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Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 558
Title: Relation between soluble phosphorus in fertilized soils and growth response of pasture forage
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027120/00001
 Material Information
Title: Relation between soluble phosphorus in fertilized soils and growth response of pasture forage
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 16 p. : ; 23 cm.
Language: English
Creator: Neller, J. R ( Joseph Robert ), 1891-
Lundy, H. W
Jones, D. W ( David W. ), 1918-
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1955
 Subjects
Subject: Plants -- Effect of phosphorus on   ( lcsh )
Phosphatic fertilizers -- Florida   ( lcsh )
Forage plants -- Fertilizers -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: J.R. Neller, H.W. Lundy and D.W. Jones.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station) ;
 Record Information
Bibliographic ID: UF00027120
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000926755
oclc - 18278246
notis - AEN7455

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Full Text



February 1955


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATIONS
GAINESVILLE, FLORIDA
WILLARD M. FIFIELD, Director










Relation Between Soluble Phosphorus in


Fertilized Soils and Growth Response

of Pasture Forage


J. R. NELLER, H. W. LUNDY and D. W. JONES









CONTENTS


Experim ental ................. ......... ...
Experiments in Central Florida ...............
An Experiment in North Central Florida
Experiments in West Florida ...............
Discussion and Conclusion .........................


Page
. --- ...- .. ... .....- 3
- .- ...-- ..- 4
.. ........... ....... 8
... ... ........... 1 1
.... ....... .......... 14


A cknow ledgm ents .... ......................... ......... ..... 1








Single copies free to Florida residents upon request to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA


Bulletin 558











TABLE 1.-YIELDS AND PHOSPHORUS CONTENT OF CARPET GRASS VERSUS SOLUBLE AND TOTAL PHOSPHORUS TOGETHER WITH
PH, ORGANIC MATTER AND MOISTURE EQUIVALENT IN SURFACE THREE INCHES OF IMMOKALEE FINE SAND WITH AND
WITHOUT SUPERPHOSPHATE FERTILIZER.
Averages of 4 replicated plots


Factors Measured



Yields, 1946-51 lb./A.,
air dry .......... ..............

'/ phosphorus in growth

Dilute acetic acid phos-
phorus in the soil lbs,/A.

Total phosphorus in soil
Ibs./A ........ ......

pH of soil, 1952 .......

Organic matter, 1952 / air
d ry ...... ....... ..... .....

Moisture equivalent, 1952,
% air dry ........... ....


No Phos
Limed
in 1945
and 1948


Superphosphate
phate Every Other Year
Limed
Limed in 1945 Limed
in 1948 and 1948 in 1948


7,524 8,958

0.213 0.231


5.1 7.1


51 49

5.76 5.22


4.21 4.68


7.87 8.49


11,370

0.242


8.6


71

6.04


4.29


8.37


Superphosphate
Each Year
Limed
in 1945 Limed
and 1948 in 1948


Least Significant
Difference (.05)
For
Phos- For
phorus Lime


9,247 10,975 11,545 1,439

0.223 0.243 0.281 0.017


6.5 12.0 9.2 2.4


56 80 62 6

5.64 6.20 5.74 0.03


4.29 4.11 4.45 Not sig.


8.15 8.11 7.99 Not sig.


Not sig.

0.016


Not sig.


4

0.05


Not sig.


Not sig.


*The soluble phosphorus ,as obtained by shaking for 'I hour, 10 gmns of air-dry soil with 50 ml. of a 0.3', acetic acid contaiinng 100 gms. of
sodium acetate per liter (Morgan's solution). Average of annual prefertilization samples.









Relation Between Soluble Phosphorus in

Fertilized Soils and Growth Response

of Pasture Forage

J. R. NELLER, H. W. LUNDY and D. W. JONES

Phosophorus differs from other nutrient elements such as
nitrogen and potassium in that it exists in combinations from
which it is released too slowly to be affected by leaching in most
types of soils. An important exception is that fertilizer phos-
phorus does leach rather rapidly from the acid sandy soils that
occupy much of peninsular Florida. It has been found 1 that
this leaching of phosphorus is decreased to a large extent by
adequate liming.
In contrast to its mobility in the sandy soils of peninsular
Florida, fertilizer phosphorus appears to be strongly fixed in
many of the soils of western Florida. These are of finer texture
and are higher in iron and aluminum. Throughout practically
all of Florida there is a marked response to phosphates on new
land.
Because of this initial lack of phosphorus and because it
leaches in some areas, it is important to know the relationship
between crop response to fertilizer phosphorus and the amount
of phosphorus extractable from the soil. The objective of the
experiments reported in this bulletin was to obtain information
of this type for soils planted to pasture.

