Advances in agronomy volume 17

Fertilizer Consumption and Use World fertilizer consumption, excluding mainland China, totaled 24,553,000 short tons of nitrogen N , phosphorus P , and potassium K 32,342,000 of

A D V A N C E S I N

AGRONOMY VOLUME 17

CONTRIBUTORS TO THIS VOLUME

ADVANCES IN

AGRONOMY

Prepared under the Auspices of the

AMEZICAN SOCETY OF AGRONOMY

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PRINTED IN THE UNITED STATES OF AMERICA

CONTRIBUTORS TO VOLUME 17

Numbers in parentheses indicate the pages on which the authors’ contributions begin

BARMORE, MARK A ( G ) , Chemist, Western Wheat Quality Laboratory, Crops Research Division, Agricultural Research Service, United States Department of Agriculture, Washington State University, Pull- man, Washington

BROOKS, HOWARD J (283) Research Horticulturist, Crops Research Division, Agricultural Research Service, United States Department

of Agriculture, Beltsville, Maryland

Collins, Colorado

CLINE, A J (233), Senior Soil Correlator, Soil Conservation Service, Fort

FARNHAM, ROUSE S ( 115), Assistant Professor, Department of Soil Science, University of Minnesota, Institute of Agriculture, S t Paul, Minnesota

FELBECK, GEORGE T., JR (327), Associate Professor, Department of Agri- cultural Chemistry, University of Rhode Island, Kingston, Rhode

Island

FINNEY, H R (115), Research Assistant, Department of Soil Science,

University of Minnesota, lnstitute of Agriculture, S t Paul, Minnesota

FOGLE, HAROLD W (283), Research Horticulturist, Crops Research Di- ukion, Agricultural Research Service, United States Department of Agriculture, Beltsville, Ma yland

GORZ, H J (la), Research Geneticist, Crops Researoh Division, Agri- cultural Research Service, United States Department of Agriculture, and Professor, Department of Agronomy, University of Nebraska,

Lincoln, Nebraska

HEHN, E R H A ~ T R (S), Head, Department of Plant and SOU Science, Montana State College, Bozeman, Montana

JOHNSON, DONAL D (233), Professor of Soils, Department of Agronomy,

MCKAY, JOHN W (283), Research Horticulturist, Crops Research Divi- sion, Agricultural Research Seroice, United States Department of Agriculture, Beltsville, Maryland

Colorado State University, Fort Collins, Colorado

PREFACE

In all countries of the world in which scientific agriculture is practiced, crop production and acre yields have increased markedly in the last two decades Fertilizers, efficiently used, have contributed substantially to this progress World-wide fertilizer consumption is steadily rising As technical and economic resources are acquired in areas now less favored,

so is it to* be expected that striking changes in production will occur The slopes may even be steeper Although specific recommendations may not be applicable, the principles of efficient practice are transfer- able, and technological improvements in fertilizer chemistry, which have made new materials available, have widened the possibilities of fertilizer choice In several earlier volumes, authors have dealt with developments

in fertilizer technology and usage, but no apology is needed for return- ing again to these topics The lead article in this volume, by L B Nelson,

is an authoritative and comprehensive review of the newer develop- ments which hold so much promise in meeting the needs for food by the expanding world population

The improvement of crop varieties through recombination of available germplasm is another powerful factor in increased yields The article

by W K Smith and Gorz on Sweetclover Improvement includes an elegant discussion of the complex considerations that must be encom- passed in a crop breeding program Similarly, when quality for a specific purpose is the primary objective, as in the case with wheat for milling and baking, the criteria to be superimposed on those relating to agro- nomic characters become quite sophisticated, Hehn and Barmore give

an account of work which, though not widely known, affects everyone's daily bread

From time-to-time, it is appropriate to include consideration of horti-

cultural crops, some of which in an era of high labor costs present severe

problems to the grower Tree fruit and nut production in the United States are discussed by Brooks, Fogle, and McKay, who stress the neces- sity for research on improvements in the characteristics of the trees and modifications in management practice to meet these new situations The remaining three chapters are examples of different types of basic work on soils G T Felbeck presents a scholarly review of the old, but ever new, problem of the chemistry of soil humus substances, a durable and recalcitrant problem, which is being reduced slowly by the appli- cation of new techniques in chemistry Organic soils have long presented difficulties in classification Systems hitherto available have been less comprehensive and firmly based than those developed for mineral soils

viii PREFACE

Farnham and Finney have faced the need for a new system, which should

be a more refined tool in mapping and management, and which incor- porates nomenclature changes consistent with those adopted in “Soil

Classification, 7th Approximation” by the Soil Survey staff of the U.S

Department of Agriculture Fascinating aspects of soil genesis are re- viewed in the chapter on Colorado Mountain Soils by Johnson and Cline This state is veritably a laboratory in which soil-forming processes may

be studied, because of the enormous range of climatic, geological, and vegetation variables that occur therein Within a few miles may be found representative soils that elsewhere lie far apart

Once again it is appropriate to conclude with a recognition of the services provided by our authors in making available to their colleagues these stimulating reviews

