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INFLUENCE OF ROCK PHOSPHATE ON AVAILABLE
PHOSPHORUS AS MEASURED BY PLANT UPTAKE

AND SOIL EXTRACTANTS

BY

Jose Espinosa

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTERS OF SCIENCE

Department of Crop and Soil Science

1979

ABSTRACT
INFLUENCE OF ROCK PHOSPHATE ON AVAILABLE
PHOSPHORUS AS MEASURED BY PLANT UPTAKE
AND SOIL EXTRACTANTS
BY

Jose Espinosa

A greenhouse and laboratory study was conducted to
determine the response of corn grown in three sandy loam
soils to application of five rock phosphates (RP). The
ACS solubility index for the five RP ranged from 22.6 to
1.2

Addition of RP to the Marlette and Tracy soils in—
creased plant growth slightly and markedly increased total
P uptake. RP addition to the Granby soil produced very
little response.

Solubility of the RP had a marked influence on the
response observed. The most soluble RP, North Carolina
and Central Florida, gave the best response. Idaho and
Tennessee RP produced only slight responses while Missouri,
the least soluble RP, gave a slightly negative response.

Yield and total P uptake correlated very well with the
amount of P extracted by Bray - 1 solution, water and 0.5
M ammonium citrate when North Carolina and Central Florida
RP were applied. The correlations were quite low when the
less soluble RP were used. Each of the three extractants

reflected reasonably well the rate of RP added to the

three soils. The highest correlation coefficients were
obtained when the most soluble RP were applied. Water
soluble P correlated with total P uptake as well or better

than Bray - 1 and ammonium citrate extractable P.

DEDICATION
to my wife Teresa and my lovely children

Jose and Paul.

ii

ACKNOWLEDGMENTS

The author wishes to express his sincere appreciation
to INIAP (Instituto Nacional de Investigaciones Agrope-
cuarias) for its financial support and stimulation that
made this graduate study possible.

A grateful acknowledgment is extended to
Dr. D. Warncke, my major professor, for his valuable
guidance, patience, and understanding that made my educa-
tional experience at Michigan State University rewarding.

The author also thanks Dr. B. G. Ellis and
Dr. S. Portch members of my thesis committee.

Finally, appreciation is expressed to all MSU soil

testing laboratory personnel for their help and friendship.

iii

TABLE

LIST OF TABLES . . . . . .

LIST OF FIGURES. . . . . .

INTRODUCTION . . . . . . .

LITERATURE REVIEW. . . . .

MATERIALS AND METHODS. . .

RESULTS AND DISCUSSION . .

LIST OF REFERENCES . . . .

APPENDIX . . . . . . . . .

OF CONTENTS

iv

page

vii

16

23

55

58

10.

11.

LIST OF TABLES

Soil Properties . . . . . . . .
ACS Solubility Index. . . . . .

Rock Phosphate Composition. . .

Total Yield (Dry Weight) of Corn in the Green-
house as Affected by Rate and Source of Phospho-

rus in Marlette Sandy Loam Soil

Total Phosphorus Uptake of Corn in the Green-
house as Affected by Rate and Source of Phospho-

rus in Marlette Sancy Loam Soil

Total Yield (Dry Weight) of Corn in the Green-
house as Affected by Rate and Source of Phospho—

rus in Tracy Sandy Loam Soil. .

Total Phosphorus Uptake of Corn in the Green-
house as Affected by Rate and Source of Phospho-

rus in Tracy Sandy Loam Soil. .

Total Yield (Dry Weight) of Corn in the Green-
house as Affected by Rate and Source of Phospho-

rus in Granby Sandy Loam Soil .

Total Phosphorus Uptake of Corn in the Green-
house as Affected by Rate and Source of Phospho-

rus’in Granby Sandy Loam Soil .

Correlation Coefficients for P Rate,
Dry Weight, Bray—1, Extractable P, Water Soluble
P and Ammonium Citrate Extractable P in Various

Combinations for the Marlette Soil.

Correlation Coefficients for P Rate,
Dry Weight, Bray-1, Extractable P, Water Soluble
P and Ammonium Citrate Extractable P in Various

Combinations for the Tracy Soil

P Uptake,

P Uptake,

25

26

27

28

30

31

32

33

Table

Page

12. Correlation Coefficients for P Rate, P Uptake,
Dry Weight, Bray-1, Extractable P, Water
Soluble P and Ammonium Citrate Extractable P
in Various Combinations for the Granby Soil . . 34
APPENDIX
I Results and Experimental Data of Marlette Sandy
Loam $011 0 O O O O C O O O O C O C O O O O O O 58
II Results and Experimental Data of Tracy Sandy
Loam'Soil . . . . . . . . . . . . . . . . . . . 59
III Results and Experimental Data of Granby Sandy

Loam SOil . O C O O O O C O O O O O O O C O C O 6 0

vi

Figure

1.

10.

LIST OF FIGURES

Page

Relationship between the rate of rock phos-
phate application and total P uptake in
Marlette soil . . . . . . . . . . . . . . . . . .

Relationship between the rate of rock phosphate
application and total P uptake in Tracy soil. . .

Relationship between total P uptake and Bray-1
extractable P for North Carolina rock phosphate
in Marlette soil. . . . . . . . . . . . . . . . .

Relationship between total P uptake and Bray-l
extractable P for North Carolina rock phosphate
in Tracy soil . . . . . . . . . . . . . . . . . .

Relationship between total P uptake and Bray-1
extractable P for Central Florida rock phosphate
in Marlette soil. . . . . . . . . . . . . . . . .

Relationship between total P uptake and Bray-1
extractable P for Central Florida rock phosphate
in Tracy soil . . . . . . . . . . . . . . . . . .

Relationship between total P uptake and water
soluble P for North Carolina rock phosphate in
Marlette $011 I O O O O O O O O O O O O O O O O 0

Relationship between total P uptake and water
soluble for North Carolina rock phosphate in
Tracy soil. . . . . . . . . . . . . . . . . . . .

Relationship between total P uptake and water
soluble P for Central Florida rock phosphate in
Marlette soil . . . . . . . . . . . . . . . . . .

Relationship between total P uptake and water

soluble P for Central florida rock phosphate in
Tracy soil. .-. . . . . . . . . . . . . . . . . .

vii

41

42

43

44

45

46

47

48

49

50

Figure

11.

12.

13.

14.

Relationship between total
nium citrate extractable P
rock phosphate in Marlette

Relationship between total
nium citrate extractable P

P uptake and ammo-
for North Carolina
soil . . . . . . .

P uptake and ammo-
for North Carolina

rock phosphate in Tracy soil. . . . . . . . .

Relationship between total
nium citrate extractable P
rock phosphate in Marlette

Relationship between total
nium citrate extractable P

P uptake and ammo—

for Central Florida

SOil O O O O O O O

P uptake and ammo-

for Central Florida

rock phosphate in Tracy soil. . . . . . . . .

viii

Page

. 54

INTRODUCTION

Many soils in the tropical areas of the world are
strongly acid, and as a consequence phosphorus (P) defi-
cient. Liming and heavy applications of superphosphates
have been used in correcting this problem, but the results
have been contradictory.

Direct application of rock phosphate on acid soils as
a source of P could be another approach which can solve
the problem. Many deposits of rock phosphates are located
in developing countries, and this fact can make the use of
rock phosphate economically attractive. Until now most of
the P applied to the soils in the tropical areas has been
in the form of superphosphate processed from rock phos-
phate. The investment and the energy expended in the
processing of rock phosphate could be considerabley less
if direct application of rock phosphate is made to the
soil.

For many years research has been done to evaluate the
agronomic effectiveness of rock phosphate. The response
obtained with applications of rock phosphate has proved to
be less than that obtained with the soluble superphos-
phate. However, the results have not always been satis—

factory and some erractic patterns in the results has

2

caused some researchers to doubt the effectiveness of the

rock phosphates.

A better understanding of the rock phosphate struc-
ture and their solubility has led to promising results in
the use of rock phosphate. Not only the properties of
the rocks tested, but the properties of the soils have
also proved to be important. Of special importance are-
pH and the influence of Ca in solution.

As the use of rock phosphates for direct application
on soils becomes popular, a good soil P extractant for
these soils is necessary. The initial availability of P
applied as rock phosphate is initially low, but as the
rock phosphate reacts with the soil, P is slowly released
to a more available form. This fact makes it difficult to
determine the amount of available P in soils after appli-
cation of rock phosphate.

