• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Table of Contents
 Introduction
 History of the soil-testing program...
 Collecting and submitting soil...
 Laboratory analysis
 Field calibration of soil...
 Fertilizer recommendations
 Current and future research...
 Literature cited
 Back Cover














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; 876 (technical)
Title: Soil-testing and fertilization recommendations for crop production on organic soils in Florida
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00086505/00001
 Material Information
Title: Soil-testing and fertilization recommendations for crop production on organic soils in Florida
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Alternate Title: Soil testing and fertilization recommendations for crop production on organic soils in Florida
Physical Description: iv, 44 p. : ill. ; 23 cm.
Language: English
Creator: Sanchez, Charles Anthony, 1958-
Publisher: Agricultural Experiment Station, University of Florida
Place of Publication: Gainesville
Publication Date: 1990
 Subjects
Subject: Fertilizers -- Application -- Florida   ( lcsh )
Soils -- Testing -- Florida   ( lcsh )
Histosols -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 35-44).
Statement of Responsibility: C.A. Sanchez.
General Note: Cover title.
General Note: "June 1990."
Funding: Bulletin (University of Florida. Agricultural Experiment Station) ;
 Record Information
Bibliographic ID: UF00086505
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 22901736

Table of Contents
    Front Cover
        Front Cover
    Title Page
        Page i
        Page ii
    Table of Contents
        Page iii
        Page iv
    Introduction
        Page 1
    History of the soil-testing program at the Everglades Research and Education Center
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
    Collecting and submitting soil samples
        Page 9
        Page 10
    Laboratory analysis
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
    Field calibration of soil tests
        Page 19
        Page 20
    Fertilizer recommendations
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
    Current and future research needs
        Page 32
        Page 33
        Page 34
    Literature cited
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
    Back Cover
        Page 46
Full Text

/9u V1990
.1Sa


DOCUMN


Bulletin 876
(technical)


Soil-testing and Fertilization
Recommendations for
Crop Production on Organic,
Soils in Florida
C. A. Sanchez..
Uu^i


Agricultural Experiment Station
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
J.M. Davidson, Dean for Research














Soil-Testing and Fertilizing
Recommendations for Crop Production on
Organic Soils in Florida


C. A. Sanchez





Author

C.A. Sanchez is Assistant Professor and Horticulturist in Vegetable Crops
at the Everglades Research and Education Center, P.O. Box 8003, Belle
Glade, Florida 33430-1101.











Table of Contents


I. Introduction ...........................................................................1

II. History of the Soil-testing Program at the Everglades
Research and Education Center. ........................................1

III. Collecting and Submitting Soil Samples..............................9
Collecting Soil Samples............................................. 10
Submitting Soil Samples ............................................ 10

IV. Laboratory Analysis ..................................... ........... .. 11
Preparation of Samples for Analysis............................ 11
Determination of pH .................................... ........... 11
Determination of Total Soluble Salts........................... 11
Determination of Soil test K, Na, Ca, and Mg............... 14
Determination of K, Na, Ca, and Mg ...........................15
Determination of Soil Test P ........................................ 16
Ashing of Sam ples .................................... ............ .. 18

V. Field Calibration of Soil Test ............................................ 19

VI. Fertilizer Recommendations .............................................21
Vegetables Crops .....................................................21
Sugarcane .....................................................................29
R ice .................................. .......................................... 32
Pastures ................................... .....................................32
Other Agronomic Crops ....................................... ... 32

VII. Current and Future Research Needs ...............................32

Literature Cited ................................... .....................................35














































































iv













I. INTRODUCTION
There are approximately 3 million acres of organic soils (His-
tosols) in the state of Florida (Figure 1). The largest area of organic
soils developed for agricultural purposes is south of Lake Okeechobee
at the northern edge of the Florida Everglades. This area, known as
the Everglades Agricultural Area (EAA), comprises about 650,000
acres or approximately one-fourth of the original Everglades. The
traditional crops of the EAA have been winter vegetables, sugarcane,
rice, pasture for beef cattle, and sod for lawns. The estimated annual
value of all crops grown on organic soils in this area is about $600
million [100]1. Other in-state areas with organic soils used extensively
for crop production include the area north of Lake Apopka near
Zellwood, and the Fellsmere-Blue Cypress Lake area west of Vero
Beach. Various vegetable and agronomic crops are grown in these two
areas. Another economically important organic soil deposit is the area
south of Lake Istokpoga, used primarily for caladium-bulb produc-
tion.
University of Florida fertilizer recommendations for crops grown
on organic soils in the state are made by the Soil Testing Laboratory
at the Everglades Research and Education Center (EREC), (formerly
the Everglades Experiment Station), near Belle Glade. These recom-
mendations are based on over 60 years of research. The objectives of
this report are to outline the approach to soil testing and to summarize
the corresponding fertilizer recommendations of this Soil Testing
Laboratory.

II. History of the Soil-Testing Program at the
Everglades Research and Education Center
The EREC was established as the Everglades Experiment Sta-
tion on June 14, 1921 by the Florida Legislature. After numerous
problems in clearing and draining the virgin muck soil, a corn crop
was planted in the summer of 1924 [120]. Almost immediately after
germination, the corn plants became chlorotic and ceased to grow.
Most of the corn plants in this first crop eventually died and no grain
was produced. In fact, crop failures on Everglades Histosols were

1. Numbers in Brackets refer to Literature Cited.













I. INTRODUCTION
There are approximately 3 million acres of organic soils (His-
tosols) in the state of Florida (Figure 1). The largest area of organic
soils developed for agricultural purposes is south of Lake Okeechobee
at the northern edge of the Florida Everglades. This area, known as
the Everglades Agricultural Area (EAA), comprises about 650,000
acres or approximately one-fourth of the original Everglades. The
traditional crops of the EAA have been winter vegetables, sugarcane,
rice, pasture for beef cattle, and sod for lawns. The estimated annual
value of all crops grown on organic soils in this area is about $600
million [100]1. Other in-state areas with organic soils used extensively
for crop production include the area north of Lake Apopka near
Zellwood, and the Fellsmere-Blue Cypress Lake area west of Vero
Beach. Various vegetable and agronomic crops are grown in these two
areas. Another economically important organic soil deposit is the area
south of Lake Istokpoga, used primarily for caladium-bulb produc-
tion.
University of Florida fertilizer recommendations for crops grown
on organic soils in the state are made by the Soil Testing Laboratory
at the Everglades Research and Education Center (EREC), (formerly
the Everglades Experiment Station), near Belle Glade. These recom-
mendations are based on over 60 years of research. The objectives of
this report are to outline the approach to soil testing and to summarize
the corresponding fertilizer recommendations of this Soil Testing
Laboratory.