Ann Arbor, Michigan

July, 1965

A G NORMAN

CONTENTS

Page

CONTRIBUTORS TO VOLUME 17 v

PREFACE vii

ADVANCES IN FERTILIZERS LEWIS B NELSON I I1 I11 IV V VI VII VIII IX Introduction 1

Fertilizer Consumption and Use 2

Nitrogen 11

Phosphorus 29

Potassium 49

Mixed Fertilizers 56

Sulfur 70

Micronutrients 74

Outlook 78

References 80

BREEDING WHEAT FOR QUALITY ERHARDT R HEHN AND MARK A BARMORE I Introduction

The Protein Story

I1 I11 IV VI Milling and Baking Research Laboratories

Microquality Flour Tests

V Micromilling Methods

Genetics and Breeding

VII Conclusions

References

CLASSIFICATION AND PROPERTIES OF ORGANIC SOILS R S FARNHAM AND H R FINNEY 85 86 88 90 99 100 111 112 I Introduction 115

11 Distribution and Extent 116

ix

111 Criteria Used in Classifying Organic Soils 117

IV Properties of Organic Soils 127

V Morphology of Organic Soil Horizons 135

VI Bases for Proposed Classification System 143

VII Summary and Conclusions 159

References 160

I I1 111 IV V VI VII VIII IX X XI SWEETCLOVER IMPROVEMENT W K SMITH AND H J GORZ Introduction

Morphology and Reproduction

Culture and Physiology

Utilization

Breeding

Coumarin

Diseases

Insects

Other Characters

Conclusions

References

Genetics and Cytogenetics

164 167 170 175 183 191 197 211 115 220 221 223 COLORADO MOUNTAIN SOILS D D JOHNSON A N D A J CLINE I Introduction 234

I1 General Soil Patterns 244

111 Characteristics of the Soils of the Mountains of Colorado 256

IV Summary 280

References 281

Selected Bibliography 281

PROGRESS AND PROBLEMS IN TREE FRUIT AND NUT PRODUCTION H J BROOKS H W FOGLE A N D J W MCKAY I Pome Fruits 283

I1 Stone Fruits ' 295

Chemical Methods of Functional Group Analysis

Humic Acid-Like Materials from Geologic Deposits Not Classified as Soils

This Page Intentionally Left Blank

ADVANCES I N FERTILIZERS

Lewis B Nelson Tennessee Valley Authority Wilson Dam Alabama

Page

I Introduction 1

I1 Fertilizer Consumption and Use 2

A World 2

B United States 6

I11 Nitrogen 11

A Sources of Fixed Nitrogen 12

B Nitric Acid 14

C Nitrogen Materials 15

I V Phosphorus 29

A Phosphate Rock 30

C Phosphorus Materials 38

V Potassium 49

A Reserves and Production 49

C Potassium Materials 53

VI Mixed Fertilizers 56

A Ammoniation 60

B Nongranulated Mixed Fertilizers 61

C Granulated Mixed Fertilizers 62

D Bulk Blends 65

E Liquid Mixed Fertilizers 67

VII Sulfur 70

VIII Micronutrients 74

IX Outlook 78

References 80

B Phosphoric Acid Production 34

B Mining and Processing 52

1 Introduction

Changes are occurring more rapidly in the world fertilizer industry than at any time in its history Consumption is climbing rapidly Crop production and world food supplies are dependent more and more upon application of fertilizers and food-deficient countries are recognizing the importance of fertilizers Additional phosphate and potash deposits have been discovered and better and more efficient mining and beneficiation methods are being developed Fertilizer materials that dominated the world market for years are giving way to newer products New and

1

2 LEWIS B NELSON

improved manufacturing processes are appearing ever more rapidly, bringing more important new materials to the front New marketing methods and innovations are exerting tremendous impact

The world fertilizer industry has become increasingly technologically minded It is more sophisticated and more e5cient Research in the chemistry and technology of fertilizers is expanding Important advances not only are coming more frequently, but also are receiving immediate and widespread adoption Farmers, particularly in the more developed countries, are showing much greater willingness to adopt fertilizer in- novations They are increasingly more knowledgeable about sound ferti- lizer practices and the economics involved

All these changes are being felt by world agriculture Prices paid by

farmers for plant nutrients are declining rather than increasing like so

many items modern farmers must buy Quality of fertilizers is improved, and application and handling have become less tedious Determination

of specific crop and soil needs has become more scientific Farmers have learned to better fit fertilizer practices into their overall farm business

It all adds up to greater returns for every dollar spent on fertilizers The rapidly changing technology of fertilizers has been presented in

Advances in Agronomy, first by Jones and Rogers (1949) and later by Jacob (1959) This paper reviews major developments since 1957, the last year covered by Jacob's review, and presents a picture of the world fertilizer industry as it exists today

II Fertilizer Consumption and Use

World fertilizer consumption, excluding mainland China, totaled

24,553,000 short tons of nitrogen ( N ) , phosphorus ( P ) , and potassium ( K ) (32,342,000 of N, Pz06, and K20) for the fertilizer year 1961-1962

[Food and Agriculture Organization of the United Nations ( FA0 ), 19631,

F A 0 studies show that consumption has climbed steadily since World War I1 and that most of the increase has been used on existing acreages For example, fertilizer consumption increased some 280 per cent since

1945-1946, while cropland acreages increased less than 20 per cent Although consumption of each primary nutrient has continued to in- crease (Table I ) , nitrogen has gained most rapidly Phosphorus, on the elemental basis, showed the smallest tonnage increase

Consumption for the various continents and the U.S.S.R is given in Table I Of interest is the fact that Europe and North and Central America together consumed about 74 per cent of the worlds NPK both

in 1956-1957 and 1961-1962 (The United States consumed about 90 per

TABLE I

World Plant Nutrient Consumption, Excluding Mainland China, for the Fertilizer

Years 1956-1957 and 1961-1962 in 1000 Short Tonsa

N Continent

4 LEWIS B NELSON

cent of that used in North and Central America.) Percentagewise, the greatest increases in fertilizer use occurred in the less developed coun- tries; but the tonnages remain small

