A STUDY OF THE BEHAVIOR OF FUSE!)
POTASSiUM PHOSPHATE EN ‘50".

M for the Doom. 0! Ph. D.
MICHIGAN STATE WWW
Rat-nan G. Manon
1960

 

 

This is to certify that the
thesis entitled

A STUDY OF THE BEHAVIOR OF FUSED POTASSIUM

PHOSPHATES IN SOIL

presented by

Raman G. Menon
has been accepted towards fulfillment

of the requirements for

Ph,D, degree in Soil Science '

24M: 07%

Major professor

Date NW «11! "7‘20 9“

0-169

LIBRARY

Michigan State
University

 

 

 

A STUDY OF THE BEHAVIOR OF FUSED POTASSIUM

PHOSPHATES IN SOIL

by

Raman G. Menon

AN ABSTRACT

Submitted to the School for Advanced Graduate Studies of
Michigan State University of Agriculture and
Applied Science in partial fulfillment of

the requirements for the degree of

DOCTOR OF PHILOSOPHY

Department of Soil Science

1960

Approved QKZ~L&1 CE/QJJidtgwmx

2

RAMAN G. MENON ABSTRACT

Experiments were conducted in the laboratory, green—
house, and field with various sized particles of potassium-
calcium pyrophosphate and potassium metaphosphate to study
the behavior of these fused phosphates in soil.

Greenhouse studies involving the effect of different
placement and particle size of the fused potassium phosphates
on the growth and potassium absorption by field bean and
Proso millet plants were conducted in several soils in 1957
and 1958. With Metea sandy loam, there was no significant
increase in growth of beans as affected by particle size
of the fertilizer or percent water soluble potassium content
of the potassium carrier. On Houghton muck soil the appli-
cation of finely divided potassium metaphosphate in mixed
placement resulted in improved growth of bean plants and
more plant uptake of potassium.

On Kalamazoo sandy loam soil, application of potassium
metaphosphate and potassium pyrophosphate materials produced
significantly higher yields of millet than potassium chloride
applications. Banding of the potassium sources was more
effective than mixed placement the potassium content of plants
increased with an increase in water soluble potassium con—
tent of the fertilizer and a decrease in particle size. On
Houghton muck soil, the yield of millet was found to be

highest from soil treated with potassium metaphosphate. With

3
RAMAN G. MENON ABSTRACT

this soil, potassium content of plants also increased with
an increase in water soluble potassium content of the
fertilizer.

In laboratory, particles of fused potassium phos-
phates were leached with water to study the rate of dis—
solution and migration of potassium. About three-fourths
of the original water soluble potassium present from all
particles was leached out with the addition of MO milli-
liters of water. The rate of release of potassium in-
creased with decrease in particle size of the fertilizer,
The medium sized particles of metaphosphate completely
disintegrated, while large fragments became rather soft.
After leaching, the large and medium sized particles of
pyrophosphate still contained all their original water-
insoluble potassium.

When the fused potassium phosphates were placed in
soil columns and leached with water, water soluble and ex-
changeable potassium was found to be concentrated in a layer
of soil, 2 inches below the place of application of the
fertilizer.

When various sized particles were incubated in moist
organic soil, 45.6 percent and 94 percent of the water
soluble potassium was released in 24 hours from the -4+14'
mesh particles of pyro- and metaphOSphate, respectively.

For both pyro- and metaphosphates of this particle size,

4

RAMAN G. MENON ABSTRACT

the amount of water soluble potassium recoverable remained
more or less constant, regardless of an increase in time
of incubation.

There was no marked difference in the amount of potas—
sium released as affected by changes in the moisture content
of the soil. For potassium pyrophosphate, particle size
also did not appreciably influence the release of potassium,
although for metaphosphates, more water soluble potassium
moved out of the —4+l4 mesh particle than from the larger
particles at the end of a 24 hour incubation period.

Approximately three-fourths of the potassium released
in the incubation studies was recoverable from a volume of
soil 2 x 2 x 10 centimeters in the center of which the
fertilizer particles were banded. Lateral movement of
potassium decreased rapidly with distance from the potassium
source. With increase in time of incubation there was an
increase in the soluble potassium content of the laterally
adjacent volume of soil but very little downward movement
of potassium in soil was recorded. The migration and dis-
tribution of potassium in Oshtemo sand was similar to that
for organic soil.

When the several potash fertilizer particles were
left exposed on the soil surface to atmospheric conditions

in the field, potassium chloride and -4+l4 mesh potassium

5
RAMAN G. MENON ABSTRACT

metaphOSphate particles could not be recovered after 20
days exposure. A short time later, the large particles
also had disintegrated. In contrast, potassium pyrophos-
phate particles were recoverable in unaltered physical
form even after 40 days exposure in the field. At the
first sampling period, potassium chloride contained about
half of its original potassium, and the smaller particles
of potassium pyrophosphate and metaphosphate lost 30.7 and
95.8 percent potassium, respectively. However, these
materials still contained a large amount of potassium.
After 40 days of exposure, the pyrophosphate had lost all
water soluble potassium, but still contained most of the

original water—insoluble fraction.

A STUDY OF THE BEHAVIOR OF FUSED POTASSIUM

PHOSPHATES IN SOIL

by

Raman G. Menon

A-THESIS

Submitted to the School for Advanced Graduate Studies of
Michigan State University of Agriculture and
Applied Science in partial fulfillment of
the requirements for the degree of

DOCTOR OF PHILOSOPHY

Department of Soil Science

1960

’ /
{,3 /5 W73

_! 7 ,3 57/551

 

 

ACKNOWLEDGMENTS

The author wishes to express his sincere appreciation
to Dr. Kirk Lawton under whose guidance, constant super-
vision, and support this investigation was carried out.

He is very grateful to Dr. R. L. Cook for his
encouragement and assistance; to Dr. K. M. Pretty for his
advice, guidance, and help in conducting the greenhouse
experiments; and to the Graduate students of the Soil
Science Department for their cooperation and suggestions.

The financial assistance given to him by the
Tennessee Valley Authority during the entire period of

these studies is deeply appreciated.

TABLE OF CONTENTS

SECTION PAGE
I. INTRODUCTION. . . . . . . . . . . 1
II. LITERATURE REVIEW . . . . . . . . . 3
III. METHODS AND MATERIALS. . . . . . . . 15
A. Greenhouse studies (1957) . . . . 16
B. Greenhouse studies (1958) . . . . 17
C. Laboratory investigations . . . . 18
Leaching experiments with water . . 18
Movements of fertilizer potassium
in soil columns. . . . . l9
Dissolution and migration of
potassium in moist soil . . . . 20
Effect of soil moisture on
dissolution . . . . . . . . 21
D. Field study. . . . . . . . . 22

Dissolution and disintigration of
fertilizer particles in the

field . . . . . . . . . . 22
E. Laboratory techniques . . . . . 23
IV. RESULTS AND DISCUSSION . . . . . . . 25

A. The effect of potassium fertilizers
on the yield and potassium uptake
by several crops in the greenhouse 25

B. Dissolution patterns of partially
soluble potash fertilizers deter—
mined by leaching . . . . 38

C. Leaching studies of potassium from
different potash fertilizers in

soil columns. 48

SECTION

D. Dissolution and migration of

potassium from several fused
potassium phosphates in moist
soil . . . . . . . .

E. Dissolution of potassium from

V. SUMMARY
LI TERATURE CI TED

partially soluble potash
fertilizers under field conditions

iv

PAGE

51

82
88
92

TABLE

LIST OF TABLES

PAGE

Some physical and chemical characteristics
of the soils used in the study. . . . . 26

Effect of water soluble potassium content of
the fertilizer on the yield and potassium
content of field beans grown on Metea sandy
loam in the greenhouse . . . . . . . 27

Effect of water soluble potassium content of
the fertilizer and method of placement on
the yield and potassium content of field
beans grown on Houghton muck soil in the
greenhouse . . . . . . . . . . . 30

.Effect of water soluble potassium content of

the fertilizer, particle size, and method

of placement on the yield and potassium con-

tent of Proso millet grown on Kalamazoo

sandy loam in the greenhouse . . . . . 32

Effect of water soluble potassium content of
the fertilizer, particle size and placement
on the yield and potassium content of Proso
millet grown on Houghton muck soil in the
greenhouse . . . . . . . . . . . 34

The dissolution of potassium from potassium
pyrophosphate fertilizer of different
particle size upon leaching with water . . 39

The dissolution of potassium from potassium
metaphosphate fertilizer of different
particle size upon leaching with water . . 47

Distribution of extractable potassium in soil
columns incubated with potassium pyrophos-
phate, potassium metaphosphate, and potas-
sium chloride of different particle sizes . 49

The quantity of water soluble potassium
remaining in fertilizer particles after
they have been incubated to various lengths
of time in muck soil at 50 percent moisture 52

TABLE
10.

ll.

12.

13.

14.

15.

16.

17.

18.

19.

Vi
PAGE

The quantity of water soluble potassium
remaining in fertilizer particles after
they have been incubated to various lengths
of time in muck soil at 100 percent
moisture. . . . . . . . . . . . . 52

The quantity of total potassium remaining in
fertilizer particles after they have been
incubated to various lengths of time in muck
soil at 50 percent moisture . . . . . . 55

The quantity of total potassium remaining in
fertilizer particles after they have been
incubated to various lengths of time in muck
soil at 100 percent moisture . . . . . . 55

Distribution of potassium at various dis-
tances and depths from the place of appli-
cation with time in muck soil at 50 percent
moisture. . . . . . . . . . . 59

Distribution of potassium at various dis-
tances and depths from the place of appli—
cation with time in muck soil at 100 percent
moisture. . . . . . . . . . . . . 60

The quantity of water soluble potassium
remaining in fertilizer particles after they
have been incubated to various lengths of
time in Oshtemo sand at 5 percent moisture . 68

The quantity of water soluble potassium
remaining in fertilizer particles after they
have been incubated to various lengths of
time in Oshtemo sand at 20 percent moisture . 68

The quantity of total potassium remaining in
fertilizer particles after they have been
incubated to various lengths of time in
Oshtemo sand at 5 percent moisture . . . . 69

The quantity of total potassium remaining in
fertilizer particles after they have been
incubated to various lengths of time in
Oshtemo sand at 20 percent moisture . . . 69

Distribution of potassium at various dis-
tances and depths from the place of appli-
cation with time in Oshtemo sand at 5 percent
moisture. . . . . . . . . . . . . Tl

vii

TABLE PAGE

20. Distribution of Potassium at various dis-
tances and depths from the place of appli-
cation with time in Oshtemo sand at 20
per cent moisture. . . . . . . . . . 72

21. Moisture content of soil surrounding potassium
metaphosphate particles incubated in
Kalamazoo sandy loam at various moisture
levels . . . . . . . . . . . . . 80

22. The quantity of water soluble potassium
remaining in granules after they have been
left in the field for various periods of

time . . . . . . . 84

LIST OF FIGURES

FIGURE PAGE

1. Dissolution of potassium from potassium-

calcium pyrophosphate upon leaching with

water. . . . . . . 4O
2. Dissolution of potassium from potassium

metaphosphate upon leaching with water. . . 4O
3. Diagram of fertilizer placement and sampling

volume relative to the fertilizer band in

the laboratory dissolution studies. . . . 53

4. Distribution of potassium at various depths
and distances from place of fertilizer
application with time in muck soil at 50
percent moisture. . . . . . . 65

5. Distribution of potassium at various depths
and distances from place of fertilizer
application with time in mineral soil at 5

percent moisture. . . . . . . . . . 73
6. Potassium remaining in potassium pyrophosphate

particles after exposure in the field for

varying lengths of time . . . . . . . 85
7. Potassium remaining in potassium metaphosphate

particles after exposure in the field for
varying lengths of time . . . . . . . 86

PLATE

LIST OF PLATES

Original —3/8+4 mesh size potassium pyro-
phosphate particle (50x). . .

Original -3/8+4 mesh size potassium metaphos-
phate particle (50x) . . . . . . . .

Surface of original -3/8+4 mesh size potassium
pyrophosphate particle (100x) . . .

Surface of leached -3/8+4 mesh size potassium
pyrophosphate particle (100x) . . .

Surface of original -3/8+4 mesh size potassium
metaphosphate particle (100x) . . .

Surface of leached —3/8+4 mesh size potassium
metaphosphate particle (100x) . . .