II. History of the Soil-Testing Program at the
Everglades Research and Education Center
The EREC was established as the Everglades Experiment Sta-
tion on June 14, 1921 by the Florida Legislature. After numerous
problems in clearing and draining the virgin muck soil, a corn crop
was planted in the summer of 1924 [120]. Almost immediately after
germination, the corn plants became chlorotic and ceased to grow.
Most of the corn plants in this first crop eventually died and no grain
was produced. In fact, crop failures on Everglades Histosols were

1. Numbers in Brackets refer to Literature Cited.






















































Figure 1. Map of Florida showing major deposits of organic soils.
2








common throughout the 1920's, and the feasibility of growing crops
on these soils remained in question. In 1926, fertility studies were
initiated using materials such as sodium nitrate, ammonium sulfate,
superphosphate, muriate of potash, and copper sulfate. By 1927,
research by Allison et al. [5] had established that copper (Cu) must be
applied to Everglades Histosols before crops would grow and produce
(Figures 2, 3).
During the early 1930's, workers also established that leaf
chlorosis of beans grown on these soils was related to manganese (Mn)
deficiency (Figures 4, 5) and that occurrence of this disorder could be
predicted from soil-pH measurements.
The EREC began to determine pH on growers' soil samples as
early as 1932 [4, 126]. During the late 1920's and early 1930's re-
searchers also demonstrated that crops grown on organic soil fre-
quently responded to additions of phosphorus (P), potassium (K), zinc
(Zn), and boron (B), in addition to Cu and Mn [4, 5] (Figures 6, 7).
In 1939 the Everglades Experiment Station began testing grow-
ers' soil samples for nitrate-nitrogen (NO,-N), P, and K. These ele-
ments were extracted from the soils by shaking 1 teaspoon of soil for
1 minute in 10 ml of 0.3 N HC1. The amounts of nutrients were
determined by color intensities developed from diphenylamine for
nitrate and from ammonium molybdate for P, and by a turbidity
measurement using cobaltous nitrate for K. The amount of element
extracted was estimated by comparing the color or turbidity develop-
ment of the sample with that of known standards. By the mid 1940's,
new soil tests for P and K were developed which showed better
correlation to crop response in the field [44, 45]. The determination of
soil-test P was made colorimetrically on an extract obtained using 2
volumes of air-dry soil and 25 volumes of water. The method of
determination for soil-test K was made by extracting 2 volumes of soil
with 5 volumes of 0.5 N acetic acid, and measuring K with a flame pho-
tometer. The acetic acid extractant also was used to determine the
amounts of extractable Ca, Mg, and Na in the soil. These same soil
tests are used at the EREC today, with two modifications: group
handling of samples is now possible and improved chemical proce-
dures and instrumentation provide better analytical precision.
The practice of testing organic soils for N was abandoned
because few crops in these early studies responded to supplementary
N. Furthermore, the high N content of these soils and the high rate of
organic matter mineralization result in such rapid changes in N both
in the field and in samples collected from the field [121] that it was
essentially impossible to find a soil test for N that correlated with crop
response.



































Figure 2. Sugarcane response to copper on raw sawgrass soil. Left
of stake, no copper; right of stake, copper sulfate at 30
pounds per acre.


Figure 3. Response of carrots to copper on raw sawgrass soil. Left,
copper sulfate at 30 pounds per acre; right, no copper.


~--A<






























2 1 4 5 4.. .. .. .

Figure 4. Foliage of bean plants showing varying degrees of manga-
nese deficiency. Left, leaves yellowish white and near
death; center, severe chlorosis; and right, normal leaf.

C k
21 3


Figure 5. Response of beans to manganese applied as nutritional
spray to the leaves under field conditions; yield increase
of #3 (sprayed) over #1 unsprayedd) was 136%.



























COMPLETE NO P203

Figure 6. Differences in tip-filling of sweet corn as influenced by P
fertilizer.


Figure 7. Effect of soil treatment on the incidence of boron defi-
ciency on sorghum leaves: 1 untreated, 2- dolomite, 3 -
dolomite plus five micronutrients including boron, 7 -
dolomite without boron, 9 basic slag, 10 basic slag plus
boron.














































Figure 8. Response of crisphead lettuce on Pahokee muck to appli-
cations of sulfur to pH below 6.0 (No. 3) and to applications
of sulfur and phosphate (No. 27). No. 1 check, no treat-
ment.


program for rice was established, based on measurements of soil pH.
These workers also found that Fe seedling chlorosis would occur on
low-Fe soils, and that the disorder could be predicted on the basis of
the color of ash remaining following the combustion of soils on which
rice was to be grown [116] (Figure 9).


8



















Figure 9. Response of rice to row-placed FeSi4. The middle two
rows that received iron are taller and greener than the
rest of the field that did not recieve iron.

Despite numerous P and K fertility experiments conducted on
organic soils that tested extremely low for P and K, rice failed to show
any response to additions of these nutrients [114, 115]. Furthermore,
the response of rice to N has been variable and inconsistent. There-
fore, no recommendations of N, P, or K are made for rice grown on
Everglades Histosols.
In the late 1970's and early 1980's, it was demonstrated that
sugarcane and rice responded to additions of calcium silicate slag on
organic soils having a low silicon (Si) content [38, 39, 60, 61, 118]
(Figure 10). Research also demonstrated that the response of these
two crop species to Si could be predicted from tissue analysis of crops
grown on these soils. Through extensive research it is now known
what areas of the Everglades Agricultural Area will produce in-
creased rice and sugarcane yields from Si additions. Subsequent
research has shown that vegetables do not respond to Si additions;
however they are not affected negatively when grown in rotation with
rice or sugarcane that has received applications of Si [112].

III. Collecting and Submitting Soil Samples
A representative sample is a prerequisite for a meaningful and
reliable soil test. However, as pointed out by Fitts and Hanway [42],
sampling the soil is the weakest and yet most important part of soil
testing. The error associated with sampling is generally greater than
that associated with chemical analysis [103]. Extensive details re-
garding procedures and techniques for soil sampling have been
described elsewhere [103, 122]. However, for clarity the following
sampling procedure is recommended for Histosols in Florida.

























Figure 10. Response of rice to calcium silicate slag. Rice in block in
front of the two posts that received slag is taller; it is also
lighter in color because it has less leaf-spot disease than
the rest of the field, which did not receive slag.

Collecting Soil Samples
Fields to be sampled should be cultivated and ready for fertiliza-
tion before samples are taken. Areas near marl roads or ditch spoil
should be avoided, or sampled separately. Begin taking samples to a
6-inch depth about 100 feet from the road near one end ofthe field, and
continue collecting samples in a zigzag fashion across the field, so as
to have a minimum of 30 cores from a 40-acre block. These 30 cores
should be composite and mixed thoroughly. Use plastic buckets for
mixing rather than galvanized buckets. A subsample should be placed
in a clean soil sample bag, and labeled properly.
Submitting Soil Samples
Soil samples should be brought or mailed to the EREC (P.O. Box
8003, Belle Glade, FL 33430-8003), or submitted through the County
Extension Agent. Information including the grower's name, correct
mailing address, field location (township, range, and section number),
past crop and fertilization history, and crop to be grown must be
provided with every sample submitted. Information sheets can be
obtained at the Soil-Testing Laboratory or through the County Exten-
sion Agent. The EREC makes fertilizer recommendations only for
vegetables produced on muck or peat soils, and for sugarcane pro-
duced on muck and mineral soils. Mineral soil samples for all crop
production except sugarcane should be submitted to the IFAS soil-








testing laboratory in Gainesville (Extension Soil Testing Laboratory,
Wallace Building No. 631, University of Florida, Gainesville, FL
32611).