F A 0 data for plant nutrient consumption per acre of arable land are given in Table 11 Europe has the most intensive fertilizer use, followed

by North and Central America and Oceania However, great variations exist among countries, depending on their stage of development, density

of population, and climate

TABLE I1 Fertilizer Consumption per Acre of Arable Land in 1960-1961a

Average pounds per acre of arable land

Asia (excluding mainland

China and North Korea) 4.54

10.96 1.40 4.05 0.90 0.90 0.43 9.98 2.91

21.50 2.48 6.21 1.63 1.74 0.30 2.25 4.80

56.42 6.87 20.95 5.09 7.18 1.96 13.21 14.65

a FA0 (1963) FA0 uses the term “arable land” to include land planted to crops ( double-cropped area counted only once), land temporarily fallow, temporary meadows, garden land, and land in fruits

Countries using over 100 pounds of N, P, and K per acre of arable

land during 1960-1961 (FAO, 1963) were as follows: the Netherlands,

332 pounds; Belgium, 250; New Zealand, 217; Japan, 215; German Federal Republic, 181; Taiwan, 154; Luxembourg, 146; Switzerland, 142; East Germany, 134; United Kingdom, 125; Norway, 121; Republic of Korea,

106; and Denmark, 104 It is interesting to note that practically all of these are well-developed countries having a high density of population

Countries using between 20 and 100 pounds of N, P, and K per arable

acre include: Austria, 80; Ireland, 75; United Arab Republic, 70; France, 65; Czechoslovakia, 61; Finland, 58; Israel, 56; Sweden, 55; Poland, 34;

Italy, 33; Peru, 32; United States, 26; Greece, 26; Bulgaria, 25; Cuba, 24; Spain, 21; and Yugoslavia, 20

Countries averaging less than 20 pounds per acre of arable land in- clude: Hungary, 19; Chile, 12; South Africa, 12; Dominican Republic, 10;

Australia, 9; Brazil, 9; Philippines, 9; Mexico, 7; U.S.S.R., 7; Algeria, 5;

Canada, 5; Rumania, 5; India, 2; and Turkey, 1 F A 0 has not provided

individual data for other low-fertilizer-using countries, apparently be- cause of lack of information

ADVANCES IN FERTILIZERS 5

Recent surveys in England, Wales, and Scotland (Fertiliser Manu- facturers Association, 1964) show that virtually 100 per cent of the acreage of cereals, sugar beets, and potatoes now receive fertilizer Per- acre rates of nitrogen applied on cereals have increased sharply in recent years, while the rates for phosphorus and potassium have held fairly con- stant Rates used on' sugar beets and potatoes have increased for all three nutrients For temporary grass, 69 per cent of the total acreage received nitrogen and about half received phosphorus and potassium For per- manent grass, 38 per cent of the acreage received nitrogen, 34 per cent

TABLE I11

Use of Primary Nutrients on Major Crops in England, Wales, and Scotlanda

Average rate per fertilized acre (pounds)

Fertiliser Manufacturers Association ( 1964)

phosphorus, and 28 per cent potassium Use of nitrogen has increased substantially on all grasslands in recent years, but there has been little change in phosphorus and potassium Average rates of application per acre for different crops are given in Table 111

Indications are that world consumption of fertilizers will continue

to increase at a rapid rate Major fertilizer-using countries are continuing

to build plants, and considerable activity is under way in construction

of new fertilizer facilities in many of the low-fertilizer-using countries Large ammonia facilities are being built or planned near sources of nat- ural gas, with the intention of exporting low-cost ammonia Phosphorus and potassium deposits are being exploited rapidly

The eventual level of fertilizer consumption in different countries is

subject to considerable speculation Coleman (1963), for example, has estimated that world requirements, excluding mainland China, will rise

to 54 million short tons of N, PzO5, and KzO by 1970 and to 77 million

6 L E W I S B NELSON

N, P205, and K 2 0 in 1960 to 39.8 million in 1980 This conclusion is based

on the current high level of nutrition in most of these countries, the comparatively low rate of increase of population, and the limited oppor- tunities for agricultural export Japan may already have reached or possi- bly exceeded its immediate total fertilizer needs Countries with more moderate fertilizer use rates, such as the United States, are likely to

increase at a more rapid rate Heady and Tweeten (1963), for example,

estimate that fertilizer consumption in the United States will increase

60 to 67 per cent by 1980 over 1960

According to Parker et d (1964), eastern Europe and the U.S.S.R are expected to increase consumption at an average annual rate of about

12 per cent from 1960 to 1970 and at a somewhat lower rate from 1970

to 1980 Total consumption of N, PZOS, and KzO on this basis would increase from 5.5 million short tons in 1960 to 27.9 million in 1980 Recent

reports indicate that steps are being taken in these countries, especially

in the U.S.S.R., markedly to increase fertilizer production and use (Anonymous, 1964h,j)

In developing countries, where the urgency to increase agricultural production is great and fertilizer use is low, fertilizers must be used in ever larger amounts to meet the needs of expected increases in popula- tion and the greater per capita food consumption associated with

economic development Estimates by Parker et d (1964) indicate that

consumption must increase at the average annual rate of 15 per cent from

1960 to 1970 and 10 per cent from 1970 to 1980 if even modest levels of

human nutrition are to be achieved This would increase the N, PzO5, and KzO consumption from 3.0 million short tons in 1960 to 31.2 million

in 1980 The task of producing these kinds of increases in nonindus-

trialized countries is formidable Lack of education of farmers, credit limitations, and the high price of fertilizers in relation to the farmers’ ability to pay, underdeveloped or inadequate transportation and market- ing systems, and many other factors must be overcome before the full potential from fertilizers as a developmental tool can be realized,

Coleman (1963) estimates that mainland China has doubled its fertilizer production since 1958 He further estimates that the minimum need for plant nutrients by 1969-1970 will be about 5.5 million short tons of N, PZO5, and KzO