Soil particles adhering to the fertilizer
particle after it is incubated in moist

soil (50x)

PAGE

36

37

42

43

46

79

INTRODUCTION

Potassium is one of the most reactive metallic chemical
elements. It has an atomic number of 19 and atomic weight of
-3l.100. Naturally occurring potassium consists of three
isotopes of mass numbers 39, 40, and 41, with relative
abundance of 93.1, 0.0119, and 6.9 percent, respectively.
Potassium belongs to the group of alkali metals and closely
resembles other members of this group. It has a single
valence electron which is easily removed. The other elec-
trones are tightly held by the nucleus in completely filled
orbitals and hence it is very reactive and is a strong
reducing agent. Although in the form of simpler chemical
compounds potassium is one of the most soluble of elements,
in the soil-fertilizer-plant system, potassium exhibits”
extreme difference in solubility and mobility.

One of the problems faced with the use of potassium in
fertilizer practice is the inefficient utilization of this
element by plants. Almost all the potash used in mixed
fertilizers or as an individual nutrient is potassium
chloride, an extremely soluble salt. Part of potassium
lapplied to soil may be lost by leaching, especially in areas
of high rainfall, part is fixed by the soil, and part is lost
in a sense through luxury consumption by plants. One of the

methods that could be used to minimize these losses is the

use of lesser soluble compounds of potassium as potash

carriers.

In this category belong the fused potassium

phosphates developed experimentally by the Tennessee valley

Authority.

The Michigan Agricultural Experiment Station

entered into cooperative studies with the Soil and Fertilizer

Branch of this agency in 1957 to study the behavior of these

potassium sources.

The objectives of the present investigation were:

I.

To compare the effectiveness of fused potassium
phosphates on the yield of and the potassium up-
take by plants grown in the greenhouse.

To evaluate the effect of leaching of fused
potassium phosphates with water to characterize
their solubility patterns.

To study the dissolution and migration of potassium
from the fused potassium phosphates when incubated
in soil.

To determine the effect of particle size on the
behavior of these potassium phosphates.

To study the dissolution and disintegration of

these fertilizer materials under field conditions.

LITERATURE REVIEW

The benefits of organic and inorganic materials con-
taining potassium were recognized by scientists for some
time past, but the significance of this element in crop
production was recognized only since the beginning of the
nineteenth century. The importance of potassium in plant
nutrition was pointed out by such workers as Boussingault,
Sprengel, Liebig, and others.

Of the major nutrient elements, potassium is usually
the most abundant in soils. Marbut (31) reported that the _'
content of potassium in soil ranges from traces as in Tifton
sandy loam to as much as 5 percent or more as in Durham sandy
loam. However, the quantity of soil potassium available to
plants at any one time is seldom more than 1 to 2 percent of
the total present. Even in soils to which potash fertilizer
has been applied, the proportion of total potassium held in
soluble and exchangeable forms is relatively small. The
majority of this element resides in potassium bearing primary
minerals of the silt and sand fractions, mainly muscovite,‘
biotite, orthoclase, and microcline. Of the clay minerals,
the illite group is considered to be the only one having a
substantial potassium content. (22)

Soil potassium is considered to occur in several forms

or fractions which have been delineated largely on the basis

a
of solubility or extractability. »First, there is a limited
amount of water soluble potassium found in the soil solution.
This fraction may be in equilibrium with a larger amount of
exchangeable potassium associated with colloidal clay and
organic matter. Exchangeable potassium, in turn, is con-
sidered to be in equilibrium with less soluble mineral
sources, primarily that in clay. It has been convenient to
classify these mineral forms as primary sources including
the micas and orthoclase feldspars, and secondary sources
such as clays of the illite group. Non-replaceable potassium,
an arbitrary category, has been defined as that removed
by more rigorous means than by leaching with ordinary salt
solutions. This form is largely held by clay minerals either
as native potassium or as potassium ions fixed within the
clay lattice structure.(l4)

According to Reitemeier (39), the various forms of
soil potassium generally are related to and comprise a system
in which an increase in one form occurs at the expense of
one or more forms and in which the net movement may occur
from less available to more available states, or the reverse,
depending on the particular stress. The availability to
plants depends on the amount and relative mobility of the
different forms, including the rate of replenishment of
depleted immediately available forms by reserve supplies.
Recently the kinetics of release of potassium from biotite

has been established by Mortland.(33)

5

Potassium is absolutely essential for plants and can-
not be replaced entirely by another element. Sodium may be
substituted for potassium to a certain degree, but by no
means entirely.(8, 32, 19) The plant can absorb from the
soil and utilize in its metabolism any soluble inorganic
compound of potassium.

The exact roles of potassium in plants are not clearly
understood, but some general relationships have been recog-
nized in the physiologic plant processes.(22) It is believed
to play a role in carbohydrate synthesis, in the uptake of
nitrate ions, the reduction of nitrates, and the synthesis
of proteins. Potassium may also play an important role in
photosynthesis and cell division. Increased resistance of
plants to disease has been attributed to adequate supplies“
of potassium. Likewise this element is considered essential
for the maintainance of turgor in plant tissues.

The most common sources of potassium used in agricul-
ture are the water soluble compounds, potassium chloride and
potassium sulphate. When introduced in moist soils, these
compounds immediately dissolve. Some of the potassium ions
exchange with other cations on the exchange complex, others
enter lattice positions of secondary micacious minerals,
and a small fraction remains in solution. Soils possessing
low exchange capacities have limited ability for retaining
potassium, and in areas of high rainfall, appreciable losses

occur by leaching, especially when there is no cover crop.

6

The use of some of the lesser soluble potassium bearing
materials has been investigated for a number of years. As
early as 1848, Magnus (30) grew a greenhouse barley crop to
maturity using powdered feldspar as the source of potassium.
Aitkan compared feldspar with potassium sulphate on peas (1)
and found that feldspar was as good a source of potassium
for peas as the sulphate salt. DeTurk (13) also found that
finely ground potassium bearing minerals increased the
yield of buckwheat in peat soils 21 to 35 percent.

Haley (18) compared the dry weight yields of buckwheat
grown in nutrient solution with the dry weight of the same
plants grown i’n'pots in which potassium was applied as
orthoclase. In this experiment a 21 percent higher dry
weight yield was obtained from plants grown in pots to
which orthoclase was added, even though the potassium con-
tent of these plants was lower. However, the majority of
workers have concluded that for practical purposes, the
orthoclase and mica-like minerals are too insoluble and
contain too little potassium. ~For example, naturally
occurring potassium bearing silicate minerals have been
compared with potassium chloride for a number of plants in;
cluding Ladino clover (l5), Costal bermuda grass (20), and
pine seedlings.(46) Application of ground feldspar, granite
dust, and other resistant minerals generally resulted in
significant potassium uptake, but concentrations in plants

were well below critical levels, resulting in poor growth.

Lunt and Kwate (28) fused orthoclase feldspar and
potassium nitrate or potassium carbonate at 22OOOF. and
obtained a glass frit containing 36 percent K20. When the
frit was air quenched, its weathering rate was very high
and solubility low. They found that weathering rate could
be controlled by alternating the fineness of the grind and P
by incorporating various impurities in the glass. This frit
was found to be a readily available source of potassium to
plants and these workers suggested that large applications
of frit may be made to plants which will supply potassium
over prolonged cropping periods.

Bartholomew and Jacob (4) studied the effects of
several phosphates including potassium metaphosphate and
potassium pyrophosphate as sources of fertilizer materials.
They found that for Sudan grass potassium metaphosphate was
75 percent as effective as monocalcium phosphate-potassium
chloride application as far as the‘growth of the plant was
concerned. Potassium pyrophosphate was prepared by heating
pure dipotassium phosphate to a constant weight at lOOOOC.
and it was thus used as a source of potassium to plants.

The yield of first cutting of Sudan grass, treated with
potassium pyrophOSphate was only half as much as that treated
with potassium chloride.- However, when yield data for three
cuttings were combined, the total dry weight of plants
treated with potassium metaphosphate and potassium pyrophos—

phate were equal to that of plants treated with potassium

8
chloride. Madorsky and Clark (29) also found that potassium

metaphosphate could be effectively used as a source of
phosphate and potassium.

Chandler (6) compared the effectiveness of potassium
metaphosphate as a source of potassium for corn, wheat,
alfalfa-orchard grass, soybeans, sudan grass and oats and
noted that over a three year period potassium metaphosphate
showed a tendency to outyield other carriers. The differ-
ences, however, were not statistically significant. In
these greenhouse studies with Ladino clover the potassium
content of plants was higher when potassium wasepplied as
potassium chloride than when potassium metaphosphate was
used as the source of fertilizer potassium. Jones and
Rogers also found (21) that potassium metaphosphate was as
good a source of potassium as potassium chloride.

Copson, gt a1. (9) developed a different process for
metaphosphate production. Phosphorus was burned with the
proper amount of air to maintain a temperature of 1000 to
lO5OOC. in a combustion chamber. Fine potassium chloride
(—14 mesh) was blown in at the top of the reaction chamber
at the proper rate to give the desired P205-K20 ratio in
the product. The fine potassium chloride was introduced at
two diametrically opposite feed holes by means of small air
jets which served to distribute it uniformly throughout the

reaction chamber. Water was added at the top of the packed

tower. The molten product collected in the combustion

9
chamber and was tapped from the furnace every two hours into

cooled steel pans where it was left to solidify. They found

that the product obtained had the following composition:

P205 K20 CaO 5103 F8203 A1203 01 Others
54.8% 38.1% 0.3% 1.3% 0.5% 0.6% 3.7% 0.7%

The melt was then ground to give different size fractions.

Potassium metaphosphate is now being produced in the
same manner in pilot plants by the Fertilizer Development
Branch of the Tennessee Valley Authority.(42) Potassium
metaphosphate thus obtained varies from 55 to 58 percent
P205, 35 to 38 percent K20, and l to 4 percent chlorine.

The water soluble potassium content varies from 13 to 20
percent. Potassium—calcium pyrophosphate is produced

through the fusion of finely ground phosphate rock, potassium
chloride, and phosphorus pentoxide.(40) The degree of
solubility of the resulting product is governed largely by
the rate of cooling of the melt. This melt is then ground

to give various fractions ranging in total potassium content
from 24 to 25 percent and water soluble potassium content
from 4 to 8 percent.

It is assumed that these thermally prepared pyrophos-
phate materials are true pyrophosphate having the P207_4 anion
with the following structure.

0 O
_ H H
0 - P - O - P - O

l l
O O

10
But there is no sound reason for this (45) since it is con-
ceivable that a substance of this composition may be a mix-
ture of ortho- and tri polyphOSphates.

Similarly the crystal structure of the metaphosphates
have not been clearly established. Three forms have been
suggested including monometa—,dimeta- and trimetaphosphates.
Although monometa- and dimetaphosphates have been described
in literature, neither of them have been proven to exist.
Dimetaphosphates probably can be prepared by low temperature
synthesis.(45) Most of the so-called monometa- and dimeta—
phosphates have been found to be mixtures of chain or ring
phosphates. The three suggested forms of metaphosphates

have the following structures:

0
0 0 O l
\ // P
P "O-P—O’/// \\\‘0—P-O_ /// \\\
I \\\\ ///' O O
0 O l l
' P-O O-P
_O O O—
monometaphosphate dimetaphosphate trimetaphosphate

Stanford and Hignett (40) reported the results of
Studies with fused potassium phosphates in the greenhouse.
Yield and potassium uptake for three successive crops from a
Huston sandly loam soil treated with potassium metaphosphate,
potassium-calcium pyrophosphate, and potassium chloride of -35

mesh size fractions showed there was no significant difference

11
among potassium sources, notwithstanding the wide range in
water solubility. The data indicated that dissolution of
these materials occurred rapidly in soils. Apparently the
degree of potassium water solubility of these fertilizer
materials had little effect on the dry matter production of
a crop such as millet. On the other hand, uptake of potas-
sium during the first week of soil-fertilizer contact,...was..,.,..I,‘.,,_..,~
proportional to the percent of potassium present in water
soluble form. When the fertilizer-soil mixture was incubated
for two weeks prior to planting this effect of water solu-
bility was not evident. Also it was observed that with
-6+9 mesh materials, leaching losses were less pronounced
from fused potassium phosphates than from potassium chloride.

