 7.4ab 7.lab 6.8b 6.0ab 6.6ab 6.2a 6.6a 6.1a 6.9a 6.7a 6.2a 6.6a
3 0.63 6.8a 7.6ab 6.5ab 7.lab 6.3ab 6.8a 6.1a 6.4a 6.9a 7.5a 6.2a 6.6a 6.7a
1.25 7.0a 7.6ab 7.4ab 7.4ab 7.0a 7.5a 6.8a 7.1a 7.1a 7.4a 6.9a 6.8a 7.2a
2.5 7.3a 8.1a 7.7a 7.8a 7.4a 8.0a 7.3a 7.3a 7.4a 7.7a 7.2a 7.0a 7.5a

CV(%) 5.7 8.0 9.1 6.7 10.7 9.9 10.6 6.8 8.6 6.6 10.1 7.5 6.3

tWithin columns for each soil, means followed by the same letter are not significantly different according to
Tukey's test (0.05).









Table 4-5. Top growth rate of St. Augustinegrass as influenced by P application rate and soils in
2005-2006 glasshouse soil study 2.

P205 rates -----------------Harvest t(g m-2 day) --------------------
Soil (g m-2 4-wk-1) 1 2 3 4 5 6 Mean

0 2.7a 1.7b 1.6b 1.2b 1.lb 1.7b 1.6b
0.31 3.5a 2.3ab 2.5a 2.0a 2.4a 2.5ab 2.5a
2 0.63 3.3a 2.4ab 2.9a 2.1a 2.5a 2.8a 2.6a
1.25 3.8a 2.6a 3.0a 2.3a 2.7a 2.9a 2.9a
2.5 3.6a 2.7a 3.0a 2.2a 2.8a 3.0a 2.8a

0 2.5a 1.5b 1.6c 1.3c 1.3b 1.5b 1.6b
0.31 3.0a 2.0ab 2.1bc 1.6b 2.lab 2.lab 2.lab
3 0.63 2.9a 1.7ab 2.2bc 1.6abc 2.lab 2.2ab 2.lab
1.25 3.2a 2.4a 2.5a 2.lab 2.5a 2.5a 2.5a
2.5 3.4a 2.5a 3.0a 2.2a 2.7a 3.0a 2.8a

CV(%) 18.1 19.7 13.5 15.2 17.6 18.0 14.0

tWithin columns for each soil, means followed by the same letter are not significantly different
according to Tukey's test (0.05).


Table 4-6. Tissue P concentration of St. Augustinegrass as influenced by P application rate and
soils in 2005-2006 glasshouse soil study 2.

P205 rates ----------------Harvest t (g kg-1) ---------
Soil (g m-2 4-wk-1) 1 2 3 4 5 6 Mean

0 1.ld 0.98c 0.94c 0.94c 1.1d 0.89c 0.98d
0.31 1.3cd 1.2c 1.2c 1.3c 1.4cd 1.3c 1.3cd
2 0.63 1.5c 1.4bc 1.4c 1.4abc 1.9c 1.6bc 1.5c
1.25 2.0b 1.8b 2.3b 2.2ab 2.9b 2.1b 2.2b
2.5 3.1a 2.7a 3.1a 3.0a 3.8a 3.3a 3.2a

0 1.ld 0.93c 1.0c 1.0c 1.0d 1.0c 1.0c
0.31 1.2c 1.0c 1.1c 1.0c 1.4cd 1.2c 1.2c
3 0.63 1.5c 1.2bc 1.2bc 1.3bc 1.9c 1.5c 1.4c
1.25 2.0b 1.7b 1.8b 1.9b 2.6b 2.2b 2.0b
2.5 3.3a 2.6a 2.5a 2.8a 3.9a 3.5a 3.2a

CV(%) 10.8 15.6 17.7 24.5 11.8 17.7 10.3

tWithin columns for each soil, means followed by the same letter are not significantly different
according to Tukey's test (0.05).












4.0


3.5 -


* .


U
EU


.

.
=U
*l
U. U


(0



E
0)

a)


0

L-

O
0-
0
H-


* 0


:12.2%
1.9


Tissue P (g kg-1)


Figure 4-18. St. Augustinegrass tissue growth rate relative to tissue P concentration in the
glasshouse soil study 2.


y =2.81 1.26(1.93 -x)2
R2 = 0.70, p<0.0001, CV
plateau =2.81 critical x:


3.0 -


2.5 -


2.0 -


1.5 -


1.0 -


.5 -


0.0
























0 I I- -- -- -- -- -- -- --I _
0 0.31 0.63 1.25 2.5
P205 application rate (g m2 4-wk )
Figure 4-19. Soil Mehlich-1 P, FeO P, and WEP concentration as influenced by P application
rate (soil sampling depth of 0-2 cm) in the glasshouse soil study 2 (soil No. 2).


0 0.31 0.63 1.25 2.5
P205 application rate (g m2 4-wk )
Figure 4-20. Soil Mehlich-1 P, FeO P, and WEP concentration as influenced by P application
rate (soil sampling depth of 0-2 cm) in the glasshouse soil study 2 (soil No. 3).












a

4

- 3




1

0


0 1 2 3 4 5 6

WEP (mg kg1)

Figure 4-21. Relationships among Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils
sampling depth of 0-2 cm) in the glasshouse soil study 2 (soil No. 2).


y 0.70x + 0.51 *
r 0.65, p<0.0001
CV 35% *






** *



3 1 2 3 4 5
Fe Oxide P (mg kg )



y 1.71x 0.19
r2 0.66, p<0.0001
CV 25. 8% *




++
4




0 1 2 3 4 5 6
Fe Oxide P (mg kg 1)



y 1.77x + 0. 16
r 0.54, p<0.0001 *
CV 29.7% *







I













b

4







1
S3


2




0


WEP (mg kg 1)

Figure 4-22. Relationships among Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils
sampling depth of 0-2 cm) in the glasshouse soil study 2 (soil No. 3).


*





*+ y = 0.75x + 0.37
Sr 0.68, p<0. 0001
CV= 24. 9%



3 1 2 3 4 5 6
Fe Oxide P (mg kg )


y 1.91x 0.72
r 2 0.72, p<0.0001
CV 27. 4%











0 1 2 3 4 5 6

Fe Oxide P (mg kg )



y =2. 04x 0. 58
r = 0.68, p<0.0001
CV 28.8%
*

o *..


% i i












S y 0.26x + 0.66
r 0.85, p<.0001
=3 CV = 18.3% *
&* *

2

.21 *


0
0 2 4 6 8 10
Mehlich-1 P (mg kg1)


y 0.40x + 0.72

r 0.46, p<0.0001 *
3 CV 15. 8%
M *
a 2 4




0
*-




0 1 2 3 4 5 6

Fe Oxide P (mg kgl)


4






*y 0.40x + 0.84
1 ** 2
r 0.35, p<0.0001
CV 19.4%
0
0 1 2 3 4 5 6
WEP (mg kg 1)

Figure 4-23. Relationships between tissue P concentration and Mehlich-1 P, Fe Oxide P, and
WEP concentrations (soils sampling depth of 0-2 cm) in the glasshouse soil study 2
(soil No. 2).














- 3. 5
M
bZ

S2.5


0 1.5


0.5


0 2 4 6
Mehlich-1 P


8
(mg kg 1)


10 12


++




y =0.54x + 0.45
r 0. 67, p<0.0001
CV 15.8%


0 1 2 3 4 5 6
Fe Oxide P, mg kg-1



y =0.58x + 0.49
r2 0.63, p<0.0001
CV 19. 4%


"... .



I II


0 1 2 3 4 5
WEP (mg kg 1)

Figure 4-24. Relationships between tissue P concentration and Mehlich-1 P, Fe Oxide P, and
WEP concentrations (soils sampling depth of 0-2 cm) in the glasshouse soil study 2
(soil No. 3).


y =0.24x + 0.79
r2 0.71, p<0.0001 *
CV 18.3%






8 i*_____















*













y 2.96 0.024(7.73 x)2
R2 = 0.54, p<0.001, CV =17.3%
plateau = 2.96 critical x = 8


Mehlich-1 P (mg kg-1)
Figure 4-25. St. Augustinegrass tissue growth rate relative to soil Mehlich-1
the glasshouse soil study 2 (soil No. 2).


P concentration in


4.0


3.5 -



3.0 -



2.5 -



2.0 -



1.5 -


(0


E
0)
a)



0
L-

O
0-
0
H-


1.0


-I.











3.2


2.8-



c) 2.4
E

S2.0
(--

y =2.74 0.017(8.78 x)2
1.6 R2 = 0.60, p<0.0001, CV = 20.2%
S/ plateau = 2.74 critical x = 9
0)
0-
-1.2



.8 I I I I I
0 2 4 6 8 10 12

Mehlich-1 P (mg kg-1)
Figure 4-26. St. Augustinegrass tissue growth rate relative to soil Mehlich-1 P concentration in
the glasshouse soil study 2 (soil No. 3).





















0 0


3.5 -



3.0 -



2.5 -



2.0 -



1.5 -


* 0
*


>.,
(c


E
0)


a)



0
L-
O
-.)
0
0
H.


-25.6%
3


Fe Oxide P (mg kg-1)
Figure 4-27. St. Augustinegrass tissue growth rate relative to soil Fe Oxide P concentration in the
glasshouse soil study 2 (soil No.2).


4.0


- ^



Sy = 2.74
*/ R2 = 0.7
plateau



/.


-0.23(3.09 x)2
2, p<0.0001, CV:
2.74 critical x=


1.0


-I.


C










3.2


2.8 -



(c 2.4-
E
0)
0 2.0 -
S/ y= 2.72- 0.21(3.08-x)2
/R2 = 0.41, p<0.01, CV= 26.4%
O plateau = 2.72 critical x = 3
o 1.6
0)
0 .
I- 1.2



.8 I I I I I
0 1 2 3 4 5 6

WEP (mg kg-1)
Figure 4-28. St. Augustinegrass tissue growth rate relative to soil WEP concentration in the
glasshouse soil study 2 (soil No.2).















07

3 -'
o 00
'6 P
v


O 0-2 cm
O 2-10 cm
B


C

-b
b b b




0 0.31 0.63 1.25 2.5
P205 application rate (g m-2 4-wk- )


Figure 4-29. Soil Mehlich-1 P concentration as influenced by P application rate and soil
sampling depth in the glasshouse study 2 (soil No. 2).


D 0-2 cm A
A
O 2-10 cm


B -


C C a a
a a




0 0.31 0.63 1.25 2.5
P205 application rate (g m-2 4-wk- )


Figure 4-30. Soil Mehlich-1 P concentration as influenced by P application rate and soil
sampling depth in the glasshouse study 2 (soil No. 3).














E 4 0 1st


E
a 2nd
E 3 1 3rd
Co 4th
t2 b a

a
l c
1 Cc b


0 0.31 0.63 1.25 2.5

P205 application rate (g m"2 4-wk"1)

Figure 4-31. Leached SRP mass as influenced by P application rate and leaching event in
glasshouse soil study 2 (soil No.2).


0.6


--
n 0.4
E

0.2


0


* 1st
* 2nd
o 3rd
o 4th


c
ccC C

-101111 = M -A


0 0.31


0.63


1.25


a

a



2.5


P205 application rate (g m-2 4-wk1)

Figure 4-32. Leached SRP concentration as influenced by P application rate and leaching event
in glasshouse soil study 2 (soil No.2).














E 4 1st
m 2nd
S3 o 3rd
S4o 4th b
cO 2
b
a1 b b bb a
bb b
-j
0 b bbb b

0 0.31 0.63 1.25 2.5

P205 application rate (g m-2 4-wk"1)

Figure 4-33. Leached SRP mass as influenced by P application rate and leaching event in
glasshouse soil study 2 (soil No.3).


0.6

-j
S0.4
E

0.2


0


0 0.31 0.63 1.25 2.5


P20s application rate (g m"2 4-wk"1)

Figure 4-34. Leached SRP concentration as influenced by P application rate and leaching event
in glasshouse soil study 2 (soil No.3).










Table 4-7. Visual quality rating of St. Augustinegrass as influenced by P application rate in 2005-2006 glasshouse soil study 3.
P205 rates ---------------------------------- Week t----------------- -------
(g m2 4-wk-1) 1 2 3 4 5 6 7 8 9 10 11 12 Mean

0 6.1b 6.2b 5.8b 5.6c 5.5b 5.2b 5.6b 5.4b 6.3b 6.9c 6.9c 6.6b 6.2b
0.31 7.2a 7.5a 6.6ab 7.1b 7.1a 7.1a 7.1a 6.6a 6.9ab 7.1bc 6.8bc 7.1a 7.0a
0.63 7.5a 7.9a 7.1a 7.7ab 7.5a 7.2a 7.2a 7.2a 7.4a 7.6abc 7.3ab 7.3a 7.4a
1.25 7.6a 7.9a 7.5a 7.8a 7.6a 7.7a 7.2a 7.3a 7.4a 7.7ab 7.5a 7.4a 7.6a
2.5 7.7a 8.0a 7.6a 7.6ab 7.6a 7.5a 7.3a 7.3a 7.2a 7.9a 7.5a 7.4a 7.5a

CV(%) 7.6 4.9 10.7 6.8 7.6 9.7 5.4 8.3 8.8 7.4 6.54 5.2 5.7

tWithin columns for each soil, means followed by the same letter are not significantly different according to
Duncan's multiple range test (0.05).


Table 4-8. Top growth rate of St. Augustinegrass as influenced by P application rate in 2005-2006 glasshouse soil study 3.

P205 rates ---------------------Harvest (g m-2 day) --------------------
(g m-2 4-wk-1) 1 2 3 4 5 6 Mean

0 3.2b 3.0a 2.8b 1.6b 2.0b 1.5b 2.4b
0.31 3.8ab 3.1a 3.0ab 1.9ab 2.5ab 1.6ab 2.6a
0.63 3.9a 3.1a 3.0ab 2.0 a 2.6a 1.7ab 2.7a
1.25 3.9a 3.3 a 3.lab 2.1a 2.7a 1.7ab 2.8a
2.5 4.3a 3.4a 3.3a 2.1a 2.7a 1.8a 3.0a

CV(%) 11.3 11.3 10.8 8.8 17.9 13.0 8.0

Within columns for each soil, means followed by the same letter are not significantly different
according to Duncan's multiple range test (0.05).









Table 4-9. Tissue P concentration of St. Augustinegrass as influenced by P application rate in
2005-2006 glasshouse soil study 3.

P205 rates -------------------------Harvest (g kg) ----------------------------
(g m-2 4-wk-1) 1 2 3 4 5 6 Mean

0 1.3d 1.4b 1.3d 1.2d 1.5d 1.5e 1.4d
0.31 1.4d 1.5b 1.7cd 1.5c 1.8d 1.9d 1.6d
0.63 1.8c 2.1a 1.9bc 1.7c 2.3c 2.5c 2.0c
1.25 2.2b 2.3a 2.3b 2.4b 3.0b 3.5b 2.6b
2.5 2.9a 2.4a 3.4a 3.3a 4.1a 4.6a 3.4a

CV(%) 15.0 20.0 14.3 8.8 14.1 9.4 8.6




Full Text

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1 PHOSPHORUS REQUIREMENT OF ST. AUGUSTINEGRASS By MIN LIU A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2007

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2 2007 Min Liu

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3 To my wife Ma, Kehong, my father, Li u, Dinghong and my mother, He, Wanmei

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4 ACKNOWLEDGMENTS I give my sincere thanks and appreciation to the chair of my supervisory committee, Dr. Jerry Sartain. It is his continuous support, guida nce, and encouragement that made this degree possible. I would also like to thank the other committee members: Dr. Laurie Trenholm for her expertise in turfgrass, Dr. Grady Miller for hi s knowledge of turfgra ss research methodology, Dr. Peter Nkedi-Kizza for his suggestion for the leach ing data analysis, Dr. Willie Harris for his knowledge in soil mineralogy, Dr. Rongling Wu for his guidance in Statistics. Thanks go to the Florida Department of Environment Protection who sponsored this research project. Special thanks go to lab pers onnel, Ed Hopwood Jr., Nahid Varshovi, Martin Sandquist, who helped me throughout my research. Sp ecially, I would like to thank my dear wife, Kehong Ma, our incoming baby, both sets of pare nts and family members for their ongoing support.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........7 LIST OF FIGURES................................................................................................................ .........8 ABSTRACT....................................................................................................................... ............11 CHAPTER 1 INTRODUCTION..................................................................................................................13 2 LITERATURE REVIEW.......................................................................................................15 Phosphorus in the Soil-Plant Environment.............................................................................15 Phosphorus Reactions in Soil..........................................................................................15 Organic Soil P..................................................................................................................16 Leached P in Turfgrass Environment..............................................................................17 Management Practices to Reduce P Leaching................................................................... 18 Conventional Soil and Tissue P Tests....................................................................................19 Soil P Extractants............................................................................................................19 Suitability of Different Extracting Procedures................................................................20 Soil P Extracting Procedures and Geographical Regions................................................21 Tissue P test.................................................................................................................. ...22 Response of Turfgrass to P Fertiliz ers and Fertilizer Recommendations...............................22 Phosphorus Toxicity Trial...............................................................................................22 Phosphorus Requirements by Turfgrasses.......................................................................23 Critical Minimum Soil P Concentrations........................................................................25 Effects of P Applicati on on Soil Test P Levels...............................................................27 Critical Tissue P Concentrations.....................................................................................28 Interaction with other Nutrients..............................................................................................30 Phosphorus and N............................................................................................................30 Phosphorus and K, Ca and Mg........................................................................................31 Phosphorus and Zn..........................................................................................................32 Effect of N, P, K, and their In teractions on Water Use Efficiency.................................. 32 3 MATERIALS AND METHODS...........................................................................................37 Glasshouse Hydroponic Study................................................................................................37 Glasshouse Soil Study 1........................................................................................................ .39 Glasshouse Soil Study 2........................................................................................................ .40 Glasshouse Soil Study 3........................................................................................................ .42

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6 4 RESULTS AND DISCUSSION.............................................................................................46 Glasshouse Hydroponic Study................................................................................................46 Turf Quality................................................................................................................... ..46 Tissue P and Root P.........................................................................................................46 Tissue Growth Rate and Root Growth Rate....................................................................47 Critical Tissue P level......................................................................................................48 Glasshouse Soil Study 1........................................................................................................ .49 Turf Quality................................................................................................................... ..49 Top Growth Rate.............................................................................................................49 Tissue P Concentration....................................................................................................50 The Critical Minimum Tissue P concentration...............................................................51 Soil Test P.................................................................................................................... ....51 The Critical Minimum Soil Test P Concentrations.........................................................52 P Downward Movement..................................................................................................53 Leached P Mass and Concentration................................................................................54 Glasshouse Soil Study 2........................................................................................................ .55 Turf Quality................................................................................................................... ..55 Top Growth Rate.............................................................................................................55 Tissue P Concentration....................................................................................................56 The Critical Minimum Tissue P concentration...............................................................57 Soil P Tests................................................................................................................... ...57 The Critical Minimum Soil Test P Concentrations.........................................................58 P Downward Movement..................................................................................................59 Leached P Mass and Concentration................................................................................60 Glasshouse Soil Study 3........................................................................................................ .61 Turf Quality................................................................................................................... ..61 Top Growth Rate.............................................................................................................62 Tissue P Concentration....................................................................................................62 Critical Minimum Tissue P Concentration......................................................................63 Soil P Tests................................................................................................................... ...63 The Critical Minimum Mehl ich-1 P Concentration........................................................65 P Downward Movement..................................................................................................65 Leached P Mass and Concentration................................................................................66 5 CONCLUSIONS..................................................................................................................108 Glasshouse Hydroponic Study..............................................................................................108 Turf Quality in Glasshouse Soil Studies...............................................................................108 Top Growth Rate in Glasshouse Soil Studies.......................................................................109 Tissue P Concentration and Crit ical Tissue P Concentration...............................................109 Soil P Tests and Critical So il Test P Concentrations............................................................109 P Downward Movement and Leached P..............................................................................110 LIST OF REFERENCES.............................................................................................................111 BIOGRAPHICAL SKETCH.......................................................................................................120

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7 LIST OF TABLES Table page 2-1 Common soil test extractants used for available P............................................................35 2-2 Critical P concentration in some subt ropical and tropical gr asses (Kamprath and Watson, 1980).................................................................................................................. ..36 3-1 Selected chemical properties used in the glasshouse soil study 1, 2, and 3.......................45 4-1 Visual quality rating of St. Augustinegrass as influenced by P application rate in 2005 glasshouse soil study 1....................................................................................73 4-2 Top growth rate of St. Augustinegrass as influenced by P application rate in 2005 2006 glasshouse soil study 1..............................................................................................74 4-3 Tissue P concentration of St. Augustinegra ss as influenced by P application rate in 2005 glasshouse soil study 1....................................................................................74 4-4 Visual quality rating of St. Augustinegrass as influenced by P application rate in 2005 glasshouse soil study 2....................................................................................84 4-5 Top growth rate of St. Augustinegrass as influenced by P applicat ion rate and soils in 2005 glasshouse soil study 2....................................................................................85 4-6 Tissue P concentration of St. Augustinegra ss as influenced by P application rate and soils in 2005 glasshouse soil study 2.......................................................................85 4-7 Visual quality rating of St. Augustinegrass as influenced by P application rate in 2005 glasshouse soil study 3....................................................................................99 4-8 Top growth rate of St. Augustinegrass as influenced by P application rate in 2005 2006 glasshouse soil study 3..............................................................................................99 4-9 Tissue P concentration of St. Augustinegra ss as influenced by P application rate in 2005 glasshouse soil study 3..................................................................................100