IV. Laboratory Analysis

Preparation of Samples for Analysis
Soil samples are placed on clean trays in the soil preparation
room and air-dried. Samples that are air dried when received are kept
in plastic bags until they are screened and ready for analysis. Samples
that are excessively wet are placed on trays and either dried at 300C
in an oven for a few hours, spread very thinly on the tray, or both. As
soon as samples are sufficiently dry they are screened through a 2-mm
sieve. For muck soil especially, samples are sieved before they are
completely dry, because lumps of organic material break up more
easily when handled at moisture levels between field-moist and air-
dry. Peat samples should not be oven-dried nor stored for more than
4 to 6 weeks after drying before analysis because of the shrinkage and
change of volume which takes place. Interpretations are based on air-
dry muck soils which test about 40 to 50% moisture on an oven-dry
basis.
Determination of pH
Fifteen milliliters of air-dry soil and 30 ml of deionized water are
measured and placed into plastic cups. After the soil-water mixture
has been allowed to stand for 2 hours with intermittent stirring, the
pH is measured by means of a glass electrode; each sample is stirred
just prior to immersing the electrode. The glass electrode and pH
meter are calibrated carefully against standards of known pH. For
most organic soils in Florida, the meter is standardized using buffers
having pH values of 4 and 7. For more details on pH determinations,
see McLean [92].
Determination of Total Soluble Salts
The methods used for the determination of total soluble salts
were developed by the U.S. Salinity Laboratory in Riverside, Califor-
nia [127]. For more details see Rhoades [105].
Moist soil samples (samples brought from the field) are passed
through a 6.4-mm sieve and dry soils are passed through a 2-mm
sieve. After 100 to 150 ml of soil is placed in a 250-ml beaker, deion-
ized water is added, with stirring, until the soil is nearly saturated. If
too much water is added, more soil is added to reach the saturated
condition. The mixture is allowed to stand overnight. The next day,








water is added, if needed, until the soil is saturated. At saturation, the
paste glistens as it reflects light.
The soil mass is transferred to a Buchner filtering funnel. An
extract is collected by vacuum for an electrical conductivity measure-
ment. An estimation of soluble salts is obtained by multiplying the EC
reading (mmho/cm) by 700. Calibration of the EC bridge is checked
frequently with deionized water and a saturated solution of calcium
sulfate. The latter solution should test 2.2 mmhos/cm at 250 C.
For organic soils, the critical salinity levels based on determina-
tions from a saturated paste are about double those for loamy soils [37,
73, 87]. A typical comparison of salinity and water relationships for a
loamy mineral soil and for an organic soil is shown in Table 1. Note
that the two soils have similar salt values when saturated; however,
at field capacity the salt concentration in the soil solution of the loam
soil is much higher than for the muck soil. For interpretations of
soluble-salt determinations, use the standards provided in Tables 2
and 3.




Table 1. A typical comparison of salt and moisture contents for
loam and muck soils which read 2 millimhos per cm for
saturated soil extracts.

Situation Loam Muck

mmhos/cm at saturation... 2.0 2.0
Dry soil weight (lbs/6" acre)... 1,900,000 550,000

At Saturation

Water content ... 40% 150%
lbs water/acre... 760,000 825,000
Salt concentration in extract (ppm).. 1,280 1,280
Total salts (lbs/acre)... 973 1,056

At Field Capacity

Water content... 20% 140%
lbs water/acre... 380,000 770,000
Salt concentration (ppm)... 2,560 1,370

Source: Adapted from Lucas [87].








Table 2. Crop response to salinity.


Crop Responses


Salinity
(EC mmhos/cm at 250)


Sandy Loam Organic
soil soil soil


Salinity effects mostly
negligible

Yields of sensitive crops
may be limited

Yields of crops with low
tolerance limited

Only very tolerant crops
yield satisfactorily


0-1 0-2 2-4


1-2 2-4 4-8


2-4 4-8 8-16


Above 16 Above 8 Above 32


Source: Adapted from Bernstein [9], Hayward and Bernstein [74],
Campbell[37], and Hammond [73].


Table 3. Relative tolerance of plants to salinity.

Low Medium High
Sensitive Tolerance Tolerance Tolerance

Radish Cauliflower Spinach Cotton
Celery Cabbage Asparagus Sugar Beet
Green Beans Potato Garden beets Barley
Field Beans Tomato Rice Bermuda
Grass
Cucumbers Sweet Corn Corn
Squash Brocolli Sorghum
Peas Soybeans
Carrot Oats
Onion Wheat
Pepper Rye
Lettuce Sugarcane

Source: Adapted from Bernstein [9], and Hayward and Bernstein [74].







Determination of Soil-Test K, Na, Ca, and Mg

Preparation of Reagents
Extracting Solution A 0.5 N acetic acid solution is prepared
by diluting 540 ml of glacial acetic to 19 liters with deionized water.

Standard Potassium Solution A 1,000 ppm stock solution
is prepared by dissolving 1.908 g of reagent-grade KC1 in the extract-
ing solution (0.5 N acetic acid), and diluting to a total volume of 1 liter
with extracting solution. A 100 ppm standard is then prepared by
diluting 25 ml of the 1,000 ppm stock solution to 250 ml with the
acetic-acid extracting solution. Additional standards containing 0, 10,
20, 30,40, and 60 ppm K are prepared by diluting 0, 10, 20, 30,40, and
60 ml, respectively, of the 100 ppm K solution to a volume of 100 ml
with extracting solution.

Standard Sodium Solution-A 500 ppm stock solution is pre-
pared by dissolving 1.271 g of reagent-grade NaC1 in the extracting
solution and diluting to a total volume of 1,000 ml with extracting
solution. Standard solutions of 0, 5, 10, 13, 20, and 25 ppm Na are
made by diluting 0, 10, 20, 30, 40, and 50 ml of the 500 ppm standard
with extracting solution to a volume of 100 ml, in volumetric flasks.

Standard Calcium Solution A 1,000 ppm stock Ca solution
is prepared by dissolving 2.498 g of reagent-grade CaCO3 in the
extracting solution and diluting it to a volume of 1,000 ml with
extracting solution. A 100 ppm standard is then prepared by diluting
25 ml of the 1,000 ppm stock solution to 250 ml with extracting
solution. Standard solutions of 0, 10, 20, 40, 60, and 80 ppm Ca are
prepared by diluting 0, 10, 20, 40, 60, and 80 ml of the 100 ppm Ca
solution to 100 ml with extracting solution.

