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II. New and Improved Fertilizer Materials
RANDALL J. JONES AND HOWARD T. ROGERS
world reserves of phosphate which, according to calculations based on
estimates made by Mansfield (1942), are distributed in three major areas
as follows: Tennessee, 1 per cent; Florida, 24 per cent; and western intermountain states, 75 per cent. Prior to 1946, Florida and Tennessee
produced approximately 95 per cent of the phosphate rock of the United
States, I n 1946, however, the western states produced more than 7 per
cent of the US. production; and in 1947, more than 13 per cent (Editorial, 1948).
Bell and Griffith (1947) have studied transportation costs in relation
to development of new phosphorus industries in the West. They have
shown that, on the basis of calculated production costs, triple superphosphate manufactured in the western phosphate fields would have a
trade area of a t least 17 western and central states. This area would be
extended to several other states if more concentrated phosphates were
a. Concentrated Superphosphate (40-50 Per cent P,05). Concentrated superphosphate, 40-50 per cent P206,
has been variously designated
as “double,” “triple,” and “treble” superphosphate. Although this
product has been manufactured for a long period on a commercial scale,
only in recent years has production expanded appreciably. According
to Jacob (1948), the amount of P20aproduced in this form increased
from about 43,000 tons in 1930 to over 170,000 tons in 1947; and a
considerable expansion of the present production capacity is anticipated.
The current demand is considerably greater than the supply,
Concentrated superphosphate is produced by t.reating phosphate rock
with phosphoric acid which is made by either the wet-process method
or by the electric-furnace process. The wet-process method is used most
extensively for current production. It involves treating phosphate rock
with sulfuric acid to obtain the phosphoric acid necessary for acidulating
additional phosphate rock. In the electric-furnace process, elemental
phosphorus is produced and then burned to form P2OS.The P2OS gas
is absorbed in water to produce phosphoric acid which is used in the
same manner as indicated for the wet process. Electric-furnace acid is
of higher purity than the wet-process acid; consequently, it has been
used extensively by the chemical industry.
Extensive tests have been conducted with concentrated superphosphate, using a wide variety of crops and soils. As a source of phosphate it is fully as effective as ordinary 18-20 per cent superphosphate.
This is borne out by results obtained in all the major agricultural regions
in the United St,ates. It should be pointed out that concentrated superphosphate made by the wet process carries only a small quantity of
sulfur (about 3 per cent Sod, whereas, ordinary superphosphate contains
NEW FERTILIZERS AND FERTILIZER PRACTICES
about 50 per cent by weight of gypsum. The amount of sulfur in superphosphate made from electric-furnace acid is negligible. This may be
an important factor in areas of sulfur-deficient soils. An average of
results obtained from 1060 cotton tests in the four states of Alabama,
Georgia, Mississippi, and Tennessee showed a 5-per cent increase in yield
from adding sulfur in the form of either gypsum or ammonium sulfate to
triple superphosphate, according to a recent summary by the Tennessee
Valley Authority (1946). Similar tests conducted wit.h wheat and corn
on many of the same soils gave no indication of sulfur response. Significant response to sulfur applications for clover has been observed in
Florida (Bledsoe and Blaser, 1947). Sulfur deficiency is probably most
acute in the western states, particularly in Oregon, California, and Washington. This lack of sulfur in most of the recently developed high-analysis phosphate fertilizers should not be overlooked.