Experimental
Grasses with and without white clover were grown on field
plots of soil types that are generally planted to pastures. The
plots were located on virgin land in central, north central and
western Florida and were fertilized with superphosphate over
a number of years. Other fertilizer materials were added to
make a complete fertilizer program and the soil was limed in
most instances. Materials applied before planting grass and
clover were disked into the surface three to four inches. All
subsequent applications were broadcast over the surface of the

Leaching of Fertilizer Phosphorus in Acid Sandy Soils as Affected by
Lime. J. R. Neller, D. W. Jones, Nathan Gammon, Jr., and R. B. Forbes.
Circular S-32, 1951, Fla. Agr. Exp. Station.






Florida Agricultural Experiment Stations


clipped sod. Growth response was obtained by clipping the for-
age frequently so as to keep it in a fairly succulent state. Thus
a condition of pasture grazing was approached to some extent.
The data of one experiment are from grazed pastures. Nitrogen
and potassium were applied uniformly to all plots of an experi-
ment, generally once a year, and lack of a sufficient amount of
these elements probably limited growth at some periods. The
main limitation of growth was lack of soil moisture at times.
Small amounts of copper, manganese, zinc and boron were added
uniformly so that these minor elements should not be a limiting
factor in the phosphorus study.
Although the fertilizer was distributed over an entire plot,
material for soil and plant samples and for growth records was
not taken closer than 11 feet from the margins of a plot. A
soil sample consisted of 8 to 10 soil tube cores per plot taken to
a depth of three inches. The methods of extraction for phos-
phorus differed in the various experiments and are recorded in
the tables.

Experiments in Central Florida
Experiment 1.-Quadruplicated plots, 10 by 15 feet in size,
were established in a randomized block design on Immokalee
fine sand at the Range Cattle Station in Hardee County. This
type of soil is representative of extensive pasture areas of the
flatwoods of peninsular Florida that extend north and south of
the location of the experiments.
Carpet grass was planted on the plots and Table 1 records
weights of total growth of clippings removed for a six-year
period, 1946-1951. Ordinary superphosphate was applied to one
group of these plots at the rate per acre of 70 pounds P205
every other year in October and to another group each year
(Table 1). Yields obtained from the check plots (no phosphate)
are probably somewhat high because of the possibility of wash-
ing of the surface applied phosphate some years when heavy
rains occurred soon after application of the phosphate. Even
so, growth on these check plots, which averaged 8,241 pounds
per acre, was significantly less than on those that received su-
perphosphate for which the averages were 10,309 and 11,260,
respectively. During the early years growth was better where
superphosphate was applied each year, but total growth for the
six-year period was little better than where the application was
made every other year.







Soluble Phosphorus and Growth Response


Nitrogen and potassium equal to the amount in 500 pounds
per acre of a 6-14-10 fertilizer were added each year. At first
one group of plots was not limed and the other received calcic
lime at one ton per acre. In 1948 all plots were topdressed with
lime at one ton per acre. This variation in the liming program
did not have any definite effect on growth.
Total phosphorus in the grass was increased significantly in
some cases by superphosphate applications every other year, for
which the average was 0.233 percent; it was further increased
to 0.262 percent for the six-year period where application was
made each year (Table 1). The average effect of the extra lime
was to increase the phosphorus content from 0.233 percent to
0.245 percent.
Each fall just previous to reapplication of fertilizer, soil sam-
ples were taken to a depth of three inches from each of the plots.
Table 1 shows that the amounts of phosphorus extracted from
these samples were higher where superphosphate had been
applied, significantly so for application each year, where the
average was 10.6 pounds per acre as compared with 6.1 pounds
on the nonphosphated plots. Additional lime increased the solu-
ble phosphorus, but not significantly.
The total phosphorus contents of the sample of soils (Table 1)
serve equally well as those of soluble phosphorus to show in-
crease in the residual phosphorus of the phosphated soil and
the effect of lime on retention of phosphorus. Average pH
values for the plots limed twice and once were 6.00 and 5.53,
respectively. Organic matter and moisture equivalent aver-
aged 4.20 and 8.12 for the relimed, and 4.47 and 8.21 for the
limed plots, with no significant difference as to effect of phos-
phating or liming.
Experiment 2.-For another experiment on virgin Immoka-
lee fine sand that was also planted to carpet grass, yields for
three years (1947-1949) are recorded in Table 2, together with
average phosphorus content of the grass. Applications of 70
and of 210 pounds P.O., per acre in superphosphate were sur-
face-applied annually to these plots. All plots received uniform
amounts of sodium nitrate and muriate of potash at 200 and
300 pounds, respectively, per acre annually. Dolomitic lime was
used at three rates and for the fertilizer phosphate comparisons
results as to lime levels are averaged (Table 2). Lack of soil
moisture was a limiting factor during the three years of this
study and may account for the comparatively low response of