Standard Magnesium Solution-A 1,000 ppm stock Mg solu-
tion is prepared by dissolving 1.665 g of reagent-grade MgO in ex-
tracting solution and diluting to 1,000 ml with extracting solution. A
40 ppm Mg solution is prepared by diluting 10 ml of the stock solution
to 250 ml with extracting solution. Standard solutions of 0, 2, 4, 8, 12,
and 16 ppm Mg are prepared by diluting 0, 5, 10, 20, 30, and 40 ml of
the 40 ppm Mg solution to 100 ml with extracting solution.

Extraction Procedure-Ten milliliters of air-dry sieved soil
and 25 ml of the 0.5 N ex-tracting solution are measured into a 25 by
200 mm screw-cap culture tube, mixed, and allowed to stand over-








night. This allows thorough wetting of the soil. The measuring scoops
are tapped firmly three times, and leveled off with a teflon-coated
stirring bar before adding the soil to the tube. A rack or racks of tubes
are then placed on an end-over-end shaker for 1 hour. After shaking,
the suspension is allowed to settle and the supernatant solution is
decanted through S & S No. 576 filter paper. The filtrate is saved for
determination of K, Na, Ca, and Mg.
Determination of K, Na, Ca, and Mg
The concentration of K in the filtrate usually can be measured
without dilution. For Ca and Mg, 1 ml of filtrate is diluted with 19 ml
of extracting solution. For Na 1 ml of filtrate is diluted with 9 ml of
extracting solution. Concentrations of Ca and Mg in the filtrate are
determined using an atomic absorption spectrophotometer. The con-
centrations of Na and K are determined using either an atomic
absorption spectrometer or a flame-emission spectrophotometer. Both
instruments are calibrated in the range of standards described previ-
ously. Additional dilutions are made as necessary to provide sample
values in the range of K, Na, Ca, or Mg concentrations described
previously. The appropriate corrections are made for all dilutions.


Calculations
One ppm (pg/ml) ofK, Na, Ca, or Mgin the filtrate converts to 3.4
lbs soil-test K, Na, Ca, or Mg, respectively per acre. An example of the
calculation is shown below:


1gg K 25 ml 6.2 x 108 ml soil
x x x
ml filtrate 10 ml soil acre



1 g 1 lb lbs K
x =
1,000,000 gg 453.6 g acre


where 6.2 x 108 ml is the volume of an acre of muck soil 6 inches deep.
Additional corrections must be made for any additional dilutions of
the filtrate. It should be stressed that expression of soil-test nutrient
level in lbs/A has been used by tradition at the Soil-Testing Labora-







tory at the EREC. However, this value has no precise quantitative
meaning with respect to actual nutrient levels in the soil; it is only a
soil-test index value. As will be explained in a subsequent section, this
value is simply a correlated extractable-nutrient level which has been
related to relative crop response in the field. The interpretation of this
number depends entirely upon the field data se against which it is
calibrated. The Soil-Testing Laboratory at the EREC is currently
reporting soil-test index values in units ofboth lbs/A and ppm in order
to phase in conversion to the latter expression.

Determination of Soil-Test P

Preparation of Reagents

Extracting Solutions Deionized water.
Standard P Solutions A 500-ppm stock solution is prepared
by disolving 1.0985 g of reagent-grade KH2PO4 in 100 ml of warm
deionized water. After cooling, the solution is diluted to a volume of
500 ml with deionized water. The stock solution is kept in a refrig-
erator, where it is stable for approximately 6 months. A 10 ppm
standard is prepared by diluting 10 ml of the 500 ppm P stock solution
to 500 ml with deionized water in a volumetric flask. Additional
standards containing 0, 0.5, 1, 2, and 3 ppm P are prepared by dilut-
ing 0, 5, 10, 20, and 30 ml of the 10 ppm P standard to 100 ml with DI
water.
Murphy-Riley Solution First, 15.192 liters of deionized
water is measured. Then 14 liters of deionized water is mixed with
1.008 liters of concentrated sulfuric acid, while stirring. After adding
the acid, 86.4 g of ammonium molybdate is added to the stock mixture.
In a separate flask, 1.973 g of antimony potassium tartrate is
dissolved in a small volume of water, while heating and stirring. Then
this solution and all remaining DI water are added to the stock
mixture.
Ascorbic Acid Stock Solution This solution is prepared by
dissolving 42.24 g of ascorbic acid in deionized water and diluting to
1 liter in a volumetric flask. This solution is stored in the dark, under
refrigeration. A new solution is prepared on a weekly basis.
Working Solution The working solution is prepared each day
by mixing 900 ml of the Murphy-Riley solution and 100 ml of ascorbic








acid. This is enough working solution for approximately 200 determi-
nations.


Extraction Procedure
Four milliliters of air-dry sieved soil is weighed into 25 x 200 mm
screw-cap culture tubes. The measuring scoops are tapped firmly
three times and leveled off with a spatula before the soil is added to
the tube. Then 50 ml of deionized water is added to the culture tubes,
and the mixture is allowed to stand overnight. This allows thorough
wetting of the soil. Racks of tubes are then placed on an end-over-end
shaker for 1 hour. After shaking, the suspension is filtered through
Whatman No. 2 filter paper. The solution is refiltered as needed until
the filtrate is clear.
Determination of P
The procedure for determining the P concentration in the ex-
tracting solution has changed over the years. The ascorbic acid
method described in North Central Regional Publication No. 221 [98]
was adopted in 1979. Stannous chloride had been used as the reducing
agent for many years. The color, however, was stable for only about 10
minutes. In contrast, the ascorbic acid method provides a stable color
for several hours. Another major advantage of this method is that it
eliminates the need to use charcoal for organic matter decoloring.
In 1984 the procedure was changed again. Currently, the Murphy-
Riley molybdate-ascorbic acid single-solution method is used [94].
This method is similar to the ascorbic acid method but represents a
slight improvement.
Five milliliters of freshly-prepared standard solution are trans-
ferred into colorimetric tubes. Then 5 ml of the working solution are
added, mixed well, and allowed to sit 45 minutes for the color to
develop. The percent transmittance is determined on a colorimeter set
at 882 nm. The amount of P in the soil extract is determined from the
standard reference curve.
For soil solutions containing more than 3 ppm P, a 50% strength
working solution is prepared by mixing equal parts of Deionized water
and working solution. This 50% solution is prepared so as to maintain
the proper pH. The appropriate adjustments are made for all dilu-
tions.