DeMent and Stanford (11) studied the availability of
potassium from a series of fused potassium phosphates, in
comparison with potassium chloride and potassium sulphate
by short term uptake tests in the greenhouse. In these ex-
periments the availability to corn of potassium from -35 mesh
potassium phosphates ranging from 4 to 100 percent water
solubility was not related to solubility. The meta and pyro
forms of potassium phosphates supplied as much potassium to
corn as did potassium chloride and potassium sulphate. Short
term uptake by millet during a one week period after appli-
cation indicated that all the small fertilizer particles had
dissolved in soils rapidly and potassium was as available as

that in potassium chloride. Potassium phosphates of lower

l2
solubility applied as -6+9 mesh particles, however, were
much lower in availability during this same period.

DeMent and Bradford (10) found no difference in avail-
ability to corn of ~35+60 mesh particles of potassium meta—
phosphates, potassium pyrophasphates, or potassium chloride
mixed throughout the soil in the greenhouse. Placing these
finely ground fertilizers on the surface of soil following
planting of the crop led to slightly lower potassium uptake
from pyrophosphate, but did not appreciably affect the
absorption of potassium from potassium metaphosphate and
potassium chloride by corn plants.

In this same study, the effect of increasing particle
size of the fused phosphates from -35+6O to 1/4 inch mesh
resulted in decreased plant availability of potassium.
Greater growth of corn plants was obtained from all appli-
cation rates from 100 to 800 milligrams potassium per pot.
There was no evidence of salt injury from any of the materials
tested. When similar particle size and placement variables
were compared, dry matter yields were usually higher from
soils receiving potassium metaphosphate than from those
treated with potassium pyrophosphate, except where both were
finely ground.

Haiao, _t _l. (17) found that the availability of potas-
sium from potassium metaphosphosphate and potassium-calcium
pyrophosphate was sufficient for good growth of Ladino clover

in the greenhouse on a Paxton loam soil, except when —6+l4

13
potassium—calcium pyrophosphate was employed. In addition, a
slight reduction in luxury uptake of potassium by Ladino
clover from the fused phosphates was noted. Laboratory ex—
periments showed that substantially less leaching of potassium
occurred from —6+l4 mesh pyrophosphate than from -35 mesh
pyrophosphate. In these studies, potassium chloride, used
as a standard, was subjected to extensive leaching.

DeMent, gt a1. (12) studied the coating of fertilizer
materials with various substances in an effort to retard the
migration of potassium from particles. They found that at
thevend of a 5 day absorption period, all coatings applied to
potassium chloride except floor wax retarded uptake of potas—
sium. Coating with paraffin resulted in least availability
of potassium during this period. At the end of two weeks,
none of the coatings reduced the availability of potassium’
appreciably.

The current investigation was undertaken in order to
obtain a better understanding of the behavior of these fused
potassium phosphates under various soil conditions. Field
experiments were conducted in Michigan with alfalfa, corn,
sugar beets, and potatoes in 1957 and 1958 using potassium-
calcium pyrophosphates, potassium metaphosphate, and potassium
chloride as the potassium carriers.(25, 38) Results showed
that there was no significant increase in the yield of any of
these crops due to the potassium carrier, particle size or

Placement. Analysis of plant samples of these crops at various

14
stages of growth indicated that during the initial stages of
growth, there was an increase in potassium content of these
plants with an increase in water soluble potassium content
of the fertilizer applied. However, as the plants reached
maturity, no significant differences in the potassium con-
tent of plants could be observed.

These studies stimulated interest in obtaining more
information as to the nature of these potassium phosphates.
To explain differences in their behavior due to potassium
water solubility and particle size, detailed experiments were
set up in the laboratory and greenhouse using the meta and

pyrophosphate forms as potassium carriers.

METHODS AND MATERIALS

In order to study the behavior of potassium fertilizers

under various soil conditions, experiments were conducted in

the greenhouse and laboratory. The fused potassium phosphates

and potassium chloride used in the experiments were produced

by the Tennessee Valley Authority. Listed below are the

materials used, together with the particle size and water

soluble potassium content of each source. There is consider-

able variability in the water soluble potassium content of
different sized fractions of the same fused potassium phosphate.
These materials are different mesh size fractions obtained by

breaking cooled melts from various chambers and not just size

fractions of the same melt.

There was a wide variation in the shape or the smoothness
of the particles, therefore, for all studies, fertilizer par-

ticles were selected for maximum uniformity.
Percent K20

 

 

Particle
Fertilizer Size Total Water Soluble
Potassium pyrophosphate -35 25.9 4.8
KQCap2o7 -4+14 25.0 5.9
-3/8+4 24.8 7.5
Potassium metaphosphate —35 31.0 20.5
KPO3 -4+l4 33.5 20.6
-3/8+4 38.9 13.0
Potassium chloride -35 59.4 59.4
-6+1O 60.6 60.6

KCl

16

In all comparisons of potassium carriers, the quantities of

fertilizers used contained equal amounts of potassium based

on their content of total potassium.

Greenhouse Studies (I951)

Greenhouse experiments were started in 1957 to study
the effect of water solubility of potassium in the fertilizer
materials, degree of fineness of the fertilizer particles
and method of placement of fertilizer on the yield and potassium
uptake of plants.

Soil: Houghton Muck soil from Muck Experimental Station
and Metea sandy loam from the University Farms were used in
this study.

Fertilizers: Three different potassium carriers,
potassium pyrophOSphate, potassium metaphosphate, and potassium
chloride, of -35 and —6+14 mesh sizes were applied at the rate
of one thousand pounds K20 per acre in both soils. Nitrogen
and phosphorus were applied at the rate of one thousand pounds
per acre of ammonium nitrate and diammonium hydrogen phosphate,
respectively.

Fertilizer placement: In Muck soil all fertilizers were
applied as mixed and banded treatments, whereas only the
mixed treatment was used in Metea sandy loam soil. In mixed
treatments, the fertilizers were thoroughly mixed with the
8011, while in banded treatments the fertilizers were applied

in circular bands 1 inch deep to the side and below the seeds.

17

Cultural practices: Two gallon glazed pots were used
in the study with four replications per treatment. Eight
seeds of Sanilac white pea beans were planted in each pot on
May 3, 1957, and on May 29th, the stand of beans was thinned
to four plants per pot. Distilled water was added to each
pot as required by weighing the pots weekly and applying
additional water by estimation between weighing periods. The
plants were harvested at the time of flowering. The above
ground parts of the plants were removed, dried in an oven at
700C. and weighed. This material was then ground in a Wiley
mill and samples were extracted with a salt solution.

Potassium in this extract was evaluated using a flame photo-

meter.

Greenhouse Studies (1958)

Soils: Greenhouse experiments were continued in 1958
on Houghton Muck soil and Kalamazoo sandy loam.

Fertilizers: The potassium carriers used were potassium
pyrophosphate, potassium metaphosphate, and potassium chloride.
Three particle sizes of —35, -6+14, and -3/8+4 mesh were used
with pyro- and metaphosphate materials, whereas only -35 and
-6+10 mesh sizes were available for potassium chloride.

Potassium was applied at the rate of 600 pounds K20 per
acre to the organic soil and 300 pounds per acre to the
Kalamazoo sandy loam. Nitrogen was added to the mineral soil

and organic soil as ammonium sulphate at the rate of 300

18
pounds and 100 pounds per acre of nitrogen, respectively.
Supplemental phosphorus application amounted to 300 pounds
P205 per acre for mineral soil and 600 pounds P205 for the
muck soil, using concentrated superphosphate as the phosphorus
source.

Fertilizer placement: All potash fertilizers were ap-
plied as mixed and banded treatments. In the former case,
fertilizers were mixed with the soil while in the latter
they were applied 1 inch below and to the side of the seed.
The nitrogen and phosphorus supplements were well mixed with
soil for all treatments.

Cultural practices: One gallon glazed pots were used
in the study, with three replications per treatment. Fifty
seeds of Red Proso variety millet were planted in the pots
on June 13, 1958. During growth, the pots were irrigated with
measured quantities of distilled water. On July 9th, the
stand of millet was thinned to 20 plants per pot. The plants
were harvested 15 days later, when they started to head. All
above ground plant parts were dried in an oven at 700C.,
weighed, and ground in a Wiley mill. Analyses for potassium
were carried out similarly as indicated for samples collected

in 1957.

Eéboratory Experiments

 

Experiment 10 To study the rates of dissolution of po-

 

tassium from the fertilizer granules, a preliminary leaching

19
experiment was set up in the laboratory. Fertilizers used
included -35, —4+l4, and -3/8+4 mesh particles of potassium
pyrophosphate, potassium metaphosphate, and potassium chloride.
Except for the finely divided materials, a specific number of
previously weighed particles selected for uniformity were
placed in a filter paper in small Buckner funnel and leached
with successive 2O milliliter portions of water at a leaching
rate of 1 liter per hour. The leachates were collected and

analyzed for potassium.

Experiment 2. In order to determine if the leaching

 

characteristics of the partially water soluble fused potassium
phosphates incorporated in soil, were similar to those when
the fertilizers were leached in funnels, an experiment was con-
ducted to study the distribution of potassium released from
these fertilizer materials in a soil column. Thbes, 24 inches
tall and 6 inches in diameter were patted uniformly with
Kalamazoo sandy loam soil up to 20 inches from the bottom.

To the soil in each tube, 2 inches of water was added and the
soil mass incubated for four days without loss of moisture.
Potassium pyrophosphate, potassium metaphosphate, and potassium
chloride, the first two in -35, —4+14, and -3/8+4 mesh sizes
and the chloride in -35 and -6+lO mesh sizes were applied at
the rate of 500 pounds potassium per acre. The fertilizers
were placed uniformly on the surface of soil and covered with

another inch of soil. Two more inches of water were then

20
added to each column and the top of the tubes covered with
polyethylene film. After a week, the tubes were opened and
the soil column was sliced to give 1 inch thick samples.

The samples were dried and analyzed for water soluble potas-

sium.

Experiment 3. An experiment was initiated to study

 

the dissolution and migration of potassium from fertilizer
particles placed in a bulk volume of soil. Wooden boxes

4.5 inches long, 4.5 inches wide, and 4.5 inches high were
used as containers, the sides of which were provided with
grooves horizontally l centimeter apart in order to facilitate
sampling of soil. The lid and one of the sides were provided
with hinges so that the box could be opened and closed from
above and from the sides.

The experiment was conducted with two soils, Houghton
muck and Oshtemo sand. The soil moisture variable included
50 percent and 100 percent moisture levels for the organic
soils and 10 and 20 percent moisture levels for the Oshtemo
sand. The soils were incubated with the necessary amount of
water for one week so as to enable the soil to react equili-
brium with water. The boxes were packed uniformly with the
moist soil to within 2 centimeters from the top.

Potassium pyrophosphate and potassium metaphosphate of
—4+14 and -3/8+4 mesh sizes were used in this study. Twenty-

five particles of the larger size particles and fifty of the

21
smaller ones which had been previously weighed, were placed
in a band at the center of the box. The boxes were then
completely filled with soil and sealed air tight. After
1, 2, 4, 8, l6, and 32 days incubation period one box from
each treatment was opened. The first centimeter of soil was
removed from the top and the fertilizer particles were re-
covered from the layer immediately below. Soil samples were
taken from the 1-3, 3-5, and 5-7 centimeter depths of the
box by introducing steel plates into the grooves. At each
depth samples were taken O-l (born directions), 1-3, and 3-5
centimeters laterally from the place of application of the
fertilizer. The soil samples were analyzed for water soluble

potassium.

Experiment 4. Dissolution and diffusion ofions from

 

fertilizers placed in soil are known to be affected by the
thickness of the water films. Therefore, an experiment was
initiated to study the effect of soil moisture content on
the rate of dissolution of the qued potassium phosphates.
Moisture cans 2 inches in diameter were filled with
Kalamazoo sandy loam soil at 2, 5, and 12 percent moisture.
Ten particles of potassium pyrophosphate of —4+l4 mesh size
were then placed at the center of the cans. The soil was
then incubated and individual cans were opened after 1, 2,
4, 8, 12, 24, 48, and 72 hours incubation period. Concentric

samples having diameters of 11, 22, 35, and 50 millimeters

22
were taken around the center of the fertilizer source. The

moisture content was determined in all soil samples taken.