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8 LIST OF FIGURES Figure page 2-1 The P cycle in soil........................................................................................................ ......34 3-1 Glasshouse solution culture P study layout.......................................................................44 3-2 Glasshouse soil P study 1 layout........................................................................................44 4-1 Turf quality response to solution P concentr ation. Turf quality is the mean of five replications over time after treatments were applied. Means marked by the same letter are not significantly differently at P = 0.05 according to Duncans Multiple Range Test..................................................................................................................... ....68 4-2 Tissue P response to solution P concentration and time....................................................68 4-3 Relationship of solution P and tissue P concentration on day 148. Means marked by the same letter are not significantly diffe rently at P = 0.05 according to Duncans Multiple Range Test...........................................................................................................69 4-4 Relationship of solution P and root P concentration on day 148. Means marked by the same letter are not significantly diffe rently at P = 0.05 according to Duncans Multiple Range Test...........................................................................................................69 4-5 St. Augustinegrass tissue growth rate relative to solution P concentration.......................70 4-6 Root growth rate relative to solution P concentration. Means marked by the same letter are not significantly differently at P = 0.05 according to Duncans Multiple Range Test..................................................................................................................... ....71 4-7 St. Augustinegrass tissue growth rate relative to tissue P concentration...........................72 4-8 St. Augustinegrass tissue gr owth rate relative to tissu e P concentration in the glasshouse soil study 1.......................................................................................................75 4-9 Soil Mehlich-1 P, Fe Oxide P, and WEP c oncentration as influenced by P application rate (soil sampling depth of 0-2 cm) in the glasshouse soil study 1..................................76 4-10 Relationships among Mehlich-1 P, Fe Ox ide P, and WEP concentrations (soils sampling depth of 0-2 cm) in the glasshouse soil study 1.................................................77 4-11 Relationships between tissue P concentr ation and Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling depth of 0-2 cm) in the glasshouse soil study 1......78 4-12 St. Augustinegrass tissue grow th rate relative to soil Me hlich-1 P concentration in the glasshouse soil study 1.................................................................................................79

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9 4-13 St. Augustinegrass tissue grow th rate relative to soil Fe Oxide P concentration in the glasshouse soil study 1.......................................................................................................80 4-14 St. Augustinegrass tissue gr owth rate relative to soil WEP concentration in the glasshouse soil study 1.......................................................................................................81 4-15 Soil Mehlich-1 P concentration as influen ced by P application rate and soil sampling depth in the glasshouse soil study 1...................................................................................82 4-16 Leached SRP mass as influenced by P application rate and leaching event in glasshouse soil study 1.......................................................................................................82 4-17 Leached SRP concentration as influenced by P application rate and leaching event in glasshouse soil study 1.......................................................................................................83 4-18 St. Augustinegrass tissue gr owth rate relative to tissu e P concentration in the glasshouse soil study 2.......................................................................................................86 4-19 Soil Mehlich-1 P, FeO P, and WEP concentr ation as influenced by P application rate (soil sampling depth of 0-2 cm) in th e glasshouse soil study 2 (soil No. 2)......................87 4-20 Soil Mehlich-1 P, FeO P, and WEP concentr ation as influenced by P application rate (soil sampling depth of 0-2 cm) in th e glasshouse soil study 2 (soil No. 3)......................87 4-21 Relationships among Mehlich-1 P, Fe Ox ide P, and WEP concentrations (soils sampling depth of 0-2 cm) in the gl asshouse soil study 2 (soil No. 2)..............................88 4-22 Relationships among Mehlich-1 P, Fe Ox ide P, and WEP concentrations (soils sampling depth of 0-2 cm) in the gl asshouse soil study 2 (soil No. 3)..............................89 4-23 Relationships between tissue P concentr ation and Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling dept h of 0 cm) in the glasshouse soil study 2 (soil No. 2)................................................................................................................... ......90 4-24 Relationships between tissue P concentr ation and Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling dept h of 0 cm) in the glasshouse soil study 2 (soil No. 3)................................................................................................................... ......91 4-25 St. Augustinegrass tissue grow th rate relative to soil Me hlich-1 P concentration in the glasshouse soil st udy 2 (soil No. 2)..............................................................................92 4-26 St. Augustinegrass tissue grow th rate relative to soil Me hlich-1 P concentration in the glasshouse soil st udy 2 (soil No. 3)..............................................................................93 4-27 St. Augustinegrass tissue grow th rate relative to soil Fe Oxide P concentration in the glasshouse soil study 2 (soil No.2)....................................................................................94

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10 4-28 St. Augustinegrass tissue gr owth rate relative to soil WEP concentration in the glasshouse soil study 2 (soil No.2)....................................................................................95 4-29 Soil Mehlich-1 P concentration as influen ced by P application rate and soil sampling depth in the glasshouse study 2 (soil No. 2)......................................................................96 4-30 Soil Mehlich-1 P concentration as influen ced by P application rate and soil sampling depth in the glasshouse study 2 (soil No. 3)......................................................................96 4-31 Leached SRP mass as influenced by P application rate and leaching event in glasshouse soil study 2 (soil No.2)....................................................................................97 4-32 Leached SRP concentration as influenced by P application rate and leaching event in glasshouse soil study 2 (soil No.2)....................................................................................97 4-33 Leached SRP mass as influenced by P application rate and leaching event in glasshouse soil study 2 (soil No.3)....................................................................................98 4-34 Leached SRP concentration as influenced by P application rate and leaching event in glasshouse soil study 2 (soil No.3)....................................................................................98 4-35 St. Augustinegrass tissue gr owth rate relative to tissu e P concentration in the glasshouse soil study 3.....................................................................................................101 4-36 Soil Mehlich-1 P, FeO P, and WEP concentr ation as influenced by P application rate (soil sampling depth of 0-2 cm) in the glasshouse soil study 3. Within columns for each soil, means followed by the same letter are not significantly different according to Duncans multiple range test (0.05).............................................................................102 4-37 Relationships among Mehlich-1 P, Fe Ox ide P, and WEP concentrations (soils sampling depth of 0 cm) in the glasshouse soil study 3..............................................103 4-38 Relationships between tissue P concentr ation and Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling depth of 0 cm) in the glasshouse soil study 3...104 4-39 St. Augustinegrass tissue grow th rate relative to soil Me hlich-1 P concentration in the glasshouse soil study 3...............................................................................................105 4-40 Soil Mehlich-1 P concentration as influen ced by P application rate and soil sampling depth in the glasshouse soil study 3.................................................................................106 4-41 Leached SRP mass as influenced by P a pplication rate and leaching event in the glasshouse soil study 3.....................................................................................................107 4-42 Leached SRP concentration as influenced by P application rate and leaching event in the glasshouse soil study 3...............................................................................................107

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11 Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy PHOSPHORUS REQUIREMENT OF ST. AUGUSTINEGRASS By Min Liu May 2007 Chair: Jerry B. Sartain Major: Soil and Water Science St. Augustinegrass [Stenotaphrum secondatum (Wa lt.) Kuntze] is widely used for Florida lawn grass. At present phosphorus (P) fertilization of Florida lawn grasses is based on soil tests which were designed for agronomic crops in a production culture. Little information exits relative to the exact P re quirement of St. Augustinegrass. The objective of this research was to determine the critical P requirement of St. Augustinegrass. Four individual studies were conducted in a glasshouse including one solution culture study and thre e soil studies. Data collected in the soluti on culture study included visual quality rating, t op growth rate, tissue P concentration. From the solution culture study, the critic al solution P concentr ation and critical minimum tissue P concentration were determined to be 111 ppb and 1.6 g kg-1, respectively. Data collected in soil studies included visu al quality rating, top growth rate, tissue P concentration, soil test P concentrations, a nd leachate volume and soluble reactive P concentration. From the soil studies, the minimu m P application rate to achieve the maximum growth rate was 0.31 g P2O5 m-2 4-wk-1; the critical minimum tissue P concentration were determined to be 1.8 g kg-1. Mehlich-1 P, Fe Oxide Strip P, and WEP were highl y correlated to each other and they were also highly correlated to tissue P concentration and top growth rate. Mehlich-1 was the best soil P extractant for St Augustinegrass. The crit ical soil Mehlich-1 P

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12 levels were in the range from 5 to 9 mg kg-1 depending on soil properties. Most of the applied concentrated superphosphate did not leach below the top 2 cm of soil. Approximately 1% of P applied leached in the 10 cm of soil profile. Larger quantity and highe r concentration of P leached in the first leaching event. Application of 0.31 g P2O5 m-2 4-wk-1 did not result in either a larger leached P quantity or a higher concentr ation. Based upon these research findings, 0.31 g P2O5 m-2 4-wk-1 is recommended for St. Augustinegrass only if the soil Melich -1 P concentration is below 10 mg kg-1. Otherwise, no P application would be recommended. Multiple applications with small quantity each time is suggested and do not apply P fertilizer before a rain event.

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13 CHAPTER 1 INTRODUCTION In the recent past, more attention has been di rected towards phosphorus (P) fertilization of Florida lawn grasses, because P is recognized as an element of impairment of water bodies and streams, which is called eutrophicaiton. Eutrophi cation of surface waters, the proliferation of aquatic plants, is caused by a su rplus of available nutrients (suc h as P and N). Eutrophication can cause a decrease in dissolved oxygen in waterways, a situation that can kill fish. Compared with the other major nutrients, phosphorus (P) is by far the least mobile a nd available to plants in most soil conditions. The poor mobility of soil inorganic phosphorus is due to the strong reactivity of phosphate ions relative to numer ous soil components and to the c onsequent strong retention of most soil phosphorus onto those components. Howeve r, a typical Florida soil is sandy and acidic, and the potential for P leaching exis ts. Ballard and Fiskell (1974) reported that most of the sandy soils of the Southeastern Coastal Plains have a very small retention capacity for water soluble P against leaching, but that the su rface horizons of Spodosols had th e lowest retention capacities. In a lysimeter study, Neller (1946) reported that in 4 months 72.4 cm of rainfall leached more than 70% of applied superphosphate-P from the surface of 20 cm of a Leon fine sand. Therefore, P applied to Florida lawn grasse s have potential to cause eutr ophication if not managed properly. At present P fertilization of Florida lawn gra sses is based on soil tests with were basically designed for agronomic crops in a production culture. Little information exists relative to the exact P requirement of Florida lawn grasses and fertilization levels required to produce the required levels in the soil. The objectives for this study are to identify th e critical P tissue P concentration of the St. Augustinegrass using so lution culture techniqu es; to determine the minimum P fertilization level on f our types of soils (three with low in Mehlich-1 P and one with medium level of Mehlich-1 P) requ ired to achieve the optimum growth; to select the best soil P

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14 test procedure for recommendation on St. Augustineg rass; and to identify the critical minimum soil test P level to achiev e the optimum growth.

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15 CHAPTER 2 LITERATURE REVIEW Phosphorus in the Soil-Plant Environment Phosphorus is a macro nutrient used by plant. Th e most essential function of P in plants is in energy storage and transfer. Phosphorus is also an important structural component of nucleic acids, coenzymes, nucleotides, phosphoproteins phospholipids, and sugar phosphates. Plant tissue P concentration ra nges between 1 to 5 g kg-1. Plants absorb either H2PO4 or HPO4 2orthophosphate ions (Havlin et al., 1999). Phosphor us ion concentration in soil solution ranges between 0.03 and 0.5 mg kg-1 in most soils (Ozanne, 1980; Mengel and Kirkby, 1987; Raghothama, 1999; Frossard et al., 2000). In general, it is beli eved that a soil solution P concentration of 0.2 mg kg-1 is adequate for most crops. Phos phorus exists in the soil solution primarily in anionic forms and the distribution among various species (H3PO4, H2PO4 -, HPO4 2and PO4 3-) in solution is governed by solution pH. In the pH domain of most soils the dominant orthophosphate ions are H2PO4 and HPO4 2-, the latter being the major species at pH above 7.2 (Lindsay, 1979). In order to ensure adequate P av ailability to plants and limit the environmental impact of P fertilization, one must thoroughly understand the P-cycle (Figure 2-1) and the dynamics of P transformations in soils. Phosphorus Reactions in Soil Phosphorus ions have a strong te ndency to form ion pairs or complex species with several metal cations, most frequently with Ca and Mg in alkaline soils, and with Fe and Al in acid soils (Lindsay, 1979). Ruiz (1992) reported that 9 and 20% of soluble P occurred as Mg-P and Ca-P complexes for a hydroxyapatite in equilibrium with a simplified nutrient solution (NH4NO3 2 mM, KNO3 3.5 mM, and MgSO4 0.5 mM) at pH values of 7 and 8.5, respectively. Phosphorus ions also readily precipitate with metal cations to form a range of P minerals in case of external

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16 concentrations. In acidic conditions P ions will precipitate as Fe and Al phosphates such as strengite, vivianite, variscite and various mi nerals of the plumbogummite group (Norrish and Rosser, 1983; Lindsay et al., 1989). With pH incr easing to neutral or alka line conditions, P ions will precipitate as Ca phosphates such as octa calcium or dicalcium phosphates, hydroxylapatite and eventually least soluble apatit es (Lindsay et al., 1989). P availa bility in most soils is at a maximum near pH 6.5. Many soil physical and chemical properties in fluence the P solubil ity and adsorption reactions in soils. Consequentl y, these soil properties also aff ect solution P concentration, P availability to plants, and rec overy of P fertilizer by crops. Sanchez and Uehara (1980) reported the influence of clay mineralogy on P adsorption. For three soil orders with >70% clay content, they found that the P adsorption occurred in the order: Mollisol soils composed mainly of montmorillonite < Oxisoil soils containing some Fe/Al oxides < the Andept soils composed principally of Fe/Al oxides and other minerals. Soils containing large quantities of clay will fix more P than soils with low clay content. Cole man et al. (1960) reported a strong positive linear relationship between exchangeable Al and P adsorption. Organic Soil P Organic soil P represents about 50% of the to tal P in soil and varies between 15 and 80% in most soils (Havlin et al., 1999). Havlin et al. (1999) also reported that soil organic P decreases with depth and the distribution with depth varies among soils. The average C/N/P/S ratio in soils is 140:10:1.3:1.3 (Havlin et al., 1999). Many of th e organic P compounds in soils have not been characterized. Most organic P compounds are es ters of orthophosphoric acid and have been identified primarily as in ositol phosphates with appr oximate proportion of 10-50%, Phospholipids with proportion of 1-5% and nucle ic acids with proportion of 0.2-2.5% (Havlin et al., 1999). In general, P mineralization is simila r to N. Dormaar (1972) reported that organic P

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17 content decreases with crop gr owth and increases again afte r harvest, which suggests P mineralization and immobilization. Tiessen et al. (1982) reported that organic P decreased an average of 21% after 60 and 70 years of cultiva tion. Sharpley (1985) reported that with an increase of total organic P cont ent, the organic P mineralizati on rate increased. Tabatabai and Dick (1979) found that P minerali zation increases with increasing total organic C. The C/P ratio of the decomposing residues regulates the pred ominance of P mineralization over immobilization as suggested by the following guidelines. Net minera lization of organic P occurs in case the C/P ratio is less than 200 and net immobilization of inorganic P would occur for a >300 C/P ratio. Leached P in Turfgrass Environment Phosphorus is an essential macronutrient re quired by turfgrass for proper growth and function. Accordingly, P is often included in fertiliz er regime used to maintain aesthetic lawns. Although P enters into many inorganic forms in natural setting, which renders it sparingly soluble by precipitation and adsorption in most cas es and not prone to leaching, a typical Florida soil is sandy and acidic, and the potential for P le aching exists. Many of Fl oridas soils have low P-retention capacities, which allow significan t P leaching. Additionally shallow groundwater intercepted by drains allows leached P to join surface water bodies. From 20 to 80% of P and other fertilizers which were app lied to Florida sandy soil may be leached (Champbell et al., 1985; Sims et al., 1998). Shuman (2001) investigated P leaching from a simu lated USGA putting green in an environmentally c ontrolled greenhouse and reported 27% of applied P was lost via leaching. Studies addressing N leaching from turfgrass environment are quite extensive (Snyder et al., 1980; Broschat, 1995; Erickson et al., 2001). Re latively few studies have addressed the P leaching under turfgrass environment. Erickson et al. (2005) examined fertilizer P leaching loss from contrasting residential landscape models (St. Augustinegrass vs. a mixed-species landscape) established on a sandy soil. They reported that during the 45 month study, cumulative mean P

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18 leached was 23 kg ha-1 from approximate 1400 kg ha-1 application on the St. Augustinegrass model. Leaching losses were high during establishment and following intense precipitation. Leaching losses of P were high enough to rais e concern over ecological impacts on neighboring hydrologically linked systems. Chung et al. (1999) evaluated the influe nce of a number of different P sources in a glasshouse study simu lating the USGA putting green root-zone mixes on bermuda ( Cynodon dactylon (L.) Pers. C. transvaalensis Burtt Davy) growth, plant uptake and leaching characteristics. They reported differenc es in P leaching characteristics among the P sources, with monopotassium phosphate contributing the largest quantity of P to the leachate, accounting for approximately 28% P applied, and c oncentrated superphosphate (CSP) the least, accounting for 13% of P applied. Brown and Sart ain (1999) studied the P retention in United States Golf Association Green s by looking at the influence of sand type (clay coated vs. uncoated), amendment sources (peat and iron huma te), and P fertilizer materials (MKP, 0-20-20, and CSP). They reported that more P leached during establishment. Coated sand retained more Mehlich-1 extractable P, which resulted in more P uptake and less P leaching. Iron humate reduced leachate P and experime nt units receiving CSP leached least P. Snyder et al. (2000) investigated coated sands for use in putting gr een construction and concluded that naturallycoated sand retained more P than uncoated and artificially-coated sand with approximately 1% leached for naturally-coated sand. Management Practices to Reduce P Leaching Different management practices have been prop osed to minimize P leaching in sandy soils. In recent years, water treatment residuals have been studied extensively to improve the P holding capacity of sandy soils. OConnor et al. (2002) ev aluated WRTs P retention capacities and found that all three WRTs tested could reduce P solubi lity by either adsorpti on, precipitation, or both mechanisms and the Al-WTR had an especially large P-sorption capacity of at least 5000 mg P

PAGE 19

19 kg-1. Decreasing P fertilizer rates or application of calcite or dolomitic limestone to increase soil adsorption capacity are the traditional ways for reducing P leaching (Sims et al., 1998). However, both procedures may lead to insufficient P avai lability to plants because liming promotes transformation of plant-available P into unavail able forms (Lindsay, 1979). Silicon fertilizers have a high adsorption capacity and positively influe nce soil physical properti es. As a result of P adsorption onto a surface of Si fertilizer, P leaching is reduced. At the same time, Si fertilizers can induce transformation of slightly soluble phosphates into plant available forms (Matichkov and Ammosova, 1996). Therefore, Si fertilizers ca n improve P nutrition in plants and keep P in the upper soil layers. Matichenkov et al. (2001) found that Si-rich s ubstances or Si fertilizers increased bahiagrass biomass and reduced P leaching by 40 to 70%. Conventional Soil and Tissue P Tests Soil P Extractants Most soil P extractants were developed to estimate the capacity of the soil to supply P. They were designed to extract some fraction of the labile P and thus provide an index of the availability of P to plants over the growing seas on. Soil P test extractants can be placed into various categories related to the chemical nature of the extracting solutions. A list of the commonly used soil test extrac tants is given in Table 2-1. Extractants Troug and Mehlich-I contain dilute concentrations of strong acids normally with a pH of 2 to 3. This provides sufficient H ion activity to dissolve th e Ca-P and some of the Al-P and Fe-P as well. Mehlich III, Bray I a nd Bray II contain both d iluted strong acids and a complexing agent, fluoride ion. Fluo ride ions are very effective in complexing Al ions from Al-P and also precipitate Ca ions to release P form Ca-P into solution. With the double effects of P

PAGE 20

20 extraction mechanism Mehlich-III, Bray-I and II tend to extract more P from the same soils than Mehlich-I and Troug would. On coarse textured Georgia Coastal Plai n soils, Gascho et al. (1990) found that Mehlich-III extracts about 1.46 times mo re P than Mehlich-I. Also, on finer textured soils Mehlich-III extractant removes about 1.6 times more P than Mehlich-I. Olsen-P extractant is so called buffered alkaline so lution containing 0.5N NaHCO3 with pH 8.5, which originally was developed for calcareous soils. The HCO3 is quite effective in replacing adsorbed P. Because of high pH Olsen-P extract ant is also very effective in extracting P from Al-P and Fe-P due to the hydrolysis of the Al and Fe. The extr actant citric acid, Egne r and Morgan, consist of diluted weak acids, which were developed based upon the idea of mimicking the root environment. The organic anions associated with the weak acids tend to a ffect the extraction in two ways. The organic anions form complexes with Ca, Al or Fe ions to release P and can also replace adsorbed P and prevent its readsorption. Modified Morgan extractant was modified from Morgan extractant by substituting NH4 for Na and adding NH4F to provide a 0.03 N F solution. NH4 is more effective in removing K from clay soils than is Na. NH4F would give a measure of a greater portion of P reserve by forming Al-F or Fe-F complexes. FeO strip P test is the so-called chemical sink-based test, which has been propos ed to rely on P sorpti ondesorption reactions instead of dissolving soil P with chem icals. It extracts P using Fe-oxide impregnated filter paper strips or discs (Chardon et al, 1996). Suitability of Different Extracting Procedures The suitability of the extracting methods can be evaluated by correlating the P extracted with plant growth parameters such as yiel d, P uptake and P concentration (Fitts and Nelson, 1956). The Olsen and Bray I methods are quite satis factory across a wide range of soil conditions and the Mehlich I appeared to be very good when used for soils with a pH of 7 or less (Fitts, 1956). The soil testing laboratory at the University of Florida is currently using the Mehlich-I