Calculations
One ppm (tg/ml) P in the filtrate converts to 17 lbs soil- test P/
A. An example of the calculation is as follows:

lpg P 50 ml DI water 6.2 x 108 ml soil
x x
ml filtrate g 4 ml soil acre

1 g 1 lb lbs P
x
1,000,000[tg 453.6 g acre

where all terms are as defined previously for K. Again we emphasize
that expressing the value as lb/A has been used by tradition, but only
as a soil-test index value.
Ashing of Samples
Ashing of organic soils is to determine the amount of mineral
matter present or to assess the Fe status of soils for rice production.
Approximately 25 g of soil, dried previously at 1050C, is weighed
to the nearest mg into porcelain evaporation dishes. These samples
are placed into a cool muffle furnace and the temperature is increased
to approximately 2000C for about 2 hours, with the muffle furnace
door left slightly ajar. The door is then closed and the temperature is
increased to about 4000C for an hour, then increased to 5500C for 3 to
4 hours. For determination of the Fe status of the soil it is not
necessary to weigh a specific amount of soil before ashing. The ash
color is compared to the colors of standard ashed soils. A light or white
ash generally means the soil is low in Fe, and rice will often respond
to supplementary Fe. If the ash has a red color the soil most likely has
sufficient Fe and a response to supplementary Fe is unlikely. The
percent ash is calculated on an oven-dry soil basis.

wt. of ash x 100
% ash =
wt. of oven-dry soil

Quality Control
A good quality-control system is necessary to ensure that no
errors are made in soil-test analyses. All standards are prepared
using only reagent-grade chemicals, which are oven-dried before
preparing stock solutions. Furthermore, all new standards and buff-







ers are crosschecked using older existing standards. All analytical
equipment is calibrated closely before and during use.
Control soil samples are prepared by collecting, drying, homoge-
nizing, and storing certain soils. Mean values for pH, P, K, Na, Ca, Mg,
and EC are established by repeated analyses of these samples. These
control soils are run with each group of twenty analyses. Periodically,
growers' samples are duplicated across batches to insure analytical
precision. The values of these checks are inspected for errors. If errors
in analysis exist, they are corrected before results are forwarded to
the grower.

V. Field Calibration of Soil Tests
As mentioned previously, the reliability of soil testing depends
on the data base used to calibrate the interpretations. The approach
used by the Soil Testing Laboratory at the EREC for P and K is based
on a double calibration technique described by Thomas and Peaslee
[123].
First, a relationship between relative crop yield as a function of
extractable or soluble nutrient is developed. A recent example of the
relationships between soil-test P and K levels and relative yields for
lettuce is shown in Figures 11 and 12. These data indicate that for
lettuce the critical soil-test values are 30 and 150 for P and K,
respectively. Above a soil-test P index level of 30, we would expect no
response of lettuce to P fertilizer and no P fertilizer would be
recommended. Likewise for K, above a soil-test Kindex level of 150 we
would expect no response to K fertilizer and no K fertilizer would be
recommended. Conversely, if the soil-test index levels are below
critical lev els for a given nutrient a fertilizer recommendation for that
nutrient is prepared. A similar calibration approach has been used to
generate c critical soil-test index values for most commodities grown on
organic so ls. Specific information for the various crops is provided in
many of tl e publications listed in the Literature Cited section of this
bulletin.
The amount of P or K fertilizer recommended for all crops
depends on how far below the critical value a given soil-test index
level falls. The amounts of fertilizer recommended over a range of soil-
test index levels are shown in Tables 5 and 6 for P and K, respectively.
These recommendations are based on research conducted over the
past 50 years. Additional work is currently in progress to further
group these recommendations based on varying fertilizer responses
across Histosols having different soil properties.
Crops grown on organic soils in Florida have traditionally shown
responses to Cu, Mn, B, and sometimes to Zn and Fe. However, there









100

90

80

S70

U 60

S50

S40

S30

20

10

0


y y


0 50 100 150 200 250 300 350

SOIL-TEST K (LBS/A)
Figure 11. Response of crisphead lettuce to soil-test P levels.


-0. 17x
(1-1.6e- )
2 = 0.66


0 10 20 30 40 50 60 70 80 90 100
SOIL-TEST P (LBS/A)

Figure 12. Response of crisphead lettuce to soil-test K levels.


95.8 (1-1.3e-003x)

r2 = 0.74


100

90

80

70

9 60

>" 50

40

1 30

20

10

C


J d


f I t i


y 96.8








is currently no soil test calibrated with respect to micronutrient
recommendations for these soils. Therefore, micronutrient fertilizer
recommendations are based on apparent annual crop requirement.
(For more information on crop nutrient requirements, see IFAS
Extension Circular 806 [75].) The recommendation for Mn depends on
soil pH. Research has shown that various crops have a threshold pH
above which they respond to supplementary Mn. A recommendation
for S also is made, based on soil pH. Supplementary Fe is recom-
mended for rice only ifthe color of the soil ash indicates that a response
to Fe is likely. In that case, iron sulfate is applied with the rice seeds.
Recommendations for crops grown on mineral soils, except for
sugarcane, are made at the IFAS Extension Soil-Testing Laboratory
in Gainesville, FL [82]. For convenience we make recommendations
for sandland cane at the Soil-Testing Laboratory at EREC. Research
has shown that sugarcane grown on sand will show a response to
supplemental Mg if the soil-test level is below a threshold value of 100
lbs Mg/A. Soil-test levels for Na and Ca are provided to growers if
requested; however, no fertilizer or management recommendations
are made by the Soil-Testing Laboratory based on these determina-
tions.

VI. Fertilizer Recommendations

Vegetable Crops

Macronutrients
The critical levels of soil-test P and K for the various vegetable
crops are shown in Table 4. Corresponding fertilizer recommenda-
tions are shown in Tables 5 and 6, respectively. The temptation often
exists to apply fertilizer in excess of the amount recommended as an
insurance policy. This practice is strongly discouraged. Excess K
fertilizer is known to aggravate physiological disorders in a number
of vegetables [18, 129]. High soil-test P also can aggravate certain
physiological disorders in vegetables [16], depress sugarcane yields
[4, 96], and induce micronutrient deficiencies in a number of crops
[90, 107]. Furthermore, the application of fertilizer in excess of the
crop needs can have an adverse impact on the environment.
Sidedress Fertilization
Broccoli There appears to be response to sidedressing 50 lbs
N/A prior to heading [22, 23].
Celery Seedbeds: Apply 1.25 lbs N per 1,000 square feet 35
days after seeding and another 1.25 lbs N per 1,000 square feet 50








days after seeding. Irrigate immediately after applying N [22, 23].
Field: On plants to be harvested before December 1, sidedress
twice with 40 lbs N/A, 40 lbs P20O/A, and 120 lbs O20/A at each appli-
cation. For a crop to be harvested between December 1 and March 31,
sidedress twice with 65 lbs N/A, 40 lbs P2O/A, and 120 lbs K2O/A. For
a crop to be harvested after April 1, sidedress twice with 30 lbs N/A,
40 lbs P2O./A, and 120 lbs O20/A. The fall and spring sidedressings
should be made during the 6th and 8th week after transplanting. The
amount of fertilizer to be applied in the sidedress should be subtracted
from the total amount applied preplant broadcast. If the soil test index
values are equal to or greater than 25 for P and 350 for K, respectively,
sidedress with N fertilizer only. During the winter crop, part of the N
can be mixed with the broadcast fertilizer [22, 23, 69].
Escarol Apply 60 lbs N/A in the broadcast fertilizer mixture
for escarole to be harvested between December 15 and March 15. In
case of 3 inches or more of rainfall in one event, N should be reapplied,
if possible, up to four weeks before harvest. For 1.5 to 3 inches of rain
in one event, one-half the seasonal amount should be reapplied [22,
23, 25, 35].
Lettuce (Romaine, Bibb, Boston, and crisphead) Apply 60 lbs
N/A sidedressed in the center of the bed at the 6 to 8 leaf stage of
growth in bed cultures. During the rainy season (fall crop) it may be
advantageous to apply part of the K fertilizer in a sidedress with the
N fertilizer. Subtract the amount of K fertilizer to be applied in the
sidedress from preplant broadcast application [22, 70, 110, 112].
Radishes Apply 50 lbs N/A at seeding time on radishes to be
harvested from December 15 to March 15 for each crop cycle [20, 23,
24].
Sweet corn Apply 40 lbs N/A about 2 to 3 weeks prior to
tasseling [109].
Banding fertilizers
Lettuce The efficiency of P fertilization for lettuce can be
improved substantially by applying part of the P fertilizer in a band
5 inches wide about 2 inches below the seed. For soils testing at a P
index level less than 20, we suggest that 40% of the total amount of
fertilizer recommended be applied broadcast and 35% be applied
band, thus saving 25% of the total. If the soil test P index level is more
than 20 but less than 30, apply 70% of the total amount of fertilizer
recommended in a band and do not apply broadcast P fertilizer. For
most lettuce fields this would represent about a 30% savings in the
total amount of fertilizer used [71, 112].
Corn Where the pH is below 6.0, there appears to be no advan-