United States consumption, including Puerto Rico, totaled 7,367,516

short tons of N, P, and K (9,532,065 tons of N, PzO5, and KzO) for the

fertilizer year 1962-1963 (Scholl et al., 1984) Consumption has increased

steadily each year since 1942 when total consumption was 1,344,000 tons

of N, P, and K (2,076,000 tons of N, P206, and KzO)

ADVANCES IN FERTILIZERS 7

Increases in fertilizer use following World War I1 resulted initially from the response of the American farmer to meet demands for increased crop production during the postwar reconstruction period when exports were high This period was immediately followed by the Korean war, which again placed a heavy demand on production Following the Korean war, however, the demand for farm products declined, but pro- duction continued to climb and farm income fell as a result Caught in

a cost-price squeeze (farm prices fell 12 per cent while the cost of many

production items rose 50 per cent) and government-imposed acreage

controls, the farmer turned to those methods available to him which would permit more production on fewer acres at less cost Chief among these was increased use of fertilizer since it was cheapest relative to the production boost it gave and capital invested in fertilizer gave quick returns During all this time, rapid introduction of new technology into the fertilizer industry, the construction of more efficient plants, and re- placement of older, more expensive forms of fertilizers by less expensive ones actually resulted in a decline in plant nutrient prices at a time when most other production costs were increasing (Fig 1) This, in turn, further encouraged greater fertilizer use relative to other input factors (Fig 2 )

Consumption of N, P, and K from 1956-1957 to 1962-1963 increased

55 per cent As elsewhere in the world, greatest gains were recorded for nitrogen, which accounted for 37 of the 55 percentile points Phosphorus accounted for 7 and potassium for 11 Tonnage gains for each of the primary nutrients are shown in Fig 3

Several factors apparently were responsible for the striking gain in nitrogen consumption These included recognition by farmers of the high requirements of major crops for nitrogen, the need for higher and higher per-acre yields in order to combat the cost-price squeeze, and the con- tinuing replacement by chemical nitrogen of nitrogen previously pro- duced by legumes in the crop rotation These, coupled with increased availability of fertilizer nitrogen at lower unit cost, all worked together

to bring about the upsurge in nitrogen consumption

Not all regions' in the United States experienced similar gains in N,

1 The units comprising the regions are: New England-Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut; Middle Atlantic-New York, New Jersey, Pennsylvania, Delaware, District of Columbia, Maryland, West Virginia;

South Atlantic-Virginia, North Carolina, South Carolina, Georgia, Florida; East

North CentrubOhio, Indiana, Illinois, Michigan, Wisconsin; West North CentraZ- Minnesota, Iowa, Missouri, North Dakota, South Dakota, Nebraska, Kansas; East South Central-Kentucky, Tennessee, Alabama, Mississippi; West South Central-

Arkansas, Louisiana, Oklahoma, Texas; Mountain-Montana, Idaho, Wyoming, Colo- rado, New Mexico, Arizona, Utah, Nevada; Pacific-Washington, Oregon, and Cali- fornia Alaska, Hawaii, and Puerto Rico are reported separately

8 LEWIS B NELSON

P, and K consumption during the period 1956-1957 to 1962-1963 (Scholl

et al., 1958, 1964) The New England States gained least-6.3 per cent and 5,600 tons-reflecting the declining agriculture and increasing urban- ization of the region Both phosphorus and potassium consumption declined slightly, increased nitrogen consumption making up the dif- ference

1

FIG 1 Prices of selected farm inputs in the United States, 1950-1962 (Plant nutrient costs based on N, P205, and K20.) Index: 1950 = 100 ( U S Department

of Agriculture and Tennessee Valley Authority )

FIG 2 Use of selected farm inputs in the United States, 1950-1962 Index:

1950 = 100 ( U S Department of Agriculture.)

ADVANCES IN FERTILIZERS 9

Modest gains, well below those experienced nationally, were recorded

in three of the older fertilizer-using regions NPK use in the Middle

Atlantic States increased by 77,000 tons or 20 per cent, in the South Atlantic by 240,000 tons or 23 per cent, and in the East South Central

by 159,000 tons or 26 per cent Consumption of phosphorus showed the least gain in all three regions, apparently reflecting the decreasing crop

1957 1959 1961 1963

Year ended June 3 0 FIG 3 Consumption of nitrogen, phosphorus, and potassium in the United States and Puerto Rico, years ended June 30, 1957-1963 ( U S Department of Agri- culture )

response to this element resulting from its large residual buildup in the soils Nitrogen and potassium use increased in all three regions, the largest increase in potassium occurring in the South Atlantic States

NPK consumption in the East North Central States increased 622,000 tons or 58 per cent, the largest gain again occurring with nitrogen In

the West North Central States, plant nutrient usage increased 802,000 tons or 136 per cent Nitrogen use more than doubled, and large increases

occurred both for phosphorus and potassium The West South Central States experienced a 408,000-ton or 110-per cent increase, with a large increase in nitrogen and smaller gains for the other two elements

In the Pacific States, NPK use increased 195,000 tons or 50 per cent from 1956-1957 to 1962-1963 Percentagewise, the increase was about

10 LEWIS B NELSON

evenly divided among the three elements, but the largest tonnage in- crease, 157,000 tons, was with nitrogen, the most used element in the re- gion (In 1962-1963, the Pacific States consumed 466,000 tons of N, 70,000

tons of P, and 44,OOO tons of K.) Consumption in the Mountain States increased 105,000 tons or 85 per cent This region, traditionally a sma11 user of potassium, used 172,000 tons of nitrogen, 50,000 tons of phos-

phorus, and 6,000 tons of potassium in 1962-1963 compared with 9O,OOO,

TABLE IV Use of Primary Plant Nutrients on Major Crops

in the United States During 19595

30,000, and 3,000 tons, respectively, in 19561957 Fertilizer consumption

in Alaska, Hawaii, and Puerto Rico changed little either in the amounts

or proportions of the elements used

The most recent US Department of Agriculture data on fertilizer

use by crops is given in Table IV The high cash return crops-tobacco,

tree fruit, vegetables, potatoes, sugar beets, and cotton-are the most completely and highly fertilized Only a relatively small percentage of the small grain acreage is fertilized, and, where applied, the fertilizer is used at relatively low rates Soybeans, which seldom respond much to fertilizer, receive very little Hay and pasture are unquestionably the most underfertilized crops in the country