Field experiment. An attempt was made to study the

 

disintigration of potassium fertilizers possessing varying
degrees of water solubility and dissolution of potassium
therefrom under field conditions. Fertilizer particlers
were placed on the surface of a Concver loam at the University
Farms. Small enclosures were made with wire mesh in order
to avoid the loss of granules by rain and wind. Three ferti—
lizer materials, potassium pyrophosphate, potassium meta—
phosphate, and potassium chloride, the first two as -6+14 and
-3/8+4 mesh materials and the last at —6+10 mesh granular
particles, were used in the study. Each group of approxi—
mately 60 fertilizer particles was selected for uniform size
and was weighed before placing the individuals on the soil
within the enclosures. Six replications of each fertilizer
treatment were laid out in a random arran-ement.

At the end of 10, 20, 30, and 40 days all-granules were
picked up from the plots. They were gently cleaned with a

brush to remove all soil particles stickin' on them an.

I 1
3

analyzed for water-soluble and total potassizn. During the
p6riod of exposure of fertilizer particles in the field, the

area received precipitation on the followin dates:

May 9 0.07 inches June 1 1.18 inches
May 18 0.05 inches June 2 0.42 inCAeS
May 23 0.10 inches June 8 0.10 inches
May 28 0.05 inches June 9 0.48 inches
May 31 0.11 inches June 10 0.17 inches

June 13 0.51 inche.

Laboratory Techniques

The soils for the experiments were analyzes for pH,

sand, silt and clay, exchange capacity, and exchangeable

bases.

Soil reaction was determined using 1:1 soil-water

ratio, by glass electrode.

Percent sand, silt, and clay were determined using

the hydrometer procedure of Bouyoucos.(5)

Exchange capacity was determined by the neutral am-

monium acetate extraction method of Peech. (36)

Individual bases were determined in the initial am-

monium acetate leachate.

was made using a flame photometer.

Analysis of exchangeable potassium

For determining exchange-

able calcium and magnesium, a Beckman DU flame photometer

was used with the following adjustments:

Wavelength
Phototube resistor
Selector
Slit
Sensitivity
a. Instrument panel
b. Photomultiplier
Zero suppression

Phototube

galeisa
4227 A0
No. 2
0.1
0.01

Variable
No. 4
1.0

Blue

Magnesium

 

2582 A0

ID

No.
0.1
0.06

Variable
Full
1.0

Blue

24

Water soluble potassium in soil was determined by
shaking 1 gram soil with 10 milliliters water for 10 minutes,
followed by filtration.

For evaluating water soluble potassium in fertilizer,

a 1 gram sample was shaken with 50 milliliters water, allowed
to remain overnight and then leached with additional water
to give a total volume of 200 milliliters.

Total potassium in fertilizer was determined by
extracting the material with concentrated hydrochloric acid
as described in A.O A C. method of analySis.(2)

Potassium in plant samples was determined by extracting
the dried, ground plant material with a 2 N ammonium acetate
and 0.2 N magnesium acetate solution as described by Attoe.(3)

Potassium extracted from all soil and plant materials
was determined using a Perkin Elmer Model 52 A flame photo-

meter or a Coleman Model 21 flame photometer.

RESULTS AND DISCUSSIONS

Greenhouse Studies

 

The effect of potassium fertilizers with varying water
soluble potassium content and particle size was evaluated in
terms of dry matter production and potassium uptake by field
beans grown on Metea sandy loam and Houghton muck in the
greenhouse. The data in Table 2 show that when the potassium
carriers were applied in granular form and mixed with this
mineral soil, no significant difference was obtained in the
yield of beans grown on Metea sandy loam, as a function of
water solubility of the fertilizers. Application of potassium
pyrophosphate in pulverized form resulted in the same yield
as that for granular form. However, bean plants grown in
soil treated with pulverized pyrophosphate removed 270.6
milligrams potassium per pot or about 14 percent more than
plants grown in pots treated with granular material. This
difference is definitely related to the greater surface area
presented by the finely divided materials.

However, With potass um metaphosphate treatments, the
mixed application of pulverized materials resulted in signifi-
cantly higher yield of beans than that of granular applications.
This could be expected since potassium metaphosphate is more

soluble than pyrophosphate and also contains more water

26

 

 

 

 

 

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TABLE 2

Effect of water soluble potassium content of fertilizer on the
yield and potassium content of field beans grown on Metea sandy
loam in the greenhouse.

 

 

 

PotaSSiam Potassium

 

 

 

 

 

 

 

Material Particle Yield Content Uptake

Size gm./pot* % mgm./pot
Potassium Granular 16.7 1.54 257
pyrophosphate Pulverized 16.5 1.64 271
Potassium Granular 17.6 1.69 297
metaphosphate Pulverized 23,5 1,43 336
Potassium Granular 16.5 1.70 289
chloride Pulverized 16.2 1.50 243
Check (NP) 17.1 1.57 268

*Average of four replications
Summary

Potassium Potassium

Yield Content UptaKe

Material gm./pot % mgm,/pot
Potassium pyrophosphate 16.6 1.59 26M
Potassium metaphosphate 20.5% 1.56 317
Potassium chloride 16.5 1.60 266

Particle Size

Granular 17.1 1.64 273
Pulverized_ 18.6% 1.52 283

 

*Significantly higher at 5 percent level.

28
soluble potassium and pulverizing the granules would result
in much better contact between soil and fertilizer particles.
Additional evidence of the difference in solubility of the
meta— and pyrophosphate forms can be seen from the fact that
bean plants absorbed 22 percent more potassium from the
pulverized metaphosphate treatments than from soil receiving
finely divided pyrophosphate. As might be expected, when
potassium chloride was used as a source of potassium, there
was no difference between the yields of beans grown in soils
treated with granular or pulverized materials. Either form
dissolves completely in moist soil.

The fact that finely divided metaphosphate produced
more growth than potassium chloride suggests that the sup-
plimental phosphate application was not sufficient for
maximum growth. In this experiment, when the various potas-
sium carriers were used in Metea sandy loam, pulverized or
granular, there was very little difference in yield. This
is due to the fact that irrespective of particle sizes, suf-
ficient soluble potassium was available for the plants
starting with the seedling stage. Data from Table 6 show
thatabout 2 percent of potassium moved out of pyrophosphate
when leached with 20 milliliters of water, whereas 8 percent
moved out of metaphosphates of -35 mesh size and 4 percent
from -4+l4 mesh particles when leached with the same amount

of water. In any case, initial supply of potassium from

29
granules was sufficient to ensure the satisfaction of potas-
sium needs of seedlings.

Examination of the data in Table 3 shows that yield
and potassium content of field beans were affected to a much
greater extent by the method of fertilizer placement than by
the kind of potassium carrier or the particle size. The
average effects given in Table 3 indicate that no difference
in growth resulted from the use of the highly soluble potas-
sium chloride or the partially soluble fused potassium phos-
phates. However, potassium content and thereby uptake of
this element was directly related to a degree with the water
solubility of the fertilizers studied.

Whether the potassium phosphates were applied as large
particles or in a fine state of subdivision, had little
influence on either yield or potassium content of field beans.

In order to logically explain the marked superiority
of mixing versus banding, it must be emphasized that this
organic soil as collected had never been fertilized and
thereby was very low in available potassium and phosphorus
as shown by chemical analysis. It is probable that sufficient
potassium was available from each potaSSium source in banded
placement. Though no observations of the root systems were
taken, root development was probably restricted to the zone
of the fertilizer band. Yield data of the nitrogen—phosphorus

treatment indicate that placement had little effect on the

30
TABLE 3

Effect of water soluble potassium content of fertilizer,
particle size, and method of placement on yield and potassium
content of field beans on Houghton Muck soil in the Greenhouse.

 

Potassium Potassium

 

 

 

 

Material Particle Place- Yield Content Uptake
Size ment gms/pot % mgms/pot*

Potassium Granular Banded 15.5 1.74 270
pyrophosphate Mixed 26.3 1.78 488
Pulverized Banded 18.8 1.53 288

Mixed 28.9 2.28 659

Potassium Granular Banded 15.3 1.83 280
metaphosphate Mixed 28.9 2.30 665
Pulverized Banded 18.9 1.42 268

Mixed 22.2 2.27 504

Potassium Granular Banded 16.8 1.78 299
chloride Mixed 31.5 2.72 857
Pulverized Banded 19.4 1.75 340

Mixed 21.0 2.58 542

Check (NP) Banded 13.6 1.19 162
Mixed 12.8 1.18 152

 

*Average of four replications

 

 

 

 

 

 

 

Summary
Potassium Potassium
Yield Content Uptake

Materials gms/pot % mgms/pot
Potassium pyrophosphate 22.3 1.83 425
Potassium metaphosphate 21.3 1.95 429
Potassium chloride 23%1 2°20 510

Particle Size '—

Granular 22.3 2°02 477
Pulverized 22.3 1°96 435

Placement
Mixed 2304* 1099*
Banded 14.8 1.43

 

*Significantly higher at 5 percent level.

31
growth of beans. In this instance no potassium was present,
which in itself limits growth and nutrient absorption. Conse-
quently unless both potassium and phosphorus were well mixed with
the soil, maximum plant development could not take place.

This experiment brings out an excellent sample of inter-
action between nutrient supply and placement in an infertile soil,
1 namely that at moderate to high rates of application, nitrogen and
phosphorus must be well mixed with soil to obtain maximum yield
and uptake of fertilizer potassium.

The growth of and abéorption of potassium by millet grown
on a Kalamazoo sandy loam soil as affected by the water soluble
potassium content, particle size and placement of several
potash fertilizers is presented in Table 4. It is quite evident
that potassium water solubility of the fertilizers was not a
factor influencing growth since chloride was less effective
than either the meta- or the pyrophosphate materials. In fact
the data suggest that either the chloride ion concentration
was detrimental or that the additional phosphorus applied with
the fused potassium phosphates was of benefit.

Variation in yield of millet for the particle size factor
within each material make it impossible to draw any conclusions.
However, considering all potash sources, the potassium content
of millet receiving the finely divided fertilizer was signifi-
cantly higher for the coarser fertilizers.

The.most interesting feature of this experiment is the
apparent superiority of banded over mixed placement. In con—

trast to the greenhouse studies conducted in 1957, the nitrogen

Effect of water soluble

32
TABLE 4

potassium content of fertilizer,

particle size, and placement on the yield and potassium

content of Proso Millet
in the greenhouse.

 

grown on Kalamazoo sandy loam soil

 

m

Potassium Potassium

 

 

 

 

 

 

 

 

 

Particle Place- Yield Content Uptake
Material Size ment gms/pot* %* mgms/pot
Potassium -35 mesh Banded 22.7 2.13 484
pyrophosphate Mixed 19.1 2.04 390
-4+l4 mesh Banded 18.7 2.24 419
Mixed 18.7 1.89 353
-3/8+4 mesh Banded 21.8 2.07 451
Mixed 15.5 2.07 321
Potassium -35 mesh Banded 16.3 2.68 43%
metaphosphate Mixed 17.7 2.53 4
-4+14 mesh Banded 20.6, 2.28 470
Mixed 13.4 2.33 312
-3/B+4 mesh Banded 21.3 2.51 535
Mixed 19.7 2.09 412
Potassium -35 mesh Banded 17.0 2.40 408
chloride Mixed 10.1 2.59 262
-6+10 mesh Banded 15.3 2.41 369
Mixed 9.7 2.04 198
*Average of 3 replications.
Summary
Potassium Potassium
Yield Content Uptake
Materials gms/pot % mgms/pot
Potassium pyrophosphate 19.8* 2.08 403
Potassium metaphosphate 17.8* 2.46* 435
Potassium chloride 13.0 2.36* 309
Particle Size
-35 17.1 2.40*
- +14 16.6 2.20
-3/8+4 19 . 6 2 . 18
Placement
Banded 19.2* 2.34 447
Mixed 15.5 2.19 337

 

 

*Significantly higher at 5 percent level.

 

33
and phosphorus supplements were mixed with this mineral soil
regardless of the nature of placement of the potash source.
Thus, any benefit ascribed to banding cannot be attributed
to greater availability of the supplemental phosphate. Yet,
the possibility of additional response arising from the phos-
phorus combined in the potash carriers cannot be overlooked.
In 7 out of 8 comparisons, potassium uptake was greater where
the fertilizers were banded, largely as a result of the com-
bination of greater yield and a higher potassium content.