b. Defluorinated Phosphates. Some of the most intensive research
during recent years directed toward the development of new fertilizer
products of commercial value has been centered on various phosphate
fusion or sintering processes. The principle of defluorination of rock
phosphate has been extensively developed by the U.S.Department of
Agriculture and the Tennessee Valley Authority. On the basis of this
research, commercial production of defluorinated phosphate is now under
way by the Curonet Phosphate Company. Also, the TVA is continuing
developmental work with defluorinated phosphate on experimental-plant
scale. Although the processes are different in certain respects, in both
cases the principal product formed is alpha tricalcium phosphate. In
the Coronet process, rock phosphate is defluorinated by adding a high
percentage of Si02 (about 45 per cent) and sintering, but not fusing, the
material. This process has been described by Whitney and Hollingsworth (1949). The final product contains about 20 per cent total P205
and 0.05 to 0.15 per cent fluorine. Because of the low fluorine content
it has been used chiefly as a mineral supplement for livestock during
the last few years, since the product commands a higher price for this
use than as a fertilizer. The effectiveness of this product as a fertilizer
material has been investigated to only a limited extent in greenhouse
pot experiments. Results from these studies show its availability as a
source of phosphorus for plants to be about equal to that of superphosphate, This material has the disadvantage of being low in P205
The TVA product, fused tricalcium phosphate, containing about 27
per cent P205, is produced by the following process: Phosphate rock is
defluorinated by heating in the presence of silica and water vapor until
the charge becomes fluid and the fluorine content is reduced to about,
RANDALL J. JONES AND HOWARD T. ROGERS
0.4 per cent. A unique feature of the process is the quenching of the
molten material as it comes from the furnace, which gives a product
approximately 90 per cent finer than 10 mesh and about 50 per cent of
which passes a 40-mesh screen. This product, like the Coronet material,
does not absorb moisture, is free-flowing, and remains in excellent physical condition. This process was described by Hignett and Hubbuch
(1946) and is illustrated in Fig. 2.
Pig. 2. Manufacture of fused tricalcium phosphate.
On the basis of greenhouse and field tests, it appears that satisfactory
crop response is obtained when the fluorine content is reduced to about
0.4 per cent (MacIntire et al., 1944; Tennessee Valley Authority, 1945;
and Terman, 1944). Rather extensive field tests have been conducted
with fused tricalcium phosphate, especially in the Southeast. The effect
of particle size on availability to crops has been of particular interest.
This product has compared favorably with concentrated superphosphate
in most tests on acid soil (Karraker et al., 1941; O’Brien, 1944; and
Roberts et al., 1942). Row crops such as corn, tobacco, and cotton,
however, do iiot appear to respond quite so well as vetch, alfalfa, and
permanent pastures. I n some experiments response has been greater
when the product was ground to pass a 40-mesh screen as compared with
the unground material screened a t 6 or 10 mesh (Tennessee Valley
Authority, 1915; Terman, 1944). Grinding, of course, increases cost of
production; and on the basis of present information, it does not appear
justifiable if approximately 50 per cent of the quenched unground material passes a 40-mesh screen.
NEW FERTILIZERS AND FERTILIZER PRACTICES
The level of phosphorus in the soil apparently affects crop response
to fused tricalcium phosphate, and crops on soils of extremely low phosphorus content give lower yields when fertilized a t low or moderate rates
with this source of phosphorus than with superphosphate.
Tests in the western states indicate that this product is not a promising source of phosphorus on alkaline and calcareous soils (Hinkle, 1942;
Jones, 1947 ”) . Investigations in this region have not been adequate for
final conclusions, but expanded research now under way should make
possible a better evaluation of this material in the near future.
Extensive solubility studies have been conducted by Jacob et al.
( 1947) with alpha phosphates, using the standard neutral ammonium
citrate and 2 per cent citric acid procedures. They use the term “alpha
phosphate” to represent a group of defluorinated phosphates that are
composed largely of alpha tricalcium phosphate and which iAcludes both
the Coronet and the TVA products. These investigators reported that
the solubility of defluorinated phosphates containing less than 0.5 per
cent fluorine ranged from approximately 65 to over 90 per cent. The
solubility was dependent, on particle size, amount of glassy material, the
fluorine content, and whether the product was fused, calcined, or sintered.
Slightly higher values were usually obtained from citric acid extraction
than from ammonium citrate.
Reynolds et al. (1934) showed that as the fluorine content of defluorinated phosphates decreased, the solubility of the phosphorus in
neutral ammonium citrate increased. MacIntire et al. (1944) reported
that the fluorine remaining in fused tricalcium phosphate exists as apatite
and is combined with about 15 per cent of the phosphorus.