Major Crops in the United States During 1 9 5 9

Nutrient use, per cent of U S total

Total acreage fertilized

-

37.7 0.5 3.1 1.1 7.0 5.0 0.2 2.9

6.1

’ 4.0 6.8 0.5

5.1

0.7 11.6 3.2 4.5 100.0

-

37.9 2.0 1.9 0.6

8.8

3.2 1.1 2.6 6.1 3.8 8.4 0.9 4.1 1.9 9.7 2.9 4.1 100.0

-

a U S Department of Agriculture

111 Nitrogen

Recent years have seen a marked revolution in the nitrogen fertilizer

industry Changes have occurred not so much from the introduction of

new materials, but in greatly expanded production and consumption, the changing importance of the different nitrogen materials, the sources of hydrogen used in the manufacture of ammonia, and in improvements of manufacturing processes

According to the British Sulphur Corporation’s statistics on world nitrogen production for 19621963 ( Anonymous, 1964d), three-fourths

of the worlds fixed nitrogen (15,434,000 short tons) is produced by nine

12 LEWIS B NELSON

countries: United States, 26.9 per cent; West Germany, 9.5; Japan, 8.4;

U.S.S.R., 8.4; France, 5.9; Italy, 5.3; United Kingdom, 4.4; and Canada and the Netherlands each 3.1 Approximately 85 per cent of all fixed nitrogen is used in fertilizers The major exporters of nitrogen fertilizers are West Germany, Italy, and Japan

The nitrogen industry is expanding rapidly (Table VI), with the greatest expansion in the United States By the end of 1985, a number

of new projects also are expected to be completed in India, Pakistan, Burma, Malaya, Vietnam, Indonesia, Republic of Korea, Japan, Philip- pines, and Australia New projects in Africa are under development and construction Central and South American countries are adding sub- stantial tonnages, The United Kingdom and other western European

TABLE VI Output and Per Cent Changes in World Production of Nitrogenous Fertilizers

between 1958-1957 and 1961-1962a

Per cent

Output, 1000 short tone N

According to Coleman (1963), world consumption of nitrogen can be expected to double between 1960 and 1970, the percentage increase being greatest in the nutritionally deficient countries In tonnage, how- ever, greatest increases are expected to be in those countries already consuming large amounts of nitrogen and in eastern Europe and the U.S.S.R

A SOURCES OF FIXED N ~ O G E N

Over 80 per cent of the estimated 20-million-ton nitrogen capacity of the world is based on synthetic ammonia In early 1963, some 278 syn- thetic ammonia plants were in operation and another 43 were under con- struction (Sweeney, 1963) The remaining 20 per cent of the worlds

ADVANCES IN FERTILIZERS 13

output is recovered from coke oven gases, by the cyanamide process, and

a small amount from natural materials

The basic synthetic ammonia process itself has changed little from the original Haber-Bosch process of 1913 in which NH3 is synthesized catalytically under pressure However, refinements in the process and improvements in plant design have brought about reduced plant invest- ments and lower operating costs Nitrogen used in the synthesis is ob- tained from the atmosphere, while hydrogen comes from a variety of sources, depending on availability and cost A discussion of synthetic ammonia manufacture is given by Sharp and Powell (1963) and Axelrod and OHare (1964)

Before World War 11, 90 per cent of the synthetic ammonia produc- tion was based on hydrogen produced by the reaction of coal and coke with water vapor Since that time there has been a rapid shift to lower cost hydrocarbon sources Latest data show that only 40 per cent of the world's synthetic ammonia is now produced through the use of coal and coke Thirty-one per cent comes from the use of natural gas, 15 per cent from fuel oil, 9 per cent from refinery gases, and 5 per cent from other sources (FAO, 1963) The wide choice of methods of obtaining hydrogen removes the necessity of locating ammonia plants near sources of coal and coke and permits them to be located nearer or in consuming areas The United States, with its abundant and low-cost supply of natural gas, has shifted almost entirely to this material for hydrogen production About 4 per cent of the ammonia is made using hydrogen from chlorine plants and refinery gas, and about 1.5 per cent using hydrogen from coke-oven gas Japan in 1953 derived 69 per cent of its ammonia from the use of coal and coke and 26 per cent from electrolytic hydrogen (Anonymous, 1964e) By 1963, these two together accounted for only

12 per cent of the total, the remainder being obtained through the use

of crude oil, natural gas, coke-oven gases, and refinery and waste gases

In 1959, the U.S.S.R derived 55.5 per cent of its ammonia from solid coal and coke, 38.8 per cent from natural gas, and 5.7 per cent from waste gases Plans call for deriving increasingly larger amounts of hy- drogen from the use of natural gas, casing head gas, and refinery waste gas (Anonymous, 1964f) Although changes in source of hydrogen are occurring rapidly in most countries, western Europe still relies on coal for more than half of its synthetic ammonia production

A major recent innovation has been that of locating a Iarge-capacity ammonia plant in Trinidad close to the source of very low-cost natural gas and moving the liquefied ammonia by specially built tankers into international commerce (Anonymous, 1964a ) Under normal situations,