The results of the greenhouse test comparing the effects
of the kind, placement and particle size of the potash fertil-
izer on the growth of millet on an organic soil is given in
Table 5. Upon averaging the effects of particle size and
placement for each potassium carrier, the potassium meta-
phosphate was of most benefit, and particularly the finer
fractions. Virtually no difference was found between yields
of plants receiving the highly soluble chloride and the
rather insoluble pyrophosphate. In terms of potassium con-
tent, the values are almost twice those for plants from the
mineral soil, but the percentage potassium in millet appears
to be rather well related to the potassium water solubility
of the fertilizer. However, considering the high values of
potassium within plants of all treatments, it is unreasonable
to assume that potassium was deficient under these conditions.

From the standpoint of dry matter production, neither

particle size nor placement had much effect, with the

TABLE 5

Effect of water soluble potassium content of fertilizer,
particle size, and placement on the yield and potassium
content of Proso Millet grown on Houghton Muck soil in
the greenhouse.

_:j
if

 

Potassium Potassium
Particle Place- Yield Content Uptake

 

Material Size ment gms/pot'ii~ %* mgms/pot*
Potassium -35 mesh Banded 22.5 5.07 1141
pyrophosphate Mixed 23.3 6.13 1428

-4+14 mesh Banded 18.2 5.10 928

Mixed 16.8 5.77 969

-3/8+4 mesh Banded 19.0 5.13 975

Mixed 20.2 5.50 1111

Potassium -35 mesh Banded 22.8 5.27 1202
metaphosphate Mixed 29.0 5.80 1682
-4+14 mesh Banded 26.7 5.60 1495

Mixed 29.8 5.83 1737

-3/8+4 mesh Banded 20.3 5.17 1050

Mixed 18.7 5.00 935

Potassium -35 mesh Banded 22.8 6.00 1368
chloride Mixed 21.8 6.07 1323
-6+1O mesh Banded 20.5 5.30 1087

Mixed 21.7 6.27 1361

 

*Average of 3 replications.

 

 

 

 

 

 

 

Summary
Potassium Potassium
Yield Content Uptake
Materials gms/pot % mgms/pot
Potassium pyrophosphate 20.2 5.52 1023
Potassium metaphosphate 27.1* 5.63 #35
Potassium chloride 21.7 5.91 1 5
Particle Size
-35 23.7 5.72*
-4+14 22.3 5.64
-3/8+4 19.0 5.20
Placement
21 6 5.33
Banded . ,
Mixed 22.6 5.78*

 

 

*Significantly higher at 5 percent level.

35
exception for metaphosphate previously mentioned. As might
be expected on the basis of solubility and fertilizer-soil
contact relationships, the potassium content of millet was
highest where the potash fertilizers were finely divided and

mixed well with the soil.

36

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38
Laboratory Studies

A preliminary test was conducted to determine the rate
of dissolution of water soluble fractions of potassium from
potassium pyrophosphate, potassium metaphosphate, and potassium
chloride. The fertilizers were leached with successive incre-
ments of water at a constant leaching rate and the leachates
analyzed for potassium.

The data presented in Table 6 show that with potassium
pyrophosphate of -35 mesh particle size, 2.85 percent potas-
sium or 59.3 percent of the total water soluble fraction was
leached out with the first increment of water. In the next
leachate 1.25 percent of potassium or 26.1 percent of the
element originally soluble in water was found, accounting for
85.4 percent of this fraction from the two leachates. Addi—
tion of 100 milliliters of water practically removed all the
existing water soluble potassium from these fine particles.
Additional increments of water removed no more potassium.

With -4+l4 mesh size particles of pyrophosphate the
rate of removal of the water soluble potassium by leaching
was slower. Considerable leaching of water soluble potassium
occurred after addition of 6 portions of water, or the equiv-
alent of 120 milliliters of water, after which the rate of
dissolution decreased. A total of 200 milliliter water was
needed to remove all the water soluble fraction of potassium
from the intermediate size particles. Further leaching

resulted in conversion of only a small fraction of water

39

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s :m s.Hw mH.o o.Hm H.mw mm.m m.wH ms.wm ss.s own
m.mm o.ms mm.m m.ow 0H.m o.m m. H ms. m s. 00H
H.mm :.ms me.m q.mH om.mm mm.: m.mn mm.mm um.m om
m.om m.mw sa.m m.mH om.ms mw.: m.mfi mm.am mm.s om
MHMH mum: saum mnma se.sm mw.m m.mH as.mm oH.s o:
3 mm mm H H w sm.:m so.m o.HH sm.mm mw.m om
ONM 0mm Gommmaom 0mm 0mm pommmamm owx 0mm vmmmmamm .00 c
HapOB .Homuomm 0mm R Hmpoe .Homuomm owx & m o . o m w *v a
on» mo R 02p m0 & one mom 0:» mo.R 0 H p e H m-o m o m m omee<
. he no m we» go’s seem:
mmam chm: s+m\m- mNHm emmz sa+s- mNHm new: mm- pcwme<

 

H

.poumz cufiz wcfisomma com: omfim o 0 use sop
no mammaafiupom mpmnamosmopma Edfimmmuoa Eons Edammmpoa mm wwfiuDmemHmewm

w mqmfifi

Cumulative percent of total

water soluble K20

Cumulative percent of total

water soluble K20

4O

 

 

 

 

 

 

_ -35
100 —4+l4
. -3/8+4
80 -
60 -
40 5 p
20 -
I—_‘——!‘—l—l—"I I i I
2 4 6 8 104 12 14 16 18
Increments of Leaching Solution (20 m1 H20)
Fig. 2. Dissolution of potassium from potassium
metaphosphate upon leaching with water.
100 -4+10

 

 

 

3378
80

[\J
O
l

L_ __,__,___._.___,_.__._.

2 4 6 8 10 12 14 16 18

Fig. l. Dissdlution of potassium from Potassium-
calcium pyrophosphate upon leaching with
water.

41

insoluble potassium to the water soluble form. With the

large particles of potassium pyrophosphate a significant re—
duction in dissolution of potassium by leaching with water

was noted as compared with the smaller size fractions. For
example, the first two 20 milliliter portions of water removed
only 26.4 percent of the total water soluble potassium, the
next portion 19.4 percent of the tototal, while a total of

60 milliliter water resulted in the removal of about 69 per-
cent of the total water soluble potassium. For this material
about 300 milliliter water was needed to leach out most of the
water soluble potassium from the particles. A comparison of
the dissolution patterns of the three size fractions is given
in Figure 1.

There was little change in the appearance of the pyro-
phosphate fertilizer particles due to leaching with water as
noted by optical examination. No physical disintegration was
visible, especially in the large size pyrophosphate particles,
even though particles appeared to be much more porous and the
surface considerably rough after leaching. An enlarged View
of the surface of the leached and unleached material is
presented in Plates 3 and 4.

With potassium metaphosphate particles, the rate of
removal of water soluble potassium from the particles also
was dependent on the particle size as noted in Table 7.

With the addition of 80 milliliters of water practically all

Soluble potassium was leached out from the -35 mesh size

42

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shoe :+m\m: Hmsawfino mo oommsSm

 

 

 

.m madam

43

me
an cm
onaop

9mm opmnam

macaw

s

.Axoo

 

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pmHm
.30

44-

particles. The rate of removal of potassium was slower

from the -4+14 mesh size particles, especially in the early
stages of leaching. For instance, only 4.2 percent of the
total water soluble potassium was leached out with the first
increment of water. Subsequent leaching removed considerably
more potassium suggesting that initial dissolution is preceded
by an absorption or soaking period. Almost all the water
soluble potassium was leached out upon addition of 200 milli-
liters of water. The release of potassium was still slower
from -3/8+4 mesh metaphosphate particles. In this case the
rate of dissolution was fairly constant for the first four
increments of water added. Thereafter potassium apparently
dissolved out of the large particles rather slowly.

The appearance of metaphosphate particles was rather
altered after leaching. The particles had become soft and
the larger particles had started to crumble. Physical dis-
integration was much more evident here than in the case of
smaller particles. A picture of the large metaphosphate
particle before and after leaching is given in Plates 5 and 6.

The total amount of potassium leached out from the
smaller sized fused potassium phosphates particles is greater
than that from the larger ones. This could be expected
since the smaller the particle size, more the greater will be
the area of direct contact between the fertilizer and the

water molecules. An exception is the -3/8+4 mesh pyrophOSphate

45

.3503 maoapnma opgamonmmpme zmofi :+w\m.. HmcHsto .wo oommnsm

 

 

.l‘ lI‘ll

 

.m madam

46

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.o mamas

47

 

 

 

 

meapmasesQ*
3:.mn mm.om oos
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mm.: H.3H sm.H m.m m.s mw.o s.sm :.H: om.m om
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mo
mmam new: s+m\m- mhfim 2mm: sa+s- mham 2mm: mm- pesoea

 

 

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mo whomaaapywm mumsamonamume Edflmmmuoa EOLM Ezflmmmuom m0 COHpSHommHU one

N mqmdfi.

48
which is more soluble than the -4+l4 mesh size particles. It
has to be borne in mind that all these samples are taken from
different melts during the manufacturing process. In addition
there is little uniformity in the shape or the size of the
particles since they are merely pieces of large lumps broken
down to give the necessary particle sizes.

Even though the rate of dissolution varied considerably
for different sized fractions of the fused potassium phos-
phates, it is very probable that sufficient potassium would
be solubilized during the early contact with soil to supply
enough potassium for plant growth.

With potassium chloride particles, addition of 20 milli-
liters water leached out practically all soluble potassium

from both -35 and -6+10 mesh size particles.

Leaching the particles in soil column. To determine
the effect of leaching under soil conditions, a soil column
study was conducted to evaluate the movement of potassium
from several potash fertilizers placed in a layer in moist
soil one inch below the surface. After leaching and an in-
cubation period of one week, the tubes were opened and the

Soil at various depths was analyzed for potassium.

The data presented in Table 8 indicate that in general

the dissolution and movement of potassium was rather limited

for the two inch application of water. Most of the potassium

liberated from the several particle size fractions of both

pyrophosphate and metaphosphate was recovered in the first

49

TABLE 8

Distribution of extractable potassium in soil columns
incubated with potassium pyrophosphate, potassium meta-
phosphate, and potassium chloride of different particle

 

 

 

 

 

 

 

 

 

 

sizes.
Parts per Million Potassium Extracted on Soil Basis*
De th of
301? Layer —3/8+4 Mesh Size -4+l4 Mesh Size -35 Mesh Size**
in InChes NHuAc H20 NHuAc H20 NH4A0 H20
Potassium Pyrophosphate
0-1 380 90 440 100
1-2 460 110 440 100 300 60
2-3 220 27 210 27 210 33
3-4 210 27 210 27 210 30
4-5 210 27 210 27 210 30
5-6*** 210 27 210 27 210 27
Potassium Metaphosphate
0—1 460 125 750 230
1-2 290 45 680 175 680 140
2-3 210 27 210 27 220 27
3-4 210 27 210 27 210 27
4-5 210 27 210 27 210 27
5—6*** 210 27 210 27 210 27
Potassium Choloride
—6+10 Mesh Size -35 Mesh Size
0-1 460 105
1-2 830 155 330 55
2-3 440 100 830 155
3-4 330 52 520 125
4-5 250 37 380 100
5-6 220 27 210 40
6-7*** 210 27 210 35

 

*Potassium extracted with l N. ammonium acetate or distilled

water.

**The soil layer containing these particles was disregarded
since the individual particles could not be removed prior
to extraction.

***No further change in potassium was noted below this depth.

50
two inches of the soil column. In fact, the sharpness of
separation in terms of both exchangeable and water soluble
potassium contained in the 1-2 and 2-3 inch layers is rather
remarkable. It is believed this phenomenon involves progres-
sive exchange between the leaching potassium ions derived
from the fertilizer source and the varied cationic species
originally present on the colloidal surfaces of the soil column.
If the columns had been subjected to more extensive leaching,
it is probable that greater downward movement would have
occurred. This supposition is based on the fact that potas—
sium from similar rates of potassium chloride was concentrated
in layers sampled to a depth of 5 inches.

The effect of fertilizer particle size on the release
and movement of potassium within the soil during and after
leaching was not as marked as was expected. For example,
values for exchangeable potassium for the pyrophosphate
materials listed in Table 8 are quite similar for the large
sized particles. However, on the basis of original water
soluble potassium contents, a clearer relationship is evident.
Though the extent of downward movement of potassium from
metaphosphate does not seem to vary for particles of different
size, dissolution is apparently considerably greater for the
medium sized and very fine fractions. This latter effect is
somewhat modified when the lower water soluble potassium con-
tent of the coarse particles is taken into account. However,

by calculation the quantities of exchangeable potassium from

51
fertilizer (parts per million in enriched 1ayer--parts per
million in lower layers) bear some relationship to quantities
of water soluble potassium present in the original fused
phosphates. Although, of course, no particles of potassium
chloride could be recovered, there is definite evidence of
greater movement of this ion in sandy soil from fine particles

than from those of -6+10 mesh size.