The objectives of this study were to:

1. Evaluate the effectiveness of five rock phosphate
materials for improving corn growth and phosphorus
uptake.

2. Evaluate three different soil extractants for their
ability to measure the availability of P in soil
which has had rock phosphate applied.

3. Relate growth responses, P uptake and extractable P

to the rock phosphate properties.

LITERATURE REVIEW

Large areas in Ecuador, located in the coastal and
the oriental parts of the country are tropical with
strongly acid soils that are deficient in phosphorus. A
number of experiments conducted in this area using super—
phosphate have found that a lot of the P applied forms
insoluble compounds in the soil and it is necessary to
apply a lot of fertilizer in order to obtain the quantity
of P necessary for plant growth.

Rock phosphate is an inexpensive source of P and it
has a promisory future improving phosphprus availability.
Hammond (15) indicates that broadcast applications of
finely ground rock phosphate can result in increased
yields of many crops grown in P deficient soils, and the
use of more reactive rock phosphate can produce yields
that are economically attractive when compared to those
obtained with the costly superphoshpate.

Howeler and Woodruff (l6) mention that rock phos-
phates are derived from apatite but they can be found as
igneous sedimentary and metamorphic rocks. The igneous
apatites are derived directly from molten magmas and

consit of Ca5(PO4)Cl or Ca5(PO When the fluor-

4’3F‘
apatite is partly calcined, the product is hydroxyapatite,

Ca5(PO4)30H. The sedimentary apatite which is the most
commercially mined rock phosphate is found as amorphous
marine deposits containing mainly fluor- and hydroxy-
apatite, and impurities like calcite clay, quartz and
mono and dicalcium phosphate. The metamorphic rock is
only mined in small quantities.

For many years investigators have done research in
order to measure the effectiveness of different rock
phosphates as sources of P.

Cook (9) indicates that the native and soluble P
applied as fertilizer are available at pH above 6.5 and
rock phosphate is usually more available in slightly acid
soils. Paauw (22) suggested that soil pH needed for a
good efficiency of rock phosphate is too acid for plant
growth. Ellis et al. (13) found that rock phosphate
should be applied to the soil at an acid pH in order to
let acidulation take place and after that soil can be
limed to a most desirable pH.

Barnes and Kamprath (2) limed an acid soil to pH 6.0
before application of rock phosphate and no response to
the addition of the rock was found. They indicated that
at pH 6.0 the soil was uncapable of acidulating the rock
making it more available. These authors also indicate
that not only P availability is influenced when rock phos-
phate reacts with the soil, but also with acidulation Ca
and pH are increased and Al is decreased. All of these

changes depend on the rate of application and in the

efficiency of acidulation of the rock.

Chien (6) concluded that the dissolution of apatites
is stimulated by a driving force, which is H+, and in
acid soils this driving force is provided. Hence, in the
pH range between 3.5 to 6.5 rock phosphate is most
responsive.

Caro and Hill (5) tested particle size, surface
area, exchangeable P and chemical solubility of rock
phosphate against yield and found a good correlation
with citric acid solubility and bound CO3 content of the
apatite. No correlation was found for surface area and
readily exchangeable P.

Bennett et a1. (3) in a greenhouse experiment tested
the availability of seven rock phosphates on two soils
with and without lime. They found some effect of lime and
soil type on the availability of the rocks, but they
concluded that the source of rock phosphate was even more
important. They also found no correlation between fluo-
rine content or specific surface area of the sources of
rock phosphate and their availability to plants. They
concluded that chemical solubility evaluates better than
physical properties the availability of rock phosphate.

Research by Ensminger et al. (12) lead to the conclu-
sion that the effectiveness of rock phosphates varied
widely among soils but was no more than one fourth of

that of superphosphate at the same rate.

Howeler and Woodruff (16) tested the P availability
of Missouri apatite of igneous origin relative to that of
Florida and Arkansas rock phosphate of sedimentary origin.
The absence of carbonate in the Missouri apatite crystal
resulted in a very strong crystaline structure. A green—
house study with corn and soybeans as well as incremental
dissolution with diluted HCl indicated that this source
of rock phosphate releases its P very slowly. The small
degree of crystallinity of the sedimentary rocks allowed
the dissolution more easily.

Barnes and Kamprath (2) comparing North Carolina and
Florida rock phosphates against superphosphate in an acid
soil found that dry weight production and P uptake by
corn were highly correlated with rates of application of
rock. They concluded that North Carolina rock phosphate
was 90 percent as effective as superphosphate, and
Florida was only 25 percent. Chien and Hammond (8)
indicate that corn responded strongly to increased rates
of application of P both from North Carolina and Sechura
rocks. They also found an increase in response with
decreasing granule size.

Paauw (22) testing Gafza and Florida rock phosphates
in an acid humic soil showed that application of rock
phosphate increased the amount of water soluble phosphorus
in the soil. He also concluded that equilibrium is obtain—

ed after a short period of time of contact between the

7

soil and the rock. After that the degree of solubility
change only slightly. Solubility of rock phosphates in
different chemical solutions has been correlated with
their reactivity in soils. Caro and Hill (5), Arminger
and Fried (1), Engelstad et a1. (11), and Lehr and
McCellan (19) concluded that ammonium citrate and citric
acid solubility tests are an effective measure of P
availability.

Lehr and McCellan (19) indicate that in the past
years the basis to select rock phosphate for direct appli—
cation and the analytical methodology used to evaluate
availability of rock phosphates ”have contributed to
erratic patterns of agronomic response." Characterization
studies have demonstrated that apatitic phosphate minerals
change markedly. These authors concluded that the solubi—
lity of rock phosphate is due to structural substitution
of P04 by C03 and F. Accordingly a statistical derived
new model that relates citrate solubility to apatite
composition was obtained; the Absolute Citrate Solubility
index (ACS) and is defined as the ratio of citrate soluble
P O to the theoretical P 0 content of any given rock.

2 5 2 5

ACS = AOAC Citrate solubility P205%

 

Theoretical P205

% of apatite
In this way the authors used the solubility index based
on apatite composition and did not relate "the citrate

soluble P205 as a fraction of the total P205 content

(grade) of the particular rock sample.

It was also found that the length of the ”a" axis
of the apatite unit cell, a0, determined by X-ray diffrac-
tion is statistically related to the ACS by

ACS = 421.4(9.369 - a0)

Greenhouse evaluations were done by Terman et al.

(25) with the principal objective of testing the validity
of the Absolute Citrate Solubility reacting scale. A
range of apatite compositions was used. Response of rice
demonstrated a close agreement between predicted reactivi-
ties of rock phosphates and dry matter production and
phosphorus uptake.

Hammond (15) after his research in Colombiam soils
concluded that rock phosphate can be described as having
high, medium or low reactivity. Citrate soluble P205 in
the range of 5.4 to 6.5 percent of the total rock was
considered high, 3.2 to 3.4 medium and 1.9 to 2.7 low.

The same author also indicated that rock phosphates chosen
for direct application on the basis of citrate solubility
will show erratic and unpredictable crop response unless
applied at high rates. He also concluded that crop
response could be influenced by reduced Al saturation and
increased exchangeable Ca.

Wilson (28) conducted a laboratory study with six
rock phosphates of a wide range of solubility according to
the ACS index, and concluded that North Carolina and

Central Florida rocks are very soluble; Tennessee, India,

and Idaho have a lower solubility; and Missouri rock is
almost insoluble. He also found that with increasing Ca
activity in solution there is decreasing phosphate solubi—
lity. An example was given to illustrate the practical
implications of the Ca activity on the solubility of rock
phosphates. Assuming 50 ppm phosphorus are needed for

plant growth, then this level of available P could be

3 3

obtained with Ca activities of 3.6 x 10‘ M, 6.8 x 10'
M, and 9.1 x 10—3 M for the India, Idaho, and Tennessee
rocks, respectively. Missouri rock phosphate will not
solubilize 50 ppm of P at any practical activity of Ca.

On the other hand North Carolina and Central Florida rocks
will release that amount of P with any practical Ca
activity.

Wilson also concluded that another factor to be
considered before rock phosphate application is the Ca:P
molar ratio. If a wide ratio is present (Missouri rock)
the Ca activity will increase to a larger extent than if
a narrow Ca:P is present in the rock. It is necessary to
take into account not only the solubility of the rock but
also the amount of Ca which will be released.

Smith et al. (24) indicated that no specific attention
has been given to evaluate the P availability of soils
which have had rock phosphate applied. Barnes and
Kamprath (2) mentioned that after rock phosphate applica-
tions the amount of available phosphorus is difficult to

determine.