A number of improvements have been made in the cyanamide process which involves the reaction of calcium carbide with nitrogen at high temperatures These improvements, mostly aimed at reducing tempera- ture requirements and increasing purity (Anonymous, 1963c), reportedly are strengthening cyanamide’s relative position as a fertilizer material However, in light of the high production costs and the large electric power requirement, it remains questionable that these improvements will keep the product competitive with other nitrogen fertilizer carriers In- dustrial consumption of cyanamide for nonfertilizer uses, however, is in- creasing At present 38 cyanamide plants are in operation, most of them

in western and eastern Europe and Japan West Germany in 1961-1962 was the largest producer (99,OOO short tons N ) , followed in turn by Japan (72,000) and Poland (41,000) No plants presently are operating in the United States

Natural deposits of nitrates, chiefly in Chile, continue to be mined and exported However, the relative importance of this source has de- clined steadily Natural organics, likewise, have become relatively unim- portant

B NITRICACJD The chief intermediate in nitrogen fertilizer manufacture is nitric acid, H N 0 3 (Sorgenti and Sachsel, 1964) It has little direct use either

in the mixed fertilizer industry or for direct application, but it is essential for the manufacture of ammonium nitrate, calcium nitrate, sodium nitrate, potassium nitrate, and nitrophosphates Nitric acid is produced almost entirely by the oxidation of ammonia with air in the presence of a platinum catalyst to form NOz, which in turn is dissolved in water to form HN03 Practically all of the recent plants in the united States use

ADVANCES I N FERTILIZERS 15

a process in which the ammonia is oxidized under pressure and the oxides are absorbed in water under pressure A number of plants in Europe, however, oxidize ammonia at atmospheric pressure and then absorb the oxides under pressure Average concentration of the acid usually ranges from 55 to 58 per cent HNOs, although some European plants produce acid in concentrations ranging from 60 to 70 per cent TVA recently has constructed the first plant in the United States for producing 65 per cent acid by direct absorption World nitric acid capacity is increasing rapidly, primarily to meet the needs for the rapidly expanding ammonium nitrate production

C NITROGEN MATERIALS

A number of nitrogen materials are available for use both in the

manufacture of mixed fertilizers and for direct application These vary considerably in properties, uses, and methods and cost of manufacture Further, different countries and even areas within countries express definite preferences

Nitrogen materials, in contrast to those of other nutrients, represent

a wide and diversified range of properties, being available in gaseous, liquid, and solid forms Each of the materials has merits that make it particularly useful under specific situations, but each also has certain disadvantages-either in manufacturing, properties, or cost Thus, there seems to be no universally acceptable nitrogen material Use of certain nitrogen materials, however, is increasing more rapidly, and these are replacing others in relative importance Some that once dominated the world nitrogen picture appear headed for comparative oblivion, as has occurred in the past with natural organics The changing trends in world output of different nitrogen materials are given in Table VII

16 LEWIS B NELSON

Of the total nitrogen used in Europe in 1961-1962 (FAO, 1963),

ammonium nitrate accounts for 40 per cent; ammonium sulfate, 20; cal-

cium nitrate, 12; sodium nitrate, 2; calcium cyanamide, 4; and urea, l

Most of the remainder goes into complex fertilizers

Of 35,OOO short tons of nitrogen consumed in Australia in 1960-1961

(Anonymous, 1962b), 64.6 per cent was ammonium sulfate, 20.9 per cent

urea, 5.7 per cent organics, 3.4 per cent complex fertilizers, 3.1 per cent

States, 1957-1963 ( U S Department of Agriculture.)

ammonium nitrate, and 2.3 per cent sodium nitrate Large use of am-

monium sulfate apparently results from the need for sulfur, especially in

the areas of higher rainfall

About two-thirds of the nitrogen fertilizer consumed in the United

States is applied directly to the soil rather than in mixtures Jacob (1959)

noted striking gains in use of ammonium nitrate and anhydrous ammonia

during the 1948-1957 period Since then (Fig 4), anhydrous ammonia

has continued to gain rapidly, while ammonium nitrate use has climbed

only moderately The use of nitrogen solutions, negligible until about

1953, has increased rapidly Solid urea, which showed little increase in

In general, the biggest shift in nitrogen materials for direct applica- tion in the United States has been from solids to liquids Anhydrous ammonia, aqua ammonia, and nitrogen solutions accounted for only 8

per cent of the total nitrogen use in 1947 Their share soared to 40.5 per cent in 1956-1957, and increased further to 59.6 per cent in 19621963 The rapid increase in use of liquid nitrogen for direct application stems from an initial cost advantage over solids, plus additional savings and convenience to the farmer in handling and application

The high-analysis solids, urea and ammonium nitrate, have gained over the lower analysis solids This again reflects the response of the farmer to a lower cost per pound of nitrogen as a result of reduced shipping, handling, storage, and application costs

Slack (1963) gives the following rough cost index of the contained nitrogen in different carriers at producing plants in the United States using current prices:

Nitrogen solution

Solid bagged fertilizer 1.87-2.48

18 LEWIS B NELSON

Solid ammonium nitrate containing about 33.5 per cent N is applied

either directly to the soil or formulated into mixed fertilizers It has particular value in the production of granulated mixed fertilizers as an aid to granulation; however, because of its hygroscopicity, it is not en- tirely suitable for use in dry mixes or bulk blends Ammonium nitrate, if improperly handled, can present fire and explosion hazards

There has been a sharp increase in world production and use of

ammonium nitrate (FAO, 1963) Nitrogen from ammonium nitrate now

exceeds that of the former leading contender, ammonium sulfate Prac- tically all the more developed countries produce ammonium nitrate, and many of them have increased their output sharply in recent years The United Kingdom, for example, practically doubled production in the