Florida Agricultural Experiment Stations


growth to phosphates. The superphosphate caused a marked
response in the total phosphorus content of the grass, ranging
from extremely low on the no-phosphate plots to very high on
those that received 210 pounds P.O, per acre per year of super-
phosphate.

TABLE 2.-TOTAL AND SOLUBLE PHOSPHORUS AND PH OF SURFACE THREE
INCHES OF IMMOKALEE FINE SAND FERTILIZED WITH SUPERPHOSPHATE
WEIGHTS AND PHOSPHORUS CONTENTS OF CLIPPINGS ARE GIVEN.
Averages of 4 replicated plots
Average
Super- Total Phos- Dilute Annual Total P
phosphate phorus Acetic pH Yeield, in Growth
as P.O; as P Acid-Sol.P.I AAir-Dry
Lbs./A. Lbs./A. Lbs./A. Lbs/A. Percent
None 48 5.9 5.23 2,157 0.137
70 58 11.6 5.11 2,219 0.250
210 90 12.3 4.93 2,680 0.497
LSD (.05) 6 1.7 0.11 Not sig. 0.054


Soil samples taken a year after the last application averaged
5.9, 11.6 and 18.1 pounds per acre of soluble phosphorus for
plots that received 0, 70 and 210 pounds P.O, of superphosphate
per acre per year, respectively. The total phosphorus contents
of these samples averaged 48, 58 and 90 pounds per acre. These
increments, as well as those for soluble phosphorus, increased
significantly with increase in rate of phosphate application. The
pH values averaged 5.23 for the non-phosphated plots to 4.93
for those of the high phosphate application.
Table 3 shows the marked effect that lime has on retention
of fertilizer phosphorus in this type of soil. Samples from the
surface three inches of the plots one year after the last applica-
tion of phosphate at 70 pounds per acre contained total phos-
phorus increasing from 46 to 71 pounds per acre as the lime
rate increased from none to two tons per acre. The parallel
change in soluble phosphorus was 7.8 increasing to 11.4 pounds
per acre. The same type of effect is apparent for the plots
treated with superphosphate at 210 pounds PO, per acre.
The pH of the soil averaged 4.49 without lime and 5.12 and
5.66 where lime had been added at one and two tons per acre,
respectively. Amounts totaling 92 and 276 pounds of phos-
phorus per acre were added in the superphosphate at two rates







Soluble Phosphorus and Growth Response


for the three years of the experiment. These amounts of phos-
phorus are considerably higher than those found in the soil
(Table 3) after deducting the phosphorus in non-phosphated soil
and the amount removed in the grass (Table 2). The results
show that lime causes an increased retention of phosphorus as
the rate of liming increases and that the highest rate, which
was two tons per acre, permitted considerable of the surface
applied superphosphate phosphorus to leach below the surface
three inches of soil.