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21 procedure. The Egner method was as effective as Olsen and Bray-I methods while the Morgan method is least satisfactory across a wide range of soils (Van Diest, 1963). In a stud y that related turfgrass growth response to extractable soil P concentration in sand greens, Guillard and Dest (2003) reported that extractable P was highly co rrelated among Mehlich -I, Bray-I and modifiedMorgan procedures with r value of around 0.9. Meh lich-I and Bray-I extracta ble P extracted four to six times more P than modified Morgan. Ex tractable P with Bray-I P was 1.3 times greater than Mehlich-I extractable P. A better correla tion was observed between Bray P and Mehlich-I P than with modified Morgan P. Soil P Extracting Procedures and Geographical Regions The compounds that control the availability of P differ with soil conditions in different geographical regions of the country and different extrac tants have been developed and used for these situations. For example, P chemistry of so ils in the southeast primarily involves factors affecting the availability of aluminum and ir on phosphates. Therefore, most commonly used extractants in these regions are the Mehlich I a nd the Mehlich III. The Morgan extractant, which is used by some states in the northeast and Pa cific northwest and contains acetic acid, is a buffered weak acid extractant. Both of the Mehlic h solutions extract more P from soils than the Morgan extractant. The Mehlich III extractant removes about 10 times mo re P from soils than the weak acid-based Morgan extractant (W olf and Beegle, 1995). The extractant used predominantly in the Midwest is the Bray-Kurtz, commonly referred to as Bray I. The extraction of P by this procedure is based upon the solubilization effect of the H+ on soil P and the ability of the F to lower the activity of A1 and to a lesser ex tent that of Ca and Fe by forming complexes in the extraction system. Clay soils with moderately high base saturation or silty clay loam soils that are calcareous or have a very high base saturation will lessen the ability of the extractant to solubilize P. Consequently, the method shoul d normally be limited to soils with pHw (soil pH

PAGE 22

22 determined in water) values less than 6.8 when the te xture is silty clay loam or finer. Calcareous soils, or high pH, fine textured soils may be te sted by this method provided the soil:solution ratio is changed from 1:10 to 1:50. However, it should be noted that the Olsen extractant is used most extensively for calcareous soils (Anonymous 1992, Knudsen and Beegle, 1988). The Olsen extractant is quite effective for soils with me dium to high CEC, high percent base saturation, moderate to high amounts of calcium phospha tes, and containing free calcium carbonates (Thomas and Peaslee, 1973). It is used extensively in states such as Arizona, California, Utah, Wyoming, and Oregon. Research also indicates that the procedure works reasonably well on moderately acid soils. However, not many laborat ories testing moderate ly acid soils use the procedure. The fact that it is not used more wi dely on these soils is proba bly due to the lack of correlation data. Tissue P test Plant tissue analysis is an indicator of atta ining or maintaining ma ximum yield or quality. Therefore, the good correlation between the concentr ation of P in plant tis sue and in the soil as well as between the concentration in plant tissu e and yield, plant growth or quality normally exists. Ballard and Pritchett (1975) reported that the relationship be tween the concentrations of P extracted from the soil by different extractants correlated highly with the concentration of P in the tissue of pine seedlings. Response of Turfgrass to P Fertilizers and Fertilizer Recommendations Phosphorus Toxicity Trial Accumulations of P in soils growing turf, citrus, vegetable crops and field crops are common when heavy application of fertilizers containing a hi gh proportion of P are usually applied frequently. Since only a portion of P adde d in fertilizers is recovered by plants, the continuous use of P fertilizers on turfgrass would be expected to raise soil P level well above the

PAGE 23

23 optimum level. In most states, soils contain subs tantial portion of clay an d P leaches very little. Scientists question whether or not these high levels are detrimenta l to plant growth. Juska et al. (1965) looked at the effects of P on the development of Red Fescue ( Festuca rubra ssp. commutata ), Merion, and Common Kentucky Bluegrass ( Poa pratensis ). The P application rates were: 0, 244, 488, 734, 978, 1222, 1466 and 1710 kg ha-1. The largest increase in weight of both tops and roots of Merion and co mmon Kentucky bluegrass resulted fr om the first increment of P. Differences among remaining increments were small. It is conceivable that P application as high as 1710 kg ha-1 did not depress top growth and P application rate of 244 kg ha-1 supplied sufficient P already. These results suggest that grasses can tolerate very high levels of P and may require low rate of P applic ation for optimum growth. Phosphorus Requirements by Turfgrasses Grasses exhibit marked species difference in response to P supply. R obinson et al. (1976) found no influence of P applications to a New Zealand browntop-New Zealand chewings fescue ( Festuca rubra var. commutate ) lawn mixture for verdure, root weights, or tiller numbers. Jones et al. (1970) grew Italian ryegrass ( Lolium multiflorum ), hardinggrass ( Phalaris tuberosa var. stenoptera ), tall fescue ( Festuca arundinace ), orchardgrass ( Dactylus glomerata), and tall oatgrass ( Arrhenatherum elatius (L.) P. Beauv .) with 0, 100, 200, 300, and 400 kg P ha-1. Tall fescue, ryegrass, and tall oatgrass produced the highest yields without P, but tall fescue and ryegrass also showed the greatest response to P fe rtilization. Christians et al. (1979) investigated the N, P and K effects on quality and growth of Kentucky bluegrass and creeping bentgrass ( Agrostis palustris ) using solution culture. No response to P levels in solution was observed, which indicated that the requirements of these tw o species for P, under the conditions established, were met at or below the lowest P level of 2 mg L-1 in solution. Fry et al. (1989) conducted a field study over 8 years on a sand medium to dete rmine creeping bentgrass quality response to P.

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24 They found that creeping bentgras s fertilized at 60 or 132 kg P ha-1 yr-1 was similar in quality. In calcareous sand greens Johnson et al. (2003) found that creeping bentgrass plots receiving 27.5 kg P ha-1 yr-1 or higher rates attained the maximum quality. Allen et al. (1977) established Pensacola bahiagrass ( Paspalum notatum ) on a Lexington silt loam that contained 34 mg kg-1 P in the surface 1.5 m soil. For 5 years they applied annually 224, 336 and 448 kg N ha-1; 112, 224 and 336 kg P2O5 ha-1; and 112, 224 and 336 kg K2O ha-1 in a complete factorial experiment. Rates of 224 and 336 kg P2O5 ha-1 accounted for increases of only 1% and 2% forage above the 49 kg P2O5 ha-1 level, respectively. Maximum yield response of bahiagrass to P fertilizer in south Florida occurred on Arenic Haplaquods at 24 kg P ha-1 (Rechcigl et al., 1992). Another study on the bahiagrass fertility requirement in south Flor ida on soils with a spodic horizon called for13 kg P ha-1, and only if >112kg N ha-1 is applied. If less than 60 kg N ha-1 is applied, no P is recommended (Sumner et al., 1991). Turner (1980) found little infl uence of P on the growth of perennial ryegrass ( Lolium perenne ), Kentucky bluegrass, or cr eeping red fescue, despite low soil P levels. Robinson and Eilers (1996) obtained 90% of maximum ryegrass dry matter yield with 45 to 50 kg P ha-1 on a Tangi silt loam (Typic Fragiudult) at pH 6. Higher rates of P had little influence on yield but significantly increased P removed by the crop. This result was consistent with the study of irrigated annua l ryegrass responses to N and P on calcareous soil by Lippke et al. (2006), in which they conclude d that increments of growth re sponses to levels of fertilizer about 39 kg applied P ha-1 were relatively small. Watschke et al. (1977) looked at the effect of P application of 0, 85, 170, 340, and 680 kg P ha-1 on soil test and tissue analyses P. Phosphorus fertilization increased the Bray extractable P from 13 to 137 mg kg-1. Treatments P1, through P5 gave P concentration of 3.2, 3.5, 3.6, 3.8, and 4.4 g kg-1, respectively, with all differences being

PAGE 25

25 significant except 3.5 and 3.6 g kg-1. When soil test P was related to yield response, the correlation was slightly lower th an those found for tissue P and yield, which was in agreement with Hall and Miller (1974) who also found that tissue P and yield were better correlated than soil test P and yield. Watschke et al. (1977) al so investigated the zone of maximum root absorption for Merion Kentucky bl uegrass as affected by P applic ation. Results indicated that P enhanced rooting, and the magnit ude of absorption from the 1.3-cm depth exemplified the need for P near the soil surface for op timum turf establishment. Juska (1959) reported that adequate P was necessary for rapid esta blishment of zoysiagrass ( Zoysia spp ) on a soil extremely low in P. St. Augustinegrass growth was affected by P most during the first 8 weeks of establishment (Wood and Duble, 1976). On P-deficient soils, McVey (1967) reported a Kentucky bluegrass seedling growth response to extremely low rates of P applications. Long-term benefits from P application to the seedbed have also been obser ved by Turner et al. (1979). He reported that 6 years after establishment, spring greening was enhanced by the orig inal seedbed P applications. Critical Minimum Soil P Concentrations The critical soil test level implies the P level above which little or no response to fertilizer P is obtained. Woodhouse (1969) and Jordan et al. (1966) reported that about 25 mg kg-1 of Mehlich-1 extracted soil P is ad equate for coastal bermudagrass ( Cynodon dactylon ) in North Carolina and Alabama. Lunt et al. (1965) indicated that about 14 mg kg-1 of Olsen extractable P was adequate for common bermudagrass harvested frequently as turfgrass; Bruce and Bruce (1972) indicated that 17.5 mg kg-1 of P extractable with 0.005 M H2SO4 was necessary for high production of various tropical gr asses. Vicente-Chandler et al. (1974) concluded that tropical species such as guineagrass ( Urochloa maxima ), napiergrass ( Pennisetum purpureum ), and stargrass ( Cynodon plectostachyus ) require fertilization w ith at least 73 kg P ha-1 annually when cut every 40 to 60 days. Annual ryegrass ( Lolium multiflorum Lam.) response to applied P

PAGE 26

26 ranged from 8300 to 8600 kg ha-1 as extractable soil P increased from 3 to 55 mg kg-1 (Hillard et al., 1992). Christians et al (1981) did not find significant quality responses for creeping bentgrass on calcareous sand greens when initial Bray-1 extractable P concentrations were 12 mg kg-1. Dest and Guillard (1987) reported that on a lo am soil with modified Morgan extractable P at 10.7 mg kg-1, quality responses of creeping bentgrass we re not affected by P fertilization. Fry et al. (1989) reported that creep ing bentgrass quality improved w ith addition of P on sand-based media putting greens only when extractable P was <5 mg kg-1. Kuo (1993) reported that Olsenextractable P concentrations at 95% of maximum clipping yi elds was from 2.8 to 4.8 mg kg-1 for the growth of annual bluegr ass and creeping bentgrass ( Agrosti stolonifera L. ). In calcareous sand greens the critical Ol sen-P level of 3.0 mg kg-1 was reported for the growth of creeping bentgrass (Johnson et al., 2003). For Pensacola ba hiagrass on a virgin Clarendon loamy sand the critical Mehlich-1 P concentration was 3 mg kg-1, which corresponded to 56 kg P2O5 ha-1 application (Burton et al., 1997). To locate the critical soil P con centration the plant growth rate or turf quality are most commonly used to relate to soil test levels. Guillard and Dest (2003) used a number of plant response variab les including shoot counts, thatch thickness, relative clipping yields, quality ratings, P defici ency ratings, tissue P concentra tions, and root weights, which resulted in different soil critical P concentrations. Selection of a particular critical extractable soil P concentration would depend on the quality or growth variable that is the most important to the individual manager. Among the three extractants modified Morgan, Bray I and Mehlich I, critical extractable P concentrations for creeping bentgrass were lowest for the modified Morgan extractant (1.4 to 12.0 mg kg-1) and greatest for the Mehlich I extractant (14.1 to 63.6 mg kg-1). The critical values are generally influen ced by soil properties, such as texture and temperature. A lower amount of P is generally ex tracted from a clayey soil than from a sandy

PAGE 27

27 soil (Woodruff and Kamprath, 1965). Rouse (1968) found that an application of 5 to 6 kg P ha-1 was required to raise Meh lich-I extractab le P 1 kg ha-1 with sandy loam to clay loam textured Ultisols, but on clayey textured soils 12 kg P ha-1 were required to change the soil test values 1 kg ha-1. Finn and Mack (1964) showed that both soil moisture and soil temperature affected P response of orchardgrass ( Dactylis glomerata ). Yields were higher at 75 than at 25% of the moisture-holding capacity at each level of P app lied. Under 75% moisture-holding capacity level, at a 10 C soil temperature, maximum yield of the S-143 cultivar occurred with 35 mg kg-1 of applied P; at 20 C, yields were still increasing with 70 mg kg-1. Effects of P Application on Soil Test P Levels When soil test P is below the critical level, the rate of fertilizer P recommended is sufficient to supply adequate P for the plant and to result in some buildup of available soil P when applied at the rate for severa l years. In trying to predict how much fertilizer P is needed to change the soil test P, information is needed a bout the P adsorption characteristic of the soil, which is related to soil te xture, as well as the initial level of soil test P. In a Honeoye fine sandy loam soil, Peck et al. (1975) found that continuous applications of concentrated superphosphate over 10 yr for a total of 248 kg P ha increased soil test P (Morgan's method) from 10 to 186 kg P ha. An application of 4 kg P ha-1 was required to raise the Bray I extractable P of mediumtextured Mollisols and Alfisols 1 kg ha-1 (Peck et al., 1971). Single applications of 22, 45, 90, and 180 kg P ha raised the levels of Olsen P by 1, 2, 4, and 8 mg P kg soil, respectively, on a glacial till soil after 16 yr of P fertilization (Halvorson and Black, 1985) In a 29-yr study on Ultisols in Alabama, Cope (1981) found that 24 and 20 kg P ha raised Mehlich-1 soil test P by 1 mg P kg when P was applied at rates of 31 and 54 kg P ha yr, respectively. For a cornsoybean rotation on a Portsmouth fine sandy loam, annual rates of 19, 38, and 57 kg P ha-1 increased the soil test levels 7, 20 and 40 mg kg-1 P over a 7-year period (Kamprath, 1964). After

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28 14 yr of annual application of P fertilizer in a Webster fine-loamy and a Canisteo fine-loamy soil located in north central Iowa, Webb et al. (1992) re ported that annual P additions required to maintain Bray-1 P values increased from 16.8 to more than 33.6 kg P ha with increases in the initial Bray-1 P value. In a Chicot sandy loam soil, an application of 14 kg P ha of net added inorganic fertilizer P was required to increase soil Mehlich-3 P by 1.0 mg P kg (Zhang et al., 1995 ). Cox (1994) showed that increases in Mehlich-3 with each unit of applied P were 0.7 units for soils with 10% clay, and it decreased exponentially to 0.2 units for soils with >50% clay. Results obtained from a study by Randall et al. (1997) in Minnesota, showed that every 1 mg P kg increase in Bray-1 extracta ble P requires 35 and 20 kg P ha in a Webster clay loam soil and 58 and 26 kg P ha in a Aastad clay loam soil when fertilizer P was added at 24 and 49 kg P ha, respectively. Many studies have shown that the amount of fertilizer P required for each unit increase of soil test P level varies with soil texture, soil test method employed, as well as the rate of fertilizer P applied. Critical Tissue P Concentrations The critical tissue P concentr ation is normally regarded as the minimum concentration associated with near maximum yield. The nutrient concentration in the plant at 90% of maximum growth has often been termed the critical con centration (Ulrich and H ills, 1967). It could be statistically determined from the shape of the yi eld response curve in rela tion to concentration of P in the selected tissue. Knowle dge of the minimum P concentrati ons for plant growth has been used as a means to diagnose the P status of many plants (Hartt, 1955; Ulrich, 1952). Jones and Eck (1973) reported that the critic al concentration of P in the sw eet corn leaf tissue was from 0.27 to 0.29% and the corresponding equilibrium so il solution P concentration was about 0.12 to 0.13 mg L-1. A similar highly positive linear correlati on between percent P in the rice tissue and

PAGE 29

29 soil solution P concentration was reported by Hossner et al. (1973). The critical tissue P concentration of 0.25% corresponds to the soil solution P of 0.1 mg L-1. Oertli (1963) reported that healthy bluegrass (Poa spp) and bermudagrass (Cynodon spp) contain 1.2 to 2.4 g kg-1 P, respectively. Tissue P-deficiency levels were found to be 0.5 to 0.8 g kg-1, respectively, for bluegrass and bermudagr ass. Martin and Matocha (1973) outlined approximate sufficient ranges for tissue P for cool-season forage grasses. For Kentucky bluegrass, values 1.8 g kg-1 were considered deficient, from 2.4 to 3.0 g kg-1 were critical, from 2.8 to 3.6 g kg-1 were adequate, and values 4.0 g kg-1 were considered high. For annual and perennial ryegrass values < 2.8 g kg-1 were deficient, from 2.8 to 3.4 g kg-1 were critical, from 3.6 to 4.4 g kg-1 were adequate, and > 5.0 g kg-1 were high. Jones (1980) s uggested that in most situations concentratio ns below about 2.0 g kg-1 indicate a deficiency for plant growth while 3.0 to 3.5 g kg-1 is usually necessary for optimum yields. Wedin (1974) reported that P concentration in cool-season grasses range from about 1.4 to 5.0 g kg-1. Johnson et al (2003) investigated the P requirement of creeping bentgras s on calcareous sand greens and found that tissue test of 4.0 g kg-1 was the optimum level for maximum quality. For warm-season grasses, the P concentration in plant tissue should be logically lower for the optimum yield compared with cool-season grasses because the higher growth rate dilutes the P concentration in plant tissue. Burton et al. (1997) reported that phosphorus concentration of the 1993 Pensacola bahiagrass forage receiving 56 kg P2O5 ha-1, above which no significant yield in crease occurred, averaged 1.5 g kg-1. When P2O5 was increased to 112 kg ha-1, forage P concentration increased to be 1.8 g kg-1. The critical P concentrations in some subtropical and trop ic grasses were shown in Table 2-2 (Kampraph, 1980).