5-year period starting with 1957-1958 During 1961-1962, production of

ammonium nitrate in short tons of N by continents was as follows:

Europe, 2,389,000; North and Central America, 470,000 (excluding that

used in solutions); South America, 10,OOO; Asia, 41,000; and Africa, 84,000 Oceania (Australia and New Zealand) does not produce am-

monium nitrate Largest producing countries are the United States, U.S.S.R., France, and West Germany in the order named Ammonium nitrate is the principal source of nitrogen in the majority of the European countries with the exception of Italy, Portugal, Spain, and the United Kingdom, which favor ammonium sulfate In the U.S.S.R., ammonium nitrate accounts for about two-thirds of the total output of all nitrog-

enous materials In the world export market, however, ammonium sul-

fate exceeds ammonium nitrate

Ammonium nitrate is sometimes mixed with powdered limestone or

calcium carbonate The product contains 20 to 21 per cent N and is a

physical mixture of the two components It is by weight about 60 per

cent ammonium nitrate and 40 per cent limestone or carbonate In Europe this proportion is varied to produce fertilizers containing higher percentages of nitrogen The addition of limestone improves the physical quality of the product, renders it nonexplosive, and reduces its fire hazard The major disadvantage of the mixture is its low analysis Largest producers are France, the Netherlands, Austria, Poland, and Czecho-

slovakia ( FAO, 1963) The material is used mostly for direct application;

however, it can be used in dry mixes

The double salt of ammonium sulfate and ammonium nitrate, (NH,) 2-

S04.NHdN03, in which the two are present in equal molecular propor- tions, is an important fertilizer material in Europe Produced by neutraliz- ing a mixture of sulfuric acid and nitric acid with anhydrous ammonia,

it contains about 27 per cent N West Germany is the major producer,

and small amounts are produced in Belgium, India, and Yugoslavia

ADVANCES IN FERTILIZERS 19 (FAO, 1963) In the United States, TVA produces ammonium nitrate sulfate by preneutralizing sulfuric acid with ammonia and granulating with ammonium nitrate crystals This product, containing 30 per cent N, has 79 per cent of its nitrogen as ammonium nitrate and 21 per cent as ammonium sulfate The chief advantage of the material is that it provides sulfur for use in areas of sulfur shortage

2 Ammonium Sulfate

Ammonium sulfate, ( NHr ) ?SO4, is usually manufactured by allowing ammonia to react with sulfuric acid; however, manufacture of ammonium sulfate by reaction of ammonia and carbon dioxide with gypsum is in- creasing in a number of countries, including the United Kingdom, India, Pakistan, and East Germany (Anonymous, 1960; Pratt, 1964-c; Sedlack, 1964) Other processes and process modifications are practiced to a limited extent

The ammonia may be either by-product, mainly from coke ovens, or synthetic About one-sixth of the world production of ammonium sulfate uses by-product ammonia and the remainder synthetic, with production from the latter gaining over by-product sources The final product con- tains around 21 per cent N and 24 per cent s

Ammonium sulfate continued until 1959-1960 as the largest single nitrogen material produced over the world (FAO, 1963) It is still the leading nitrogen source in Asia, Africa, and Oceania, but in Europe and North and Central America it has been replaced by the higher analysis ammonium nitrate In the United States, ammonium sulfate has held its own in tonnage About one-third of the total nitrogen output in the

U.S.S.R is ammonium sulfate, compared with about two-thirds from ammonium nitrate Ammonium sulfate remains the prime export mate- rial, representing approximately one-third of all nitrogen fertilizer exports New plants are being added, although their numbers do not approach those for ammonium nitrate and urea

The major drawback of ammonium sulfate is its low analysis and the acid reaction that it produces in soils Its sulfur content is a definite asset

on sulfur-deficient soils, and it mixes well with practically all other fertilizer materials except those of high alkalinity Ammonium sulfate is well adapted to dry-mix formulations and bulk blends because of its low hygroscopicity

20 LEWIS B NELSON

phase under high temperature and pressure to form ammonium car- bamate, NH2COONH4, as in intermediate compound which is later dehy- drated to urea Carbon dioxide of suitable quality is a by-product of the ammonia plant operation There are a number of competing processes,

differing mostly in the method of treating off-gases (ammonia and C02)

from the carbamate-urea reactor These are described by Kolterman and Rennie (1960) and Church (1964)

Toxicity of biuret, NH2CONHCONH2, in urea has been of major con- cern to agronomists Biuret is formed by reaction of urea with its decom- position product, isocyanic acid, during the concentration and evapora- tion step in the formation of the crystalline or prilled product However, advances and technological developments in urea plants during the past few years now make it possible to hold the biuret content to less than

1 per cent, an amount that is not likely to injure crops even in spray applications (Anonymous, 1963e)

In the soil, urea hydrolyzes to ammonium carbonate The reaction

is catalyzed by the enzyme urease found in most groups of bacteria, actinomycetes, and fungi, as well as in crop residues When urea is hydrolyzed in the soil, the ammonium carbonate produced causes a marked increase in pH Free NH3 may be present above pH 7.0, which can cause plant damage When pH values are higher than 7.7, nitrite oxidation may be inhibited, which allows nitrite accumulation, possibly

in toxic amounts (Court et al., 1964) Urea which hydrolyzes at the soil surface or on surface plant material also may lose ammonia to the atmos- phere However, urea losses can be largely avoided if it is incorporated

in the soil Also, direct contact with the seed must be avoided A compre- hensive review of the use of urea as a fertilizer has been made by Gasser

(1964)