TABLE 3.-EFFECT OF LIME ON PH AND ON RETENTION OF SUPERPHOSPHATE
IN IMMOKALEE FINE SAND GROWING CARPET GRASS.
Averages of 4 replicated plots

Pounds per Acre
Superphosphate Lime pH Surface 3 Inches
Added (PO-,) Rates of Soil Dilute Acid-
Total P. Soluble P.
Lbs./A. Tons A.
None None 4.70 51 (.1
None 1 5.16 46 .8
None 2 5.84 48 4.7
70 None 4.40 14 7.8
70 1 5.19 58 10.1
70 2 5.74 71 11.4
210 None 4.38 38 7.5
210 1 5.02 98 19.3
210 2 5.39 135 25.1
LSD (.05) for
P and for lime 0.11 6 1.7


Experiment 3.-In October 1944 soil samples of Immokalee
fine sand were obtained from the surface three inches of dupli-
cate pastures at the Range Cattle Station. The samples were
analyzed for dilute acetic acid-soluble phosphorus, as recorded
in Table 4. These pastures received superphosphate in 1942
and again in November 1943. Lime was added in 1942, except
that none was added to the non-phosphated pastures of carpet
and of Bahia grass.
An average of 4.9 pounds per acre of soluble phosphorus was
obtained from the soils of the non-phosphated pastures and of
7.9 pounds from those that received superphosphate, except for
the more heavily phosphated pastures, where 18.0 pounds of
soluble phosphorus per acre was found. Average pH values







Florida Agricultural Experiment Stations


were 4.36 for unlimed pastures and 5.34 and 6.11 for those
limed with one and two tons, respectively. Organic matter,
root weights and moisture equivalents tended to be higher for
the phosphated pastures.

TABLE 4.-SOLUBLE PHOSPHORUS, PH, ORGANIC MATTER, MOISTURE EQUIVA-
LENT AND ROOT DENSITY OF THE SURFACE THREE INCHES OF IMMOKALEE
FINE SAND PASTURES.*

SDilute
Super- Acetic
phosphate I Acid- I Moisture Relative
Forage Treatment Soluble pH I Organic Equiva- Weights
(P?20) Phos- Matter lent of Roots
phorus
Lbs./A. Lbs./A. Percent Percent
Carpet grass None 4.9 4.36 5.43 8.00 57
Carpet grass 64 6.3 5.07 5.55 8.35 97
Carpet grass
and clover 166 1.8.0 6.11 4.70 9.19 100
Bahia grass None 4.8 4.36 5.43 8.00 48
Bahia grass 64 9.5 5.61 4.17 8.44 74

Lime at one ton per acre was added two years previously, except that none was added
on the non-phosphated carpet and Bahia grass pastures. A second ton of lime was added one
year later to the carpet grass and clover pasture, the soil of which had a pH of lill.

All Experiment in North Central Florida

In November 1946, in Alachua County, an area of newly
cleared flatwoods soil (Rutlege fine sand) of a type where soil
moisture conditions are fairly good was prepared for grass
and clover by disking dolomitic lime into the surface four
inches at the rate of two tons per acre. An 0-14-10 mixture at
500 pounds per acre was disked into the surface three inches
of plots, 12 by 15 feet in size, replicated six times in a ran-
domized block design. The area was seeded with inoculated
white clover and with Pensacola Bahia grass seed. Some of
the plots were prepared and managed in the same way except
that the superphosphate was omitted from the fertilizer every
other year. A minor element treatment was made initially on
all of the plots and uniform applications of potash were made
each year, thus making it possible for the main limiting factor
of growth to be the omission of superphosphate every other
year.







Soluble Phosphorus and Growth Response


TABLE 5.-TOTAL AND SOLUBLE PHOSPHORUS, PH, ORGANIC MATTER AND
MOISTURE EQUIVALENT IN SURFACE THREE INCHES OF LIMED PHOSPHATED
RUTLEDE FINE SAND. WEIGHTS OF CLIPPED GRASS AND CLOVER ARE
GIVEN.
Averages of six replicated plots

Analysis. Surface 3 Inches of Soil
Dilute Forage in
Year Acetic Organic Moisture Cuttings
Total P. Acid-Solu- pH Matter Equiva- Air-dry
ble P. lent
Lbs./A. Lbs. A. Percent Percent Lbs./A.
Superphosphate Each Year Beginning in 1946

1947 79 3.8 5.42 3.07 7.53 2,195
1948 52 4.0 5.48 ....... 3,357
1949 83 7.2 5.09 3.60 5.70 7,529
1950 6.4 ... .... ... 5,308
1951 94 5.8 5.16 4.63 7.60 5,226