PAGE 30

30 Some factors may modify the critical P con centration of plants such as growth rate (Terman et al., 1972), plant tissue age (Jones et al ., 1970) and cultivar effects (Terman et al., 1975), thus making the conclusion between tissue P concentration and yield difficult. Therefore, in many cases, the variability in the P concentrat ion does not allow a high degree of accuracy in the prediction of the increments of plant growth or yield. Consequently, th e critical concentration range of P in the plant is usually the criterion th at is used in differentia ting P deficiency from P sufficiency and the decision to simply apply P or not is usually made. Interaction with other Nutrients Phosphorus and N Increased P absorption by plants is a common consequence of adding N fertilizers (Grunes, 1959). Templeton et al. (1969) c onducted a study showing the effects of N on P response of orchardgrass. At each level of P applied, with in creased N rate plant gained increased weight increased top growth, increased r oot growth, altered metabolism, and increased solubility of soil applied among three levels of N applications. In a study on response of bahiagrass to N, P and K on an Ultisol in North Florida, Rhoads et al (1997) found that there were no interactions between N and P rates with respect to bahiag rass yield. However, th ere were significant interactions in 1996 between N and K rates and betw een P and K rates with respect to bahiagrass yield. Hylton et al. (1965) repor ted that for Italian ryegrass ( Lolium multiflorum Lam ), as the P supply increased from 0.16 to 0.64 mg per plant, the tissue NO3-N concentration decreased from 13.2 g kg-1 with 0.16 mg of P per plant to a low of 7.6 g kg-1 with 0.64 mg. Engelstad and Allen (1971) found that root yiel ds and root P contents were increased by N fertilizer, with ammonium being superior to nitrat e. The addition of KNO3 to the pellet reduced the P content of the tops. Sartain and Dudeck (1982) studied the effect of N fertilization on the P uptake of Tifway bermudagrass and overseeded ryegrass. Tissue P content was significantly reduced by each

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31 increasing N rate on the ryegrass. The reduction in tissue P could possibly be attributed to a diluted effect caused by greater growth rate. Hi gher tissue N content was observed for Tifway bermudagrass by excluding P, which implied a possible nutrient uptake competition between NO3-N and H2PO4-P. Sartain (personal communication) found that bermudagrass growth rate was reduced each of three years by the applicatio n of additional P. A reduction in N uptake was observed in conjunction with the reduction in grow th rate. It was suggested that the competition effects of the NO3-N and H2PO4-P anions may have been responsible for the observed reduction in N uptake and subsequent growth rate. Watschke et al. (1977) reported that clipping yield and rooting of Merion Kentucky bluegrass ( Poa pratensis L. ) were enhanced by the application of additional P. In case NH4-N was applied during cool season, NH4-N would be the major N form available for plant uptake because of reduced nitrification of the applied NH4-N (Parker and Larson, 1962). The increased growth rate may possibl y due to the fact that additional P enhanced N uptake for the cool season Kent ucky bluegrass. Bluegrass tissu e P levels were more than sufficient (3.2 g kg-1) for all treatments, which indicate that the positive growth response to P was not related physiologically to P. With th e exclusion of P fertilization the number of H2PO4-P anions would be reduced and the quantity of NH4-N cations that can be accumulated would also be reduced, therefore, a yi eld reduction was expected. Phosphorus and K, Ca and Mg Enhanced P utilization due to K appli cations was observed for stargrass (Cynodon nlemfuensis Vanderyst var. nlemfuensis) by Pant et al. (2004). The app lications of 10 and 93 kg ha-1 yr-1 of P and K, respectively, provided effi cient P utilization. Phosphorus mass balance showed that stargrass removed maximum P (161%) of the applied P by uptake from soils. This may indicate that the supply of sufficient K appear s to be crucial for efficient P utilization by forages, reducing potential adverse effects of P over-fertilization on water quality. When the

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32 different P:K ratios were related to the total dr y matter yield, the application of 10 and 93 kg ha-1 yr-1 of P and K, respectively, achieved almost 90% of the maximum total dry matter yield, which indicates that application of 10 kg P ha-1 yr-1 was critical for stargra ss to achieve maximum dry matter yield. Greenwood and Hallsworth (1960) f ound no direct effect of P on Ca uptake, but found that earlier and more severe symptoms of Ca deficiency occu rred where P levels were high. Mg has been ascribed the function of P carri er in plants (Truog et al., 1947), based on a positive correlation between the Mg and P contents of plants or between fertilizer P efficiency and the supply of available Mg. Phosphorus and Zn Phosphorus and Zinc nutrition in plants have often been related. In P deficient plants additional P promoted plant growth resulting in depressed Zn concentrations in tissue and possible Zn deficiency conditions. In P sufficient plants additional P increase concentrations to toxic levels producing necrotic symptoms in old leaves and depressi ng new growth. Sartain (1992) investigated the influence of Zn and th e interaction of P an Zn on the growth of bermudagrass. Application of Zn did not influenc e growth nor Zn uptake rate. Extractable soil Zn levels over 252 mg kg-1 did not affect bermudagrass gr owth nor quality. In effect, bermudagrass can tolerate high levels of soil ex tractable P and Zn without exhibiting toxicity effects. Effect of N, P, K, and their Interactions on Water Use Efficiency When water resources become limited, it is important for turfgrass manager to use many different cultural practices to reduce water loss thr ough turfgrass evapotrans piration rate (ET). Nitrogen application enhanced th e ET by promoting the top growth and total leaf area. Ebdon et al. (1999) investigated the interaction of N, P and K on ET rate of Kentucky bluegrass. The nature of the interaction between N, P, and K on Kentucky bluegrass water use can only in part

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33 be explained by the interaction e ffects of N, P and K on shoot gr owth response. No relationship between clipping yield and ET rate at high P appl ications was found. They also discovered that at N and P levels that are rout inely applied (147 kg N and 21.5 kg P ha-1 yr-1 and lower), increasing K levels minimized Kentucky bluegrass water use.

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34 Plant and a nimal Fertilizer Plant residuals Figure 2-1. The P cycle in soil. SOLUTION P H2PO4 HPO4 2Adsorption Desorption Dissolution Precipitation Dissolution Mineralization Immobilization Leaching (Labile P) Plant Uptake SOIL ORGANIC MATTER MICROBIAL P (Nonlabile P) ADSORBED P (Labile P) SECONDARY MINERALS Fe/AlPO4 CaHPO4 (Nonlabile P) PRIMARY MINERALS (Nonlabile P)

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35 Table 2-1. Common soil test extract ants used for available P. Soil/solution Common name Extractant ratio Reference Troug 0.002N H2SO4 buffered at 1:100 Troug (1930) pH 3 with (NH4)2SO4 Mehlich -I 0.05N HCl + 0.025N H2SO4 1:4 Mehlich (1953) Mehlich-III 0.2N CH3COOH + 0.25N NH4NO3 1:10 Mehlich (1984) + 0.013N HNO3 + 0.015N NH4F + 0.001M EDTA Bray0.025N HCl + 0.03N NH4F 1:10 Bray & Kurtz (1945) Bray0.1N HCl + 0.03N NH4F 1:17 NDSU (1980) Olsen 0.5N NaHCO3 pH 8.5 1:20 Olsen et al. (1954) Citric acid %1 citric acid 1:10 Dyer (1894) Egner 0.02N Ca lactate + 0.02N HCl 1:20 Egner et al, (1960) Morgan 0.54N HOAc + 0.7N NaOAc pH 4.8 1:10 Morgan (1941) Modified Morgan 0.54N HOAc + 0.7N NH4OAc 1:10 McIntosh. (1969) + 0.03N NH4F pH 4.8 FeO strip 0.02 N CaCl2 + FeO-coated filter 1:40 Chardon et al. paper strip (1996)

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36 Table 2-2. Critical P concen tration in some subtropical and tropical grasses. Critical P Age or concentration, Grass identification stage of growth % Reference Bermudagrass 4-5 weeks 0.20-0.26 Martin and Matocha, 1973 Midland and common Bermudagrass 4-5 weeks 0.24-0.28 Panicum Maximum, VAR 3-4 leaf 0.55 Smith, 1975 Trichoglume, cv. Petrie 4-5 leaf 0.32 6-7 leaf 0.15 I.P.F. (57days) 0.20 Andrew and Robins, 1971 Kikuyugrass I.P.F.(45 days) 0.22 Pearl millet 4-5 weeks 0.16-0.20 Martin and Matocha, 1973 Staria spacelata, cv 4-l eaf 0.46 Smith, 1975 Nandi 5-leaf 0.36 6-leaf 0.24 7-leaf 0.14 Staria anceps, cv Nandi I. P.F.(57 days) 0.21 Andrew and Robins, 1971 Dallisgrass I.P.F.(57 days) 0.25 Pangolagrass I.P.F.(45 days) 0.16 4 weeks 0.12-0.16 Martin and Matocha, 1973 Buffelgrass I.P.F.(57 days) 0.25 Andrew and Robins, 1971 (whole plant tops 0.16 Smith, 1975 inflorescences just appearing) youngest expanded 0.17 leaves sampld Buffelgrass I.P.F.(39 days) 0.26 Christie and Moorby, 1975 46 days 0.30 Rhodesgrass, cv Pioneer I.P.F.(57 days) 0.22 Andrew and Robins, 1971 Molassesgrass I.P.F.(57 days) 0.18 Johnsongrass boot stage 0.16-0.20 Martin and Matocha, 1973 Sorghum-sudangrass 4-5 weeks 0.14-0.20 and sudangrass I.P.F. means immediate preflo wering stage of growth. Most analyses apply to whole plants unless otherwise specified.

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37 CHAPTER 3 MATERIALS AND METHODS This research consisted of one glasshouse hydr oponic study and three gla sshouse soil studies. Glasshouse Hydroponic Study A glasshouse hydroponic study was conducted at the Turfgrass Envirotron at the University of Florida, Gainesville, Florida. St Augustinegrass var. Floratam was chosen as the testing cultivar based on its greatest use among a ll St. Augustinegrass cultivars. Six levels of P (0, 1.24, 6.2, 31, 155 and 775 mg m-3) with five replicates were used to test for P response. Certified sod collected from the G.C. Horn Tu rfgrass Field Laboratory at the University of Florida in Gainesville was washed to remove soil from the root system. Sod was cut to a size of 15cm 30cm rectangle and transferred to the hydroponics system on June 27, 2004. Nalgene tubs (31cm 16cm 12cm) were us ed as the hydroponic c ontainers. The outside surfaces of the containers were painted with bl ack latex paint first and white afterwards to prevent light penetration. A 10-mm inner diameter polynvinyl chloride (PVC) pipe was used to make a rectangle frame (15cm 30c m). The frame was attached with a piece of poly-hardware cloth and fitted on the corners of opening of the container to form a grass bedding surface. Since the frame was not fixed to the container, the fram e/screen with grass could be removed to change solution or check solution pH periodically. The grass pieces (15cm 30cm) were placed on the bedding surfaces. Nutrient solution level in the c ontainer was adjusted to touch the screen to induce root growth. Roots penetr ated the screen and grew into the solution after about three weeks. Then the solution volume was reduced to approximately 1.5 cm below the frame to create an air zone between grass stolons and solution surface to avoid water damage and algae growth on the grass. An air compressor was used to s upply air to the nutrient solution. A 5-m long with 7-mm inside diameter tygon tubing was fitted to th e outlet of the air compressor at one end and

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38 the other end was plugged. Along the 5-m plastic tube the containers were laid out on both sides with 15 tubs on each side. Another tube of the same diameter, but shorter length was used for each solution tub with one end fitting with a need le and the other end going to the solution. The needle penetrated the main tube and through th e short tube air was blown into each solution. Smaller size of needles was used at the positions closer to the ai r compressor and larger sizes of needles for the far positions. By doing this, the ai r pressure due to distance difference between each tub and air compressor was roughly regula ted and each solution achieved approximately the same air bubbling speed. Figure 3-1 shows the experiment layout. Nutrient solution was slightly modified from what was reported by Breeze et al. (1984) by replacing Sequestrene Fe 138 with Sequestrene Fe 330, eliminating CaSO4 and doubling the concentrations of nutrients they used. The nutrient solution was changed every other day to regulate pH, maintain nutrient concentrations and minimize salt accumulation. The P treatments were applied on October 17, 2004 at which time th e turfgrass was exhibiting P deficiency. The study was terminated on March 14, 2005. The treatments were arranged in a randomized complete block design. Computer controlled overhead exhaust fa ns, a wall-length humidifier, and an automatic roof window were used to ma intain relatively consta nt conditions in the glasshouse. Glasshouse temperature was maintained at an average 22C with a range of 18C to 30C. The relative humility was maintained at approximately 75%. Top growth was clipped to 7.5 cm approxima tely monthly, once the dry matter production reached harvestable quantities, fo r a total of seven co llections. Clippings were dried at 70C for 48 h, and weighed. Root materials were clippe d to 4 cm on September 8, 2004 and November 27, 2004. At root collection time the root density in the container was high. Root materials were washed with distilled water to remove the poten tially adsorbed salts, dried at 70C for 72 h and

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39 weighed. The dry tissue and root samples we re ground to 2-mm and ashed. Samples were analyzed for P by spectrophotometry using the molybdenum-reduced molybdophosphoric method (Hanlon et al., 1994). Turf visual qualit y was rated biweekly using a scale of 1 to 9 where 1 represents brown, dormant turf and 9 re presents superior quality (Skogley and Sawyer, 1992). Statistical analysis (analysis of variance) was performed by SAS (SAS Inst., 1987). Mean separation was done using Duncans Multiple Ra nge test at a 0.05 significant level. The relationship between turfgrass ti ssue growth rate and solution P and tissue P were determined using linear plateau analysis (PROC NLIN). Glasshouse Soil Study 1 With the information of the critical minimu m tissue P required by St. Augustinegrass from the hydroponic study, a study to dete rmine the critical minimum soil test P concentration was initiated. This glasshouse soil study was conducted at the Turfgrass Envirotron at the University of Florida, Gainesville, Florida. The soil chosen in this study was collected from the A horizon of a soil mapped as Pomona sand. It containe d very low levels of Mehlich-1 P (2 mg P kg-1). The Pomona series is in the family of Sandy, S iliceous, Hyperthermic U ltic Alaquods. Selected chemical properties for this soil (soil No. 1) are shown in Table 3-1. Nalgene tubs (53cm 38cm 12cm) were used as the growth container. Outs ide surfaces of the contai ners were painted with white latex paint first and black afterwards to prevent light pene tration. Certified sod with high initial tissue P concentration was washed to re move soil, then cut to a size of 53cm 38cm rectangle and transferred to th e growth container on May 8, 2005. After P deficiency was induced, P2O5 rate of 0, 0.31, 0.63, 1.25, and 2.5 g m-2 per four weeks were applied initially on April 12, 2006 and reapplied 3 times during the 16-week growth period. Treatments were arranged in a randomized complete block design with 5 replications for

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40 each treatment. Computer controlled overhead ex haust fans, a wall-lengt h humidifier, and an automatic roof window were used to maintain relatively constant conditions in the glasshouse. Glasshouse temperature was maintained at an average 24 C with a range of 18C to 30 C. The relative humility was maintained at approximately 75%. The e xperiment layout was shown in figure 3-2. Top growth was clipped to 7.5 cm every other week for a total of 8 collections. Clippings were dried at 70 C for 72 h, and weighed. Tissu e growth rate was calcu lated by dividing tissue dry weight by growth days. The dry tissue sa mples were ground to 2-mm and ashed. Samples were analyzed for P by spectrophotometry using the molybdenum-reduced molybdophosphoric method (Hanlon et al., 1994). Turf visual quality was rated weekly using a scale of 1 to 9 where 1 represents brown, dormant turf and 9 represents superior qualit y (Skogley and Sawyer, 1992). Soil samples were taken at termination using a 3.0-cm via. soil probe. Soil samples were separated into soil depths of 0 cm and 2 cm. Mehlich-1 extractable P was determined for the soil samples in depth of 0 cm and 2 cm Water extractable P and FeO-strip P were determined for the 0 cm soil depth. At one week intervals, one-half pore volume of water was applied to all growth containers to aid in the collection of leach ate. Leachate volume, pH, and EC were measured. A sub-sample was collected and frozen until soluble reactive P was analyzed. Statistical analysis (analysis of varian ce) was performed by SAS (SAS Inst., 1987). Duncans multiple range test with fixed variable was used for all the mean separation in this study. Means marked by the same letter ar e not significantly di fferently at P = 0.05. Glasshouse Soil Study 2 An attempt was made to verify the critical so il test P concentration obtained in the glass house soil study 1. Two soils different from the one used in the previous study were chosen for

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41 this study based on their low Me hlich-1 P concentrations ( 5 mg kg-1). Samples from the A horizons were collected from soils mapped as Tavares sand and Pottsbur g sand. Classifications of the soils were Tavares (Hyperthermic Un coated Typic Quartzipsamments) and Pottsburg (Sandy, Siliceous, Thermic Grossarenic Alaquods), respectively. Selected chemical properties for soil No. 2 and 3 are shown in Table 3-1. This glasshouse soil study was conducted at the Turfgrass Envirotron at the University of Florid a, Gainesville, Florida. Nalgene tubs (53cm 38cm 12cm) were used as the growth containe rs. Outside surfaces of the containers were painted with white latex paint fi rst and black afterwards to prev ent light penetration. Certified sod with high initial tissue P concentration was wash ed to remove soil, then cut to a size of 53cm 38cm rectangle and transferred to th e growth container on Septemer 28, 2005. After P deficiency was induced, P2O5 rate of 0, 0.31, 0.63, 1.25, and 2.5 g m-2 per four weeks were applied initially on June 20, 2006 and reapplied 2 times during the 12-week growth period. The treatments were arranged in a 2 by 5 factorial design with 2 soils and 5 rates of P application. Each treatment was replicated 5 times. Computer c ontrolled overhead exhaust fans, a wall-length humidifier, and an automatic roof window were used to maintain relatively constant conditions in the glasshouse. Glasshous e temperature was maintained at an average 24 C with a range of 18C to 30C. The relative humility was maintained at approximately 75%. Top growth was clipped to 7.5 cm every other week for a total of 8 collections. Clippings were dried at 70C for 72 h, and weighed. Tissue growth rate was calculated by dividing tissue dry weight by growth days. The dry tissue sa mples were ground to 2-mm and ashed. Samples were analyzed for P by spectrophotometry using the molybdenum-reduced molybdophosphoric method (Hanlon et al., 1994). Turf visual quality was rated weekly using a scale of 1 to 9 where 1 represents brown, dormant turf and 9 represents superior qualit y (Skogley and Sawyer, 1992).

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42 Soil samples were taken at termination using a 3.0-cm dia. soil probe. Soil samples were separated into soil depths of 0-2 cm and 2 cm Mehlich-1 extractable P was determined for the soils samples in depth of 0 cm and 2 cm Water extractable P and FeO-strip P were determined for the 0 cm soil depth. At one week intervals, one-half pore volume of water was applied to all growth containers to aid in the collection of leach ate. Leachate volume, pH, and EC were measured. A sub-sample was collected and frozen until soluble reactive P was analyzed. Analysis of variance was perf ormed by SAS (SAS Inst., 1987). Tukeys test was used for all the mean separation in this study. Means ma rked by the same letter are not significantly differently at P = 0.05. Glasshouse Soil Study 3 Observing St. Augustinegrass growth responses on three soils low in P, a study was undertaken to evaluate growth on a soil containing a medium level of P. This soil study was conducted at the Turfgrass Envirotron at the Univ ersity of Florida, Gain esville, Florida. The Tavares soil used in this experiment was chosen based on it having a medi um level of Mehlich-1 P (17 mg P kg-1) and was classified as Hyperthermic Uncoated Typic Quartzipsamments. Selected chemical properties for this so il (soil No. 4) are shown in Table 3-1. Nalgene tubs (53cm 38cm 12cm) were used as the growth containers. Outside surfaces of the containers were painted with white latex paint first and black afterwards to prevent light penetration. Certified sod with high initial ti ssue P concentration was washed to remove soil, then cut to a size of 53cm 38cm rectangle and transferre d to the growth c ontainer on May 8, 2005. After P deficiency was induced, P2O5 rate of 0, 0.31, 0.63, 1.25, and 2.5 g m-2 per four weeks were applied initially on August 18, 2006 and reapplied 2 times during the 12 week growth period. Treatments were arranged in a randomized complete block design with 5

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43 replications for each treatmen t. Computer controlled overhea d exhaust fans, a wall-length humidifier, and an automatic roof window were us ed to maintain relatively constant conditions in the glasshouse. Glasshouse temperature was maintained at an average 24C with a range of 18C to 30C. The relative humility was maintained at approximately 75%. Top growth was clipped to 7.5 cm every other week for a total of 6 collections. Clippings were dried at 70C for 72 h, and weighed. Tissue growth rate was calculated by dividing tissue dry weight by growth days. Dry tissue sample s were ground to 2-mm and ashed. Samples were analyzed for P by spectrophotometry using the molybdenum-reduced molybdophosphoric method (Hanlon et al., 1994). Turf visual quality was rated weekly using a scale of 1 to 9 where 1 represents brown, dormant turf and 9 represents superior qualit y (Skogley and Sawyer, 1992). Soil samples were taken at termination usi ng a 3.0-cm diameter soil probe. Soil samples were separated into soil depths of 0 cm and 2 10 cm. Mehlich-1 extractable P was determined for both depths. Water extractable P and FeO-strip P were determined for the soil samples in the depth of top 0 cm. At one week intervals, one-half pore volume of water was applied to all growth containers to aid in the collection of leach ate. Leachate volume, pH, and EC were measured. A sub-sample was collected and frozen until soluble reactive P was analyzed. Statistical analysis (analysis of varian ce) was performed by SAS (SAS Inst., 1987). Duncans multiple range test was used for all the mean separation in this study. Means marked by the same letter are not si gnificantly different at P = 0.05.

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44 Figure 3-1. Glasshouse soluti on culture P study layout. Figure 3-2. Glasshouse soil P study 1 layout.

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45 Table 3-1. Selected chemical properties of soils used in the glasshouse soil study 1, 2, and 3. Soil Study Soil No. Classification name Series name pH (1:2) OM (g kg-1) Mehlich-1 P (mg kg-1) Oxalate Al (mg kg-1) Oxalate Fe (mg kg-1) 1 1 Sandy, Siliceous, Hyperthermic Ultic Alaquods Pomona 4.6 9 2 32 42 2 Hyperthermic Uncoated Typic Quartzipsamments Tavares (a) 5.1 15 3 77 60 2 3 Sandy, Siliceous, Thermic Grossarenic Alaquods Pottsburg 4.7 9 5 49 27 3 4 Hyperthermic Uncoated Typic Quartzipsamments Tavares (b) 4.8 13 17 173 154 : soil pH was determined in 1:2 soil/water ratio. : Organic Matter content was determined by ignition.