10

and Idaho have a lower solubility: and Missouri rock is
almost insoluble. He also found that with increasing Ca
activity in solution there is decreasing phosphate solubi—
lity. An example was given to illustrate the practical
implications of the Ca activity on the solubility of rock
phosphates. Assuming 50 ppm phosphorus are needed for

plant growth, then this level of available P could be

3 3

obtained with Ca activities of 3.6 x 10- M, 6.8 x 10—
M, and 9.1 x 10-3 M for the India, Idaho, and Tennessee
rocks, respectively. Missouri rock phosphate will not
solubilize 50 ppm of P at any practical activity of Ca.

On the other hand North Carolina and Central Florida rocks
will release that amount of P with any practical Ca
activity.

Wilson also concluded that another factor to be
considered before rock phosphate application is the Ca:P
molar ratio. If a wide ratio is present (Missouri rock)
the Ca activity will increase to a larger extent than if
a narrow Ca:P is present in the rock. It is necessary to
take into account not only the solubility of the rock but
also the amount of Ca which will be released.

Smith et al. (24) indicated that no specific attention
has been given to evaluate the P availability of soils
which have had rock phosphate applied. Barnes and
Kamprath (2) mentioned that after rock phosphate applica-

tions the amount of available phosphorus is difficult to

determine.

11

Ellis et al. (13) reported that 0.002 M H2504
extracted solubilized unreacted rock phosphate in soils.
Bray and Kurtz (4) developed an extracting solution,

"Bray 1” (0.03 M NH F + 0.025 M HCl), which has been

4
widely used in the determination of available P. Fitts
(14) indicates that "Bray 1” gives results that are high-
ly correlated with crop response to phosphate fertiliza-
tion.

Smith et al. (24) concluded that “Bray 1” appeared
to be a good evaluating method of P availability in
soils to which rock phosphate has been added, and it seems
to measure the release of unavailable phosphorus in rock
phosphate to an available soil form.

Peaslee (23) on the other hand, found a poor corre-
lation between the plant availability coefficient ratio
and ”Bray 1'I extracting coefficient ratio for Iowa soils
to which a Florida rock phosphate had been applied. They
found a better correlation with an anion exchange resin.

Ensminger et a1. (12) referring to the soil extrac—
tants used in evaluating the effectiveness of rock phos-
phate concluded that, since the forms of accumulated P
resulted from superphosphate and rock phosphate may be
quite different, the extractants used were selected
because they tend to be selective in dissolving certain
forms of P. Dilute acids dissolve calcium phosphate, but
are not very effective in dissolving iron and aluminum

phosphate. The opposite is true for neutral ammonium

12

flouride. These authors report that for most of the soils
used in their investigation, neutral ammonium fluoride
extracted considerably less P from the rock phosphate
treated soils than it did from soils that had received

the same amount of P205 from superphosphate. They con-
cluded that much of the rock phosphate had not reacted
with the soil. They also reported that the amount of P
released to an anion exchange resin was related to the
total water soluble P present in the soil.

As cited previously, when Barnes and Kamprath (2)
limed an acid soil to pH 6.0 no response to the addition
of rock phosphate was observed. Soil pH had the same
effect in soil analysis with ”Bray 1". The acid soil had
more available P than the limed soil. On the other hand
the double acid extractant (0.05 M HCl + 0.025 H2804)
extracted the same amount of P from the limed and unlimed
soils.

Chien (7) mentioned that the combination of HCl and
NH4F in "Bray 1” is designed to remove easily acid soluble
forms of P largely calcium phosphates, other than apatite
and a portion of the iron and aluminum phosphates. He
also indicated that in the past many attempts to measure
the available phosphorus with ”Bray 1" on soils treated
with rock phosphate were made in limed soils or neutral to
slightly acid soils, and the rock phosphates were unreac-

tive. Poor results were obtained because "Bray 1" cannot

dissolve the unreacted rock phosphate. The conditions

13

change when acid soils and relatively reactive rock
phosphate are used.

An experiment of incubation, rate of application,
and time of reaction of different rock phosphates was
made by Chien (7) to prove the above statements. The
results of the incubation indicated that incubation
increases the amount of "Bray 1" extractable P from a soil
treated with eight different rocks. The amount of
”Bray 1” extractable P varied with the source of rock
phosphate from 9.6 ppm with Tapira rock phosphate to 93.7
ppm with the North Carolina rock. This represents 1.1 to
11.6 percent of added P.

The results of rate of application were obtained
testing North Carolina and Tennessee rock phosphates which
represent high and low solubility. The amounts of "Bray 1"
extractable P from the North Carolina rock were greater
than those with Tennessee rock, both before and after
incubation. The amount of "Bray 1" extractable P also
increased as the application rates increased.

The time of reaction experiment showed that the
reaction of the rock phosphate with the soil seems to
approach a maximum at about 90 days of incubation at room
temperature.

Since unreacted rock phosphate in the soil may still
be in the original form and only a small portion of added
phosphate was extracted by "Bray 1”, Chien suggested that

a comparison of ”Bray 1” extractable P from the soil

14

treated with rock phosphate before and after incubation
may be used to estimate the P contributed by the unreacted
phosphate rock to the total "Bray 1" extractable phospho—
rus. He concluded that although ”Bray 1” does not signi—
ficantly dissolve the unreacted rock phosphate in the soil
in terms of total phosphorus added, it may dissolve some
and contribute to the total "Bray 1” extractable P. Both
sources, unreacted rock phosphate and reaction products,
can provide available P to the plant, especially in
strongly acid soils with low buffering capacity and if the
rock phosphates are relatively reactive in a short period
of time.

Chien also mentioned that it can be seen in the
literature that many workers report a good correlation
between the reactivities of rock phosphate as measured by
neutral ammonium citrate and plant growth. He tested a
correlation between “Bray 1" extractable P for a soil
treated with eight different rock phosphates, before and
after incubation, and their ammonium citrate solubility.
He found a very good correlation so he suggested that
"Bray 1” extractable P should correlate in the same
fashion with crop response.

Mehlich (21) working with pure North Carolina and
Florida rock phosphates found that, after five minutes of

shaking, the double acid (0.05 M HCl + 0.025 M H 804) and

2
"Bray 2” (0.1 HCl + 0.03 M NH4F) achieve a complete disso—

lution of both rocks. Using 0.025 M HCl 92 percent of the

15

North Carolina rock and 93 percent of the Florida rock
were dissolved. "Bray 1" (0.025 M HCl + 0.03 NH4)
dissolved 43 percent of North Carolina and 27 percent of

Florida rock. 0.05 M NH dissolved 0.3 percent of North

4
Carolina and 0.1 percent of Florida. One hour and over—
night shaking did not give significant change in the

analytical results.

MATER IALS AND METHODS

An experiment with corn grown in three different
soils was conducted in the greenhouse to compare five
different rock phosphates as sources of P. Yield and
total P uptake were obtained to evaluate the response of
the soils to the direct addition of rock phosphates. Three
soil extractants: Bray—l, water soluble, and ammonium
citrate were tested on the three soils and correlated
with yield and total P uptake.

The three Michigan soils used in the experiment are:
Marlette sandy loam, Granby sandy loam, and Tracy sandy
loam. The characteristics of the soils are described in
Table 1.

The five rock phosphates used in this experiment:
Idaho, Central Florida, North Carolina, Tennessee, and
Missouri, were selected to represent a range of P solubi-
lity. They were characterized by Lehr and McCellan (1972).
Missouri rock phosphate is of an igneous origin and the
others are sedimentary. Their P205 content varies from
29.9 to 34.7%. The apatite composition and theoretical

citrate solubility are given in Tables 2 and 3.

16

l7

 

 

Table 1. Soil Properties
Marlette Granby Tracy
Sandy Loam Sandy Loam Sandy Loam
U.S. Classi- Glossoboric Typic Ultic
fication Hapludalf, Haplaquoll Hapludalf
Fine Loamy Sandy, Coarse-Loamy
Mixed Mesic Mixed Mesic Mixed Mesic
Clay (%) 18.4 14.4 16.4
Silt (%) 22.0 13.0 21.0
Sand (%) 59.6 72.6 62.6
pH 6.6 6.9 5.6
Total P
(ppm) 260.0 310.0 400.0
Bray P—l
(ppm) 11.0 25.0 26.0
Exch K
(meg/100gm) 0.087 0.092 0.307
Exch Ca
(meg/100gm) 38.5 82.5 33.4
Exch Mg
(meg/100gm) 3.81 16.66 5.7
Zn (ppm) 2.0 2.0 7.0
Mn (ppm) 10.0 34.0 59.0
Cu (ppm) 1.0 3.0 2.0
Fe (ppm) 20.0 48.0 36.0
C.E.C.
(meg/100gm) 8.85 17.75 7.18
Organic
Matter (%) 1.3 14.82 1.67

 

18

Table 2. ACS Solubility Index*

 

 

 

 

Solubility
5 Index (ACS)

TVA No. Rock Phosphate Source aO x-ray Chemical
MR-464 Central Florida

(Polk County Peeble) 9.345 10.1 14.0
MR—465 Idaho Shale Phosphate 9.356 5.48 9.37
MR—467 North Carolina

clastic phosphorite 9.322 19.8 22.6
MR—468 Tennessee Brown

(Columbia, Tenn) 9.358 5.06 13.7
MR—505 Missouri (by product

concentrate) 9.373 1.20 1.20

 

a: = length of a axis of apatite unit cell.

