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II. New and Improved Fertilizer Materials

II. New and Improved Fertilizer Materials

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42



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

produced.

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



43



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

content.

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,



44



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



45



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.



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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



47



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-



TUNER



ORUM



w L % 2 k % w T E

PULVERIZER



Fig. 3. Calcium metaphosphate process.



ing the most recent process improvements is now under construction by

the TVA.

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



48



RANDALL J. J O N E S AND HOWARD T.



product to be quite satisfactory as a source of phosphorus (Chandler and

Musgrave, 1944).

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



49



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

potash.

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

twelve tests.

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

not known.

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



50



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

western states.

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



51



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



52



RANDALL J. JONES AND HOWARD T. ROGERS



nitrogen contents of 36 to 38 per cent. These products are not yet in

commercial production.

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



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