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46 CHAPTER 4 RESULTS AND DISCUSSION Glasshouse Hydroponic Study Turf Quality St. Augustinegrass visual quality increased with each increm ental increase in solution P concentration in the ra nge from 0 to 775 mg m-3 (Figure 4-1). St. Augustin egrass treated with the two highest P concentr ations, 155 and 775 mg m-3, recovered from the P deficiency conditions and attained mean turf quality values of 6.8 and 7.2, respectively (Figure 4-1). The turf treated with zero P in solution suffered severely from P deficiency with a mean turf quality value of 2.5 (Figure 4-1). Turf treated with zero P declined in quality ove r time and by the end of the study was dead. Solution P levels of 1.24, 6.2, and 31 mg m-3 were generally insufficient in P for turf to recover from deficiency and promote optimum growth. Mean turf quality values from these treatments were below 5.5, which is widely used as a minimum value for acceptable turf quality. Tissue P and Root P The initial tissue P concentration of the St Augustinegrass tested was as high as 4.8 g kg1 on a dry weight basis. After three harvests prio r to treatment applicati on, P deficiency (<1.0 g kg1 on dry weight basis) was induced. Over time, tissue P concentration changed for the six P treatments as shown in Figure 4-2. Tissue P conc entration of turfgrass receiving no P declined over time until it reached a value of 0.48 g kg-1 after the fourth harvest. By the end of the study most of the turfgrass was dead, but those porti ons which were still a live contained 0.45 g P kg-1. This could be considered the minimum P concentration to keep St. Augustinegrass alive. The relationship between tissue P levels and so lution P concentration is presented in Figure 4-3. The highest tissue P level was achi eved with applic ation of 775 mg m-3 solution followed by

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47 P treatment of 155 mg m-3. There were no differences in P c oncentration among the four lowest P treatments. One possible reason for this observation is that the turfgrasses with the four lowest P levels remained P deficient du ring the experimental period. The relationship between root P levels and so lution P concentrations is shown in Figure 44. Root P levels increased with increasing so lution P concentration. The highest P treatment resulted in the highest root P concentration (Figure 4-4). Root P concentration differences among the four lowest solution P levels were noted by Duncans Multiple Range test compared with no significant differences among tissue P levels, which indicates that the primary use of P is for root growth rather than top growth when P is defici ent. Moreover, the root P concentration (Figure 44) with the two highest P levels was lower than those in foliage tissu e (Figure 4-3) when P supplies were sufficient. But the root P concentrat ion resulting from the four lowest P levels was identical or even slightly higher than levels found in leaf tissue when P supplies were deficient. This suggests that roots require less P than tissue when P is suffi cient, but when P is deficient root growth requires a higher level of P. It is possible that when P is deficient a higher quantity of P is required in order to produce mo re roots to overcome the P deficiency. Tissue Growth Rate and Root Growth Rate Phosphorus fertilization influence on tissue growth rate is rarely observed in St. Augustinegrass because of the generally medium to high available P status in Florida soils and relatively low P requirement by St. Augustinegrass. Tissue growth rate (Fi gure 4-5) was affected by solution P concentration. Tissue growth rate increased with solution P levels in a quadratic manner to a maximum value. According to line ar plateau regression an alysis (Figure 4-5), solution P concentrations beyond 111 mg m-3 did not result in increa sed tissue growth rate (r2 = 0.88, p<0.0001, CV = 15.5). Asher and Loneragan (1967) reported that P at 155 mg m-3 produced maximum dry weights of clover ( Trifolium subterraneum L.), erodium ( Erodium

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48 botrys (Cav.) Bertol.) and yields of brome grass ( Bromus rigidus Roth) and cape weed ( Cryptostemma calendula (L.) Druce) were close to ma ximum in a similar hydroponics study. Root growth rates (Figure 46) were affected by soluti on P concentration although the effect was less as compared with tissue grow th rates. Turfgrass re ceiving P at 31 mg m-3 attained the highest root growth rate among the P levels applied according to D uncans Multiple Range test. Asher and Loneragan (1967) reported that P at 31 mg m-3 produced maximum top and root growth for sliver grass ( Vulpia (Festuca) myuros (L.) Gmel.). Root P concentration in the presence of P at 31 mg m-3 was 0.7 g kg-1, which indicates that roots require a smaller quantity of P for optimum growth than tissue (Figure 4-7). Only three mean categories were separated for root growth rates (Figure 4-6) in dicating that the extent of the e ffect of solution P concentration on root growth was less than that on tissue growth. Additionally, turf receiving no P produced substantial root growth (Figure 4-6). The large reserve of P in the parent plant (approximately 5 g kg-1 P in tissue (Figure 4-1) and correspondingly hi gh P level in stolons (not measured)) can be a P source for root growth in case there was no P application or P supplies were not sufficient. Critical Tissue P level A yield response curve in relation to concentratio n of P in the selected tissue is commonly used to determine the critical P concentration. Tissue growth rate was increased with tissue P concentration in a quadratic manner to a ma ximum value (Figure 4-7). The slope of the regression curve can be defined as the change of tissue growth rate over the change of tissue P concentration. The nearly vertical portion of the regression curve shows relatively steeper slopes and the horizontal portion has a sl ope of zero. The transition zone is the area of the curve where the vertical and horizontal portions converge. With the increase of the tissue P concentration the slope gradually decreases until it reaches zero, whic h is the plateau of the curve. According to

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49 linear plateau regression analysis, the critical tissue P level was 1.6 g kg-1 on dry weight basis for the optimum growth (R2 = 0.88, p<0.0001, CV = 15.4). Glasshouse Soil Study 1 Turf Quality For each week across 16 weeks, the hi ghest P application rate of 2.5 g m-2 4-wk-1 resulted in the best turf quality (Table 4-1). There was no differe nce between turf quality ratings associated with the highest P rate and the second highest P rate except for the first week (Table 4-1). The third highest P application rate also achieved best turf quality except for the first three weeks (Table 4-1). With the P deficiency indu ced for St. Augustinegrass before P application, it took some time for St. Augustinegrass to recover from the P deficiency after P application. The higher the P rates applied, the shorter the time required for it to recover and produce the best quality. The second lowest P application rate of 0.31 g m-2 4-wk-1 resulted in the best turf quality in 12 out of 16 weeks (Table 4-1), which provided some evidence that the minimum P application rate was somewhat above 0.31 g m-2 4-wk-1 for this soil. The turf quality of the control treatment remained above 6.0 for the firs t 10 weeks and started to decline afterwards. By the last two weeks, the turf qua lity was below 5.5, which is widely used as a minimum value for acceptable turf quality (Table 4-1). Overall, the tu rf quality ratings were above 5.5 except for the turf with control during the last four weeks. This indicate d that St. Augustineg rass could sustain for months with very low soil P concentrations and deficient P levels in plant tissue. Top Growth Rate St. Augustinegrass top growth res ponded to P applica tion rates (Table 4-2). Turf receiving no P produced the lowest amount of top biomass acr oss eight harvests (Table 4-2). The largest increase on top growth rate was observed with th e first incremental P application (Table 4-2). Turf with three highest P application rates achieve d the highest top growth rate across the eight

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50 harvests. For six out of eight harvests, turf with the second lowest P appl ication rate of 0.31 g m-2 4-wk-1 produced the same top growth as higher P a pplication rates (Table 4-2). The mean value of turf top growth rate with the P application rate of 0.31 g m-2 4-wk-1 across eight harvests was 2.7 g m-2 day-1 and the highest mean value of top growth rate was 3.0 g m-2 day-1 (Table 4-2). The top growth rate for turf with the P application rate of 0.31 g m-2 4-wk-1 was reduced by 10% from the maximum growth rate. By definition, th e amount of nutrient applie d that results in 10% reduction in maximum growth is defined as the critical minimum requirement for that nutrient. Moreover, when the overall means of top growth rate for each P application rate were compared, turf with the P a pplication of 0.31 g m-2 4-wk-1 produced tissue dry weight that was not significant different from those with higher P a pplication rates by Duncans multiple range test (Table 4-2). By either definition of critical minimum nutrient requirement or Duncans multiple range test, P application rate of 0.31 g m-2 4-wk-1 satisfied the minimum P requirement of St. Augustinegrass in this soil. Tissue P Concentration The initial St. Augustinegrass tissue P con centration tested was as high as 4.9 g kg-1 on a dry weight basis. Over time before P applic ation, tissue P concentration dropped from 4.9 g kg-1 to 1.2 g kg-1 on dry weight basis. With no P applicati on to turf and very low soil P concentration, it took almost one year to induce P deficiency (<1.6 g kg-1 on dry weight basis). Tissue P concentration of St. Augustinegrass as influenced by P applic ation rate is shown in Table 4-3. With each incremental P applica tion, tissue P concentration increased across the eight harvests. The highest tissue P level was achieved with application of 2.5 g P2O5 m-2 4-wk-1 and was followed by application of 1.25, 0.63, and 0.31 g P2O5 m-2 4-wk-1 (Table 4-3). Turfgrass receiving no P maintained a P concentration of 1.0 g kg-1, with which turfgrass showed P deficiency symptoms, reduced turf quality (Table 4-1), and reduced growth rate (Table 4-2). In

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51 particular, the mean value of tissue P concen tration with P applic ation rate of 0.31 g P2O5 m-2 4wk-1 was 1.4 g kg-1, which was slightly lower than the cr itical minimum tissue P concentration according to the previous glasshouse hydroponic st udy. This indicated that P application of 0.31 g P2O5 m-2 4-wk-1 was about to achieve the critical mini mum tissue P concentra tion in this soil. This is consistent with the previous discussion on top growth rate conc luding that P application rate of 0.31 g P2O5 m-2 4-wk-1 satisfied the minimum P requirem ent of St. Augustinegrass in this soil. The Critical Minimum Tissue P concentration A yield response curve in relation to concentratio n of P in the selected tissue is commonly used to determine the critical P concentration. Tissue growth rate was increased with tissue P concentration in a quadratic manner to a ma ximum value (Figure 4-8). The slope of the regression curve can be defined as the change of tissue growth rate over the change of tissue P concentration. The nearly vertical portion of the regression curve shows relatively steeper slopes and the horizontal portion has a sl ope of zero. The transition zone is the area of the curve where the vertical and horizontal portions converge. With the increase of the tissue P concentration the slope gradually decreases until it reaches zero, whic h is the plateau of the curve. According to linear plateau regression analysis, the critical tissue P level was 1.8 g kg-1 on dry weight basis for the optimum growth (R2 = 0.77, p<0.0001). Soil Test P Mehlich-I procedure is widely used in the southeast region of US for agronomic crop soil tests. Fe Oxide P and WEP procedures are us ed for environmental impact prediction. Soil Mehlich-I P, Fe Oxide P, and WEP concentratio ns as affected by P application are shown in figure 4-9. With increased P appli cation rates, Mehlich-1 P, Fe Oxide P and WEP concentrations increased incrementally. For each P application, th e Fe Oxide procedure extracted approximately

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52 the same quantity of P as water, which means th at the labile P portion with sorption/desorption process was soluble, suggesting there is lit tle Al/Fe oxides in this soil. Mehlich-1 P concentrations were all higher than the concen trations of Fe oxide P or WEP, which was consistent with Pautler and Sims (2000). Figure 4-11 shows the relationship among Mehlich-1 P, Fe Oxide P, and WEP concentrations. They were pa irwise linear dependent with r2 s of 0.91, 0.90, and 0.85 for WEP vs. Fe oxide P, Mehlich-1 P vs. Fe oxide P, and Mehlich-1 P vs. WEP, respectively. All the pairwise relationships we re highly significant with p values less than 0.0001. Pautler and Sims (2000) reported a better relationshi p of Fe oxide P vs. WEP than that of Mehlich-1 P vs. WEP. This was true for this study. The explanation could be the nature of Fe oxide P procedure that it does not dissolve water insolubl e P components. While, Mehlich-1 extractant contains diluted strong acids which could pa rtially dissolve water in soluble P components. In order to select the best soil test pro cedure for P recommendation on St. Augustinegrass, Mehlich-1 P, Fe Oxide P, WEP concentrations were related to turf tissue P concentration (Figure 4-11). All the pairwise relati onships were highly significant with p values less than 0.0001, which means that all three soil P test methods could potentiall y be used as an index for P nutrition of St. Augustinegrass. Mehlich-1 P obt ained the best correlation against tissue P concentration with r2 of 0.84 better than 0.77 and 0.79 for Fe Oxide P and WEP respectively. The Critical Minimum Soil Test P Concentrations Application of the various P2O5 rates up to 2.5 g P2O5 m-2 4-wk-1 resulted in a range of extractable soil P concentration (0.5 to 16.7 mg kg-1 for Mehlich-1, 0.4 to 7.7 mg kg-1 for Fe Oxide, and 0.4 to 7.6 mg kg-1 for WEP). Growth rate of St. Augustinegrass was affected by extractable soil P concentrati ons (Figure 4-12; Figure 4-13; Figure 4-14). Responses were described relatively well by the quadratic respons e and plateau model with the coefficients of

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53 determination being generally high (0.71 for Me hlich-1, 0.68 for Fe Oxide, and 0.62 for WEP) and p values of less than 0.0001. Critical concentr ation of the extractable P was greatest for Mehlich-1 of 7 mg kg-1 compared 3 and 3 mg kg-1 for Fe Oxide P and WEP, respectively. This is to be expected, because Mehlich-1 extractant co ntains diluted strong acids which could dissolve water insoluble P compounds. Critical concentrati on of the extractable P for Fe Oxide and WEP was the same. This indicated that P adsorbed on soil particles was soluble. CSP applied was partially dissolved in soil solution and partiall y reacted with soil chemicals to form insoluble compounds. Previously, Mehlich-1 soil P below 16 mg kg-1 was categorized as low and below 10 mg kg-1 as very low P. Phosphorus fertilization woul d be recommended in those cases. These data showed that P levels can be kept very low for St. Augustinegrass optimum growth. Phosphorus fertilization would not result in gr owth response above 7, 3, and 3 mg kg-1 for Mehlich-1, Fe Oxide, and WEP, respectively. Mehlich-1 P ha d the best correlation against both tissue P concentration and top growth rate in this soil, therefore it is the best soil P test for St. Augustinegrass among the three used in this study. P Downward Movement Soil samples in depth of 0-10 cm were ini tially taken and analyzed for Mehlich-1 P. However, Mehlich-1 P concentrations for the whol e depth of 0-10 cm were generally very low, and there was no difference in Mehlich-1 P c oncentrations among P application rates by Duncans multiple range test (data not shown) An attempt was made to investigate the downward movement by separating the soil dept h into 0-2 cm and 2-10 cm. Soil Mehlich-1 P concentration as influenced by P application and soil sampling depth are shown in Figure 4-15. Control soils contained 0.6 mg kg-1 Mehlich-1 P, which indi cated extremely low soil P availability without P applica tion during the study. Soil Mehlich1 P concentration in top 2 cm

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54 depth increased with each incremental P applicat ion. Soil Mehlich-1 P concentrations in depth of 2 cm increased with P application, but were all very low in the range of 0.6 to 1.1 mg kg-1. Considering 0.6 mg kg-1 was the baseline of Mehlich-1 P with control, the highe st P application rate of 2.5 g P2O5 m-2 4-wk-1 resulted in Mehlich-1 P of 1.1 mg kg-1 in soil depth of 2 cm. Moreover, for each P application other than contro l soil, Mehlich-1 P conc entration in depth of 0 cm was higher than that in depth of 2 cm. This suggests that little to none of the CSP applied to the turfgrass moved dow nward and the majority remained in the top 2 cm of soil. Leached P Mass and Concentration Phosphorus treatments were appl ied every four weeks for a to tal of four times. Leachates were collected weekly. Sixteen leachates were collected during the study period. The sum of the soluble reactive P (SRP) leached during the first, second, third and fourth leaching collections is presented in Figure 4-16. Chung et al. (1999) has shown that a great er quantity of P leached from sand root-zone mixture during the first two leaching events. However, a natural soil was used in this study, for each P application a greater quantit y of P leached during the first leaching event than those during following leachate collections. Soil receiving 2.5 g P2O5 m-2 4-wk-1 leached a total of 11.8 mg P, followed by 5.9, 2, 1.3, and 0.9 mg P from application of 1.25, 0.63, 0.31 and 0 g P2O5 m-2 4-wk-1, respectively. The two highest P application rates resu lted in larger quantities of P leached and no differences in P leached we re detected among the three lower P application rates. In effect, soil with application rate of 0.63 g P2O5 m-2 4-wk-1 did not leach a larger quantity of P than control soil. This result showed the im portance of small P appli cation rate to prevent P leaching to ground waters. Not to mention the P re quirements for certain crops could be less than recommended, the best management practice could be to suggest multiple P applications with a smaller quantity each time. Leached SRP concentr ation as affected by P application rate and leaching event followed the same pattern as leached SRP mass (Figure 4-17). The highest P

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55 concentration was detected in the leachates collec ted in the first leaching event. An application of 0.63 g P2O5 m-2 4-wk-1 did not result in a higher SRP concentration than control soil. Leachates collected from soil receiving 2.5 and 1.25 g P2O5 m-2 4-wk-1 contained as high as 0.89 and 0.5 mg P kg-1, respectively, which could cause envir onmental concerns. Notice that both of these rates are commonly applied to St. A ugustinegrass and applica tion rate of 1.25 g P2O5 m-2 4wk-1 is the standard in summer months based on the 4:1:2 ratio of N: P2O5: K2O. Glasshouse Soil Study 2 Turf Quality Quality ratings were influenced by P applicati on rate for both soil No.2 and 3 (Table 4-4). Twelve weeks of turf quality da ta were collected. For individu al weekly evaluations across the 12 week experiment period, P application of 0.63g P2O5 m-2 4-wk-1 and above resulted in the best turf quality for both soils (Table 4-4). P application of 0.31 g m-2 4-wk-1 achieved the best turf quality in 11 out of 12 weeks fo r both soils (Table 4-4), which pr ovided some evidence that the minimum P application rate was somewhat above 0.31 g m-2 4-wk-1 for these two soils. For the control turf, turf quality remained above accepta ble level 5.5 for the first 4 and 3 weeks for soil No.2 and 3, respectively, and declined afterwar ds. Overall, the turf quality ratings were somewhat lower than that in the glasshouse soil study 1, which was mainly due to an incidence of disease. Turf with no P application barely recovered from the incidence of disease, which implied the importance of P nutrition in case of disease damage recovery. Top Growth Rate St. Augustinegrass top growth rate varied with P application and soil (Table 4-5). Control turf produced the lowest quantity of top dry ma ss across six harvests in both soil conditions (Table 4-5). The largest increase on top growth rate occurred in the first incremental P application for both soils (1.6 to 2.5 and 1.6 to 2.1 g m-2 day-1 for soil No.2 and 3, respectively)

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56 (Table 4-5). For soil No.2 the top growth rate for turf with P app lication rate of 0.31 g m-2 4-wk-1 was reduced by approximately 10% from the op timum growth rate. Mo reover, turf with P application rates of 0.31 g m-2 4-wk-1 and above achieved equivalent mean top growth rates by Tukeys test. Therefore, by either definiti on of critical minimum nutrient requirement or Tukeys test, P application rate of 0.31 g m-2 4-wk-1 satisfied the minimum P requirement of St. Augustinegrass in soil No.2. However, for soil N o. 3 the top growth rate for turf with P application rate of 0.31 g m-2 4-wk-1 was reduced by approximate ly 30% from the optimum growth rate of 2.9 g m-2 day-1. When the 6-harvest means of top growth rates were subjected to Tukeys test, there were no differences among gr owth means receiving P application of 0.31 g m2 4-wk-1 and above. This was probably due to a la rger variation on top growth rate that occurred when grown in soil No. 3. This larger variation may have resu lted from more severe disease damage in soil No. 3, which particularly influenced growth more on turf with lower P application rates (0.63 g m-2 4-wk-1 and below) (Table 4-5). It has been previously shown that P application improved recovery of tu rf quality from disease. These data also showed the benefits of P application on top growth rate in case of disease incidence. Tissue P Concentration The initial tissue P concentration of the St. Augustinegrass was 4.1 g kg-1 on a dry weight basis. Over 9 months before P applicati on, tissue P concentrati on dropped from 4.1 g kg-1 to 1.2 g kg-1 on dry weight basis. Both soils cont ained very low Mehlich-1 P (< 5 mg kg-1). Tissue P concentration of St. Augustinegrass vari ed with P rate and soil (Table 4-6). In both soils, a maximum tissue P level was achieved (3.2 g kg-1) in response to P2O5 applied at 2.5 g m-2 4-wk-1. Turfgrass receiving no P main tained a value of 1.0 g kg-1, with which turfgrass showed P deficiency symptoms, reduced turf quality (Table 4-6), and reduced growth rate (Table 4-5). Tissue P concentration increased with each incremental P application across six

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57 harvests for both soils. Maximum top growth rate was achieved at 0.31 g P2O5 m-2 4-wk-1, suggesting that application of additional P doe s not enhance top growth rate but P uptake. Greater tissue P concentrations and top growth rates were obser ved in soil No. 2 than No. 3, indicating a greater P uptake occurred in soil No 2, possibly caused by a mo re severe incidence of disease in soil No.3. The Critical Minimum Tissue P concentration In a previous solution culture study, the critic al tissue P concentration was determined to be 1.6 g kg-1. In the glasshouse soil study 1, the criti cal minimum tissue P concentration was estimated to be 1.8 g kg-1. In this study including two so ils, the critical minimum tissue P concentration was 1.9 g kg-1 (Figure 4-18), according to non-lin ear plateau regr ession analysis (R2 = 0.70, p<0.0001). The coefficient of determina tion could be improved from 0.70 to 0.75 by removing two outliers. The maximum top growth rate estimated in the quadratic relationship was 2.8 g kg-1, which was the same as the optimum grow th rates corresponding to the highest P application rate of 2.5 g P2O5 m-2 4-wk-1, suggesting a reasonable plateau. Soil P Tests Soil Mehlich-1 P, Fe Oxide P, and WEP varied with P application for soil No. 2 (Figure 419) and No. 3 (Figure 4-20). With increased P ap plication soil test P levels increased for both soils. For each P rate, Fe Oxide procedure extracted approximately the same quantity of P as water, which was consistent with the findings in glasshouse soil study 1. This was possibly due to a low bonding energy of P sorp tion/desorption with absence of Al/Fe oxides in these soils. The portion adsorbed on soil particles eventually dissolved in the water extraction procedure. Mehlich-1 P concentration was more or less double the concentration of Fe oxide P or WEP, which was consistent with the observations in the glasshouse soil study 1. The explanation could be the nature of Fe oxide P procedure that is based upon sorption/desorption process and does