*From Lehr and McCellan (19)

 

 

 

 

Table 3. Rock Phosphate Composition*

ROCK PHOSPHATE
Compo— Central North ‘ Tennes- Mis— Idaho
nent Florida Carolina see souri
CaO 47.5 48.6 42.3 50.1 46.8
P205 32.7 29.9 30.7 34.7 32.3
F 3.6 3.5 3.2 3.4 3.2
CO2 3.3 5.4 1.4 2.8 2.4
NaZO 0.66 0.99 0.40 0.27 0.96
K20 0.15 0.13 0.65 0.16 0.36
MgO 0.32 0.55 0.28 0.63 0.37
A1203 1.20 0.46 1.40 0.34 1.10
Fe203 1.45 0.68 1.20 2.60 0.44
5102 5.2 1.6 10.00 2.8 5.4
S 0.4 1.1 0.2 0.08 0.9

 

* From Lehr

and McCellan (19)

2O

Greenhouse Experiment

The soils upon arrival at the greenhouse were air-
dried, screened, and mixed. Three kilograms of soil were
weighed into plastic bags. Each of the sources of P was
added to the soils at rates to supply 50, 100, 200, and

400 ppm P mixed, and left to incubate for two months.

205.
Solutions of KNO3, NH4NO3, MnSO4, and ZnSO4 were
applied to the soils to supply 57 mg K/kg, 32 mg N/kg,
3 mg Mn/kg, and 2 mg Zn/kg for the Marlette soil;
57 mg K/kg, 32 mg N/kg, and 2 mg Zn/kg for the Granby soil;
15 mg K/kg, 32 mg N/kgc and 2 mg Zn/kg for the Tracy soil.
All solutions were thoroughly mixed with the soil prior
to planting.
After incubation the soils were transferred to plas—
tic pots and planted with corn, Variety-Pioneer 3780.
Ten seeds were planted per pot and thinned to four plants
per pot 10 days after emergence. The pots were arranged
in a complete randomized design with four replications.
The corn was harvested, oven dried, and weighed

seven weeks after planting. Soil samples were collected

from the pots after harvesting.
Laboratory.Procedures

Plant analysis:
The oven dried plant samples were ground and analyzed

following a digestion of 1.0 gm of plant tissue with a

21

mixture of nitric and percloric acids. The digested
material was diluted to 50 ml with distilled water. P
was analyzed by the use of a Technicon—Autoanalyzer II
(880 nm), employing the ascorbic acid-molybdate colori-
metric method. From the results total P uptake was
calculated.
Soil analysis:

All soil samples were air-dried, ground and sieved
to pass a 20 mesh sieve.

Extractions with Bray 1, water, and ammonium citrate
solutions were made for each soil sample. Bray 1 extract-
able P was extracted for 10 minutes with the Bray 1 solu—

tion (0.03 M NH F + 0.025 M HCl) at a 1:10 soil-solution

4
ratio.

Water soluble P was determined in a 1:10 soil—water
ratio after 10 minutes of shaking. The soil water mixture
was first filtered through a Whatman #40 filter paper and
then spun down for 15 minutes in an International centri—
fuge.

Ammonium citrate extractable P was extracted for one
hour with 0.5 M ammonium citrate at pH 5.5 A 5 ml aliquot
of the extract was dried in a sand bath and ashed in a

muffle furnace at 400°C. The ash was then brought into

solution and analyzed for P (Wilson, 1979).

22

Statistical Analysis

A statistical analysis of variance was conducted for
the data collected from the greenhouse experiment. A
Duncan's Multiple Range Test was used to identify statis-
tical differences between treatments.

Simple correlations were calculated to test associa-
tion between rate of rock phosphate application and yield,
total P uptake, Bray P—l extractable P, water soluble P,
and ammonium citrate extractable P. In the same way corre—
lations of yield and total P uptake with Bray 1 extractable
P, water soluble P, and ammonium citrate extractable P

were also calculated.

RESULTS AND DISCUSSION

Five rock phosphates were evaluated in the green-
house in three different soils using corn as the test
plant.

In Michigan it was difficult to find soils with low
P contents, especially in combination with acid pH. The
soils selected for this study were chosen for their rela—
tive low P content for the region, but only one soil, a
Tracy sandy loam had an acid pH. The other two soils, a
Marlette sandy loam and a Granby sandy loam had 6.6 and
6.9 pH's, respectively (Table 1).

Increasing rates of rock phosphate resulted in differ-
ing growth and total P uptake responses. Average dry
weights and total P uptake values are presented in Tables
4 and 5 for the Marlette soil and in Tables 6 and 7 for the
Tracy soil. An analysis of variance confirmed that statis-
tically significant differences in yield and total P up—
take occurred in response to rock phosphate addition to
these two sandy loam soils. The degree of response in
total P uptake is illustrated by the linear regression
lines in Figures 1 and 2.

According to a Duncan's Multiple Range test for yield
the order of response in the Marlette soil (Table 4) was:

North Carolina rock phosphate (RP) Central Florida RP =

23

24

Tennessee RP Missouri RP Idaho RP. When treated by to—
tal P uptake (Table 5) the order was: North Carolina RP
Central Florida RP = Tennessee RP Idaho RP = Missouri RP.

The Tracy soil showed (Table 6 and 7) North Carolina
RP Central Florida RP = Tennessee RP = Idaho RP = Mis-
souri RP for both yield and total P uptake. In this soil
only North Carolina Rock phosphate is statistically dif—
ferent from the others. Looking at the results it can be
seen that there is a marked increasing trend in yield and
total P uptake with increasing rates of application for
Central Florida rock phosphate. It is also interesting
to observe that for both Marlette and Tracy soils the
trend with the Missouri rock phosphate is negative. As
the rate increases both yield and total P uptake decreases.
This aspect will be discussed later.

The rock phosphates produced responses according to
what was expected on the basis of the absolute citrate
solubility defined by Lehr and McCellan (19). North
Carolina always gave the best response because it was the
most soluble rock. On the other hand Missouri gave no
response because of its low solubility. These results are
also in agreement with those obtained by Wilson (28) in
his laboratory study. He indicated that the pattern in
rock phosphate solubility was North Carolina RP Central
Florida RP Tennessee RP Idaho RP Missouri RP. He con—
cluded that North Carolina and Central Florida rock phos-

phates are highly soluble while Missouri is almost

25

Table 4. Total Yield (Dry Weight) of Corn in the
Greenhouse as Affected by Rate and Source
of Phosphorus in Marlette Sandy Loam Soil.

 

 

 

 

Rate of Application (ppm P205)
50 100 200 400 Average*
g/pot
Idaho Shale
Phosphorite 11.5 12.0 11.6 12.9 12.0 d
Central Florida
(Polk County Peeble) 13.1 15.8 16.2 19.1 16.2 b
North Carolina
Clastic Phosphorite 16.2 19.0 19.6 20.4 18.8 a
Tennessee Brown
(Columbia, Tenn) 12.9 15.4 14.4 16.1 14.7 bc
Missouri (by—pro-
duct concentrate) 13.8 13.7 13.6 12.7 13.4 c

 

* Means with the same letter are not significantly differ-
ent with Duncan's Multiple Range Test (p = .05)

26

Table 5. Total Phosphorus Uptake of Corn in the
Greenhouse as Affected by Rate and Source of
Phosphorus in Marlette Sandy Loam Soil.