The somewhat lower rate of solubility of the defluorinated phosphates,
as compared with superphosphate, may result in increased residual effects
on crop yields. There is some indication that this is true, but additional
long-term field tests are needed to establish this point.
Production of phosphate fertilizer by defluorination of rock phosphate
appears to be a promising process economically. Such products are not
as concentrated as would be desired, and they must also be considered
for use primarily as straight materials since they are not suitable for
use in mixtures containing ammonium salts.
c. Phosphate Roclc-Magnesium Silicate Glass. A process developed
by Walthall and Bridger (1943) has led to commercial production on
the West Coast of a fertilizer produced by the fusion of phosphate rock
with magnesia and silica. The original process involved fusing a mixture
of rock phosphate and olivine in an electric furnace. Defluorination is not
* Designates references to work as yet unpublished.
RANDALL J. JONES AND HOWARD T. ROGERS
required in this process, although part of the fluorine is volatilized during
fusion. The product obtained was a glass containing about 22 per cent
P206which had a high solubility in ammonium citrate. Limited greenhouse tests on two Tennessee soils (pH 6.0 and 6.3) indicated that this
phosphate was virtually as effective as superphosphate.
A modification of this process in which serpentine is substituted for
olivine has been adopted by the Permanente Metals Corporation in
California. . The product has been marketed under the name “ThermoPhos.” Greenhouse tests with this and similar products conducted by
Hill et al. (1948) showed that when these materials are ground finer than
100-mesh, crop response compares favorably with superphosphate on
acid soils. Their results on calcareous soils were not consistently so
favorable. Quenched material that only passed a 6-mesh screen gave
consistently lower plant growth response and particularly so on calcareous
soil. It was indicated that R fineness exceeding 60 mesh was required
for satisfactory plant response to this material.
Field tests in California and Washington indicate that the coarse
material (passing a 6-mesh screen) is inferior to superphosphate;
whereas, the finely ground product appears to give satisfactory results
(Lorens, 1948; Wheeting, 1948) .”
The Manganese Products, Inc., of Seattle, Washington, is producing
a fertilizer material containing about 20 per cent P205by fusing olivine
and rock phosphate, as reported by Moulton (1947) and Granberg
(1048). This is essentially the same process as described by Walthall
and Bridger (1943) above. Although no experimental data are available
for evaluating this product, it is assumed that crop response would be
about the same as for the products described above.
A considerable expansion of field experimenk is needed to evaluate
these products adequately. The process of fusing rock phosphate with
magnesia and silica appears to have possibilities for the production of a
low-cost phosphate fertilizer.
d. Metaphosphates. (1) Calcium Metaphosphate. The high phosphorus content of calcium metaphosphate (60-63 per cent P206) has
made this product of particular interest in certain areas since it was first
produced by the TVA in 1935, as reported by Curtis et al. (1938). Since
that time several thousand tons have been produced in pilot plants and
in a full-scale unit for use in an experimental testing program on field
plots and on test-demonstration farms in cooperation with the land-grant
colleges in a large number of states.
The process for producing calcium metaphosphate has gone through
several stages of development. Originally the method was essentially
one of burning elemental phosphorus with air and reacting the hot
NEW FERTILIZERS AND FERTILIZEB PRACTICES
products of combustion with lump rock phosphate in a vertical shaft.
The molten material collected in the bottom of the reacting chamber and
was tapped from the furnace periodically. The resulting glassy product
was then ground. Improvements have been made in the process which
involve blowing fine phosphate sands into a combustion chamber in
which the phosphate fines react with hot Pz05. The PzOsthat does not
react in the combustion chamber passes into an absorption tower packed
with lump phosphate rock. A flow diagram giving the essential steps in
the process is shown in Fig. 3. A new experimental-scale plant embody-
w L % 2 k % w T E
Fig. 3. Calcium metaphosphate process.
ing the most recent process improvements is now under construction by
Tests to determine the efficiency of calcium metaphosphate as a source
of phosphorus have been conducted throughout the United States. Crop
response data are rather conclusive in showing that this product is equal
to superphosphate as a phosphorus source on acid soils of the humid
region. Thus, O’Brien (1944) reported calcium metaphosphate to be an
effective fertilizer for a wide variety of crops grown in rotation a t eight
different locations in Virginia on major soil types.