tage or disadvantage to banding P at recommended rates. However,
when the pH is greater than 6.0, all of the P fertilizer should be
banded. This is especially true for soil having a high mineral content
like the Torry muck soil near Lake Okeechobee. The Mn should also
be applied in the fertilizer band on these soils. By applying P fertilizer
in a band, the total P rate required for optimal yields is reduced about
25% compared to broadcast fertilization [23, 24].
Secondary Nutrients
The levels ofCa, Mg, and S in organic soils are usually adequate
for vegetable production [50]. However, because of the immobility of
Ca, disorders caused by a deficiency of this nutrient can occur. One of
the most common Ca-related disorders is called blackheart (Figure
13). Blackheart is common in spring-grown celery and can occur in
escarole. Blackheart is controlled easily with Ca sprays [18, 68].
Beginning about April 1, it is recommended that growers routinely
apply weekly sprays containing 5 lbs of CaC12 or 10 lbs of CaNO3 per
100 gallons of solution to the hearts of plants. After May 1, it may be
necessary to apply sprays twice weekly. Spraying should start about
50 days after transplanting. Spray machines with special nozzle
arrangements that will thoroughly wet the heart, should be used.
After the plants have been in the field 70 days, apply Ca in 200 gallons
of water. Avoid over-fertilizing with K fertilizers, because this may
aggravate the incidence of blackheart [128, 129].


Figure 13. Blackheart in celery, a calcium-related disorder common
on celery grown on organic soils.








Table 4. Critical soil-test levels of pH, P, and K for selected vege-
table and agronomic crops grown on Histosols in Florida.

Data
Critical level Source
Crop pH P K

Blackeyed peas <6.0 5 150 99
Broccoli <6.0 10 150 22, 23
Cabbage <6.0 20 150 4, 112
Carrots 16 150 34, 128
Celery a 25 350 4,26,27,30,32,
33,49 69, 77
Celery seedbeds 14 200 22, 23,46
Field corn 15 200 4, 56, 113
Grain sorghum 10 150 4

Leafy Crops
Escarole a <6.0 30 200 4, 21, 28, 35
111,112
Endivea <6.0 20 150 4, 21, 35, 111,112
Romaine <6.0 27 200 21, 35
lettuce a
Crisphead <6.0 30 150 4,70,71,72,89,106
lettuce a 108,110
Chinese 20 150 21, 35
cabbage
Parsley 20 250 23

Okra 15 150 23
Pepper 12 250 76
Potatoes <6.0 14 150 4
Radishes a <6.0
(three crops) 14 175 29, 112
(one crop) 8 100 29, 112
Snapbeans <6.0 8 100 4, 57
Sweet corn 15 150 4, 19, 23, 91, 107, 112

aSee special considerations in text.








Table 5. Phosphorus fertilizer recommendations for various
vegetables across a range of soil-test-P index levels.

Soil-test index levels a
Crop 3b 6 9 12 15 18 21 24 27 30

Fertilizer Recommendations
------------ -lbs P20 /A-------------


Broccoli
Blackeyed
peas
Cabbage
Carrots
Chinese
cabbage
Celery
Celery
seedbeds
Crisphead
lettuce
Endive
Escarole
Okra
Potatoes
Radishes
(three crops)
(one crop)
Romaine
lettuce
Sweet corn


80 20 0 0 0 0 0 0
40 0 0 0 0 0 0 0

140 80 20 0 0 0 0 0
260 200 140 80 20 0 0 0
280 220 160 100 40 0 0 0

440 380 320 260 200 140 80 20
220 160 100 40 0 0 0 0

540 480 420 360 300 240 180 120

340 280 220 160 100 40 0 0
540 480 420 360 300 240 180 120
240 180 120 60 0 0 0 0
220 160 100 40 0 0 0 0

220 160 100 40 0 0 0 0
100 40 0 0 0 0 0 0
480 420 360 300 240 180 120 60


240 180 120 60


0 0 0 0


0 0
0 0

0 0
0 0
0 0

0 0
0 0

60 0

0 0
60 0
0 0
0 0

0 0
0 0
0 0

0 0


a Soil-test-P index levels are determined using a water soluble P extraction.

b Soil-test-P index levels are rarely below 3 under any cropping system and are
rarely below 10 in soil cropped previously to vegetables.








Table 6. Potassium fertilizer recommendations for various vege-
tables across a range of soil-test-K index levels.

Soil-test index K levels

50b 80 110 140 170 200 230 260 290 320 350
Crop

lbs K20/A
Fertilizer Recommendations


200 140 80 20 0 0 0
200 140 80 20 0 0 0

200 140 80 20 0 0 0
200 140 80 20 0 0 0
200 140 80 20 0 0 0


0 0 0 0
0 0 0 0


0 0 0
0 0 0
0 0 0


600 540 480 420 360 300 240 180 120 60
300 240 180 120 60 0 0 0 0 0


200 140 80 20 0 0 0

200 140 80 20 0 0 0
300 240 180 120 60 0 0
200 140 80 20 0 0 0
400 340 280 220 160 100 40
200 140 80 20 0 0 0


0 0 0 0


Broccoli
Blackeyed
peas
Cabbage
Carrots
Chinese
cabbage
Celery
Celery
seedbeds
Crisphead
lettuce
Endive
Escarole
Okra
Peppers
Potatoes
Radishes
(3 crops)
(1 crop)
Romaine
lettuce
Sweet corn


a Soil-test-K index levels are determined using a 0.5 N acetic acid extraction.
b Soil-test-K index levels are rarely below 50 under any cropping system.


250 190 130 70 100 0 0 0 0 0 0
100 40 0 0 0 0 0 0 0 0 0
300 240 180 120 60 0 0 0 0 0 0

200 140 80 20 0 0 0 0 0 0 0







Table 7. Summary of amounts of sulfur recommended for pH
correction on selected vegetable crops.