 

Rate of Application (PPm P205)

 

 

 

50 100 200 400 Average*
mg/pot

Idaho Shale
Phosphorite 13.2 13.2 15.3 17.4 15.1 c
Central Florida
(Polk County Peeble ) 14.9 18.0 25.3 37.1 22.6 b
North Carolina
Clastic Phosphorite 19.6 26.4 39.4 45.6 32.8 a
Tennessee Brown
(Columbia, Tenn) 15.8 18.3 17.0 18.2 17.3 bc
Missouri (by—pro—
duct concentrate) 14.3 13.8 13.1 12.0 13.3 c

 

* Means with the same letter are not significantly differ-
ent with Duncan's Multiple Range Test (p = .05)

27

Table 6. Total Yield (Dry Weight) of Corn in the
Greenhouse as Affected by Rate and Source of
Phosphorus in Tracy Sandy Loam Soil.

 

 

 

 

Rate of Application (Ppm P205)
50 100 200 400 Average*
g/pot

Idaho Shale
Phosphorite 8.1 7.5 8.7 9.1 8.3 b
Central Florida
(Polk County Peeble) 8.4 8.0 9.4 10.5 9.1 b
North Carolina
Clastic Phosphorite 12.0 11.2 12.8 11.1 11.8 a
Tennessee Brown
(Columbia, Tenn) 7.6 7.2 7.8 7.9 7.6 b
Missouri (by—pro—
duct concentrate) 7.7 7.6 8.5 8.2 8.0 b

 

* Means with the same letter are not significantly differ-
ent with Duncan's Multiple Range Test (p = .05)

Table 7.

28

Total Phosphorus Uptake of Corn in the

Greenhouse as Affected by Rate and Source
of Phosphorus in Tracy Sandy Loam Soil.

 

 

 

 

Rate of Application (ppm P205)
50 100 200 400 Average*
mg/pOt

Idaho Shale
Phosphorite 7.0 7.2 7.9 8.8 7.7 b
Central Florida
(Polk County Peeble) 7.6 7.9 10.4 13.6 9.9 b
North Carolina
Clastic Phosphorite 14.3 18.1 23.9 21.4 19.4 a
Tennessee Brown
(Columbia, Tenn) 6.4 6.0 6.3 7.5 6.6 b
Missouri (by-pro—
duct concentrate) 6.2 6.5 6.3 6.0 6.3 b

 

* Means with the same letter are not significantly differ-
ent with Duncan's Multiple Range Test (p = .05)

29

insoluble. The results obtained with the Marlette and
Tracy soils study indicate that the more soluble the rock
phosphate the greater the crop response to the direct
application of rock phosphate.

In contrast to the Marlette and Tracy soils none of
the rock phosphate materials produced a significant re—
sponse in yield or total P uptake when applied to the
Granby soil (Tables 8 and 9). The neutral pH and the high
amount of exchangeable Ca may have had an adverse effect
on the availability of P from the rock sources.

When rock phosphate is used as a P source in direct
application on soils, it is necessary to look for a good
soil extractant which can evaluate the real P availability
reflected in a concommitant crop response. Thomas and
Peaslee (26) mention that "when selecting a soil extractant
one should always consider the degree of correlation of
the extractant with plant response to soil and fertilizer
P”.

In this study, the degree of correlation between
rate and yield, total P uptake, Bray — 1 extractable P,

water soluble P and ammonium citrate extractable P was
calculated (Tables 10, 11, 12). The Marlette (Table 10)
and Tracy (Table 11) soils showed a high degree of associa-
tion between rate and all the variables tested for North
Carolina and Central Florida rock phosphates. In the
Tennessee and Idaho rock phosphates the correlations were

poor, while the Missouri rock phosphate gave a negative

Table 8.

30

Total Yield (Dry Weight) of Corn in the

Greenhouse as Affected by Rate and Source
of Phosphorus in Granby Sandy Loam Soil.

 

 

 

 

Rate of Application (ppm P205)
50 100 200 400 Average*
g/pot

Idaho Shale
Phosphorite 8.9 8.1 8.9 9.9 8.9 a
Central Flofida
(Polk County Peeble) 9.3 9.6 9.2 10.3 9.6 a
North Carolina
Clastic Phosphorite 10.1 8.8 10.2 10.1 9.8 a
Tennessee Brown
(Columbia, Tenn) 10.7 9.3 10.3 10.2 10.1 a
Missouri (by—pro-
duct concentrate) 10.3 10.1 11.0 9.4 10.2 a

 

* Means with the same letter are not significantly differ—
ent with Duncan's Multiple Range Test (p = .05)

Table 9.

31

Total Phosphorus Uptake of Corn in the

Greenhouse as Affected by Rate and Source
of Phosphorus in Granby Sandy Loam Soil.

 

Rate of Application (ppm P205)

 

 

 

50 100 200 400 Average*
mg/pot

Idaho Shale
Phosphorite 8.2 7.4 7.5 9.3 8.1 a
Central Florida
(Polk County Peeble) 8.8 10.1 9.1 9.8 9.4 a
North Carolina
Clastic Phosphorite 10.3 8.5 9.1 10.0 9.5 a
Tennessee Brown
(Columbia, Tenn) 10.7 8.4 11.1 8.9 9.8 a
Missouri (by-pro—
duct concentrate) 9.5 9.1 9.1 8.7 9.1 a

 

* Means with the same letter are not significantly differ-
ent with Duncan's Multiple Range Test (p = .05)

32

Table 10.
Dry Weight, Bray-1,

Correlation Coefficients for P Rate,
Extractable P, Water

P Uptake,

Soluble P and Ammonium Citrate Extractable P in
Various Combinations for the Marlette Soil.

 

Uptake Dry

Weight

Ammonium
Citrate

Water
Soluble

Bray
P-l

 

mg P/POt gm/pot
Idaho

Rate (mg PZOS/kg) 0.49 0.09
Uptake (mg P/pot)

Dry Weight (gm/pot)

———————mg P/kg soil——-

Central Florida

Rate (mg PZOS/kg) 0.95
Uptake (mg P/pot)

Dry Weight (gm/pot)

North Carolina

Rate (mg PZOS/kg) 0.95 0.80
Uptake (mg P/pot)
Dry Weight (gm/pot)

Tennessee
Rate (mg PZOS/kg) 0.52 0.58
Uptake (mg P/pot)
Dry Weight (gm/pot)

Missouri

-0.44 0.07

Rate (mg PZOS/kg)
Uptake (mg P/pot)

Dry Weight (gm/pot)

0.30 0.03 0.53
0.05 0.22 0.32
0.13 0.20 0.31
0.77 0.92 0.93
0.75 0.94 0.94
0.58 0 85 0.83
0.97 0.96 0.97
0.96 0.92 0.90
0.81 0.78 0.70
0.73 0.52 0.48
0.10 0.45 0.55
0.10 0.49 0.60
—0.65 0.01 0.25
0.05 0.19 0.07
0.23 0.24 0.31

 

33

Table 11. Correlation Coefficients for P Rate, P Uptake,
Dry Weight, Bray-1, Extractable P, Water
Soluble P and Ammonium Citrate Extractable P in
Various Combinations for the Tracy Soil.

 

Uptake Dry Bray Water Ammonium
Weight P—1 Soluble Citrate

 

mg P/pot gm/pot ——————-mg P/kg

Idaho SOil
Rate (mg PZOS/kg) 0.74 0.48 0.11 0.04 0.59
Uptake (mg P/pot) 0.03 0.28 0.21
Dry Weight (gm/pot) 0.04 0.25 0.08
Central Florida
Rate (mg PZOS/kg) 0.97 0.84 0.96 0.64 0.98
Uptake (mg P/pot) 0.91 0.63 0.93
Dry Weight (gm/pot) 0.79 0.50 0.84
North Carolina
Rate (mg PZOS/kg) 0.75 0.46 0.99 0.89 0.99
Uptake (mg P/pot) 0.80 0.85 0.67
Dry Weight (gm/pot) 0.46 0.56 0.37
Tennessee
Rate (mg PZOS/kg) 0.49 0.29 0.69 0.53 0.79
Uptake (mg P/pot) 0.25 0.26 0.22
Dry Weight (gm/pot) 0.05 0.12 0.17
Missouri
Rate (mg PZOS/kg) -0.31 0.35 -0.05 0.01 0.05
Uptake (mg P/pot) 0.15 0.01 0.01

Dry Weight (gm/pot) 0.03 0.03 0.01

 

34

Table 12. Correlation Coefficients for P Rate, P Uptake,
Dry Weight, Bray-1, Extractable P, Water
Soluble P and Ammonium Citrate Extractable P in
Various Combinations for the Granby Soil.