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58 not dissolve any water insoluble P components. However, Mehlich1 extractant contains diluted strong acids which could pa rtially dissolve water in soluble P components. Figure 4-21 showed the relationships am ong Mehlich-1 P, Fe Oxide P, and WEP concentrations for soil No.2. They were pairwise linear dependent. All the pairwise relationships were highly significant with p values less than 0.0001. In the previous glasshouse soil study 1, a better correlation of Fe oxide P vs. WEP than that of Mehlich-1 P vs. WEP was observed. This was true for soil No. 2 in this study with r2 s of 0.65 and 0.54 for WEP vs. Fe oxide P and Mehlich-1 P vs. WEP, respectively. For soil No. 3, an identical coefficient of determination (r2) of 0.68 was obtained for relationships of Fe Oxide P vs. WEP and Me hlich-1 P vs. WEP. A higher coefficient of determ ination was recorded for Mehlich-1 P vs. Fe Oxide P (r2=0.72) (Figure 4-22). In the glasshouse soil study 1, Mehlich-1 P co rrelated better with tissue P concentration than Fe Oxide P and WEP (Figure 4-12). Tissue P concentration and soil test P concentrations for soil No. 2 (Figure 4-23) and soil No. 3 (Figur e 4-24) showed the same trend. For soil No. 2, Mehlich-1 P obtained the best correlation against tissue P concentration with r2 of 0.85, which was higher than 0.46 and 0.35 for Fe Oxide P and WEP, respectively. For soil No. 3, r2 of 0.71 was obtained for Mehlich-1 P vs. tissue P, which was higher than 0.67 and 0.63 for Fe Oxide P and WEP vs. tissue P, respectivel y. Overall, the three soil P test s concentration were correlated to tissue P concentration with Mehlich-1 P obtai ning the best prediction on tissue P levels. The Critical Minimum Soil Test P Concentrations The growth rate of St. Augustinegrass was affected by soil Mehlich-1 P concentration (Figure 4-25 for soil No. 2; Figure 4-26 for soil N o. 3), Fe Oxide P (Figure 4-27 for soil No. 2), and WEP concentration (Figure 4-28 for soil No. 2). Applicati on of phosphate up to 2.5 g P2O5 m-2 4-wk-1 resulted in a range of ex tractable soil P concentrati ons (0.2 to 10.5 and 0.6 to 9.5 mg

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59 kg-1 for Mehlich-1 in soil No. 2 and 3, resp ectively; 0.6 to 5.2 and 0.8 to 5.5 mg kg-1 for Fe Oxide in soil No. 2 and 3, respectively; 0.8 to 4.0 and 0.9 to 4.6 mg kg-1 for WEP in soil No. 2 and 3, respectively). Growth rate vs. Mehlich-1 P in both soils and growth rate vs. Fe Oxide P and WEP in soil No.2 were described relatively well by the quadratic res ponse and plateau model with the coefficients of determination being generally acceptable (0.54 and 0.60 for Mehlich-1 in soil No. 2 and 3 respectively, 0.72 for Fe Oxide in soil No. 2, and 0.41 for WEP in soil No. 2). When top growth rate was related to Fe Ox ide P and WEP in soil No. 3, top growth rate increased with increasing Fe Oxide P or WEP con centrations and thus fa iled to converge to a plateau (data not shown). This was possibly due to a low correlation between growth rate and Fe Oxide P or WEP concentration and a large varia tion among replications. The critical Mehlich-1 P concentration obtained for soil No. 2 and 3 were 8 and 9 mg kg-1, respectively, which was close to the critical Mehlic h-1 P concentration (7 mg kg-1) determined in the previous glasshouse soil study 1. For soil No. 2 the critical Fe Oxide P and WE P concentration was 3 mg kg-1. These data suggest that optimum growth of St. Augustine grass can be attained at very low soil lest P levels. Phosphorus fertilization would not resu lt in growth response above 8, 3, and 3 mg kg-1 for Mehlich-1, Fe Oxide, and WEP, respectively for soil No. 2. Mehlich-1 P had the best correlation against both tissue P concentration and top growth rate in both so ils with exception of correlation of top growth rate against Fe Oxide P was bette r than that against Mehlich-1 P. Overall, Mehlich-1 P test was the best so il P test for St. Augustinegrass among the three extractants used. P Downward Movement In the glasshouse soil study 1, CSP applied to the turfgrass did not move downward and the majority stayed in the top 2 cm in that soil. In this study soil samples were separated into 0 cm and 2 cm depths. Soil Mehlich-1 P concentra tion as influenced by P application rate and soil sampling depth are shown in Figure 4-29 (soil No. 2) and Fig. 4-30 (so il No. 3). Mehlich-1 P

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60 concentration (0-2 cm depth) w ith P application rate of 2.5 g P2O5 m-2 4-wk-1 was increased from 1 to 7.9 and 1.1 to 9.3 mg kg-1 for soil No. 2 and 3, respectivel y. Many studies have shown that the amount of fertilizer P required for each unit increase of soil test P level varies with soil texture, soil test method employed, as well as the rate of fert ilizer P applied. In a 29-yr study on Ultisols in Alabama, Cope (1981) found that 24 and 20 kg P ha raised Mehlich-1 soil test P by 1 mg P kg when P was applied at 31 and 54 kg P ha yr, respectively. An application of 4 kg P ha-1 was required to raise the Bray I extractable P of medium-textured Mollisols and Alfisols 1 kg ha-1 (Peck et al., 1971). Cox (1994) showed that incr eases in Mehlich-III with each unit of applied P were 0.7 units for soils with 10% clay, and it decreased exponen tially to 0.2 units for soils with >50% clay. In this study tota l applications of 9.4, 18.8, 37.5, and 75 kg P2O5 ha raised the levels of soil Mehlich-1 P in top 2 cm soils by 2, 2, 4, and 7 mg P kg soil, respectively, for soil No. 2 and by 2, 3, 5, and 8 mg P kg soil, respectively, for soil No. 3 after 12 week of P fertilizatio n. Soil Mehlich-1 P concentrations in depth of 2-10 cm increased with P application of 2.5 g P2O5 m-2 4-wk-1 for soil No. 2, but soils with lower P rates did not result in increased Mehlich-1 P concentration (Fig. 4-29). For soil No. 3 P application did not influence the Mehlich-1 P levels in soil depth of 2-10 cm (Figure 4-30). This suggests that most of CSP applied to the turfgrass stayed in the top 2 cm soil depth and that a low application P rate would be helpful in preventing P downward movement. Leached P Mass and Concentration Phosphorus treatments were appl ied every four weeks for a to tal of three times. Leachates were collected weekly after e ach P application. Twelve leac hates were collected during the study period. The sum of the soluble reactive P (S RP) leached during the first, second, third and fourth leaching collections is presented in Figur e 4-31 (soil No. 2) and Figure 4-33 (soil No. 3), respectively. In the glasshouse soil study 1, it wa s observed that for each P application rate a

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61 substantial greater quantity of P leached during the first leaching event and th at little P leached in subsequent leachate collections. This was true for both soils in this study. Soil No. 2 which receiving 2.5 g P2O5 m-2 4-wk-1 leached an average of 8.4 mg P, followed by 4.3, 1.6, 1.5, mg P from application of 1.25, 0.63, 0.31 g P2O5 m-2 4-wk-1, respectively, among which 48%, 44%, 44%, and 34% was leached in the first leaching event. Soil No. 3 leached an average of 10.3 4.3, 3.2, 1.8, mg P from applications of 2.5, 1.25, 0.63 and 0.31 g P2O5 m-2 4-wk-1, respectively, among which 42%, 47%, 47%, and 55% was leached in the first leachat e collection. Not only was there a higher percentage of P mass leached in the first leaching event, but also the SRP concentration was higher in the first leachate than the subsequent leachates in soil No. 2 (Figure 4-32 ) and soil No. 3 (Figure 4-34). These findi ngs suggest the importance of P application timing. To avoid P application before a rain even t would be beneficial in preventing P leaching and runoff. P application of 1.25 and 2.5 g P2O5 m-2 4-wk-1 resulted in larger quantities of P leached and higher SRP concentration in soil No. 2 a nd there were no differences among leached P mass and SRP concentrations resulted from the thr ee lower P application rates. For soil No. 3, P application of 2.5 g P2O5 m-2 4-wk-1 resulted in a larger quantity of P loss and higher SRP concentration through leaching and there were no differences among leached P mass and SRP concentrations at the lower P a pplication rates. This suggests th at P loss through leaching can be prevented by small P application rate. Glasshouse Soil Study 3 Turf Quality Quantity of applied P influenced St. A ugustinegrass quality (Table 4-7). A P2O5 application of 0.31 g m-2 4-wk-1 resulted in the best turf quality in 10 out of 12 weeks (Table 4-7). Duncans multiple range test of turf quality rating versus rate of P applied revealed differences in

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62 mean turf quality rating up to 0.31 g P2O5 m-2 4-wk-1. Application of additional P beyond 0.31 g P2O5 m-2 4-wk-1 did not increase turf quality. A total of 0.93 g P2O5 m-2 was applied, and this equates to an N: P2O5 application ratio of 16:1, which is substantially higher than common used 4:1 ratio. The previous glasshouse study 1 and 2 re ported the same response to P application for St. Augustinegrass growing in course textured sandy soils. The overall turf quality including controls was generally good, possibly because th e relatively sufficient labile soil P prevented severe P deficiency on St. Augustinegrass. The so il used in this study initially contained 17 mg kg-1 Mehlich-1 P. By the time P treatments were applied, it was believed that this soil still contained a substantial amount of plant available P, which was c onfirmed by soil analysis at the end of the study. The soil Mehlich-1 P con centration in control soils was 2.7 mg kg-1, obviously due to a relatively high residue soil P con centration in the beginning of the study. Top Growth Rate St. Augustinegrass top growth rate responded to P applica tion (Table 4-8). Duncans multiple range test of top growth rate versus P application rate revealed differences in mean top growth rate up to 0.31 g P2O5 m-2 4-wk-1. Application of additional P beyond 0.31 g P2O5 m-2 4wk-1 did not increase top growth (Table 4-8) Relatively smaller growth rate reduction (approximately 25%) was observed in controls in this study compared with those in previous studies. This was due to a higher initial soil Mehlich-1 P concentr ation in this soil so that P deficiency on St. Augustinegrass was mildly de veloped. A CV of less than 10% suggests that there is a small variation among replications. Tissue P Concentration The initial tissue P concentration of the St. Augustinegrass was 5.0 g kg-1 on a dry weight basis. Over 15 months before P application, tissue P concentr ation dropped from 5.0 to 1.3 g kg-1 on dry weight basis. The soil Mehlic h-1 P decreased from 17 to 4 mg kg-1 by the time P was

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63 applied. Tissue P concentration of St. Augustineg rass responded to P appl ication (Table 4-9). Tissue P concentration increased with each incr emental P application across six harvests. A maximum tissue P level (3.4 g kg-1) was achieved in response to phosphate applied at 2.5 g m-2 4-wk-1. Turfgrass receiving no P ma intained a value of 1.4 g kg-1, which was higher than those found in the previous study 1 and 2 (1.0 g kg-1). This explains the smaller top growth rate reduction in controls and only mild P deficiency symptoms observed in this study. The soil used in this study supplied a substant ial quantity of P for St. Augus tinegrass growth over the entire experiment period. Critical Minimum Tissue P Concentration In the previous solution culture study, the crit ical tissue P concentration was determined to be 1.6 g kg-1. In the glasshouse soil study 1 and 2, the critical minimum tissue P concentration was estimated to be 1.8 and 1.9 g kg-1, respectively. The critical minimum tissue P concentration in study 3 was 1.8 g kg-1 (Figure 4-35), according to non-line ar plateau regression analysis (r2 = 0.48, p<0.001). The coefficient of determination was lower than that found in previous soil study 1 and 2. This was possibly due to three or four outliers. The maximum top growth rate estimated in the quadratic relationship was 2.9 g kg-1, which was consistent with the optimum growth rates (2.9 and 2.8 g kg-1 for soil study 1 and 2, respectively), suggesting a reasonable plateau. Soil P Tests Soil Mehlich-1 P, Fe Oxide P, and WEP varied with P application in soil study 3 (Figure 436). With each incremental increased P applic ation soil Mehlich-1 P levels increased. Higher soil test P values were only obser ved for the application of 2.5 g P2O5 m-2 4-wk-1 in Fe Oxide P, 1.25 and 2.5 m-2 4-wk-1 in WEP, respectively (Figure 4-36). In the glasshouse soil study 1 and 2, Fe Oxide strip procedure and water extraction procedure extracted approximately the same quantity of P in those soil conditions. However, in this study Fe Oxide procedure extracted

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64 greater quantities of P than water for each P application, which suggests a higher bonding energy of P sorption/desorption with the Al/Fe oxides in this soil. Some portion of P ions adsorbed on soil particles was not extracted by water extractio n procedure but by Fe Oxide strip procedure. Mehlich-1 P concentration was more or less double the concentration of WEP, which was consistent with the observations in the glasshouse soil study 1 and 2. Figure 4-37 shows the relationship among Mehlich-1 P, Fe Oxide P, and WEP concentrations in glasshouse soil study 3. They were pairwise lin ear dependent. In the previous glasshouse soil study 1 and 2, a better correlation of Fe oxide P vs WEP than that of Mehlich-1 P vs. WEP was observed. This was true in this study with r2 s of 0.52 and 0.35 for WEP vs. Fe oxide P and Melich-1 P vs. WEP, respectively. Moreover, the relationship of Fe oxide P vs. WEP (p<0.0001) had a smaller p value than that of Mehlich-1 P vs. WEP (p<0.01). A smaller coefficient of determination for each pairwise lin ear regression was obtained than those in the glasshouse soil study 1 and 2. This wa s possibly due to narrower range s of soil test P extracted in this soil with Mehlich-1 P, Fe Oxide P a nd WEP mostly varied in 3, 1.5, and 1.5 mg P kg-1, respectively (Figure 4-37). Thes e narrow ranges of soil test P revealed a strong bonding force of P sorption/desorption and a small solubility of P compounds in water and dilute acids. These narrow ranges of Fe Oxide P and WEP also affect the correlations against tissue P concentration. The coefficients of determination for Fe Ox ide P vs. Tissue P and WEP vs. Tissue P were 0.21 and 0.23, respectively, which were lower than thos e previously observed in the glasshouse study 1 and 2 (Figure 4-38). Soil Mehlich-1 P obtai ned the best correlation against tissue P concentration with r2 of 0.70, higher than 0.21 and 0.23 for Fe Oxide P and WEP, respectively (Figure 4-38). Overall, the three soil test P concentration were correlated with tissue P

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65 concentration (p<0.05) with Mehl ich-1 P obtaining the best predic tion on tissue P levels, which was consistent with observations in the previous studies. The Critical Minimum Mehlich-1 P Concentration Not only were the correlations of tissue P c oncentration against soil test P reduced by the narrow range of soil test P concen trations, but also the relationsh ip between top growth rate and soil test P concentrations were reduced. Soil Fe Oxide P and WEP were poorly correlated with top growth rate. Top growth rate continued to increase with increased Fe Oxide P or WEP concentrations so that it did not converge to a plateau (data no t shown). Therefore, it was not possible to establish a critical minimum level fo r Fe Oxide P and WEP. Growth rate vs. Mehlich1 P was described well by the quadratic response and plateau model with the coefficients of determination of 0.27 and p value less than 0.05. Th e critical Mehlich-1 P concentration obtained was 5 mg kg-1, which was somewhat lower than the cri tical Mehlich-1 P concentrations of 7, 8, and 9 mg kg-1 determined for soil No. 1, 2, and 3, respectively. This was expected because this soil contained a larger quantity of Al/Fe oxides and has a larger P buffering capacity. For each unit of soil test P level decrease, it supplied a la rger quantity of P for plant uptake. These data suggest that P levels can be kept very low for St. Augustinegrass optimum growth. Phosphorus fertilization would not result in growth response above 5 mg kg-1 for Mehlich-1 P in this soil. Mehlich-1 P had the best correlation against both tissue P concentration a nd top growth rate and therefore is the best soil test method for St. Augustinegrass among th e three tests used. P Downward Movement Soil samples were separated into 0 cm and 2 cm depths. Soil Mehlich-1 P concentration as influenced by P application and soil sampling depth was shown in Figure 4-40. Compared with control, Mehlich-1 P concentrat ion (0 cm depth) with P application of 2.5 g P2O5 m-2 4-wk-1 increased from 2.5 to 5.6 mg kg-1. Total applications of 9.4, 18.8, 37.5, and 75

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66 kg P2O5 ha raised the levels of soil Mehlich-1 P in top 2 cm soils by 0.6, 1, 1.6, and 3.1 mg P kg soil, respectively, after 12 weeks of P fertiliza tion. Soil Mehlich-1 P concentration in top 2 cm soils increased with P application, however, P levels in the 2-10 cm depth was not affected (Figure 4-40). This suggests that CSP applied to the turfgrass st ayed in the top 2 cm soil depth and downward movement of P was minimal. Leached P Mass and Concentration Phosphorus treatments were appl ied every four weeks for a to tal of three times. Leachates were collected one, two, three and four weeks af ter each P application. Twelve leachates were collected. The sum of the SRP quantity leached du ring the first, second, third and fourth leaching collections is presented in figure 4-41. It was observed that for each non-zero P application substantially greater quantities of P leached during the first tw o leaching events than in the following two leachate collections. This was consis tent with the glasshouse soil study 1 and 2. Soils applied with 2.5 g P2O5 m-2 4-wk-1 leached an average of 9.5 mg P, followed by 4.1, 3.5, 1.9 mg P from application of 1.25, 0.63, 0.31 g P2O5 m-2 4-wk-1, respectively, among which 71%, 68%, 74%, and 63% was leached out in the firs t two leaching events. Not only was there a substantial higher percent of P mass leached in the first two le aching events, but also the SRP concentration was higher in the first two leachat es than followings (Figure 4-42). These findings suggest timing could be an issue for P applicatio n. To avoid P application before a rain event would be beneficial in preventing P leaching. For each P application rate, the overall percentage of P loss due to leaching for application of 0.31, 0.63, 1.25, and 2.5 g P2O5 m-2 4-wk-1 were 1.9%, 1.8%, 1.0% and 1.2%, respectively. The percentage were relatively small, but P application of 1.25 and 2.5 g P2O5 m-2 4-wk-1 resulted in larger quantities of P leached and P application of 2.5 g P2O5 m-2 4-wk-1 led to higher SRP concentration. P application of 0.63 g P2O5 m-2 4-wk-1 and below did result in neither a

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67 greater P quantity loss nor a highe r SRP concentration than contro l. This suggests that small P application rate was effective in preventing P loss through leaching.

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68 1 2 3 4 5 6 7 8 9 01.246.231155775Solution P (mg m-3)Turf qualit y A B F E D C Figure 4-1. Turf quality response to solution P concentration. Turf quality is the mean of five replications over time after treatments were applied. Means marked by the same letter are not significantly differently at P = 0.05 according to Duncans Multiple Range Test. 0 1 2 3 4 5 6 7/198/189/1710/1711/1612/161/152/143/16Tissue P (g kg-1) 0 1.24 6.2 31 155 775 Figure 4-2. Tissue P response to solu tion P concentration and time. P, mg m-3 No P applied before this point Month/Day (2004)

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69 0 0.5 1 1.5 2 2.5 3 3.5 01.246.231155775Solution P (mg m-3)Tissue P (g kg-1) Figure 4-3. Relationship of solu tion P and tissue P concentrati on on day 148. Means marked by the same letter are not significantly diffe rently at P = 0.05 according to Duncans Multiple Range Test. 0.2 0.4 0.6 0.8 1 1.2 1.4 01.246.231155775Solution P (mg m-3)Root P (g kg-1) Figure 4-4. Relationship of solu tion P and root P concentration on day 148. Means marked by the same letter are not significantly differently at P = 0.05 according to Duncans Multiple Range Test. A B BC CD CD D A B C C C C

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70 Solution P (mg m-3) 0100200300400500600700800 Tissue growth rate (g m-2 day-1) 0.0 .2 .4 .6 .8 1.0 1.2 Figure 4-5. St. Augustinegrass ti ssue growth rate relative to solution P concentration. y = 0.9938 0.00004(x 110.9)2 R2 = 0.86, p< 0.0001, CV = 15.5 plateau = 1 critical x =111

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71 1 1.5 2 2.5 3 3.5 01.246.231155775Solution P (mg m-3)Root growth rate (g m-2 day-1) Figure 4-6. Root growth rate relative to solu tion P concentration. Means marked by the same letter are not significantly differently at P = 0.05 according to Duncans Multiple Range Test. AB B AB AB B A

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72 Tissue P (g kg-1) 0.0.51.01.52.02.53.03.5 Tissue growth rate (g m-2 day-1) 0.0 .2 .4 .6 .8 1.0 1.2 Figure 4-7. St. Augustinegrass ti ssue growth rate relative to tissue P concentration. y = 1.0456 -0.5056(x 1.5614)2 R2 = 0.88, p<0.0001, CV = 15.4 plateau = 1 critical x = 1.6

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73 Table 4-1. Visual quality rating of St. A ugustinegrass as influenced by P applicati on rate in 2005 gla sshouse soil study 1 P2O5 rates -----------------------------------------------Week --------------------------------------------------------------(g m-2 4-wk-1) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Mean 0 6.4c 6.5c 5.9c 7b 6.7b 6.8b 6.6b 6.9c 6.2b 6.2b 5.7c 5.4b 5.4b 6.1b 4.5b 4.6b 6.3c 0.31 7.0b 7.4ab 7.3b 7.4ab 7.3a 7.5a 7.4a 7.4bc 7.2a 7.7a 7.3b 7.6a 7.2a 7 .9a 7.1a 7.4a 7.4b 0.63 6.9b 7.3b 7.2b 7.6ab 7.2a 7.7a 7.2ab 7.6ab 7.2a 7.6a 7.5ab 7.7a 7a 7 .9a 7.5a 7.4a 7.4b 1.25 6.9b 7.7ab 7.7ab 7.8a 7.6a 7.8a 7.6a 7.9ab 7.6a 8a 7.8ab 7.8a 7.5a 8.1a 7.5a 7.7a 7.7ab 2.5 7.4a 8.0a 8.1a 8.0a 7.8a 8.1a 7.8a 8.1a 7.7a 8.1a 8.0a 8.0a 7.8a 8.2a 7.6a 7.9a 7.9a CV(%) 4.3 6.3 6.4 7.4 6.1 5.6 6.3 5.5 6.2 5.9 6.1 4.8 8 .7 6.9 6.0 8.8 4.7 Within columns, means followed by the same letter are not signifi cantly different according to Duncans multiple range test (0 .05).