Soil pH S Recommendation a

lbs S/A

<6.1 0
6.1-6.3 500
6.4-6.5 1000
6.6 1500
6.7-6.8 2000
>6.8 4000
a pH adjustment is recommended only for certain vegetables; see Table 4.

Adjustment of Soil pH
Agricultural sulfur can be used to adjust soil pH downward.
Research indicates that the most desirable pH for vegetable produc-
tion on Histosols is about 6.0 [88]. Research has also shown that the
pH of a soil after flooding may drop about a half a unit after it has been
drained for three weeks. Early work indicated that about 500 lbs S/A
lowered soil pH about 0.3 unit, 1,000 lbs S/A lowered the pH 0.5 unit,
1500 lbs S/A lowered pH about 0.7 unit, 2000 lbs S/A lowered pH about
0.8 unit, and 4000 lbs S/A lowered pH about 1.0 unit [27, 28, 31]. The
critical pH levels for selected vegetables are shown in Table 4. The cor-
responding S recommendations are shown in Table 7.
Recent work indicates that many organic soils are highly buff-
ered against pH reductions [13]. This of course, varies with the soil.
Although an S recommendation is made for selected commodities
based on soil-pH determinations, final decisions concerning the use of
S must be based on economic considerations made by the grower.
Recent research suggests that it may be more economical to correct
pH-related micronutrient deficiencies with the use of foliar sprays
[11, 12, 14]. Apply micronutrient sprays only when a specific defi-
ciency has been diagnosed. Do not apply mixed micronutrient sprays
in "shot gun" fashion.
Micronutrients

Manganese Recommendations for Mn are based on soil pH.
Where soil pH is 5.7 or lower, no Mn is required [4, 5, 43, 48, 50, 51,
53, 124, 126]. The current recommendation is to apply 8 lbs Mn/A
where soil pH is 5.8 or higher. Research has shown that on organic
soils, sulfate sources of Mn are superior to oxide sources [63]. Crops








with a high Mn requirement may require additional Mn sprays if soil
pH is 6.0 or higher. Often the Mn contained in a frequently used
fungicide (Manzate, etc.) will provide sufficient Mn for these crops.
Sweet corn, celery, and Boston lettuce seem particularly susceptible
to Mn deficiency on high pH soils. On such soils the foliar application
of about 1 lb Mn/A applied once a week for 4 weeks usually corrects the
problem.
Boron Boron recommendations are based on crop require-
ment [4, 15, 16, 17, 18, 50, 104]. Because B is readily leached from
organic soils by rainfall this nutrient is recommended for nearly every
crop cycle. On previously uncultivated land, the application of 2 lbs B/
A is recommended for all crops. On soils which have been cropped pre-
viously, the B recommendation depends on the apparent crop require-
ment. The application of 1.2, 1.8, and 2.4 lbs B/A is recommended for
crops with low, medium, and high B requirements, respectively (Table
8). Numerous physiological disorders in celery are associated with B
nutrition hence, celery has a high B requirement [18] (Figure 14).
Where a crop with a low B requirement such as sweet corn is to follow
a crop with a high B requirement such as celery, no further application
of B is needed.

Table 8. Relative micronutrient requirement of selected vege-
tables.

Crop Micronutrient Requirement

Manganese Boron Copper Other

Beans high very low low -
Broccoli medium medium medium -
Cabbage medium medium medium -
Celery medium high medium -
Chinese medium medium medium -
cabbage
Endive high medium medium -
Escarole high medium medium -
Lettuce high medium high -
Onions high very low high -
Parsley low medium medium -
Peas high very low low -
Potatoes high low low -
Radish high low medium zinc
Sweet corn high low medium zinc

Source: Adapted from Burdine [24].









Copper Twelve pounds per acre of Cu should be incorporated
thoroughly into the plow layer of all previously uncultivated soils
prior to planting any vegetable crop. After plowing for the next crop,
4 lbs Cu/A should be applied in the broadcast fertilizer and cultivated
into the soil. Following this no further Cu deficiencies have been
observed [4, 5, 43, 47, 84]. Research has shown that copper oxide
materials are equally as effective as sulfate materials in satisfying the
nutritional requirements of crops [55, 84].
Zinc Many crops grown on organic soils seem susceptible to Zn
deficiencies [5, 48, 125]. Zinc recommendations are based on apparent
crop requirement. Currently, 8 lbs Zn/A are recommended for suscep-
tible crops. For certain cases, soil applications of Zn are only margin-
ally effective. In such instances, the foliar application of 0.25 lb Zn/A
applied twice a week for a two week period usually corrects the
problem.
Iron Deficiencies ofFe are rare on organic soils in Florida and
generally no recommendation of this nutrient is made for vegetables.
Occasionally Fe deficiencies have been observed on fall grown sweet
corn and celery, especially on soils with a high content of free carbon-
ates [22]. In such cases, soil applications of Fe have not been effective.
Four foliar applications of 0.25 lb Fe/A applied twice a week for two
weeks seems to eliminate this deficiency.
Sugarcane

Macronutrients
The current P and K recommendations for sugarcane are shown
in Tables 9 and 10. Recommendations for P should be followed closely
because excess P will depress sugar yields. No N fertilizer is recom-
mended on muck soils. However, 30 lbs N/A and 110 lbs N/A are
recommended on sandy mucks and mucky sands, respectively.
Special Considerations
There is an advantage to row-directed application of P fertilizer
in some cases, especially if the soil pH is high. It may also be advan-
tageous to place K, S, and micronutrients in the furrow at planting. On
sandy mucks and mucky sands, however, broadcast fertilization of P
is favored [6, 7].
Secondary Nutrients
For sandy muck and mucky sand soils which test less than 100
lbs soil-test Mg/A apply 6 lbs Mg/A [7].








Table 9. Recommended P fertilization for sugarcane at various
levels of soil-test P.

First Second Subsequent
Soil-test P Plant Ratoon Ratoon Ratoon

lbs P20/A
0 75 75 70 40
1 75 75 50 40
2 70 70 40 40
3 60 60 40 40
4 60 40 40 40
5 40 40 40 40
6 40 40 40 40
7 0 40 40 40
8 0 40 40 40
9 0 0 40 40
10 0 0 40 40
>10 0 0 0 40

Source: Adapted from Anderson [6], Gascho and Freeman [64], Gascho and
Freeman [65], Gascho and Kidder [66],Iley and LeGrande [78], LeGrande
[85], and LeGrande et al. [86].


Table 10. Recommended K fertilization for sugarcane at various
levels of soil-test K.

Soil-test K First Second Subsequent
level Plant Ratoon Ratoon Ratoon

lbs K20/A
0-29 250 250 150 150
30-59 250 150 150 150
60-89 150 150 150 150
90-149 100 150 150 150
150-179 0 150 150 150
180-299 0 0 150 150
>299 0 0 0 150

Source: Adapted from Anderson [6], Gascho and Freeman [64], and Gascho
and Kidder [66].