Movement ofgpotassium in bulk volume of soil. In order
to study dissolution and movement of potassium from particles
of fused potassium phosphates under moist soil conditions, a
laboratory experiment was set up using Metea sandy loam and
Houghton much soil. The rate of movement of potassium from
particles incubated in soils previously brought to specific
moisture levels was found to vary with the water solubility
and particle size of the potassium source and the moisture
content of the soil. The data relative to the percent of
water soluble and total potassium remaining in fertilizer
particles recovered after moist incubation in organic soil
held at 50 and 100 percent soil moisture levels are given in
Tables 9, 10, 11, and 12. The distribution of potassium in
water soluble form with respect to distance from the fertil-
izer source in the muck soil is presented in Tables 13 and 14.

It is quite evident that a large proportion of the
water soluble potassium moved out of potassium pyrophosphate
and potassium metaphosphate of both —4+14 and -3/8+4 mesh size

particles in a relatively short period of time. Analysis of

52

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0.0m sm.0 He.0 m0.0 mm.0 mm.0 HH.H semessmwm- meseemmmmmwmmm
m.s - mm.m Hm.m mm.m HH.m 00.m mH.m ewes + m- m
m.m ,.00.m om.m 00.0 mn.m mm.m HH.m chessswms- sanemmwmmmmmm
pCmmmpm mm ma m s m H mNHm maofipnmm mHmHCmumall
hHHMCHtho CoaumnzoCH mo mama
owe mansnom
C0903 pCoonom moaofiuamm

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zoCu Copmm mmaoappma CoNHHHuCom CH mCHCHmEmC EC

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prCmH mCOHCm> on
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OH mum<E
0.mH 00.: ma.: no.3 mm.m 00.: Hm.: gems s+m\m- mpseamosameme
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m.b. 00.: Ho.: mm.m H:.m mm.m w:.m CmoE :+m\mu mumCCmOCConha
m.m HN.N m©.N mm.N wm.w OH.m Hm.m Smmg #Hluil gfimmdpom
pCmmoCm mm @H m z m H oNHm ofloaphmm mamasmpmz
kHHmCawHCo CoaumnsoCH mo mama
0mm mansaom
moaoflqum

C0903 pCooCom

Ca wCHCHmEoC 0mm mHQCHom Copmz pCmoCmm

 

.oHCumHoE uCoonoQ 0m 90 HHom xoCE CH oEHu mo memCmH mCoHCm> on oopmnsoCH Coop m>dC
hon hopmm moaoaphmn thHHHuCoM CH wCHCHmEoC ECsmmtpOC oHQSHom seems no mpHpCmCo one

Q amaqh.

Depth in centimeters

53

Lateral distance in centimeters
Fertilized band

5 3 . 5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 3.

Diagram of fertilizer placement and
sampling volumes relative to the
fertilizer band in the laboratory
dissolution studies.

54
recovered particles indicate that 45.6 percent and 94 percent
of the total water soluble potassium fraction in -4+l4 mesh
pyrophosphate and metaphosphate, respectively, was released
in a 24 hour period in muck soil containing 50 percent mois—
ture. For both the pyro- and metaphosphates of this particle
size, with increase in time of incubation the amount of water
soluble potassium recoverable remained more or less constant.
This relationship suggests that upon dissolution of the water
soluble fraction of potassium, a small part of water insoluble
form is converted into water soluble state. It is also quite
possible that because of the development of a high concen-
tration of soluble potassium in soil immediately adjacent to
the granule, an equilibrium condition exists between potassium
ions in the soil solution and that in the porous structure or
matrix of the fertilizer particle. This would tend to maintain
a constant concentration of water soluble potassium within the
particle.

At the high moisture level (100 percent) a similar pat—
tern was evident as shown in Table 10. But in this case, the
amount of water soluble potassium remaining was some what less
than that found in the particles incubated in soils at 50 per-
cent moisture. With potassium pyrophosphates of the smaller
particle size 47.6 percent of water soluble potassium was
released offer the first 24 days of incubation, whereas 95
98rcent moved out of potassium metaphosphate particles of

—4+14 mesh size. During the succeeding 31 days further

155

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00.mm 00.Hm 00.Hm Hm.Hm 0H.mm mm.mm mH.mm gems sH+sn ssHmmmpom
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mHHmmeHCo mm 0H m z m H oNHm mHoHqum mHmHCopmz

0 2

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popmnCoCH Coop m>mC thu Copmm mmHoHpCmQ CH.wCHCHmEoC ECHmmMCOQ H000» mo mquCmCU 0C5

HH mqm<8

56
decreases in water soluble potassium content were rather
minor.

In comparing the particle sizes of the two sources for
the effect of this factor on the release of potassium, it was
noted that for pyrophosphates, the -3/8+4 mesh size particles
behaved somewhat similar to the smaller particles. -For
example, in muck soil at 50 percent moisture level, 45.6 per-
cent of the total water soluble potassium moved out of the
small particles in one day whereas 53.6 percent of water
soluble potassium was released from the larger particles
during the same period of time. However, the water soluble
potassium contents of the pyrophosphates studied are not
exactly the same, and Tennessee Valley Authority reports
indicate that the degree of crystallinity of these materials
may be somewhat different which could influence rate of re-
lease of potassium from the water soluble form.

For metaphosphates the results obtained were substan—
tially different. From data in Tables 9 and 10 it can be
calculated that about 95 percent of the water soluble potas-
sium moved out of the ~4+l4 mesh particles within 24 hours
time, while from -3/8+4 size particles 67-68 percent dis-
solved out during the same period of time. After a month of
moist incubation of the organic soil, this relationship did
not change appreciably for either the low or the high soil

moisture levels.

57

The physical appearance of the recovered particles
after incubation in moist soil for one month was different
for the pyrophosphates and metaphosphate materials. There
was practically no change in the appearance of pyrophosphate
particles of either the small or large sizes after they were
incubated. It was very easy to separate the fertilizer
particles from the surrounding soil. But with metaphosphate
particles it was very difficult since the particles had be-
come soft and the external surface was completely covered
with and cemented to the soil.

Evaluation of data in Table 11 indicate that 1.88 per-
cent or 7.5 percent of the original potassium, was lost from
-4+l4 mean pyrophosphate granules during the first 24 hours
incubation in organic soil at 50 percent moisture. From the
larger —3/8+4 mesh particles, 3.4 percent or 13.7 percent of
the total potassium was lost during the same period. The
greater loss from the larger particles can be accounted for
in part by the fact that they originally contained more
water soluble potassium. After the first 24 hours incubation
there was a gradual migration of potassium from both groups
of pyrophosphates resulting in a further reduction of 7 to 8
percent of the original potassium content of this fused potas-
Sium phOSphate.

In contrast, about 55 percent of the total potassium
was lost from the -4+l4 mesh size metaphosphate during the

first day of incubation assuming there was no physical

58
sloughing of the softened particle surface. During the next
31 days a gradual dissolution of potassium occurred, so that
at this time, 60.0 percent of the original potassium had
migrated from the small metaphosphate particles. With respect
to -3/8+4 mesh size particles of metaphosphate it was found
that only 21.3 percent of the original potassium was released
during the first 24 hours incubation at 50 percent soil
moisture level. At the end of 32 days 72 percent of the
total potassium or 28 percent K20 remained within the particles.
Upon subtracting the water soluble potassium content of pyro—
phosphate and metaphosphate materials from the values for
total potassium and comparing the results with potassium
content of particles recovered after full incubation, it is
noted that they are quite similar. This agreement is con—
sidered as evidence of the release of water soluble potassium
with only slight loss of this element from water insoluble
form.

With the particles incubated at the 100 percent moisture
level, the results obtained were similar as noted in Table 12.
Here again the amount of potassium lost during incubation was
slightly greater than that released from granules at 50 per-
cent moisture.

The distribution of water—extractable potassium with
respect to the position of the fertilizer source in moist
organic soil with time is presented in Tables 13 and 14. The

water soluble potassium content of the original muck soil was

 

 

 

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H0.0 H0.0 00.0 H0.0 H0.0 00.0 00.0 0H.00 H0.00 0
00.H HH.0 HH.0 HH.0 0H.0 00.0 HH.0 00.0H 00.00 0
00.H 00.0 H0.0 H0.H HH.0 00.0 00.0 00.00 00.H0 0
H0.H 00.0 H0.0 00.H 00.H 0H.0 00.H 00.HH 00.00 H 0000 0+0\0-
00.H 00.0 H0.0 H0.0 0H.0 H0.0H 00.0 00.0H 00.00 00
HH.0 0H.0 00.0 H0.0 00.0 H0.0 H0.0 00.0H H0 00 0H
00.0 00.0 00.0 00.H 00.0 00.0 00.0 HH.HH H0.00 0
H0.H 0H.0 00.0 00.H 0H.0 00.0 00.0 00.0H H0.00 0
H0.H 00.0 HH.0 00.H 00.0 H0.0 HH.0 H0.HH 00.00 0 0000000000000
00.0 00.0 H0.0 H0.H H0.0 00.0 00.H HH.HH H0.Hs H 0000 0H+0- 00H0000o0
080 050 CO0C0o 0E0 080 CO0C0O 080 050 C00C0O CoH00Q 0NHm 0H0H0C0m 0H0HC0002
0-0 0-H 0-0 0-H 0-0 0-H -000H
0
000 0-0 00000 000 0-0 00000 000 0-H 00000 0m00

 

050 000300HQ ECH0000om 0HCCHom C0003 H0098 mo 0C00C0m

 

.0CC0mHoE 0C00C0Q OOH 00 HH00 X055 CH 0EH0 C0H3

CoH000HHQQ0 00 000H0 0C0 EOCm 000000 0C0 000C000H0 mCoHC0> 00 ECH000000 0o CoH0CQHC0mHQ

0H 00000

61
extremely low as indicated in Table 1. However, this quan-
tity of potassium present in the soil has been subtracted
from the values obtained after incubation and so the values
given in the table essentially represent the amount of water
soluble potassium released from the fertilizer particles.

Approximately three-fourths of the potassium leached
from the fertilizer source was recovered after one day in
the 2 x 2 x 10 centimeter volume of organic soil (low moisture
level) in the center of which the fertilizer band was placed.
Lateral movement of potassium decreased rapidly with distance
from the potassium source. For instancg for the -4+l4 mesh
pyrophosphate in the 2 x 2 x 10 centimeter volume of soil im-
mediately to the side of the first sampling volume, 12.2 per-
cent of the leached potassium was found, whereas 3-5 centimeter
away from the fertilizer band only 1.4 percent of the water
soluble potassium was recovered. Directly below the fertil-
izer band, values of 3.1 and 2.1 percent were recorded for
depths of 3-5 and 5-7 centimeters. _As further indication of
limited migration at the 50 percent moisture level, only 1.7
percent of the leached potassium was found 3-5 centimeters
below the second sampling volume as shown in Table 13. The
downward movement of potassium from a position 3-5 centi-
meters laterally from the place of application of fertilizer
was very small with only 1 percent of potassium having been

recovered at 3-5 and 5-7 centimeter depths.

62

Incubating the soil for 4 days resulted in similar
trends in the amounts of water soluble potassium diffusing
away from the potassium pyrophosphate in organic soil at low
moisture content. The concentration of potassium in the
2 x 2 x 10 centimeter volume of soil in the center of which
the fertilizer band was placed continued to decrease, while
the lateral movement of potassium increased. A total of 15.5
and 4.5 percent of the total water soluble potassium dissolved
from this fertilizer was recovered from the two lateral
sampling volumes adjacent to the first sampling volume. The
downward movement of potassium also increased as shown by
the fact that immediately below the fertilizer band after
four days incubation the amount of potassium increased to
6.6 percent of the total recovered, whereas at the two lateral
samples at this depth 2.1 and 2.0 percent of the diffusable
water soluble fraction were found. Downward and lateral mi-
gration of potassium also continued in the slice of soil 4
centimeters below the place of application of fertilizer for
the period of 2 to 4 day incubation period.