 

Uptake Dry Bray Water Ammonium
Weight P-l Soluble Citrate

 

 

mg P/pot gm/pot -——————mg P/kg

Idaho 5011
Rate (mg PZOS/kg) 0.14 0.03 0.08 0.28 0.79
Uptake (mg P/pot) 0.32 0.21 0.14
Dry Weight (gm/pot) 0.33 0.13 0.13
Central Florida
Rate (mg PZOS/kg) 0.02 0.18 0.18 0.63 0.73
Uptake (mg P/pot) 0.04 0.03 0.07
Dry Weight (gm/pot) 0.09 0.04 0.18
North Carolina
Rate (mg PZOS/kg) 0.03 0.13 0.98 0.43 0.97
Uptake (mg P/pot) 0.04 0.11 0.01
Dry Weight (gm/pot) 0.09 0.04 0.18
Tennessee
Rate (mg PZOS/kg) 0.10 0.06 0.43 0.23 0.33
Uptake (mg P/pot) 0.08 0.07 0.18
Dry Weight (gm/pot) 0.04 0.03 0.13
Missouri
Rate (mg PZOS/kg) —0.22 -0.08 —0.27 0.23 0.28
Uptake (mg P/pot) 0.14 0.12 0.35

Dry Weight (gm/pot) 0.08 0.13 0.05

 

35

correlation when comparing rate vs. total P uptake

—0.44), and rate vs. Bray — 1 extractable P

(r

(r —0.65).
Increasing rates of North Carolina rock phosphate
applied on the Marlette soil correlated well with all the
variables (Table 10): yield, r = 0.08: total P uptake,
r = 0.95; Bray - 1 extractable P, r = 0.97; water soluble
P, r = 0.96: and ammonium citrate extractable P, r = 0.97.
Similar correlations in the Tracy soil (Table 11) were:
yield, r = 0.46; total P uptake, r = 0.75; Bray —1 extract—
able P, r = 0.99: water soluble P, r = 0.89; and ammonium
citrate extractable P, r = 0.99.

. With the Central Florida rock phosphate the results
are quite similar to those of North Carolina in both
Marlette and Tracy soils. Increasing rates of Tennessee
rock phosphate showed an appreciable correlation with
Bray - 1 extractable P, r = 0.73 for the Marlette soil and
r = 0.69 for Tracy soil, Chien (7) obtained similar results
when he tested Bray — 1 as an extractant in soils applied
with increasing rates of North Carolina and Tennessee rock
phosphates. He concluded that Bray — 1 estimates P availa—
bility although the extractant does not dissolve all the
unreacted rock phosphate in the soil in terms of P added,
but it can dissolve some unreacted rock as well as reaction
products of the dissolved rock.

As mentioned before the correlations of rate against

all the variables with North Carolina and Central Florida

36

rocks are quite similar. A significant statistical
difference was found in the greenhouse. This difference
in response due to the difference in solubility is not
reflected in the correlation coefficients but in the
absolute values of the variables. (Appendix Tables I, II,
III). For the 400 ppm P205 rate in the Marlette soil
(Appendix I) the North Carolina rock produced an average
yield of 20.4 gm/pot while Central Florida produced
19.5 gm/pot. Total P uptake with North Carolina RP was
42.6 mg P/pot and was 32.1 mg P/pot with Central Florida
RP. Bray - 1 extractable P was 55.7 ppm P with North
Carolina RP and 29.5 ppm P with Central Florida RP. Water
soluble P was 4.9 ppm P with North Carolina RP and 1.9 ppm
P with Central Florida RP. Ammonium citrate extractable P
was 202.2 ppm P with North Carolina RP and 97.5 ppm P with
Central Florida RP.

The same effect was observed in the Tracy soil (Appen—
dix II). Respective values for North Carolina and Central
Florida rock phosphates were: yield 11.1 and 10.6 gm/pot:
total P uptake 21.4 and 13.6 mg P/pot; Bray - 1 extractable
P 42.2 and 19.0 ppm P; water soluble P 2.4 and 0.8 ppm P:
ammonium citrate extractable P 186.0 and 82.5 ppm P. For
both Marlette and Tracy soils total P uptake evaluated the
availability of P from rock phosphates better than yield.

In the Granby soil (Table 12, as expected because of
the lack of response to rock phosphate additions, almost

all correlations were very poor. A significant correlation

37

between rate of application and ammonium citrate extract—
able P was found for North Carolina, Central Florida, and
Idaho rock phosphates with correlation coefficients of
0.97, 0.73 and 0.79, respectively. This indicates that
ammonium citrate is dissolving unreacted rock phosphate.
The correlation for rate of application vs. Bray - 1
extractable P proved to be significant in this soil only
for North Carolina rock phosphate, r = 0.98. This indi—
cates that Bray — 1 solution is dissolving some of the
unreacted rock phosphate, and this fraction is related to
the rate of application.

The Missouri rock phosphate applied on the Marlette
soil (Table 10 and Figure 1) showed a negative correlation
for rate vs. uptake, r = -0.44, and for rate vs. Bray - 1
extractable P, r = -0.65. In the Tracy soil (Table 11 and
Appendix II) the negative trend can be seen but the corre—
lations are very poor. Theses results, especially on the
Marlette soil, agree with the results obtained by Wilson
(28) in his laboratory study. He concluded that increas-
ing amounts of Ca activity in the soil solution decreases
the solubility of rock phosphate, and the use of a rock
phosphate with a wide Ca:P molar ratio like Missouri (20:1)
would add a larger amount of Ca to the solution upon
dissolution than release of P. In this way, increasing
rates of Missouri rock phosphate increased the Ca activity

in the soil solution resulting in decreased phosphate

38
solubility, and as a consequence a decreased total P
uptake.

Yield and total P uptake were correlated against
Bray - 1 extractable P, water soluble P, and ammonium
citrate extractable P. (Tables 10, 11, 12). Significant
associations were found with North Carolina and Central
Florida rock phosphate for all the variables in the Mar—
lette and Tracy soils. In all cases total P uptake rather
than yield gave the better correlation. The relationships
between total P uptake and Bray — 1 water soluble, and
ammonium citrate extractable P for Marlette and Tracy soils
are shown in Figures 3 and 14 where either North Carolina
or Central Florida rock phosphate was applied. Comparing
the regression equations for water soluble P versus total P
uptake (Figures 7, 8, 9, 10) reveals that all data points
fall along a common regression line. The slopes and
intercepts of all four regression equations are quite
similar. Comparing the regression equations for Bray — 1
and ammonium citrate extractable P reveals a less clear
picture. The slopes and intercepts are quite variable
between soils.

In the Granby soil no significant relationships
existed between any of the extractants and total P uptake
regardless of rock phosphate source. Hence, writing
regression equations would be meaningless. Even with the
poor correlations it was apparent that values obtained with

the Granby soil were related to a regression line different

39

from that for the Marlette and Tracy soils.

North Carolina and Central Florida rock phosphates,
when applied on Marlette and Tracy soils, gave a response
which correlated with all of the extractants tested. The
difference between extractants is the amount of P they
extracted from the soils. (Appendix I, II, III). Water
soluble P ranged from 0.23 to 0.58 ppm P in the check
samples which is relatively high because the soils before
rock phosphate application had an appreciable amount of P
(Table 1). However, response to the addition of North
Carolina and Central Florida rock phosphates in the Mar-
lette and Tracy soils was evident. These two rock phos-
phates are soluble enough to increase the amount of water
soluble P which is readily available to the plant.

Bray - 1 extractable P is extracting the native P in
the soil and the reaction products of the solubilized rock
phosphate. Barnes and Kamprath (2) after their study with
North Carolina and Central Florida rocks concluded that
corn yield correlates well with Bray - 1 extractable P.
They also mentioned that as the dissolution of rock phos-
phate is a slow process, the amount of P extracted with
Bray - 1 is only a very small fraction of the total P
applied.

On the other hand, the amount of P extracted by

ammonium citrate is the largest for all extractants used,

with both North Carolina and Central Florida rock phosphate

40

treatments. At the rate of 400 ppm P of North

205
Carolina rock approximately 80% of the P applied is
extracted, and with Central Florida rock the average
amount extracted for all three soils was 20%. These
results indicate ammonium citrate is dissolving an appre-
ciable amount of unreacted North Carolina rock phosphate.

The rate of solubilization of Idaho, Tennessee, and
Missouri rock phosphates was not high enough to give a
response in yield or total P uptake. Also, their small
solubilities could not be detected in the three soils when
extracted with ammonium citrate.

Using ammonium citrate directly as a soil extractant
on soils fertilized with rock phosphate the amount of
soluble rock phosphate can be detected. The effectiveness

of this extractant in evaluating the available P is relat-

ed to the solubility of the rock phosphate applied.