I n a series of greenhouse tests with three important soil types in
Alabama, Volk (1944) concluded that calcium metaphosphate compared
favorably with superphosphate. Results from field-plot experiments in
New York with legume and grass hay, corn, and wheat showed this
RANDALL J. J O N E S AND HOWARD T.
product to be quite satisfactory as a source of phosphorus (Chandler and
A summary of several hundred field experiments with calcium metaphosphate conducted in the states of Alabama, Georgia, Kentucky, Mississippi, North Carolina, Tennessee, and Virginia showed an average
relative crop yield of 99 as compared with a value of 100 for superphosphate (Tennessee Valley Authority, 1946). These tests were conducted with cotton, corn, wheat, and legume hay.
Results from field experiments on alkaline soils in the western states
are conflicting. Variable results were reported by Toevs and Baker
(1939) in Idaho from two alfalfa experiments in which one test showed
no increase in yield from calcium metaphosphate ; whereas, met.aphosphate was about 70 per cent as effective as superphosphate in the
other test. On the other hand, Hinkle (1942) reported calcium metaphosphate to be only slightly less effective than superphosphate for
alfalfa in New Mexico experiments. Alway and Nesom (1944) found
in alfalfa experiments in Minnesota that calcium metaphosphate was as
effective as superphosphate when incorporated with the soil prior to
seeding the crop, except on calcareous soils.
Placement of fertilizer, soil moisture, and rate of hydrolysis of metaphosphate to orthophosphate may be factors which affect the efficiency
of calcium metjaphosphate as a source of phosphorus. A careful study
of these and other factors should be made along with additional experiments to determine crop yield response.
The calcium metaphosphate process looks promising as an economical
method for producing phosphate. Because of its high concentration, this
material would seem particularly well suited for areas, such as the Midwest, distant from the phosphate deposits.
(2) Potassium Metaphosphate. Potassium metaphosphate, like calcium metaphosphate, has the advantage of being a fertilizer material
of high analysis. Potassium metaphosphate from pilot-plant production
contains approximately 55 per cent PzOs and 35 per cent KzO. Considerable work was done by the U.S. Dept. Agr. on the development of
this product on a laboratory scale (Madorsky and Clark, 1940).
The Tennessee Valley Authority produced potassium metaphosphate
on a pilot-plant scale by blowing powdered muriate of potash into a
phosphorus combustion chamber where the temperature was maintained
at 800-900°C.(Copson e t al., 1942). The molten material was then
tapped from the furnace and cooled to form a crystalline product which
was ground for fertilizer use. Hydrochloric acid is formed as 8 byproduct from the muriate of potash. Thus far the economics of production of potassium metaphosphate do not appear to be promising, since the
NEW FERTILIZERS AND FERTILIZER PRACTICES
cost of production exceeds to a considerable extent the cost of equivalent
quantities of PeOa and K 2 0 contained in superphosphate and muriate of
Potassium metaphosphate, like calcium metaphosphate, is only
slightly soluble in water, but. it hydrolyzes in the soil to form orthophosphate which is a more soluble product.
Chandler and Musgrave (1944), in New York, reported that potassium metaphosphate was fully as effective as calcium metaphosphate and
superphosphate in field experiments with wheat, alfalfa, and legume-grass
hay. Houghland et aZ. (1942) used potassium metaphosphate, along with
several other phosphate sources, in potato experiments. From the results
obtained on Caribou loam in Maine, yields from potassium metaphosphate either equaled or exceeded the yields obtained from superphosphate.