The distribution of water soluble potassium from fertil-
izer for the 32 day incubation period can be more clearly
seen in Figure 4. For example, after approximately one month
incubation the potassium level in soil around the fertilizer
dropped to 56 percent of that leached out, while 1-3 centi—
meters to the side, the percentage did not change. As might

be expected in the area 3-5 centimeters to the side of the

63
fertilizer band, an increase of from 1.4 to 5.6 was recorded.
Although there are minor irregularities with time for potas-
sium distribution, migration of potassium away from the
fertilizer source in both lateral and vertical directions
in organic soil was noted.

With potassium pyrophOSphate, with one exception there
was no marked difference in the behavior of particles of dif-
ferent sizes with respect to the movement of potassium from
the water soluble fraction. For the -3/8+4 mesh pyrophos-
phate, values for the soil volume 1-3 centimeters away and
at the same level as the fertilizer band were exceptionally
high after the 24 hour incubation period. For instance, the
water soluble potassium moved out after two days increased
from 8.9 to approximately 19 percent, to 22 percent after
4 days and to about 25 percent after 8 days incubation.

After 32 days, 24 percent of the diffusable potassium was
still located in this volume of soil. No explanation can be
offered for the behavior of the soluble potassium within this
zone, other than that mentioned previously in dissolution
studies.

With potassium metaphosphates the results obtained for
movement of water soluble potassium with time were similar
to those for pyrophosphate. With the smaller sized particles
incubated in muck soil at 50 percent moisture, 72 percent of
the water soluble potassium was concentrated in the zone of

'Soil 2 x 2 x 10 centimeters in the center of which the

64
fertilizer was placed. The amount of soluble potassium with-
in this volume of soil decreased with an increase in incubation
time. After 2 days 71 percent of this diffusible fraction was
found in this zone, decreasing to about 68, 61, 57, and 51 per-
cent of the total potassium moved out after 4, 8, 16, and 32
days indubation, respectively. In the laterally adjacent
soil volume after 1 day incubation, 9.2 percent of the dif-
fusible water soluble potassium remained in the -4+l4 mesh
metaphosphate particles. Here there was only slight change in
the amount of soluble potassium with an increase in time of
incubation. However, there was a significant increase in
concentration of water soluble potassium 3-5 centimeters away
from the place of application of fertilizer with time, ranging
from 2.4 percent after 1 day to 6.0 percent after 32 days in-
cubation. Some effect of particle size on a reduction in
migration is evident in data in Table 13 for the metaphosphate
sources. In all probability this is in reality an expression
of a decrease in rates of dissolution. However, no proof for
this is available from these data since all calculations have
been made on basis of 100 percent. It can be noted from
Figure 4 that downward as well as lateral movement of potassium
ions occurred with time. An interesting point of these
migration studies is that especially in the early stages of
incubation, a considerably higher proportion of the diffusable
potassium was found in the laterally adjacent zone rather than

in the vertically adjacent volume. This phenomenon was less

65

Distance in Centimeters

l 3 5 l l 3 5 l l 3 5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1
76.4 12.2 1.4 61.3 15.6 4.8 56.0 12.4 5.6
X X X
3
3.1 1.7 1.0 7.4 2.1 2.5 15.2 .2.8 2.2
5 .1 '
2.1 1.0 1.0 3.8 1.5 1.1 3.2 2.0 0.7
. 7
1 day ‘ 8 days 32 days

K2 Ca P207 - -4 + 14 mesh

 

1 3 5 1 1 3 51 1 3 5

 

Depth in Centimeters

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1
76.0 8.9 1.6 55.1 24.9 2.0 50.2 24.2 3.6
x x x
3
2.1 2.2 1.8 6.9 4.1 1.0 7.9 4.2 2.1
5
2.1 2.2 3.0 3.2 1.0 1.0 4.9 1.9 1.0
7
1 day 8 days 32 days
K2 Ca P207 — —3/8 + 4 mesh

Fig. 4. Cross-section distribution of potassium at
various distances and depths from place of
fertilizer application (x) with time in
muck soil at 50% moisture, expressed as per-
cent of total water soluble potassium
released.

Depth in Centimeters

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 4.

66

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Distance in centimeters
1 1 5 1 1 3 5 1 1 3 5
’ 1
72.0 9.2 .4 61.2 10.4 4.6 51.0 12.0 6.0
x x x 3
4.9 2.4 .O 6.0 2.5 2.2 8.7 6.1 3.4
‘ 5
3.2 2.0 .91 5.3 4.4 3.3 6.1 4.2 2.5
1 day 8 days 32 days
K P03 ~ —4 + 14 mesh
1 1 5 1 1 3 5 l l 3 5
81.0 8.2 .2 69.8 12.1 3.2 64.5 12.0 5.1
x X X 3
2.0 1.0 .O 5.1 2.0 1.6 6.9 3.0 1.6
5
2.0 2.5 .4 4.0 2.2 0.8 3.9 2.0 1.0
1 day 8 days 16 days

KPO3 - -3/8 + 4 mesh

Continued

 

67
marked at the end of the incubation period, but only for the
smaller sized fused potassium phosphates.

A comparison of data in Tables 13 and 14 on the effect
of soil moisture level on migration of soluble potassium in-
dicates that doubling the percent moisture from 50 percent
to 100 percent had very little effect on the outward movement
of potassium from the fertilizer source. 1

A dissolution-migration study similar to that discussed

for organic soil was conducted using Oshtemo sandy soil.

“Vum-g- , - a. ,
.

Except for a few variations the quantities of potassium
remaining in soluble form in recovered pyrophOSphate and
metaphosphate particles were similar to those found for com-
parable materials recovered from the organic soil. The dis-
crepancies in question involve the fact that no water soluble
potassium was found in either -3/8+4 mesh pyrophosphate or
-4+14 mesh metaphosphate particles at the end of the incubation
period in Oshtemo sand with a high water content. However,
moisture characteristics of the two soils and fertilizer dis-
solution data point to the fact that there is more available
moisture in Oshtemo sand containing 20 percent moisture than
there is in Houghton muck at 100 percent moisture. Thus,
maximum dissolution of soluble fertilizer potassium should
occur with the sandy soil system.

The loss of total potassium from the two types of

fertilizers is presented in Tables 15 and 16. Actual dis-

solution with time was similar to the patterns already

m

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70
described for organic soils. The large particle of potassium
pyrophosphate again lost more potassium than the smaller ones
while the reverse was true for the metaphosphates. From
these data it is evident that the release of total potassium
from the two types of fused phosphates was not appreciably
different for a wide variation in soil moisture level, although
a minor exception would be -4+l4 mesh pyrophosphate.

It is interesting to compare the actual loss of total
potassium from the fertilizer particles with that representing
the difference between the water soluble fractions before and
after in the recovered particles. In general, the loss based
on total analysis are larger by values up to 2.7 percent.
This suggests that during incubation some of the less soluble
potassium within the particle was changed to a water soluble
state, which would be evaluated as a higher percent of water
soluble potassium remaining in the fertilizer. The one
exception to this trend is the erratic behavior of the -3/8+4
mesh pyrophosphate particles.

When the several fertilizer materials were placed in
moist sandy soil, the distribution pattern of water soluble
potassium from soil at different distances from the fertil-
izer band was quite similar to that found for organic soil.
With potassium pyrophosphate of smaller size, a large amount
Of potassium was concentrated around and below the place of
application of the fertilizer. From Figure 5 it can be seen

that in a volume of soil 2 x 2 x 10 centimeters in the center

 

 

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'Depth in Centimeters

Distance in Centimeters

l l 3 5 l l 3 5 l l 3 5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 1
78.7 10.8 1.5 69.2 15.8 3.2 64.9 9.2 1.6
x x x
3 3
2.4 1.9 1.3 1.8 1.8 1.9 3.9 8.2 4.4
5 5
0.9 1.0 1.6 2.6 1.8 1.1 3.3 2.6 1.9
7 ’ 7
1 day 8 days 32 days
K20a P207 - -4 + 14 mesh
11 1 3 5 1 1 3 5 1 l 3 51
80.1 6.2 2.7 57.6 27.9 4.4 55.5 23.3 6.7
3 x x x 3
1.6 1.8 1.8 3.0 4.3 1.6 5.2 5.7 2.4
5 5
2.0 2.0 2.1 0.8 1.7 1.7 2.5 0.5 0.4
1 day 8 days 32 days

KQCa P207- -3/8 + 4 mesh

Fig. 5. Cross—section distribution of potassium at
various distances and depths from place of
fertilizer application (x) with time in
sandy soil at 5% moisture, expressed as per-
cent of total water soluble potassium released.

Depth in Centimeters

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

22.7

 

 

 

 

 

 

 

 

28.8

1.0

 

0.8

0.5

 

 

 

 

 

 

0.3

 

0.5

 

0.4

 

 

 

 

 

Distance in Centimeters
l 3 5 l 3 5
74.5 8.7 2.4 57.9 28.0 2.8
x x
2.4 2.4 2.7 3.7 1.8 1.8
2.4 2.4 2.1 1.6 0.9 1.5
1 day 8 days
KPO3 - -4 + 14 mesh
1 1 5 l 3 5
91.5 4.7 0.6 74.7 19.6 0.8
x x
0.6 0.5 0.8 2.0 l 2 0.5
0.3 0.4 0.6 0.3 0.3 0.5
1 day 8 days
KPO - -3/8 + 4 mesh'
Fig. 5. Continued

16 days

75

of which the fertilizer material was banded, almost 80 per-
cent of potassium was concentrated, and during 32 days of
incubation only 16 percent of this moved out. To a distance
of 1-3 centimeters from the fertilizer band about 10 percent
of the water soluble potassium moved out during the first
day of incubation. In this area there was a gradual increase
of potassium with time. After 16 days incubation as much l
as 30 percent of the water soluble potassium released was I
concentrated in this zone. But 3-5 centimeters from the ‘
first sampling area, the amount of potassium recovered was i
very small. Below 2 centimeters from the place of appli-
cation of the fertilizer there was very little movement of
potassium laterally or vertically.

With pyrophosphate of ~3/8+4 mesh particle size, about
80 percent of the migrated potassium was concentrated on the
first day in a volume of soil 2 x 2 x 10 centimeters in the
center of which the fertilizer was banded. After 8 days this
was reduced to about 58 percent after which further migration
was slight. Here again there was very little downward move-
ment of potassium below the fertilizer source. The puzzling
feature of the migration pattern is the concentration of
soluble potassium in the first sampling volume adjacent to
that enclosing the band of fertilizer. At this period ap—
proximately 28 per cent of the total water soluble potassium
migrated was concentrated in this 2 x 2 x 10 centimeter zone
as compared to only 3 percent immediately below the potassium

pyrophosphate particles.

76

From a theoretical standpoint, potassium ions from a
fertilizer source should diffuse outward in equal concen—
tration for all directions in a soil mass of uniform moisture
content. However, in these studies movement in the upward
direction is soon limited by the presence of the soil surface.
Assuming these ions concentrate near the surface, they would
then migrate laterally in perhaps the upper half centimeter
of soil to the adjuacent sampling volume.

In soil supplied with smaller sized potassium metaphos-
phate, 74 percent of the diffusible water soluble potassium
was concentrated in a volume of soil.2 x 2 x 10 centimeters
in the center of which the fertilizer was banded. There was
a gradual reduction in the amount of water soluble potassium
in this area till at the end of 32 day period only 50 percent
of potassium dissolved from the fertilizer was located in
this zone. In the sampling volume immediately below this
position the potassium concentration increased from 2.4 per-
cent after one day incubation to 4.2 percent at the end of
the study. However, in the first layer of soil 2 centimeters
away from the place of application of the fertilizer, the
concentration of water soluble potassium increased from 8
percent of the total moved out in 1 day to almost 23 percent
in 32 days. This again is considered to be a reflection of
position of the fertilizer band relative to the respective

sampling volumes of soil.

 

77

With the metaphosphate particles of larger size,
slightly more than 91 percent of the total water soluble
potassium dissolved was concentrated in the volume of soil
in which the fertilizer was banded after 24 hours of moist
incubation. Thirty—two days later, 61 percent was still
located in this position. In the laterally adjacent volume,
the concentration of water soluble potassium increased from
4 to 28 percent in 32 days time. Yet there was very little
change in the potassium content of soil below or to the side
of this volume of soil.