50

45

mg Plpot
u
u

3

8

TOTAL P UPTAKE,

3

IO

41

      

North Carolina
y: I5.82+0.08x
" r= 0.95
_. Control Florida

y=I4.02+0.05x
I'= 0.95

Tomaso“

Y=I4.98+O.le
r=0.52

Idaho
y=l3.90+0.008x
no.» #

Y=I4.39-O.le
H“ 0.44

l l 1 4]

 

O 30 I00 200 400
RATE OF ROCK PHOSPHATE APPLICATION, mg P205!“

Figure 1. Relationship between the rate of rock phosphate

application and total P uptake in Marlette soil.

2’4

20

I4

TOTAL P UPTAKE, maP/pot

42

 
  
 

Norm Corollno
.. Y=IO.36+0.04X
r. 0.75

  

Control Fiorldo
v: 6.33+0.02x
T: 0.97

 
 
  
  
 

ldoho
y=6.38+0.0lx
T: 0.74

  
   

 

 

 

TCMIIICCC
F 6.02 40.003)!
"0.49
i n 1 A
O 50 IOO 200 400

RATE OF ROCK PHOSPHATE APPLICATION, mo Pans/Ito

Figure 2. Relationship between the rate of rock phosphate

application and total P uptake in Tracy soil.

EXTRACTABLE P. M PM

BRAY'I

58

53

 

 

43

3: 817+ 0.98::
T=O.96

l A I l I l n L I l 4

I4 I8 22 28 30 34 38 42 48 80
TOTAL P UPTAKE, my Plpol

Figure 3. Relationship between total P uptake and Bray-1

extractable P for North Carolina rock phosphate'
in Marlette soil.

45-

8 8 3 3

EXTRACTABLE P, mg Plkq

G
I

BRAY-I

IO'

 

Figure 4.

44

y: l.48+l.35x
r=O.8O

I L l

5 IO I5

TOTAL P UPTAKE, mo Plot"

1 I

20 25

Relationship between total P uptake and Bray-1
extractable P for North Carolina rock phosphate

in Tracy soil.

30 r

28

N
b

GRAY-I EXTRACTABLE P, mg Plkg
N
N

N
O

 

Figure 5.

 

45

Y= I6.03+O.36x o ,
r=0.75

l l 1 l . l I 3

l2 IS 20 24 28 32 36
TOTAL P UPTAKE, mg P/pot

Relationship between total P uptake and Bray-1
extractable P for Central Florida rock phosphate
in Marlette soil.

 

46

y=4.88+l.02x .
r=O.9I

 

A l l l 1 l I I L l J

 

20-
I9-
l8”
I7 -
a)
.8
\
“to--
a)
E
rm-
'5'
.n I4 '
Id
5
.¢ I3 '
C?
F'
X ..
“:2
,1”-
.‘
a:
”'0!-
P
9..
t
Figure 6.

4 5 6 7 8 9 IO II I2 H3 I4
TOTAL P UPTAKE, mo Plpoi
Relationship between total P uptake and Bray-1

extractable P for Central Florida rock phos-
phate in Tracy soil.

47

44 -
o

4.0 - =-O.87+O.lx
r=0.92

3.8

3.2

WATER EXTRACTABLE P, mg PIKQ
53 :' :- '° I“ I“
o N a b o o

9
(b

 

 

o .1 L .1 I L. L L I # I I
I

I4 IO 22 26 3O 34 36 42 46 60
TOTAL P UPTAKE, mg Plpol .

Figure 7. Relationship between total P uptake and water
soluble P for North Carolina rock phosphate in

Marlette soil.

48

3.2 r

y=*O.84+O.II
|’=O-85

my PIN
:- r- Iv go
N G 'o «b
O

WATER, EXTRACTABLE P,

o
a
U

0.4 ’

 

 

 

o ”i I l l l J
8 I2 I 8 20 24

TOTAL P UPTAKE, mg Plpot
Figure 8. Relationship between total P uptake and water'

soluble P for North Carolina rock phosphate in
Tracy soil.

49

2.0 - ’3'0.5040.07K
r: 0.94

WATER EXTRACTABLE P, M PIIIg

 

 

0 LA‘; . I I I I . I #1
I2 I6 20 24 26 32 36
TOTAL P UPTAKE , mg Plpot

 

Figure 9. Relationship between total P uptake and water

soluble P for Central Florida rock phosphate
in Marlette soil.

LO

0.8

0-8

0.7

m9 PI kg

0.6

O
in

(14

(13

WATER E X TRAC TABLE P,

0.2

DJ

50

fi-O.I9+0.06x
I: 0.63 o

 

 

 

o O ‘ 9
v# I I J J I I I I 1 I
8 7 8 9 I0 II I2 I3 I4

TOTAL P UPTAKE, mg PJpoI

Figure 10. Relationship between total P uptake and water

soluble P for Central Florida rock phosphate
in Tracy soil.

200

no PI In
8 3 8 3 3

Q
o

ANNOHIUM CITRATE EXTRACTABLE P,
O
O

«I.
0

Figure

51

' ys-7.72+3.83x
"IO-80

 

 

 

I
L; I I I I I I I I I I
I

I4 I. 22 26 30 34 36 42 46 60
TOTAL P UPTAKE, mg Nut

11. Relationship between total P uptake and
ammonium citrate extractable P for North
Carolina rock phosphate in Marlette soil.

52

200 r o
O
0
I80 ' FT I3.37+ 5.62:
I: 0.67 0
G
g I60 -
O
E
. PHD-
0.

I20

I00

80

80

4O

AHMOHIUM CITRATE EXTRACTABLE

 

 

o [I I I I I _I

8 I2 I6 20 24
TOTAL P UPTAKE, mg P/pol

Figure 12. Relationship between total P uptake and
ammonium citrate extractable P for North
Carolina rock phosphate in Tracy soil.

 

 

53

 

I00 " o o
:3 ° 0
a 1:24.6402J8X
a ”0.90
a so I-
of
MI
.J
O
.‘E
0 80 "'
I<
K
P)
X
III
I3 70 -
.¢
8
I:
0
II
:3 so -
2
CI
1:
2i
1<

50 "

I2 I8 20 24 28 32 36

Figure 13.

TOTAL P UPTAKE, mg Wpot

Relationship between total P uptake and
ammonium citrate extractable P for Central
Florida rock phosphate in Marlette soil.

54

9OIT

80 . ’3'l4.|4§6.7°X o
r= 0.93

AUMOHIUN CITRATE EXTRACTABLE P, mo Plkg

 

 

a
LL I I I I I I I I J
I

6 7 6 9 IO II I2 I3 [4
TOTAL P UPTAKE, mg Plpot

 

Figure 14. Relationship between total P uptake and
ammonium citrate extractable P for Central
Florida rock phosphate in Tracy soil.

LIST OF REFERENCES

10.

LIST OF REFERENCES

Arminger, W. H., and M. Fried. 1957. "The Plant
Availability of Various Sources of Phosphate
Rock." Soil Sci. Soc. Amer. Proc. 21:183-188.

Barnes, J. S., and E.S. Kamprath. 1975. Availability
of North Carolina Rock Phosphate Applied to Soils.
North Carolina Experimental Station Tech. Bull.
No. 229.

Bennett, 0. L., L. E. Ensminger, and R. W. Pearson.
1957. ”The Availability of Phosphorus in Various
Sources of Rock Phosphate as Shown by Greenhouse
Studies.” Soil Sci. Soc. Amer. Proc., 21:521-524.

Bray, R. N., and L. T. Kurtz. 1945. "Determination
of Total, Organic, and Available Forms of
Phosphorus in Soils." Soil Science, 59:39-45.

Caro, J. H., and W. L. Hill. 1956. "Characteristics
and Fertilizer Value of Phosphate Rock from
Different Fields." Jour. Aqr. and Food Chem.,
4:684-687.

Chien, S. H. 1977. "Thermodynamic Considerations on
the Solubility of Phosphate Rock.” Soil Science,
123:117—121.

Chien, S. H. 1977. "Interpretation of Bray I Extract-
able Phosphorus from Acid Soil Treated with
Phosphate Rock.” Soil Science, 126:34-39.

Chien, S. H., and L. L. Hammond. 1978. "A Simple
Chemical Method for Evaluating the Agronomic
Potential of Granulated Phosphate Rock." Soil
Sci. Soc. Amer. Proc., 42:615—617.