Averages 77 5.8 ......... 4723

Superphosphate Added Every Other Year Beginning in 1946

1947 56 3.4 5.37 3.57 7.41 2.305
1948 73 5.1 5. ...... 2,064
1949 88 6.1 5.05 3.90 6.24 6,900
1950 ... 2.5 ...... 3,202
1951 94 4.0 5.17 4.63 8.25 5,287

Averages 85 4.0 .....3,952


Each fall after soil samples were taken from each plot to
a depth of three inches, fertilizer was surface applied. Table
5 records results of analyses of these samples, as well as the
total growth clipped from the plots each year for five years.
The average dilute acetic acid-soluble phosphorus of samples
taken in the fall of each year for five years was 5.8 pounds per
acre where the superphosphate was applied each year and 4.0
pounds per acre where it was applied every other year. Com-
parable amounts of total phosphorus in the soil were 77 and
85 pounds per acre, while those of phosphorus added in the
superphosphate were 152 and 92 pounds per acre. There are
about 50 pounds per acre-three-inches of phosphorus native to
this soil. Hence, had there been no leaching of phosphorus,
the amounts present at the end of the five-year period would
have been 144 and 101 pounds per acre after adding 50 pounds







Florida Agricultural Experiment Stations


of soil phosphorus and deducting 58 and 41 pounds, respectively,
for the phosphorus removed in the cuttings. These results show
that a considerable part of the fertilizer phosphorus was re-
tained in the surface three inches of this soil that had been
limed at the rate of two tons per acre.
Table 5 shows that pH values decreased with increase in
time from application of lime to about the extent that might
be expected. The soil samples of 1951 were higher in organic
matter and moisture equivalent, indicating that the soil which
was heavily sodded had increased in organic matter content.
The average annual weight of cuttings removed (Table 5)
where superphosphate had been added each year was 19.5 per-
cent larger than those from plots that received superphosphate
every other year. Gypsum was added in the years that super-
phosphate was omitted, except in 1948, to insure that sulfur
was not lacking for optimum growth. The increased amount
of forage on the plots phosphated annually contained more
clover, a factor of importance because of the larger amount
of protein in the clover and associated grass and because the
clover grew during the winter months when there was defi-
ciency of pasture growth for grazing.
TABLE 6.-SOLUBLE SOIL PHOSPHORUS AND PH OF SOILS FOR THE EXPERI-
MENTS RECORDED IN TABLES 1, 2, 4 AND 5, TOGETHER WITH NOTES ON
GROWING CONDITIONS OF FORAGE.
Annual
Rate of Dilute
Source of Superphos- Acetic Acid- Growth Notes of Forage
Data phate Soluble Clipped Periodically or
Application Phosphorus pH of Grazed (Table 4)
(PO,) as P Soil
Lbs./A. Lbs./A.
None 5.1 5.76 Carpet grass response to
Table 1 35 8.6 6.04 phosphate but growth was
70 12.0 5.74 slow because of lack of soil
moisture.
S None 5.9 5.23 Carpet grass grown under
Table 2 70 11.6 5.11 conditions much the same as
210 17.3 4.93 for Table 1.
None 4.9 4.36 Carpet grass and white
Table 4 f 64 6.3 5.07 clover pastures under mod-
166 18.0 6.11 erately good growing con-
ditions.
S 35 4.0 5.29 Pensacola Bahia grass and
Table 5 70 5.8 5.19 white clover under moder-
SIate to good growing condi-
tions.







Soluble Phosphorus and Groiwth Response


A survey of results recorded in Tables 1, 2, 4 and 5 obtained
from four locations on the fine sandy soils of central and north
central Florida is given in Table 6. The phosphorus and pH
data are of soil samples taken at least a year after application
of phosphate and lime from sodded plots that were clipped
periodically, except for the data of Table 4, where the forage
was grazed by cattle. Growth of carpet grass was slow and
poor, chiefly because of lack of moisture. The soluble and
available phosphorus in the soil was not utilized to the extent
that it would have been under more luxuriant growth and the
soluble phosphorus levels are probably high. Growth rates
were more nearly normal in the experiments recorded in Tables
4 and 5 and the soluble phosphorus levels are lower.