In greenhouse experiments conducted by Brown and Clark (1943), using
millet, oats, and wheat as indicator crops on four different soils, potassium
metaphosphate gave higher yields than superphosphate in six out of
A summary of unpublished data from the states of North Carolina,
Georgia, Virginia, Kentucky, Alabama, and Mississippi shows that out
of a total of 71 tests, 34 gave yields for potassium metaphosphate higher
than those for superphosphate. On the other hand, 215 tests out of a
total of 233 test3sin Tennessee gave yields which were somewhat below
those from superphosphate. The explanation as to why the results in
Tennessee should be consistently low for pot.assium metaphosphate is
Unless process improvements are made which would lower the cost
of production, it would not be feasible to manufacture this material on
a commercial basis. If developments lead to more economical production, this material should be more thoroughly tested, particularly in the
midwestern and northeastern states where highly concentrated fertilizers
are in demand.
2. Phosphorus-Nitrogen Fertilizers
There has been increased interest recently in the possibility of lowering the cost of nitrogen and phosphate fertilizers by the use of processes
in which both nutrients are combined either as single compounds or in
mixtures. Some of these products have been used as fertilizer for many
years, while others are of comparatively recent development.
a. Ammonium Phosphates. Monoammonium phosphate has been in
commercial production a number of years, but it is mentioned here because the total production and area of distribution appear t o be expanding to some extent. The product is manufactured either in the form of
RANDALL J . JONES AND HOWARD T. ROGERS
a straight material analyzing 11 per cent nitrogen and 48 per cent PzOb
or in combination with ammonium sulfate which results in 8 16-20-0
fertilizer. I n Nort-h America, the 11-48-0grade is now produced only a t
Trail, British Columbia, while the 16-20-0grade is made a t Trail and
a t Pasadena, Texas.
The use of these products as fertilizer materials is generally accepted.
As pointed out by Volk et a!. (1945),however, the acidity resulting
from ammonium phosphate must be corrected by liming; and in some
cases, continued use of this form of nitrogen and phosphorus results in
a sulfur deficiency.
Although only negligible quantities of diammonium phosphate for use
as fertilizer have been produced in the United States, the fertilizer grade
of this compound has been used for some years in Europe, both as an
individual material and as a constituent of some of the Nitrophoska types
of mixed fertilizers. I n these forms it was imported into the United
States in certain years before World War 11.
More recently a process has been developed by the TVA for producing
diammonium phosphate which gives a product of superior physical
characteristics for use as a fertilizer material. It analyzes approximately
21 per cent nitrogen and 54 per cent P20B,
giving a high-analysis fertilizer. The process, developed on a pilot-plant scale, consists of reacting
anhydrous ammonia and electric-furnace phosphoric acid in a saturator
to form aggregates of thin tabular crystals which are primarily diammonium phosphate with small amounts of monoammonium phosphate.
The material is not hygroscopic, and it handles satisfactorily in ordinary
fertilizer distributors. The economics of this process for the manufacture
of ammonium phosphates appear attractive.
The ammonium phosphates are particularly suitable for use in highanalysis mixed fertilizers and may be used for direct application where
only nitrogen and phosphorus are required, as is the case in many of the
b. Dicalcium Nitraphosphate Products. Within the last year renewed attention has been given in the United States to processes which
involve treating raw rock phosphate with a mixture of nitric and phosphoric acids. Many such processes have been investigated, and some of
them have been used in Europe. It is understood that large-scale production of a dicalcium phosphate-ammonium nitrate mixture (20-20-0)is
in operation in Holland a t present.
A process has been developed on a pilot-plant scale by the TVA. One
of the materials that is produced contains dicalcium phosphate and ammonium nitrate and analyzes about 17 per cent nitrogen and 22 per cent
P20e.The phosphorus is 98 per cent citrate-soluble and the nitrogen
NEW FERTILIZERS AND FERTILIZER PRACTICES
is water-solublc. This process, though in its early stages of development,
promises to be an economic source of nitrogen and phosphate fertilizer,
since the nitric acid which is normally used for making ammonium nitrate
can be put to double use by acidulation of rock phosphate prior to
ammoniation. The physical condition of this product appears to be
satisfactory since it is free-flowing. Preliminary greenhouse tests indicate that both the nitrogen and phosphorus are available for plant growth
and are approximately as efficient as superphosphate and ammonium nitrate on acid soils.
c. Ammoniated Superphosphate. Ammonia and ammonia solutions
have been used to ammoniate superphosphate since about 1928. This
has afforded a convenient way of utilizing a form of nitrogen which is
relatively low in cost. The practice of ammoniating superphosphate has
continued to expand until more than 250,000 tons of nitrogen are now
used annually for this purpose.