Cook, R. L. 1935. "Divergent Influence of Degree of
Base Saturation of Soils on the Availability of
Native, Soluble, Rock Phosphates." Amer. Soc. of

AQEQflo: 27:279-311.
Chu, C. R., W. W. Moschler, and G. W. Thomas. 1962.

”Rock Phosphate Transformations in Acid Soils.”
Soil Sci. Soc. Amer. Proc., 26:476—478.

55

ll.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

56

Engelstad, O. P., A. Jugsujinda, and S. K. DeDatta.
1974. "Response by Flooded Rice to Phosphate
Rocks Varying in Citrate Solubilities.“ Soil
Sci. Soc. Amer. Proc., 38:524-529.

Ensminger, L. E., R. W. Pearson, and W. H. Arminger,
1967. Effectiveness of Rock Phosphate as a
Source of Phosphorus for Plants, USDA-ARS Bull.
No. 41-125.

Ellis, R. M., M. A. Quader, and E. Truog. 1955.
"Rock Phosphate Availability as Influenced by
Soil pH.“ Soil Sci. Soc. Amer. Proc., 19:484-
487.

 

Fitts, S. W. 1956. Soil Tests Compared with Field,
Greenhouse, and Laboratory Results. North
Carolina Agric. Exp. Station Tech. Bull. No. 121.

 

 

Hammond, L.L. 1975. Effectiveness of Phosphate Rocks
in Columbian Soils as Measured by Crop Response
and Soil Phosphorus Levels. Ph. D. Thesis,
Michigan State University, p. 193.

 

 

Howeler, R. H., and C. M. Woodruff. 1968. ”Dissolu-
tion and Availability to Plants of Rock Phosphate
of Igneous and Sedimentary Origin." Soil Sci.
Soc. Amer. Proc., 32:79—81.

 

Jackson, M. L. 1958. Soil Chemical Analysis.
Prentice—Hall, Inc., Englewood Cliffs, N. J.

Joos, L. L., and C. A. Black. 1950. "Availability of
Phosphate Rock as Affected by Particle Size and
Contact with Bentonite and Soil of Different pH
Values.” Soil Sci. Soc. Amer. Proc., 15:69-75.

Lehr, J. R., and G. H. McCellan. 1972. A Revised
Laboratory Reactivity Scale for Evaluating Phos—
phate Rocks for Direct Application. Tennessee
Valley Authority Bulletin Y—43, Muscle, Shoals,
Al.

 

Lindsay, W. L., and E. C. Moreno. 1960. "Phosphate
Phase Equilibria in Soils.” Soil Sci. Soc. Amer.
Proc., 24:177—182.

Mehlich, A. 1978. ”Influence of Fluoride Sulfate, and
Acidity on Extractable Phosphorus, Calcium,
Magnesium, and Potassium." Comm. Soil Sci. Plant
Ana1., 9(6):455-476.

22.

23.

24.

25.

26.

27.

28.

57

Paauw, F. van der. 1965. "Factors Controlling the
Efficiency of Rock Phosphates for Potatoes and
Rye on Humic Sandy Soils.” Plant and Soil,
22:81-98.

 

Peaslee, D. A., C. A. Anderson, G. R. Burns, and C. A.
Black. 1962. "Estimation of the Reactive Value
of Rock Phosphate and Superphosphate to Plants
and Different Soils.” Soil Sci. Soc. Amer. Proc.,
26:566-570.

 

Smith, H. F., B. G. Ellis, and J. Grava. 1957. "Use
of Fluoride Solutions for the Extraction of
Available Phosphorus in Calcareous Soils and in
Soils to which Rock Phosphate Has Been Added.”
Soil Sci. Soc. Amer. Proc., 21:400-404.

Ternam, G. L., S. E. Allen, and O. P. Engelstad. 1970.
"Response by Paddy Rice to Rate and Sources of
Applied Phosphorus." Aqr. Journal, 62:390-396.

Thomas, G. W., and D. E. Peaslee. 1973. "Testing
Soils for Phosphorus." In Soil Testing and
Plant Analysis. L. M. Walsh, and J. D. Beaton,
editors. Soil Science Society of America,
Madison, Wisconsin.

Watanabe, F. S., and S. R. Olsen. 1965. ”Test of an
Ascorbic Acid Method for Determining Phosphorus
in Water and NaHCO3 Extracts from the Soil."
Soil Sci. Soc. Amer. Proc., 29:677-678.

 

Wilson, M. A. 1979. Solubility of Rock Phosphates
as Influenced by Calcium Ion Activity in Solutiony
and Surface Area. Master Thesis, Michigan State
University, p. 39.

 

APPENDIX

58

APPENDIX I. Results and Experimental Data of Marlette
Sandy Loam Soil*

 

 

 

 

Rate Uptake Dry Bray Water Ammonium
Weight P-1 Soluble Citrate
mg P205/ mg P/pot gm/pot mg P/kg
kg Idaho
0 14.2 12.4 22.5 57.0
50 13.9 11.5 16.2 57.5
100 13.6 12.0 16.2 62.5
200 15.3 11.5 18.5 60.5
400 17.4 12.9 19.7 65.0
Central Florida
0 14.2 12.4 22.5 57.0
50 14.9 13.1 18.7 54.2
100 18.0 15.8 20.5 60.5
200 25.3 16.2 27.7 80.0
400 32.0 19.5 29.5 97.5
North Carolina
0 14.2 12.4 22.5 57.0
50 19.5 16.2 23.5 45.0
100 26.3 19.0 33.5 78.7
200 39.4 19.6 42.7 115.2
400 45.6 20.3 55.7 202.2
Tennessee
0 14.2 12.4 22.5 57.0
50 15.8 12.8 23.2 59.2
100 18.3 15.4 22.7 61.0
200 16.9 14.3 23.7 57.0
400 18.2 16.0 25.0 66.2
Missouri

0 14.2 12.4 22.5 57.0
50 14.3 13.8 24.2 60.5
100 13.8 13.6 22.5 66.2
200 13.0 13.5 21.0 59.2
400 12.0 12.6 19.2 61.7

 

* Average of Four Replications

59

APPENDIX II. Results and Experimental Data of Tracy
Sandy Loam Soil*

 

 

 

Rate Uptake Dry Bray Water Ammonium
Weight P—l Soluble Citrate
mg P205/ mg P/pot gm/pot mg P/pot
kg Idaho
0 7.4 10.8 28.1
50 8.0 10.2 23.5
100 7.5 11.5 34.7
200 8.6 11.0 34.0
400 9.0 11.0 36.5
Central Florida
0 7.4 10.8 28.1
50 8.3 11.0 31.5
100 8.0 14.0 42.5
200 9.4 15.0 50.0
400 10.5 19.0 82.5
North Carolina
0 7.4 10.8 28.1
50 12.0 15.2 36.0
100 11.1 21.0 55.5
200 12.8 29.7 95.5
400 11.0 42.2 186.0
Tennessee
0 7.4 10.8 0 2 28.1
50 7.5 12.0 0 4 26.7
100 7.1 12.7 0 6 32.2
200 7.8 13.7 0.5 37.2
400 7.9 13.2 0.7 39.7
Missouri
0 7.4 10.8 0 2 28.1
50 7.7 11.0 0 3 36.7
100 7.6 11.2 0 4 28.7
200 8.5 10.7 0.3 29.2
400 8.1 11.0 0.4 30.0

 

* Average of Four Replications

60

APPENDIX III. Results and Experimental Data of Granby
Sandy Loam Soil*

 

 

 

 

Rate Uptake Dry Bray Water Ammonium
Weight P—l Soluble Citrate
mg P205/ mg P/pot gm/pot mg P/kg
kg Idaho
0 9.7 18.7 34.5
50 8.9 20.5 32.0
100 8.1 19.5 33.2
200 8.9 20.0 36.5
400 9.9 18.7 45.0
Central Florida
0 9.7 18.7 34.5
50 9.3 19.0 38.5
100 9.6 19.2 55.5
200 9.1 20.7 51.7
400 10.3 19.7 62.5
North Carolina
0 9.7 18.7 34.5
50 10.1 24.5 48.0
100 8.8 29.0 63.7
200 10.1 35.7 103.5
400 10.0 49.5 172.4
Tennessee
0 9.7 18.7 34.5
50 10.6 24.0 33.2
100 9.3 23.0 40.5
200 10.2 22.2 41.7
400 10.2 22.5 36.5
Missouri

0 9.7 18.7 34.5
50 10.3 20.7 40.5
100 10.1 20.7 39.7
200 10.9 21.5 38.7
400 9.4 20.0 37.0

 

* Average of Four Replications

"IIIIIILIIIIIIIIIIIIIIII