Experiments in West Florida

In October 1948 a series of soil treatments involving different
rates of superphosphate was established on Carnegie and Tifton
fine sandy loams at the West Florida Station, Santa Rosa
County, using plots 20 by 20 feet replicated four times in ran-
domized blocks. The land was cleared of stumps, limed, fer-
tilized and planted to Dallis grass and white clover in the
manner described in Circular S-19.2 This circular records first-
year yields from various phosphates and levels of potash. Ta-
ble 7 records the yields of Dallis grass-white clover cuttings
obtained 1949-1952, inclusive, on those plots where superphos-
phate was applied annually at four rates, together with uniform
potash and dolomitic lime treatments to all plots. It may be
observed that the response to superphosphate at all levels,
marked in 1949-50, was not so marked in 1951-52 for annual
applications of phosphate higher than 100 pounds P.,O, per
acre.
In April 1949 soil samples were obtained from the surface
three inches following the first cutting of a good stand of white
clover from the plots. The dilute sulfuric acid-soluble phos-
phorus increased from 5.2 on the non-phosphated check plots
to 18.6 pounds per acre where superphosphate at 200 pounds
per acre P,O. had been disked into the surface two to three
inches of soil six months previously (Table 7). One ton per

First Year Yields on Louisiana White Clover-Dallis Grass Pasture
Plots on Carnegie and Tifton Fine Sandy Loams. Nathan Gammon, Jr.,
W. H. Lundy, J. R. Neller and R. A. Carrigan. Fla. Agr. Exp. Sta. Circu-
lar S-19. 1950.







Florida Agricultural Experiment Stations


acre of dolomite lime disked into the soil caused a slight but
not significant increase in soluble phosphorus where it had
been applied at 100 pounds P2O per acre. Increasing amounts
of lime decreased the soluble phosphorus significantly where
the lime had been added at the rate of four tons per acre.
The average pH of the unlimed soil was 5.38. Addition of lime
caused a marked increase in growth of clover.

TABLE 7.-SOLUBLE AND TOTAL PHOSPHORUS AND PH OF SURFACE THREE
INCHES OF LIMED AND PHOSPHATED TIFTON AND CARNEGIE FINE SANDY
LOAMS. GROWTH AND PHOSPHORUS CONTENT OF DALLIS GRASS-WHITE
CLOVER COVER ALSO ARE GIVEN.
Averages of 4 replicated plots


S
a


Nc
5(
101
20'


Rates of Soil Samples Growth Data Air-
uperphosphate During Cuttings of 1949 dry 1949-1950 Yields
Lbs. P2Os/A., Dilute I Average 1951
nd Tons/A. of Sulfuric I Total P !P. Content and
Lime Acid-Solu-! P. pH Yields of 1952
uble P** : Cuttings
SLbs./A. Lbs./A. Lbs./A. Percent Lbs./A.
Superphosphate Effect with All Treatments Limed at 1 Ton per Acre
I
phosphate 5.2 119 5.78 2,924 0.12
0 lbs. phosphate 7.2 129 5.80 6,302 0.22 4,589
3 lbs. phosphate 11.2 148 5.83 8,377 0.22 10,188
0 lbs. phosphate 18.6 173 5.77 11,325 0.25 11,458

Lime Effect with Superphosphate at 100 Lbs. P;O per Acre


No lime
1 ton lime
2 tons lime
4 tons lime
L.S.D. (.05)


2,182 0.22 4,835
8,377 0.22 10,188
8,755 0.24 8,759
9,804 0.24 8,837
784 0.01 1,437


Phosphate applications were made each fall for four years (1948-1951).
** The soluble phosphorus was obtained by extraction for 1 hour of 5 gms. of air-dry
soil in 200 mis. of a 0.002 N sulfuric acid solution containing 3 gms. of ammonium sulfate
per liter (Truog's solution).
T The no-phosphate checks were used for other purposes after 1950.