3. Nitrogen Fertilizers
a. Ammonium Nitrate. Since 1943 ammonium nitrate for direct application has been used in increasing quantities until in the year ended
June 30, 1947,there were 367,093 tons used in the United States (Scholl
and Wallace, 1948). Interest in ammonium nitrate as a fertiliaer material
was greatly stimulated during World War I1 due to the expansion in
plant capacity for producing ammonium nitrate for munitions.
The major problem that originally restricted the use of -ammonium
nitrate was its tendency to absorb moisture. Ross et al. (1946)described
in detail methods which have been used for treating ammonium nitrate
to make it a suitable fertilizer product. Ammonium nitrate is treated
with suitable conditioning agents to give it satisfactory physical properties. The final product contains 32 to 34 per cent nitrogen,
As summarized by Whittaker et al. (1948) field tests with a number
of common crops show conclusively that ammonium nitrate is a satisfactory source of nitrogen for crop production. The indications are that
the use of this product will continue to expand in this country because
of economy of production, high analysis, and satisfactory crop response.
b. Urea-Form. A reaction product of urea and formaldehyde designated as “urea-form,” which is slightly soluble in water and nitrifies
slowly in the soil, has been developed recently by the U.S.Dept. Agr.
Armiger et al. (1948)of the U.S. Dept. Agr. have studied the properties
of this product and have tested it both in greenhouse and field experiments. It is reported by Fuller and Clark (1947)that the most promising products have urea-formaldehyde mole ratios of 1.2 to 1.4 and
RANDALL J. JONES AND HOWARD T. ROGERS
nitrogen contents of 36 to 38 per cent. These products are not yet in
Nitrification tests reported by Yes and Love (1946) indicate that the
rate of nitrate formation in the soil is sufficient to meet crop needs. Ureaform appears to be particularly well suited for grasses and other crops
which require an available source of nit,rogen over a long period. Extensive cooperative field tests now under way between the U.S. Dept. Agr.
and several state agricultural experiment stations should give fairly conclusive data as to the suitability of this product,. Since urea-form can
absorb a high percentage of moisture without any change in its physical
condition, it appears to be well suited for use as a conditioning agent
in mixed fertilizers and, as suggested by Jacob and Mehring (1947)’
could replace to advantage some of the inert or low-analysis materials
now used for such purposes.
c. Anhydrous Ammonia. The use of anhydrous ammonia as a nitrogen
fertilizer was initiated by the Shell Chemical Company in California in
the 1930’s. This practice has increased to a great extent in that area
as well as in other western states. A method for direct fertilization of
the soil with anhydrous ammonia was patented by Leavitt (1942). Recently there has been considerable interest in other parts of the United
States in the use of anhydrous ammonia for direct application. I n 1943,
research on the use of anhydrous ammonia was initiated by the Mississippi Agricu!tural Experiment Station in cooperation with TVA, and
the practice has spread to several other southern states.
Since the cost of anhydrous ammonia per unit of nitrogen is much
lower than that of any other presently available nitrogen source, it appears to be a potentially important source of fertilizer nitrogen for certain areas. A discussion of the use of this material and crop response
data will be given under Section 111-2.
4. Potash Fertilizers
The outstanding contributions made in the manufacture of potash
fertilizers in recent years have been in improved technology for producing
high-analysis nuriate of potash. According to Jacob and Mehring
(1947), approximately 80 per cent of the potash now consumed as fertilizer in the United States is in the form of potassium chloride containing
60 per cent KzO. Large quantities of concentrated muriate of potash are
used in the manufacture of high-analysis mixed fertilizers.
Turrentine (1943) has given an excellent discussion of recent advances
made in the technology of potash production in the United St.ates.
Potassium metaphosphate was discussed in the section dealing with
phosphates, but it should be mentioned here also since it is a new type