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74 Table 4-2. Top growth rate of St. Augustinegra ss as influenced by P application rate in 2005 2006 glasshouse soil study 1. P2O5 rates -------------------------Harvest (g m-2 day-1) -----------------------------------(g m-2 4-wk-1) 1 2 3 4 5 6 7 8 Mean 0 2.2b 2.1b 2.1b 1.9b 2.0c 2.1c 2.1b 1.9b 2.1b 0.31 2.9ab 2.6ab 2.6a 2.3ab 2.4bc 2.5bc 2.9a 2.7a 2.7a 0.63 3.0a 2.6ab 2.9a 2.4ab 2.7ab 2.7ab 3.0a 3.0a 2.7a 1.25 3.0a 2.9a 3.0a 2.5ab 2.9a 3.0ab 3.1a 3.1a 3.0a 2.5 3.4a 3.0a 3.0a 2.5a 3.0a 3.1a 3.1a 3.1a 3.0a CV(%) 18.8 15.4 18.5 16.9 12.7 16.6 8.5 12.9 10.6 Within columns, means followed by the same lette r are not significantly di fferent according to Duncans multiple range test (0.05). Table 4-3. Tissue P concentration of St. Augustinegrass as influen ced by P application rate in 2005 glasshouse soil study 1. P2O5 rates ---------------------------------Harvest (g kg-1) ------------------------------------(g m-2 4-wk-1) 1 2 3 4 5 6 7 8 Mean 0 1.1d 1.1d 1.1d 1.0d 1.0d 1.0d 0.8d 1.0e 1.0e 0.31 1.5cd 1.5cd 1.5c 1.4c 1.5c 1.3cd 1.3d 1.5d 1.4d 0.63 1.7c 1.6c 1.7c 1.7c 1.7c 1.8c 1.8c 2.1c 1.8c 1.25 2.5b 2.3b 2.6b 2.3b 2.4b 2.4b 2.7b 3.0b 2.5b 2.5 3.5a 3.2a 3.3a 3.1a 3.5a 3.3a 3.4a 4.1a 3.4a CV(%) 17.7 18.8 15.3 15.1 15.3 19.5 17.5 8.1 11.2 Within columns, means followed by the same lette r are not significantly di fferent according to Duncans multiple range test (0.05).

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75 Tissue P (g kg -1 ) 1234 Top growth rate (g m -2 day -1 ) 1.6 2.0 2.4 2.8 3.2 3.6 Figure 4-8. St. Augustinegrass tissu e growth rate relative to ti ssue P concentration in the glasshouse soil study 1. y = 2.91 1.57 (1.76 x)2 R2 = 0.77, p<0.0001, CV=10.9% plateau = 2.91 critical x = 1.8

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76 a a b a b b b bc bc c c c ddd Figure 4-9. Soil Mehlich-1 P, Fe Oxide P, and WEP concentration as influenced by P application rate (soil sampling depth of 0-2 cm) in the glasshouse soil study 1.

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77 Figure 4-10. Relationships among Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling depth of 0-2 cm) in the glasshouse soil study 1.

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78 Figure 4-11. Relationships between tissue P conc entration and Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling depth of 0-2 cm) in the glasshouse soil study 1.

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79 Mehlich-1 P (mg kg -1 ) 024681012141618 Top growth rate (g m -2 day -1 ) 1.6 2.0 2.4 2.8 3.2 3.6 Figure 4-12. St. Augustinegrass ti ssue growth rate relative to so il Mehlich-1 P concentration in the glasshouse soil study 1. y = 2.93 0.02(6.94 x)2 R2 = 0.71, p<0.0001, CV=20.7% plateau = 2.93 critical x = 7

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80 Fe Oxide P (mg kg -1 ) 02468 Top growth rate (g m -2 day -1 ) 1.6 2.0 2.4 2.8 3.2 3.6 Figure 4-13. St. Augustinegrass tissu e growth rate relative to soil Fe Oxide P concentration in the glasshouse soil study 1. y = 2.90 0.13(3.10 x)2 R2 = 0.68, p<0.0001, CV = 18.9% plateau = 2.90 critical x = 3

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81 WEP (mg kg -1 ) 02468 Top growth rate (g m -2 day -1 ) 1.6 2.0 2.4 2.8 3.2 3.6 Figure 4-14. St. Augustinegrass ti ssue growth rate relative to soil WEP concentration in the glasshouse soil study 1. y = 2.90 0.11(3.31 x)2 R2 = 0.62, p<0.0001, CV = 14% plateau = 2.90 critical x = 3

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82 0 4 8 12 16 00.310.631.252.5P2O5 application rate (g m-2 per 4 wks)Soil Melich1 P (mg kg-1) 0-2 cm 2-10 cm D C BC cb bc B A a c Figure 4-15. Soil Mehlich-1 P concentration as influenced by P application rate and soil sampling depth in the glasshouse soil study 1. 0 1 2 3 4 5 6 00.310.631.252.5 P2O5 application rate (g m-2 4-wk-1)Leached SRP mass (mg) 1st 2nd 3rd 4th a b c c c a b c c c a b bc c c a b c c c Figure 4-16. Leached SRP mass as influenced by P application rate and leaching event in glasshouse soil study 1.

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83 0 0.2 0.4 0.6 0.8 1 00.310.631.252.5 P2O5 application rate (g m-2 4-wk-1)Leached SRP concentration (mg L-1) 1st 2nd 3rd 4th a b c c c a b c c c a b c c c a b c c c Figure 4-17. Leached SRP concentration as influe nced by P application ra te and leaching event in glasshouse soil study 1.

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84Table 4-4. Visual quality rating of St. A ugustinegrass as influenced by P applicati on rate in 2005 gla sshouse soil study 2 P2O5 rates -----------------------------------------------Week---------------------------------------Soil (g m-2 4-wk-1) 1 2 3 4 5 6 7 8 9 10 11 12 Mean 0 6.5a 6.7b 6.4a 5.7b 5.3b 5.5b 4.7b 4.5b 4.7c 4.5b 5. 0b 4.4b 5.3b 0.31 7.3a 7.8ab 7.3a 7.6a 6.9a 7.3a 6.3a 6.8a 6.6b 7.4a 6.5 a 6.8a 7.0a 2 0.63 6.9a 7.6ab 7.3a 7.4a 7.2a 7.5a 6.8a 7.1a 7.3ab 7.6a 6.6a 7.0a 7.2a 1.25 7.3a 8.1a 7.3a 7.6a 7.4a 7.7a 7.1a 7.2ab 7.3ab 8.0a 7.0a 7.1a 7.4a 2.5 7.1a 7.8a 7.5a 7.7a 7.4a 7.8a 7.4a 7.4a 7.3a 7.6a 7 .1a 7.0a 7.4a 0 6.5a 6.7b 6.3b 5.4c 5.1b 5.3b 4.2b 4.2b 4.3b 4.5b 4. 7b 4.5b 5.1b 0.31 6.9a 7.4ab 7.1ab 6.8b 6.0ab 6.6ab 6.2a 6.6a 6.1a 6.9a 6.7a 6.2a 6.6a 3 0.63 6.8a 7.6ab 6.5ab 7.1ab 6.3ab 6.8a 6.1a 6.4a 6.9a 7.5a 6.2a 6.6a 6.7a 1.25 7.0a 7.6ab 7.4ab 7.4ab 7.0a 7.5a 6.8a 7.1a 7.1a 7.4a 6.9a 6.8a 7.2a 2.5 7.3a 8.1a 7.7a 7.8a 7.4a 8.0a 7.3a 7.3a 7.4a 7.7a 7 .2a 7.0a 7.5a CV(%) 5.7 8.0 9.1 6.7 10.7 9.9 10.6 6.8 8.6 6.6 10.1 7.5 6.3 Within columns for each soil, means followed by the same letter are not significantly different according to Tukeys test (0.05).

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85 Table 4-5. Top growth rate of St Augustinegrass as influenced by P application rate and soils in 2005 glasshouse soil study 2. P2O5 rates -------------------Harvest (g m-2 day-1) ----------------------Soil (g m-2 4-wk-1) 1 2 3 4 5 6 Mean 0 2.7a 1.7b 1.6b 1.2b 1.1b 1.7b 1.6b 0.31 3.5a 2.3ab 2.5a 2.0a 2.4a 2.5ab 2.5a 2 0.63 3.3a 2.4ab 2.9a 2.1a 2.5a 2.8a 2.6a 1.25 3.8a 2.6a 3.0a 2.3a 2.7a 2.9a 2.9a 2.5 3.6a 2.7a 3.0a 2.2a 2.8a 3.0a 2.8a 0 2.5a 1.5b 1.6c 1.3c 1.3b 1.5b 1.6b 0.31 3.0a 2.0ab 2.1bc 1.6b 2.1ab 2.1ab 2.1ab 3 0.63 2.9a 1.7ab 2.2bc 1.6abc 2.1ab 2.2ab 2.1ab 1.25 3.2a 2.4a 2.5a 2.1ab 2.5a 2.5a 2.5a 2.5 3.4a 2.5a 3.0a 2.2a 2.7a 3.0a 2.8a CV(%) 18.1 19.7 13.5 15.2 17.6 18.0 14.0 Within columns for each soil, means followed by the same letter are not significantly different according to Tukeys test (0.05). Table 4-6. Tissue P concentration of St. Augustinegrass as influen ced by P application rate and soils in 2005 glas shouse soil study 2. P2O5 rates ----------------Harvest (g kg-1) --------------Soil (g m-2 4-wk-1) 1 2 3 4 5 6 Mean 0 1.1d 0.98c 0.94c 0.94c 1.1d 0.89c 0.98d 0.31 1.3cd 1.2c 1.2c 1.3c 1.4cd 1.3c 1.3cd 2 0.63 1.5c 1.4bc 1.4c 1.4abc 1.9c 1.6bc 1.5c 1.25 2.0b 1.8b 2.3b 2.2ab 2.9b 2.1b 2.2b 2.5 3.1a 2.7a 3.1a 3.0a 3.8a 3.3a 3.2a 0 1.1d 0.93c 1.0c 1.0c 1.0d 1.0c 1.0c 0.31 1.2c 1.0c 1.1c 1.0c 1.4cd 1.2c 1.2c 3 0.63 1.5c 1.2bc 1.2bc 1.3bc 1.9c 1.5c 1.4c 1.25 2.0b 1.7b 1.8b 1.9b 2.6b 2.2b 2.0b 2.5 3.3a 2.6a 2.5a 2.8a 3.9a 3.5a 3.2a CV(%) 10.8 15.6 17.7 24.5 11.8 17.7 10.3 Within columns for each soil, means followed by the same letter are not significantly different according to Tukeys test (0.05).

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86 Tissue P (g kg -1 ) 1234 Top growth rate (g m -2 day -1 ) 0.0 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Figure 4-18. St. Augustinegrass ti ssue growth rate relative to tissue P concentration in the glasshouse soil study 2. y = 2.81 1.26(1.93 x)2 R2 = 0.70, p<0.0001, CV = 12.2% plateau = 2.81 critical x = 1.9

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87 a a ab a b ab b bc ab ab cd bc d c b Figure 4-19. Soil Mehlich-1 P, FeO P, and WEP concentration as influenced by P application rate (soil sampling depth of 0-2 cm) in the glasshouse soil study 2 (soil No. 2). a a b a b ab bc c b b c bc c c b Figure 4-20. Soil Mehlich-1 P, FeO P, and WEP concentration as influenced by P application rate (soil sampling depth of 0-2 cm) in the glasshouse soil study 2 (soil No. 3).

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88 Figure 4-21. Relationships among Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling depth of 0-2 cm) in the gl asshouse soil study 2 (soil No. 2).

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89 Figure 4-22. Relationships among Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling depth of 0-2 cm) in the gl asshouse soil study 2 (soil No. 3).

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90 Figure 4-23. Relationships between tissue P conc entration and Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling dept h of 0 cm) in the glasshouse soil study 2 (soil No. 2).

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91 Figure 4-24. Relationships between tissue P conc entration and Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling dept h of 0 cm) in the glasshouse soil study 2 (soil No. 3).

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92 Mehlich-1 P (mg kg -1 ) 024681012 Top growth rate (g m -2 day -1 ) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Figure 4-25. St. Augustinegrass ti ssue growth rate relative to so il Mehlich-1 P concentration in the glasshouse soil st udy 2 (soil No. 2). y = 2.96 0.024(7.73 x)2 R2 = 0.54, p<0.001, CV =17.3% plateau = 2.96 critical x = 8

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93 Mehlich-1 P (mg kg -1 ) 024681012 Top growth rate (g m -2 day -1 ) .8 1.2 1.6 2.0 2.4 2.8 3.2 Figure 4-26. St. Augustinegrass ti ssue growth rate relative to so il Mehlich-1 P concentration in the glasshouse soil st udy 2 (soil No. 3). y = 2.74 0.017(8.78 x)2 R2 = 0.60, p<0.0001, CV = 20.2% plateau = 2.74 critical x = 9

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94 Fe Oxide P (mg kg -1 ) 0123456 Top growth rate (g m -2 day -1 ) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Figure 4-27. St. Augustinegrass tissu e growth rate relative to soil Fe Oxide P concentration in the glasshouse soil study 2 (soil No.2). y = 2.74 0.23(3.09 x)2 R2 = 0.72, p<0.0001, CV = 25.6% plateau = 2.74 critical x = 3

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95 WEP (mg kg -1 ) 0123456 Top growth rate (g m -2 day -1 ) .8 1.2 1.6 2.0 2.4 2.8 3.2 Figure 4-28. St. Augustinegrass ti ssue growth rate relative to soil WEP concentration in the glasshouse soil study 2 (soil No.2). y = 2.72 0.21(3.08 x)2 R2 = 0.41, p<0.01, CV = 26.4% plateau = 2.72 critical x = 3

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96 0 2 4 6 8 10 00.310.631.252.5P2O5 application rate (g m-2 4-wk-1)Soil Mehlich1 P (mg kg-1) 0-2 cm 2-10 cm C C C b b b B A a b Figure 4-29. Soil Mehlich-1 P concentration as influenced by P application rate and soil sampling depth in the glasshouse study 2 (soil No. 2). 0 2 4 6 8 10 00.310.631.252.5P2O5 application rate (g m-2 4-wk-1)Soil Mehlich1 P (mg kg-1) 0-2 cm 2-10 cm C C C a a a B A a a Figure 4-30. Soil Mehlich-1 P concentration as influenced by P application rate and soil sampling depth in the glasshouse study 2 (soil No. 3).

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97 0 1 2 3 4 5 00.310.631.252.5 P2O5 application rate (g m-2 4-wk-1)Leached SRP mass (mg) 1st 2nd 3rd 4th a b c c c a b c a b bc c c a b c c b bb Figure 4-31. Leached SRP mass as influenced by P application rate and leaching event in glasshouse soil study 2 (soil No.2). 0 0.2 0.4 0.6 0.8 00.310.631.252.5 P2O5 application rate (g m-2 4-wk-1)Leached SRP concentration (mg L-1) 1st 2nd 3rd 4th a b c c c a b c a b bc c c a b c bc b bb Figure 4-32. Leached SRP concentration as influe nced by P application ra te and leaching event in glasshouse soil study 2 (soil No.2).

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98 0 1 2 3 4 5 00.310.631.252.5 P2O5 application rate (g m-2 4-wk-1)Leached SRP mass (mg) 1st 2nd 3rd 4th a b a b a b a b b b b b bb b b b b b b Figure 4-33. Leached SRP mass as influenced by P application rate and leaching event in glasshouse soil study 2 (soil No.3). 0 0.2 0.4 0.6 0.8 00.310.631.252.5 P2O5 application rate (g m-2 4-wk-1)Leached SRP concentration (mg L-1) 1st 2nd 3rd 4th a b a b a b a b b b b b bb b b bb b b Figure 4-34. Leached SRP concentration as influe nced by P application ra te and leaching event in glasshouse soil study 2 (soil No.3).

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99 Table 4-7. Visual quality rating of St. A ugustinegrass as influenced by P applicati on rate in 2005 gla sshouse soil study 3 P2O5 rates --------------------------------------------Week ---------------------------------------(g m-2 4-wk-1) 1 2 3 4 5 6 7 8 9 10 11 12 Mean 0 6.1b 6.2b 5.8b 5.6c 5.5b 5.2b 5.6b 5.4b 6.3b 6.9c 6.9c 6.6b 6.2b 0.31 7.2a 7.5a 6.6ab 7.1b 7.1a 7.1a 7.1a 6.6a 6.9ab 7.1bc 6.8bc 7.1a 7.0a 0.63 7.5a 7.9a 7.1a 7.7ab 7.5a 7.2a 7.2a 7.2a 7.4a 7.6abc 7.3ab 7.3a 7.4a 1.25 7.6a 7.9a 7.5a 7.8a 7.6a 7.7a 7.2a 7.3a 7.4a 7.7ab 7.5a 7.4a 7.6a 2.5 7.7a 8.0a 7.6a 7.6ab 7.6a 7.5a 7.3a 7.3a 7.2a 7.9a 7.5a 7.4a 7.5a CV(%) 7.6 4.9 10.7 6.8 7.6 9.7 5.4 8.3 8.8 7.4 6.54 5.2 5.7 Within columns for each soil, means followed by the same letter are not significantly different according to Duncans multiple range test (0.05). Table 4-8. Top growth rate of St. Augus tinegrass as influenced by P applicati on rate in 2005 glasshouse soil study 3. P2O5 rates ------------------------Harvest (g m-2 day-1) ----------------------(g m-2 4-wk-1) 1 2 3 4 5 6 Mean 0 3.2b 3.0a 2.8b 1.6b 2.0b 1.5b 2.4b 0.31 3.8ab 3.1a 3.0ab 1.9ab 2.5ab 1.6ab 2.6a 0.63 3.9a 3.1a 3.0ab 2.0 a 2.6a 1.7ab 2.7a 1.25 3.9a 3.3 a 3.1ab 2.1a 2.7a 1.7ab 2.8a 2.5 4.3a 3.4a 3.3a 2.1a 2.7a 1.8a 3.0a CV(%) 11.3 11.3 10.8 8.8 17.9 13.0 8.0 Within columns for each soil, means followed by th e same letter are not significantly different according to Duncans multiple range test (0.05).

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100 Table 4-9. Tissue P concentration of St. Augustinegrass as influen ced by P application rate in 2005 glasshouse soil study 3. P2O5 rates -----------------------------H arvest (g kg-1) -------------------------------(g m-2 4-wk-1) 1 2 3 4 5 6 Mean 0 1.3d 1.4b 1.3d 1.2d 1.5d 1.5e 1.4d 0.31 1.4d 1.5b 1.7cd 1.5c 1.8d 1.9d 1.6d 0.63 1.8c 2.1a 1.9bc 1.7c 2.3c 2.5c 2.0c 1.25 2.2b 2.3a 2.3b 2.4b 3.0b 3.5b 2.6b 2.5 2.9a 2.4a 3.4a 3.3a 4.1a 4.6a 3.4a CV(%) 15.0 20.0 14.3 8.8 14.1 9.4 8.6

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101 Tissue P (g kg -1 ) 1.01.52.02.53.03.5 Top growth rate (g m -2 day -1 ) 2.0 2.4 2.8 3.2 Figure 4-35. St. Augustinegrass ti ssue growth rate relative to tissue P concentration in the glasshouse soil study 3. y = 2.86 1.16(1.80 x)2 R2 = 0.48, p<0.001 plateau = 2.86 critical x = 1.8 CV = 8.6%

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102 a a ab a b b b bc b b c b c b b Figure 4-36. Soil Mehlich-1 P, FeO P, and WEP concentration as influenced by P application rate (soil sampling depth of 0-2 cm) in the glasshouse soil study 3. Within columns for each soil, means followed by the same letter are not significantly different according to Duncans multiple range test (0.05).