The third application of superphosphate was made on these
plots in October 1950 and the soil was disked slightly and
planted to Ladino clover. Growth response for 1951 and 1952
(Table 7) shows much the same trend as for 1949-1950. No
phosphate was added in the fall of 1952 but uniform appli-
cations of gypsum and potash were applied so as to measure
the residual phosphorus of the superphosphate applied an-
nually the previous four years. There were significant in-







Soluble Phosphorus and Growth Response


creases in growth (Table 8) which may be attributed to the
residual phosphorus previously applied in superphosphate to-
taling 200, 400 and 800 pounds PRO; per acre. Where 400 pounds
P.O per acre in superphosphate had been added, the dolomitic
lime applications of 1948 were without much effect, except for
a significant increase in growth where lime had been used at
four tons per acre. The phosphorus content of the clover was
increased somewhat by increasing amounts of lime and con-
siderably by superphosphate totaling 400, as compared with
200, pounds per acre P005.

TABLE 8.-RESIDUAL EFFECTS OF SUPERPHOSPHATE AND OF LIME IN RELA-
TION TO SOLUBLE PHOSPHORUS IN TIFTON AND CARNEGIE FINE SANDY
LOAMS AND TO YIELD AND PHOSPHORUS CONTENT OF DALLIS GRASS-
WHITE CLOVER FORAGE.
Averages of 4 replicated plots

Soil Data After Cuttings of 1953 Total
Superphos- Dilute Dilute I Weight of Phosphorus
phate (POs, Sulfuric Hydro- Cuttings of Clover
1948-51) Acid- chloric of 1953 (Second
and Lime Soluble Acid- pH Air-dry C;tth..
(Tons, 1948) Phosphorus Soluble '''. .)
Phosphorus*
Lbs.-
Tons/A. Lbs. A. Lbs./A. Lbs. A. Percent
Superphosphate Effect with Lime at 1 Ton per Acre in 1948
-------------------------------- -----
200 lbs. 4.4 11.0 5.72 4,490 0.26
400 lbs. 8.7 25.8 5.66 5,756 0.32
800 lbs. 26.1 102.5 5.67 7,348 0.32

Lime Effect with Superphosphate at 400 Lbs. P O, per Acre, 1948-1951

0 tons 9.5 39.3 5.26 5,421 0.31
1 ton 8.7 25.8 5.66 5,756 0.32
2 tons 10.1 38.3 6.09 5,637 0.32
4 tons 9.6 31.5 6.33 6,348 0.33
L.S.D. (.05) 6.2 11.1 0.26 824 0.02

These soluble phosphorus values were obtained by extraction for 1, hour of 10 gms.
in 100 ml. of a solution of 0.1 N hydrochloric acid (Bray's solutions.

The pH values of soil samples taken in 1953 were about the
same as those taken in the fall of 1949, six months after the
dolomite had been disked into the surface soil (Table 8). Sam-
ples taken in 1950 had pH values somewhat above those taken
in 1949. The levels of phosphorus extracted with dilute sul-
furic acid were about the same for samples taken in 1949 and






Florida Agricultural Experiment Stations


in 1953. They were not affected by rate of liming in either
year, except for a depression in amount extracted in 1949 where
four tons of dolomite had been applied (Table 7). For both
years there was a significantly larger amount of phosphorus
extracted for increasing rates of application of superphosphate.
The dilute hydrochloric acid solution extracted from three to
four times as much phosphorus, but in about the same relative
amounts (Table 8) with respect to a given phosphate-lime treat-
ment.
In general, the experiment on Tifton and Carnegie fine sandy
loams in western Florida showed that a marked growth and
phosphorus content response to superphosphate resulted when
a virgin soil was planted to clover and grass. Although the
intensity of this response decreased after a few annual appli-
cations of superphosphate, the amount of growth in 1953 (Ta-
ble 8) after phosphate applications had been discontinued was
larger where the most superphosphate had been added in pre-
vious years. Addition of one to two tons of dolomite to these
soils caused a marked response to clover but had a negligible
effect on amount of phosphorus extracted with a dilute acid.