Adjustment of Soil pH
Sulfur is recommended for increasing micronutrient availability
when the soil pH is more than 6.6. The current recommendation is to
apply 500 lbs S/A for muck and sandy muck and 300 lbs S/A for mucky
sand [7]. All applications of S should be made in the furrow at
planting. As with S use for vegetables, growers must consider econom-
ics when making decisions concerning the use of S.








Application of Si
On soils low in Si apply up to 3 tons of slag/A for a three- crop cycle
[38, 39]. If sugarcane is grown in rotation with rice which has received
Si, no further application of Si may be necessary. Careful considera-
tion should be given to the economics of using Si for sugarcane produc-
tion.
Micronutrients
If the pH is greater than 6.0, apply 5 lbs Mn/A. The use of micro-
nutrients for sugarcane are based on apparent crop requirement.
Currently, 2 lbs Cu/A, 2 lbs Zn/A, and 1 lb B/A are recommended. No
micronutrients are recommended for ratoon cane [6, 7, 80, 81].


Figure 14. Cracked stem in celery caused by a boron deficiency.







Rice


Macronutrients
Rice does not appear to respond to supplementary N, P, or K on
organic soils in south Florida. Therefore no recommendation of these
nutrients is made [114, 115].
Application of Si
For rice produced on Histosols low in Si apply 3 tons of slag/A
[118].
Micronutrients
If the soil pH is more than 6.0, it is recommended that about 20
lbs Mn/A be drilled in with the seed at planting [114]. The application
of Zn and B is based on apparent crop requirement. Currently, 5 lbs
Zn/A and 1 lb B/A applied preplant broadcast is recommended for rice.
For soils low in Fe, 50 to 100 lbs iron sulfate should be drilled in with
the seeds at planting [116].


Pastures
Macronutrient fertilizer recommendations for pasture are based
on apparent crop requirement [98, 101]. Apply 300 to 500 lbs/A of 0-
10-20 annually. On soil cropped previously, micronutrients are ap-
plied as recommended by plant tissue test.

Other Agronomic Crops
The fertilizer recommendations for selected agronomic crops
grown on Histosols are shown in Table 11. If the soil pH is above 6.0
apply Mn with the broadcast fertilizer at 8 lbs/A. Also apply 8 lb Zn/
A and 1.2 lbs B/A. Sod may require additional foliar sprays of Mn or
Fe as indicated by tissue analysis.

VII. Current and Future Research Needs
Soil-test correlation and calibration research is a never-ending
process. Because of continual development of new crops or cultivars
and ever-changing crop cultural practices, research always should be
in progress to improve and refine soil-test fertilizer recommenda-
tions. Another confounding factor with organic soils is the fact that in
a drained state soil subsidence continues and with time a number of
physical and chemical properties of the soil also change. For these
reasons, studies are always in progress to improve the data base from
which soil-test fertilizer recommendations are made.
32







Table 11. Phosphorus fertilizer recommendations for various ag-
ronomic crops across a range of soil-test-P index levels.

Soil-test index values
2 4 6 8 10 12 14 16
Crop

Fertilizer Recommendations
----------- lbs P205/A-------------

Field Corn 260 220 180 140 100 60 20 0
Grain sorghum 160 120 80 40 0 0 0 0
Sod 160 120 80 40 0 0 0 0


Table 12. Potassium fertilizer recommendations for various agro-
nomic crops across a range of soil-test-K index levels.

Soil-test index values
40 60 80 100 120 140 160 180 200
Crop

Fertilizer Recommendations
------------ lbs KO/A-------------

Field corn 320 280 240 200 160 120 80 40 0
Grain sorghum 220 180 140 100 60 20 0 0 0
Sod 120 80 40 0 0 0 0 0 0


Many of the organic soils in south Florida overlay limestone bed-
rock, and with continual cropping and continual soil subsidence,
carbonates are moved into the surface layers of the soil by diffusion
and mass flow with soil water. This process has resulted in an increase
of the pH in many soils and a corresponding increase in pH-related
nutritional problems. Much of the research effort over the next few
years must address pH-related problems [10]. Furthermore, recent
work suggests that the water-soluble P test currently used by the
laboratory may not be satisfactory for soils having a wide range in pH
values [112]. Organic soils vary in amounts of carbonates Fe, Al, and
other soil properties which influence the P buffering capacity of soils
[87]. Research is currently in progress to explore the possibility of
using other extractants which might better characterize the available
P in organic soils having a wide range in soil properties.
The soil-test Na levels in Histosols of the Everglades Agricul-
tural Area have recently been increasing [112]. This increase proba-
bly results from recent canal dredging in the area which exposes
saline waters from shallow aquifers to mixing with surface waters.
The soil-test Na increase is especially pronounced following fallow

33







flooding in the summer, a common practice on vegetable fields.
Research is needed to access the effect of these increase sodium levels
on crop growth.
There is no soil-test calibrated for micronutrient fertilizer rec-
ommendations on organic soils. However, relatively large amounts of
Mn, B, and Zn are recommended. Currently, the recommendations are
based on apparent crop requirement and soil pH. Fertilizer-Fe recom-
mendations are based on ash color [116]. Research is needed to
calibrate a soil test for micronutrients on organic soils. Work is also
needed to explore the possibility of developing a soil test for Si
recommendations.
Recently, many crops grown on Histosols in the Everglades
which did not respond previously to N fertilization are showing
responses to additions of this nutrient [35, 70, 109, 110, 112]. There
are a number of reasons for this response including the development
of new higher-yielding cultivars having a higher N requirement,
increased plant populations increasing the demand for N on a per area
basis, and the cultivation of shallower soils following years of subsi-
dence which decreases the soil N on a per area basis. However, for
reasons mentioned previously the development of a chemical soil test
for N for organic soils is unlikely. Nitrogen-fertilizer recommenda-
tions currently are based on apparent crop requirement and the
probability of obtaining a response which seems to be associated with
season. However, additional research is needed to develop models
which predict the N-fertilizer requirement of crops using weather-
related data.
Recent work with lettuce has shown that the efficiency of fertili-
zation can be improved substantially by the directed placement of
nutrients. Additional research is needed to explore the possibility of
banding nutrients for other crops and recommending the appropriate
combination of broadcast and banded fertilizers based on the soil-
testing program.
Finally, research is needed to calibrate plant-tissue testing to
use in combination with soil-test for improving fertilizer recommen-
dations. Recent work has shown tissue analysis to be a promising tool
for refining fertilizer recommendations for sugarcane [40, 41, 62] and
pasture [117]. Furthermore, many leafy vegetable crops accumulate
70% of their nutrients during the last 30% of the growing periods and
tissue-testing could be a helpful tool in correcting nutrient deficiencies
midseason [130, 131]. Tissue-testing also might be helpful in diagnos-
ing nutritionally-related physiological disorders in vegetables [18]. If
the critical nutrient level concept [93] or the Diagnostic and Recom-
mendation Integrated System (DRIS) approach [8] is used, much more
research is needed to fully exploit the benefits of tissue analysis for
crops grown on organic soils.








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