Similar migration patterns for potassium were obtained
with the fused potassium phosphate incubated in Oshtemo
sandy loam at the higher moisture level as shown in Table 20.
In all cases, the concentration of potassium in the volume
of soil in which the fertilizer was located was less on the
first day, whereas more potassium was located in the volume
of soil next to this. Slightly more downward movement of
potassium was also noted here.

In all cases studied, a large portion of the water
soluble potassium moved out in relatively short period of time.
Apparently, these fertilizer particles are hygroscopic. As
soon as they are placed in moist soil, they start absorbing
moisture from the surrounding medium.

Data presented in Table 21 show that when potassium
metaphosphate particles of -4+l4 mesh size were incubated in
Kalamazoo sandy loam containing 2.1 percent moisture, the per—

cent water in an area immediately surrounding the particles

78
increased. In 12 hours time in this zone there was 3.8 per—
cent moisture and in 24 hours time the moisture content
increased to 4.6 percent. Similarly when the soil mass con—
tained 5.2 percent moisture, within 24 hours time there was
an increase of moisture to 6.1 percent in the soil adjacent
to the fertilizer particle. This effect is similar to that
reported by Lawton and Vomocil (26) for superphosphate
granules.

Close examination of unweathered particles of pyrophos-
phate and metaphosphate under a microscope show that they
contain rather rough or uneven surfaces, often with the
presence of pores or crevices. Some surfaces of potassium-
calcium—pyrophosphate particles appear quite dense with few
cavities, while others are extremely uneven with a multitude
of crevices and needle-like crystals bridging the pockets.
The metaphosphate particles generally exhibit a more solid,
though rough surface with few visible pores. Many small
elongated crystals can be found in the minor depressions.
These observations indicate that water should be able to dis—
solve and penetrate these materials with relative ease.

It is believed that moisture movement to the fertilizer
particles is controlled by vapor diffusion as proposed by
Lehr, gt al. (27) for granules of monocalcium phosphate placed
in moist soil.

With the entry of water into the particles the soluble

substances contained therein dissolve. This results in the

79

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80

TABLE 21

Moisture content of soil surrounding potassium
metaphOSphate particles incubated in Kalamazoo
sandy loam at various moisture levels.

 

Percent Moisture in Soil Adjacent to Particle*

 

Time of Incubation in Hours 1

 

0 1 2 4 8 12 24
2.1 2.1 2.6 2.8 3.0 3.8 4.6 ii
5.2 5.2 5.2 5.4 5.8 6.0 6.1

12.0 12.0 12.0 12.4 12.8 13.6 14.0

 

 

*Sampling volume represented by a cylinder 20 millimeters in
diameter and 20 millimeters in length.

81

formation of a very highly concentrated solution in and
closely surrounding the fertilizer particles. Since water
has a very high dielectric constant, the electrical proper-
ties of the solvent weakens bonding forces between ions and
molecules resulting in the rapid dissolution of the particles.
In the case of the pyrophosphate, the matrix of the particle
remain relatively stable because of resistant P-O-P bonding,
whereas solubility of metaphosphate proceeds to completion
upon exposure to moisture.

The relationships between solubility and particle size
of compounds such as fertilizers is well known. If the
solvent comes in contact with a greater surface it will be
able to dissolve the solid more rapidly. In addition to in—
creasing the rate of solubility, the particle size also influ-
ences actual solubility. The smaller the size, greater would
be the solubility.

The difference in concentration of the solution inside
and outside results in a diffusion process. In an ideal
system, the osmotic pressure causes the ions or molecules
of the stronger solution to be transferred to the weaker
solution until the osmotic pressures are equalized, when
equilibrium is attained. In other words, the strong solution
gradually becdmes more dilute, so that the existence of
osmotic pressure causes the progressive dilution by the entry
of water. In an ideal solid—liquid or liquid-liquid system,

with time, equilibrium is reached whereby the concentration

82

of the solutions becomes the same. But this is unlikely to
occur in a soil-water-fertilizer system. First of all water
may act as a limiting factor here. Free movement of dis-
solved ions of a solid can take place only if there is a cone

‘ tinuous water film outward from the dissolving solid. With

a relatively low water content in moist soil, water is drawn
as it were, from the surrounding soil towards the fertilizer
particles. This results in zones of progressively diminishing
moisture contents from the particles towards the outer mass

of soil. As a result the potassium released from the particles
tend to be concentrated in areas adjoining the fertilizer
source. Also the lack of continuity of capillary pores may
impede outward diffusion of dissolved salts. Equilibrium
between the solution within the fertilizer particles and that
in the surrounding soil may be difficult to establish due to
continued fixation of potassium by soil minerals, though in
this zone, fixation is probably overshadowed by an extremely

high concentration of potassium ions in solution.

Dissolution ofgparticles of potash fertilizers under
field conditions. In another experiment an attempt was made
to study the dissolution and disintegration of fertilizer
particles placed on the soil surface under field conditions.
During the 40 day period which the particles were exposed in

the field, the area received a total of 3.84 inches of precip-
itation.

83

During the first 10 days, only 0.12 inches of rain fell
and particles of all materials were recovered. However, after
20 days exposure during which several light showers occurred,
the potassium chloride granules had dissolved and in addition
it was impossible to recover the -4+l4 mesh metaphosphate
particles. The next exposure period included heavy rains of
1.6 inches on June 1 and 2. After the beating action of these
rains, many of the fertilizer particles were embedded in the
soil surface, but it was still possible to recover the large
metaphosphate particles as well as both large and small pyro-
phosphate materials. After 40 days exposure to the elements,
all particles of potassium metaphosphate had disintegrated
partly due to the physical action of an additional 1.26 inches
of rain. Particles of pyrophosphate could be easily recovered,
but they appeared to have undergone solvent action and some
physical disintegration.

The analysis of fertilizers after varying exposure
periods to field conditions are listed in Table 22. At the
first sampling date potassium chloride particles contained
50.7 percent of the original potassium, while the —4+l4 mesh
pyrophosphate and metaphosphate had lost 31.7 and 95.8 percent
of their water soluble potassium, respectively. The larger
particles of fused potassium phosphates retained about the
same percent of their water soluble potassium content. After
20 days exposure, about 70 percent of the water soluble

potassium from pyrophosphate particles of both sizes had been

 

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1
25 - -3/8 + 4 mesh
20'-
15 - ___
10‘- Total Potassium

 
   

Percent K20 in Particles

Water SolublePotassium
I

10 20 30 40
Time in Days

25 I - 4 + 14 mesh

 

 

Total Potassium

 
 
   
   

Water
Soluble Potassium
I

I
10 20 30 40
Time in Days

 

Percent K20 in Particles

Fig. 6. Potassium remaining in potassium
pyrophOSphate particles after
exposure in the field for varying
lengths of time.

Percent K20 in Particles

86

.Ilm’h:“'\£

mmi- - ‘.
5'1.

  
    

35- - 3/8 + 4 mesh

30-
25-

20-

15- Total Potassium \ \

Water Soluble Potassium

1'0 20 3'0 7 7 7 48

Time in Days

Fig. 7. Potassium remaining in potassium

metaphosphate particles after

exposure in the field for varying
lengths of time.

87

leached out. Virtually no water soluble potassium was present
at the end of the experiment.

Data presented in Figure 6 show that although there was
no water soluble potassium present in the granules after 40
days exposure in the field, 6.6 percent total potassium was
still retained in the smaller size pyrophosphate granules and
13.7 percent in the larger ones. The pattern of dissolution
of potassium from the large particles of metaphosphate as

given in Figure 7 is somewhat similar to that for pyrophosphate

 

for the first 30 days exposure. However, in the 10 day period if
thereafter, complete dissolution and/0r disintegration of

these metaphosphate particles occurred. It is interesting to

point out that large potassium-calcium pyrophosphate particles

were recovered from a 1957 field experiment about 10 months

after a surface application. At this time they contained

3.54 percent K20, which was probably about 50 percent of their

original potassium content.

SUMMARY

Upon comparing the pyrophosphate, metaphosphate, and
chloride forms of potassium in the greenhouse in 1957, it

was found that the yield of beans grown on Metea sandy loam
in which these various potassium fertilizers were mixed was
significantly higher from pots receiving pulverized potassium
metaphosphate materials. However, the potassium content of
plants was not affected by the type of carrier or the particle
size. When bean plants were grown on organic soil, yield

and potassium uptake were not significantly influenced by the
water solubility of the potash source or the particle size.
The mixed application of the fertilizer resulted in signifi—
cantly higher yield and potassium uptake by plants grown on
this soil, indicating that to obtain maximum effectiveness

of fertilizer potassium it was necessary to mix the supple-
mental nitrogen and phosphate fertilizer throughout the
entire volume of organic soil.

Water solubility of the potassium carrier was not a
factor in the yield of millet grown on Kalamazoo sandy loam
in the greenhouse in 1958. Application of finer particles
resulted in slightly better growth than did the use of
coarser ones, and banding of the fertilizer was more effective

than mixing. When the same plants were grown on Houghton

0771-”???
. —.V X,,;

“finm‘fl‘égl‘f ‘3'.“ 1

89
muck soil, highest yields were obtained with applications
of metaphosphate. Potassium content of plants increased
with increase in water solubility of the fertilizer, but
neither particle size nor placement had any significant
influence on uptake of potassium except in the case of the
metaphosphate material. In general, it can be concluded
that all the potassium sources were about equally effective
in promoting the growth of plants even though potassium
content of plants increased with increase in soluble
potassium content of the fertilizer.

The dissolution patterns of potassium—calcium pyro—
phosphate and potassium metaphosphate involving continued
leaching with water show that the water soluble potassium
content was rapidly released from both materials. No marked
difference was noted between the meta- and pyro- compounds
except that the small metaphosphate particles disintegrated
after continued leaching. Even after considerable leaching,
only a small release of the initially non-water soluble
fraction was noted in several instances.

When the fused potassium phosphates were leached with
water in soil column, recovery of potassium from the soil
was fairly well correlated with the original water soluble
potassium contents of the fertilizer. A direct, though im-
perfect relationship was noted between particle size of a
specific potash source and the potassium released from the

fertilizer. The exchangeable and water soluble potassium

 

90

fractions, representing loss from fertilizers, were found
concentrated near the surface. Demarcation between the
advancing front of leaching potassium ions from fertilizer
and the uniform ion concentration of the soil mass below
was quite sharp.

Studies of the dissolution and migration of potassium
from the metaphosphate and pyrophosphate fertilizers under
conditions similar to those in the field also showed that
the water soluble fraction rapidly diffuses out of both the
large and small particles. However, loss from the large
particles was found to be somewhat slower. After 1 to 2
days moist soil contact the release of potassium from the
fertilizer source was very slow during the following 30
days period. Some water soluble potassium remained in the
fertilizer particles largely as a result of equilibrium
with a high concentration of soluble potaSsium in soil
adjacent to the fertilizer source. Only very minor conver—
sion of initially non-water soluble potassium to a soluble
form is believed to have occurred.

In incubation studies, approximately three-fourths of
the potassium dissolved out of the fertilizers was recovered
from a volume of soil 2 x 2 x 10 centimeters in the center
of which the fertilizer was banded. Lateral movement of
potassium decreased rapidly with distance from the potassium
source. With an increase in time of incubation there was

an increase in the soluble potassium content of the lateral

91

adjacent volume of soil but there was very little downward
movement of potassium.

When the several potash fertilizers were placed on
the soil surface in the field for a period of 40 days all
potassium chloride granules and potassium metaphosphate
of —4+l4 mesh particle size disintegrated after 20 days
exposure to weather. Large and small potassium pyrophos-
phate particles were recoverable even after 40 days.

After 10 days exposure, potassium chloride was found to
contain only 50.7 percent of its original potassium.
During the same period —4+l4 mesh pyrophosphate and meta-
phosphate lost 30.7 and 95.8 per cent of the water soluble
potassium, respectively, but little or no potassium from
their water insoluble fractions. After 20 days exposure
70 percent of the water soluble potassium was missing
from pyrophosphates of both sizes. Analysis of the large
pyrophosphate particles after long exposure periods indi-

cates the original water-insoluble potassium is released

very slowly.

 

LI TERATURE CI TED

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DeMent, J. D., and Stanford, 0., Effect of water solubility
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T"

 

 

 

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_.—_—zn_‘nl.iflfi

ml v.24)“ . . - .
J

_ _ .- n

‘ 1.05%"!1.

 

 

 

 

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95

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Wilde, S. A., and Rosendahl, R. 0., Values of feldspar
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43:366-367 (1945).

 

 

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