Discussion and Conclusion
The five experimental areas, four in peninsular and one in
western Florida, reported in this bulletin were started on new
land that had not been cropped or fertilized. This was done
for two reasons: One was to know accurately how much fer-
tilizer had been put on the land and the manner of its applica-
tion; the other was that there are large areas of new land typi-
fied by the experimental tracts that may be planted to fertilized
pastures. In fact, about 200,000 acres have been so planted an-
nually for the past several years. The experiments were con-
tinued for five to six years with annual fertilizer applications,
so at their conclusion the land was no longer newly cropped.
The data of the experiments are not strongly definite rela-
tive to the amount of phosphorus added to the soil and the
amount extracted with buffered dilute acid solutions. This is
in spite of definite efforts from the first to have good control
of operations. Thus a given experimental tract was selected
for uniformity and the plot areas and amounts of fertilizer used
per plot were accurately measured. Treatments were replicated
and randomized to permit statistical interpretation. The fer-
tilizer was distributed by hand as carefully as possible and soil






Soluble Phosphorus and Growth Response


samples consisted of 8 to 10 cores per plot, of 1/100 acre or
less, taken to a specified depth and composite for sampling. It
is considered that the distribution of the fertilizer was more
uniform and the sampling of the soil more accurate than is
or can be done in farming operations.
In spite of these efforts to control experimental conditions,
the amounts of phosphorus extracted from soil samples from
replicated plots varied considerably, as is evidenced by no
significance between treatments or by high values necessary
for an accepted degree of significance (LSD .05). Since there
is a lack of data of the type obtained in these experiments
where the fertilizer, crop response and soil sampling history is
accurately known, it was thought wise to publish the results
with the understanding that the general conclusions obtainable
from the experiments apply only to the types of soil used and
managed as in the manner of the experiments.
Consideration of the data obtained on the sandy soil flatwood
areas of peninsular Florida indicate that if the amount of phos-
phorus extracted from the surface three inches of soil with
buffered dilute acetic acid (Morgan's solution) is less than
five to six pounds per acre the pasture is in need of phosphate;
that soils yielding eight to 10 pounds of phosphorus per acre
may need phosphate and that those containing 12 to 14 pounds
have sufficient available phosphorus. These are the results ob-
tained on the acid sandy flatwood soils that had been limed
with about two tons per acre or sufficient to raise the pH to
a minimum of 5.5. If these acid sandy flatwoods soils are
not limed, much of the phosphorus of the added superphosphate
that is not taken up by the growing plants will leach from
the surface layers during a season of summer rainfall.
Consideration of the data from experiments in western Flor-
ida on Tifton and Carnegie fine sandy loam leads to the con-
clusion that soils of these types fertilized with superphosphate
will respond to phosphate fertilizer if the surface three inches
of soil yield less than 10 to 35 pounds of phosphorus per acre,
respectively, by extraction with buffered dilute sulfuric acid
(Truog's solution) or with 0.1 N hydrochloric acid solution con-
taining ammonium fluoride (Bray's solution).
The soils of western Florida have a strong fixing power for
phosphorus and strong acid extracting solutions are needed for
these to obtain sufficient phosphorus for accurate measurement.
In contrast, the fine sands of the flatwoods of peninsular Florida






Florida Agricultural Experiment Stations


do not fix phosphorus so firmly and for these the acetic acid
extractant is sufficiently strong. This weaker solution should
be used whenever possible for two reasons: (1) it does not ex-
tract an excessive amount of phosphorus from a soil to which an
insoluble phosphate, such as rock phosphate, has been added
and hence is not so likely to lead to an erroneous recommenda-
tion where the fertilizer history of the field or pasture is not
definitely known; and (2) it gives a solution that can be used
also for an evaluation of plant food elements other than phos-
phorus.
The levels of phosphorus given for the above pasture experi-
ments may be too low for field crops or vegetables, since they
have a shorter growing season, and, at first at least, a much
more restricted root system; and therefore a smaller volume of
soil from which to obtain phosphorus. These levels may be too
low also for a pasture under a more intensive management pro-
gram than that of these experiments. Thus, frequent appli-
cations of potash and nitrogen at high rates on soils where
moisture is not limiting, by virtue of irrigation if necessary,
could create a potential for growth that would be limited unless
the levels of soluble phosphorus were higher.

Acknowledgments
In several instances the authors are cooperating with other staff mem-
bers in experiments on soils in pastures and they wish to mention the in-
terest and cooperation of Doctors C. E. Hutton, Nathan Gammon, Jr., E. M.
Hodges, G. B. Killinger and W. G. Blue in reference to phases of the ex-
periments reported in this bulletin. William H. Kelly rendered helpful
assistance, particularly in the laboratory work.













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