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103 Figure 4-37. Relationships among Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling depth of 0 cm) in the glasshouse soil study 3.

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104 Figure 4-38. Relationships between tissue P conc entration and Mehlich-1 P, Fe Oxide P, and WEP concentrations (soils sampling depth of 0 cm) in the glasshouse soil study 3.

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105 Mehlich-1 P (mg kg -1 ) 234567 Top growth rate (g m -2 day -1 ) 2.0 2.4 2.8 3.2 3.6 Figure 4-39. St. Augustinegrass ti ssue growth rate relative to so il Mehlich-1 P concentration in the glasshouse soil study 3. y = 2.87 0.08(4.59 x)2 R2 = 0.27, p<0.05, CV = 19.4% plateau = 2.87 critical x = 5

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106 0 2 4 6 00.310.631.252.5P2O5 application rate (g m-2 per 4 wks)Soil Mehlich1 P (mg kg-1) 0-2 cm 2-10 cm C C BC aa a B A a a Figure 4-40. Soil Mehlich-1 P concentration as influenced by P application rate and soil sampling depth in the glasshouse soil study 3.

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107 0 1 2 3 4 00.310.631.252.5 P2O5 application rate (g m-2 4-wk-1)Leached SRP mass (mg) 1st 2nd 3rd 4th a b b b b a b b a b b b b a b b bc c bc Figure 4-41. Leached SRP mass as influenced by P application rate and leaching event in the glasshouse soil study 3. 0 0.15 0.3 0.45 0.6 00.310.631.252.5 P2O5 application rate (g m-2 4-wk-1)Leached SRP concentration (mg L-1) 1st 2nd 3rd 4th a b bc b c a b b a b b b b a b bc b c c bc Figure 4-42. Leached SRP concentration as influe nced by P application ra te and leaching event in the glasshouse soil study 3.

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108 CHAPTER 5 CONCLUSIONS Glasshouse Hydroponic Study The best turf quality was achieved by the highest P treatment. Turfgrass receiving P at 31 mg m-3 attained the highest root growth among the treatments. The critical solution P concentration for optimum shoot growth was 111 mg m-3. St. Augustinegrass can be predicted to respond favorably to P applications if the ti ssue P concentrations are less than 1.6 g kg-1. Otherwise, no additional shoot growth would be expected if all other growth factors were adequate. In practice, conventiona l P fertilization programs normally use soil test P status as an index which categories soil P into very low, low, medium, high, very high levels. However, the soil P value range for each category was initia lly designed for agronomic crops and possibly does not apply to St. Augustinegrass. Future st udies may include determining a suitable soil testing procedure for St.Augustinegrass P recomme ndations and establishing the critical soil P level by relating it to the cri tical plant tissue P level. Turf Quality in Glasshouse Soil Studies In the glasshouse soil study 1, P application above 0.31 g m-2 4-wk-1 on soil No.1 did not result in better turf quality in 12 out of 16 weeks. For soil No.2 (Tavares sand) and 3 (Pottsburg sand) in the glasshouse soil st udy 2, P applica tion of 0.31 g m-2 4-wk-1 achieved the best turf quality in 11 out of 12 weeks. For soil No.4 (T avares sand) in the gl asshouse soil study 3, P application of 0.31 g m-2 4-wk-1 resulted in the best turf quali ty in 10 out of 12 weeks. These suggest that in terms of turf quality the minimum P application rate was somewhat above 0.31 g m-2 4-wk-1, which equates to an N: P2O5 application ratio of 16:1 assuming 5 g N m-2 4-wk-1 was applied. This is substantially higher than common used 4:1 ratio. This finding could be used to modify the N:P:K ratio recommended for St. Augustinegrass.

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109 Top Growth Rate in Glasshouse Soil Studies Additional phosphate ap plication beyond 0.31 g m-2 4-wk-1 did not result in increased top growth for the soils tested except soil No.3 (Pottsburg sand). The top growth rate with P application of 0.31 g m-2 4-wk-1 for soil No.3 was reduced by approximately 30% from the maximum growth rate of 2.9 g m-2day-1. A larger variation on top growth was observed and it may be due to more severe disease dama ge for soil No.3. Generally speaking, phosphate application of 0.31 g m-2 4-wk-1 is the minimum rate to achieve the optimum top growth. In case of disease damage, higher rate of P applica tion would be beneficial for recovery. Tissue P Concentration and Critical Tissue P Concentration Tissue P concentration varied from 1.0 to 3.6 g kg-1 with P application rates. For soil No.1 (Pomona sand), 2 (Tavares sand), and 3 (Pottsbu rg sand), turfgrass receiving no P maintained a value of 1.0 g kg-1, with which turfgrass showed P defici ency symptoms, reduced turf quality, and reduced growth rate. Turfgrass receiving no P in soil No.4 maintained a value of 1.4 g kg-1, which was possibly due to a higher residual labile P concentration in soil No.4. In the glasshouse soil study 1, 2, and 3, the critical minimum tissu e P concentration determined was 1.8, 1.9, and 1.8 g kg-1, respectively. Therefore, the critical minimum tissue P concentration for St. Augustinegrass is 1.8 g kg-1 to achieve the optimum growth. This differs from solution study possibly because plants biologi cally behave slight differen tly in soil from solution. Soil P Tests and Critical Soil Test P Concentrations Mehlich-1 P, Fe Oxide Strip P, and WEP were highly correlated to each other and they were also highly correlated to tissue P concen tration and top growth rate. Among these three extractants, Mehlich-1 is the best soil P extr actant for St. Augustinegrass because of higher r2 and smaller p values. The critical WE P and Fe oxide strip P were 3 mg kg-1. The critical soil

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110 Mehlich-1 P levels were in the range from 5 to 9 mg kg-1 depending on soil properties. The critical soil Mehlich-1 P le vel tends to be lower in presence of Fe/Al oxides. P Downward Movement and Leached P Majority of CSP applied remained in the t op 2 cm soil. Approximately 1% of P applied leached down the soil profile. Larger quantity and higher concentration of P leached in the first leaching event one week after P application. Th is suggests the importance of P application timing. To avoid P application before a rain even t would be beneficial in preventing P leaching loss. Application of 0.31 g P2O5 m-2 4-wk-1 did not result in either a larg er leached P quantity or a higher concentration. This suggests that P loss through leaching can be prevented by small application rate.

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111 LIST OF REFERENCES Allen, M., P.E. Schilling, E.A. Epps, C.R. M ontgomery, B.D. Nelson, a nd R.H. Brubuches. 1977. Response of bahiagrass to nitrogen ferti lizer. Louisiana Agic. Exp. Sta. Bull. 701. Andrew, C.S., and M.F. Robins. 1971. The eff ect of phosphorus on the growth chemical composition and critical phosphorus percentages of some tropical pa sture grasses. Aust. J. Agrc. Res. 22:693. Anonymous. 1992. Determination of phosphor us by Bray P1 extraction. p. 70. In Handbook on Reference Methods for Soil Analysis, Soil an d Plant Analysis Council, Inc., Athens, GA. Ballard, R., and J.G.A. Fiskell. 1974. Phosphorus retention in Coastal Plain Forest Soils: 1. relationship to soil properties. Soil Sci. Soc. Am. Proc. 38:250. Ballard, R., and W.L. Pritchett. 1975. Evaluation of soil testing methods for predicting growth and reponse of Pinus elliottii to phosphorus fe rtilization. Soil Sci. Soc. Am. Proc. 39:132. Bray, R.H., and L.T. Kurtz. 1945. Determination of total, organic a nd available forms of phosphorus in soils. Soil Sci. 59:39. Brown, E.A., and J.B. Sartain. 1999. Phosphorus retension in Unite d States Golf Association greens. Soil and Crop Sci. Soc. Florida Proc. 59:112. Broschat, T.K. 1995. Nitrate, phosphate, and pota ssium leaching from container-grown plants fertilized by several methods. HortScience 30:74. Bruce, R.C., and I.J. Bruce. 1972. The correlatio n of soil phosphorus analyses with response of tropical pastures to superphosphate on soil Nort h Queensland soils. Aust. J. Exp. Agric. Anim. Husb. 12:188. Burton G.W., R.N. Gates, and G.J. Gascho. 1997. Re sponse of Pensacola bahiagrass to rates of nitrogen, phosphorus and potassium fertilizers. Soil Crop Sci. Soc. Florida Proc. 56:31. Champbell, K.L., J.S. Rogers, and D.R. Hens el. 1985. Drainage water quality from potato production. Trans. ASAE 28:1798. Chardon, W.J., R.G. Menon, and S.H. Chien. 1996. Ironoxide impregnated filter paper (Pi test): I. A review of its development and methodologi cal research. Nutr. Cycl. Agroecosyst. 46:41. Chung, K.Y., J.B. Sartain, and E.W. Hopwood. 1 999. Leaching characteristics and nutrient supplying potentials of selected P and K fertili zer sources. Soil Crop Sci. Soc. Florida Proc. 58:72. Christians, N.E., D.P. Martin, and K.J. Ka rnok. 1981. The interrelationship among nutrient elements applied to calcareous sand greens. Agron. J. 73:929.

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112 Christians, N.E., D.P. Martin, and J.F. Wilkinson. 1979. Nitrogen, phosphorus, and potassium effects on quality and growth of Kentucky blue grass and creeping bentgrass. Agron. J. 71:564 567. Christie, E. K., and J. Moorby. 1975. Physiologica l responses of semi-arid grasses. I. The influence of phosphorus supply on growth and phos phorus absorption. Aust. J. Agrc. Res. 26: 423. Coleman, N.T, J.T. Thorup, and W.A. Jackson. 1 960. Phosphate-sorption reacations that involve exchangeable Al. Soil Sci. 90:1. Cope, J.T., Jr. 1981. Effects of 50 years of fer tilization with phosphorus and potassium on soil test levels and yields at six locations. Soil Sci. Soc. Am. J. 45:342. Cox, F.R. 1994. Predicting increases in extractab le phosphorus from fertilizing soils of varying clay content. Soil Sci. Soc. Am. J. 58:1249. Dest, W.M., and K. Guillard. 1987. Nitrogen and phosphorus nutritional influence on bentgrassannual bluegrass community composition. J. Am. Soc. Hortic. Sci. 112:769. Dormaar J. F. 1972. Seasonal Pattern of soil organic phosphorus. Can. J. Soil Sci. 52:107. Dyer, B. 1894. On the analytical determination of probable available mineral plant food in soils. Trans. Chem. Soc. 65:115. Ebdon, J.S., A.M. Petrovic, and R.A. White 1999. Interaction of nitrogen, phosphorus, and potassium on evapotranspiration rate and growth of Kentuc ky bluegrass. Crop Sci. 39:209. Egner, H., H. Riehm, W. R. Domingo. 1960. German (Germany). Untersuchungen uber diechemische Bodenanalyse als Grundlage fur die Beurteilung des Nahrstoffzustandes der Boden: II. Che-mische Extraktionsmethoden zur P hosphorund Kalium-bestimmung. Kungliga Lantbr.Hogsk. Ann., Uppsala. 26:199. Engelstad, O.P., and S.E. Allen. 1971. Effect of form and proximity of added nitrogen on crop uptake of phosphorus. Soil Sci. 112:330. Erickson, J.E., J.L. Cisar, J.C. Volin, and G. H. Snyder. 2001. Comparing nitrogen runoff and leaching between newly established St. Augustin egrass turf and an al ternative residential landscape. Crop Sci. 41:1889. Erickson, J.E., J.L. Cisar, G.H. Snyder, and J.C. Volin. 2005. Phosphorus and potassium leaching under contrasting residential landscap e models established on a sandy soil. Crop Sci. 45:546. Finn, B.J., and A.R. Mack. 1964. Differential re sponse of orchardgrass varieties (Dactylis glomerata L.) to nitrogen and phosphorus under c ontrolled soil temperature and moisture conditions. Soil Sci. Soc. Am. Proc. 28:782.

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113 Fitts, J.W. 1956. Soil tests compared with field, greenhouse and laboratory results. N.C. Agric. Exp. Stn. Tech. Bull. 121. Fitts, J.W., and W. L. Nelson. 1965. The determina tion of lime and fertil izer requirements of soils through chemical tests. Advan. Agron. 8:241. Fry, J.D., M.A. Harivandi, and D.D. Minner. 19 89. Creeping bentgrass response to P and K on a sand medium. HortScience 24:623. Frossard E., L. M. Condron, A. Oberson, S. Sina j, and J. C. Fardeau. 2000. Processes governing phosphorus availability in temperat e soils. J. Environ. Qual. 29:12. Gascho, G.J., T.P. Gaines, and C.O. Plank. 1990. Co mparison of extractants for testing Coastal Plain soils. Soil Sci. Plant Anal. 21(13-16), 1051. Greenwood, E.H.N., and E.G. Hallsworth. 1960. Studies on the nutrition of forage legumes. II. Some interactions of calcium, phosphorus, coppe r, and molybdenum on the growth and chemical composition of Trifolium subterraneum L. Plant soil 12:97. Grunes, D.L. 1959. Effect of nitrogen on the ava ilability of soil and fe rtilizer phosphorus to plants. Adv. Agron. 11:369. Guillard K. and W.M. Dest. 2003. Extractable soil phosphorus concentrations and creeping bentgrass response on sand greens. Crop Sci. 43:272. Hall, J.R., and R.W. Miller. 1974. Effect of phosphorus, season, and method of sampling on foliar analysis of Kentucky bluegrass. p. 155. In E.C. Roberts (ed.) Proceedings of the second international turfgrass research conference. Am. Soc. Agron. and Crop Sci Soc. Am., Madison, WI. Halvorson, A.D., and A.L. Black. 1985. Long-te rm dryland crop responses to residual phosphorus fertilizer. Soil Sci. Soc. Am. J. 49:928. Hanlon, E.A., J. G. Gonsalez, J. M. Bartos. 1994. Colormetric so il P determination. P. 17-18. In IFAS extension soil testi ng laboratory chemical procedures a nd training manual. Fla. Coop. Ext. Ser. Cir. 812. Univ. of Florida, Gainesville. Hartt, C.E. 1955. The phosphorus nutrition of sugar cane. Hawaiian Planterss Record. LV(1):33. Havelin J.L., J.D. Beaton, S. L. Tisdale and W. L. Nelson. 1999. Soil Fertility and Fertilizers. 6th edition. p. 164. Hillard, J.B., V.A. Haby, and F.M. Hons. 1992. Annual ryegrass response to limestone and phosphorus on an Ultisol. J. Plant Nutr. 15:1253. Hossner, L.R., J.A. Freeouf, and B.L. Fols om. 1973. Solution phosphorus concentration and growth of rice ( Oryza sativa L.) in flooded soils. Soil Sci. Soc. Am. Proc. 37:405.

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114 Hylton, L.O., Jr., A.Ulrich, D.R. Cornelius, a nd K. Okhi. 1965. Phosphorus nutrition of Italian ryegrass relative to growth, mo isture content, and mineral constituents. Agron. J. 11:505. Johnson P.G., R.T. Koenig and K.L. Kopp. 2003. Nitrogen, phosphorus and potassium responses and requirement in calcareous sand greens. Agron. J. 95:679. Jones, J.B, and H.V. Eck. 1973. Plant analysis as an aid in fertilizating corn and grain sorghum. p. 349. In Leo M. Walsh and James D. Beaton (ed.) So il testing and plant analysis. Soil Sci. Soc. Am., Madison, WI. Jones, M.B., L.M. Freitas, and k.H. de Mohrdi eck. 1970. Differential resp onse of some coolseason grasses to N, P, and lime. IRI Res. Inst. Bull. no. 37, 24p. Jones, J.R., Jr. 1980. Turf analysis Golf Course Manage. 48(1):29. Jordan, C.W., C.W. Evans, and R. D. Rouse. 1966. Coastal bermudagrass response to application of P and K as related to P and K levels in the soil. Soil Sci. Soc. Am. Proc. 30: 477. Juska, F.V. 1959. Response of Meyer zoysia to lime and fertilizer treatments. Agron. J. 51:81. Juska, F.V., A.A. Hanson, and C.J. Erickson. 196 5. Effect of phosphorus and other treatments on the development of red fescue, Merion, and common Kentucky bluegrass. Agron. J. 57:75. Kamprath, E.J. 1964. Optimum soil fertility leve ls for corn and soybeans. Plant Food Rev. 10(3):4. Kamprath, E.J. (Ed.). 1980. The role of phosphorus in agriculture. Am. Soc. of Agron., Crop Sci. Soc. of Am., Soil Sci. So c. of Am., Madison, WI. Knudsen, D. and D.Beegle. 1988. Recommended phosphorus tests. p 12. In Recommended Chemical Soil Test Procedures for the North Central Region. Bull. No. 499. ND Agric. Exp. Sta., ND State Univ., Fargo, ND. Kuo, S. 1993. Effect of lime and phosphate on the growth of annual bluegrass and creeping bentgrass in two acid s ils. Soil. Sci. 156:94. Lindsay W.L. 1979. Chemical equilibrium in soils John Wiley and Sons, New York, USA, p449. Lindsay W.L., P.L. Vlek G and S.H. Chien. 1989. Phosphate minerals. In Minerals in soil environment, 2nd edn. Eds J. B. Dixon and S. B. Weed. pp. 1089. Soil Science Society of America, Madison, WI. Lippke H., V.A. Haby and T.L. Provin. 2006. Irriga ted annual ryegrass response to nitrogen and phosphorus on calcareous so il. Agron. J. 98:1333. Lunt, O.R., R.L. Branson, and S.B. Clark. 1965. Re sponse of five grass species to phosphorus on six soils. p. 419. the cattle dung patch. 3. Distri bution and rate of de cay of dung patches and their influence on grazing behavi or. J. Br. Grassl. Soc. 27:48.

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115 Matichenkov, V.V., D.V. Calvert and E.A. Bo charnikova. 2001. Effect of Si fertilization on growth and P nutrition of bahiagrass. So il Crop Sci. Soc. Florida Proc. 60:30. Matichenkov, V.V., and Y.M. Ammosova. 1996. Eff ect of amorphous silica on soil properties of a sod-podzolic soil. Eurasi an Soil Sci., 28(10):87. Martin, W.E., and J.E. Matocha. 1973. Plant analysis as an aid in the ferti lization of forage crops. p. 393. In L. M. Walsh and J.D. Beaton (ed.) Soil testing and plant analysis. Rev. Ed. Soil Sci. Soc. Am., Madison, WI. McIntosh, J.L. 1969. Bray and Morgan soil extract ants modified for testing acid soils from different parent material. Agron. J. 61:259. McVey, G.R. 1967. Response of seedlings to various phosphorus sources. p.53. In Agronomy abstracts. ASA, Madison, WI. Mehlich, A. 1953. Determination of P, Ca, Mg, K, Na and NH4 by North Carolina soil testing laboratories. Mimeo. North Carolina Depa rtment of Agriculture, Raleigh, N.C. Mehlich, A. 1984. Mehlich soil test extractant: A modification of Mehlich extractant. Commun. Soil Sci. Plant Anal. 15:1904. Mengel K. and Kirkby E. A. 1987. Principles of Plant Nutrition. 4th end. International Potash Institute, Bern, Switzerland, 687 p. Morgan, M. F. 1941. Chemical so il diagnosis by the universal te sting system. Conn. Agric. Exp. Stn. Bull. 450. NDSU. 1980. Chemical soil test procedures for the North Ce ntral Regin. No. 499 revised. pp. 14. North Dakota State University. Neller, J.R. 1946. Mobility of phosphates in sa ndy soil. Soil Sci. Soc. Am. Proc. 11:227. Norrish K. and Rosser H. 1983. Mineral phosphate In Soils: and Australian viewpoint. p. 335 361. Academic Press, Melbourne, CSIRO/London, UK, Australia. OConnor, G.A., H.A. Elliott, and P. Lu. 2002. Characterizing water treatment residuals phosphorus retention. Soil Crop Sci. Florida Proc. 61:67. Oertli, J.J. 1963. Nutrient disorder s in turfgrass. California Turfgr ass Culture, Vol. 12 (3): 17. Olsen, S.R., C.V. Cole, F. S. Watanabe, and L. A. Dean. 1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate. USDA Circ. 939. Ozanne, P.G. 1980. Phosphate nutrition of plants general treatise. In The role of phosphorus in agriculture. EDs. F. E. Khasawneh, E. C. Sa mple and E. J. Kamprath. p. 559. American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, Madison, WI.

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120 BIOGRAPHICAL SKETCH Min Liu was born in Jingzhou, Hubei Provi nce, China, on December 13, 1978. After receiving his bachelors degree in soil and plant nutrition sc ience from China Agricultural University in 2001, he came to the United States attending the University of Georgia. He received his master's degree in soil fertility with Dr. David E. Kissel working on lime requirement of acid soils. Right after that, he moved to Gainesville as a Ph.D student with Dr. Jerry B. Sartain in 2003. He met his wife, Kehong Ma, during 2003 Ch ristmas vacation in China and married her on April, 26, 2004. Throughout the next 3 years as a graduate student in the Soil and Water Science Department at the University of Florid a, he investigated the phosphorus requirement of St. Augustinegrass. After earning his degree, Min w ould like to continue using his knowledge and skills in fertilizers and soil fertility at either a university or industry position.