Urea, which was introduced as a fertilizer in the 1930's, made a very slow start, and it was not until the mid-1950's that it became much of a factor on the world fertilizer market The slow start was due to a host

of factors including doubts as to agronomic suitability, gaseous loss when surface-applied, and frequent instances of biuret toxicity Also, manu- facturing costs were high relative to competing materials However, intel- ligent use and improved processes and plant operating techniques have largely overcome the earlier drawbacks These, along with its desirable properties of high analysis, nonexplosiveness, and effectiveness as a nitro- gen carrier, and a substantial price decrease in early 1962, have resulted

in its rapid rise in popularity Urea, particularly, has become an important material in the world export market where it is safer and less expensive

to ship and handle Its higher analysis gives it a distinct advantage over ammonium sulfate

ADVANCES IN FERTILIZERS 21 The increase in the use of urea as a major nitrogenous fertilizer has been one of the most significant features of the industry during the past

5 years (Anonymous, 1963d) Estimated world production capacity was 198,000 short tons in 1950, 2,132,000 in 1959, and 5,290,000 in 1963, and

it is expected to double again by 1966 Some 45 countries had urea plants

in 1963 including 22 in the United States, 22 in western Europe, and 17

in Japan Eight were in Communist countries, 6 in Asia, 5 in Latin America, 3 in Canada, and 1 in Africa Not all urea plants in the United States make solid urea, since much of that produced goes into nitrogen solutions

Japan and the United States are the largest consumers of urea, fol- lowed by the Republic of Korea, India, Mexico, and Sudan (FAO, 1963)

Most of that consumed in the United States is an ingredient of nitrogen

solutions The use of urea in bulk blends is increasing, and it has been gaining steadily as a direct application material since 1960 It is used to some extent as a foliar spray on horticultural crops or applied in mixture with certain insecticides and fungicides Urea is also applied in irriga- tion water, and prilled urea is well adapted to aerial application Japan, the Republic of Korea, and India use it mostly in solid form, largely as

a rice fertilizer; however, its use on other crops is increasing Sudan uses

it as a cotton fertilizer

4 Calcium Cyanamide

The manufacture of calcium cyanamide, CaCN2, is described in Sec- tion 111, A Cyanamide contains up to 2.2 per cent N The unit cost of nitrogen in cyanamide is generally higher than that of competing mate- rials Cyanamide has additional benefits as a herbicide and pesticide and contains up to 15 per cent Ca( OH)2, which helps correct soil acidity

It is also used as a defoliant for cotton prior to mechanical picking The use of calcium cyanamide as a fertilizer material has been declin- ing throughout the world and now represents only 2 per cent of the worlds fertilizer nitrogen output The decline has resulted from increas- ing cost, the development of alternative uses of calcium carbide, and competition from higher analysis nitrogenous fertilizers (Anonymous,

1 9 6 3 ~ ) World production for fertilizer use was 34,000 short tons of N

in 1958-1959 and 305,000 tons in 1961-1962 In West Germany, use of calcium cyanamide is second only to use of ammonium nitrate

5 Anhydrous Ammonia for Direct Application

Use of anhydrous ammonia, 82 per cent N, started in the United

States during World War I1 when shortages of other forms of nitrogen encouraged farmers to learn to handle and apply it even though its han-

22 LEWIS B NELSON

dling presented certain hazards As shown in Fig 4, its use as a straight

material has skyrocketed Large amounts are applied also in Mexico, but very little is used in other countries

It is lower in initial cost than any other nitrogen fertilizer Shipping and storage costs, however, are higher for anhydrous ammonia than other materials because of the special equipment needed Cost of ap- plication equipment also is higher than for solids and nonpressure liquids but is about the same as for other pressure liquids Detailed information

on the handling and use of anhydrous ammonia is given by Slack (1960)

and Adams et al (1961) Still, its high nutrient content and low initial cost combine to result in a significantly lower delivered price per pound

of N to the farmer

Considerable precautions are required in handling ammonia It is a gas at normal pressure It can cause severe burns and asphyxiation, and

it is flammable and explosive when mixed with air in certain proportions

As a result, numerous regulations and suggestions for safe use and handling have been formulated in the United States by the Interstate Commerce Commission, the Compressed Gas Association, Inc., the National Safety Council, the Agricultural Ammonia Institute, and others Anhydrous ammonia for direct application is usually stored at the ammonia plant under pressure or refrigeration and then is moved to bulk distribution centers under high pressure in tank cars, trucks, or barges From here it is transported to the field in the dealer’s tank truck and transferred to the farmer’s applicator tank; or the dealer may trans- fer a nurse tank or a farmer-owned portable tank directly to the farm Anhydrous ammonia for introduction in irrigation waters is stored in cylinders and trucked to the field Considerable ammonia is custom- applied Storage tanks are of mild steel, built to withstand pressures of

265 psig or more, and equipped with relief valves

Because ammonia is volatile, it is injected beneath the soil surface to depths averaging about 6 inches The opening made by the injection equipment is immediately closed The ammonia develops sufficient pres- sure in the applicator tank to force it through the injectors into the soil Uniformity of application can be achieved with valves, a constant pres- sure on the injector orifices, and a constant speed of the tractor, plus use of calibration charts Flowmeters can be used instead of valves, and metering pumps driven by an applicator or tractor wheel have been developed which remove the necessity of uniform tractor speeds Under normal soil conditions, very little ammonia is lost into the atmosphere Most that is lost escapes along the sides of the soil openers

or from the furrows before they are closed Losses of ammonia from irrigation water may vary greatly (Adams et aZ., 19sl) Various studies

ADVANCES IN FERTILIZERS 23

have indicated losses ranging from negligible to as high as 80 per cent Losses, however, can be minimized by irrigating on cool, humid and quiet days, maintaining a concentration of not over 110 parts per million

of ammonia in the water, and keeping the exposed surface of the flowing water to a minimum

Response of crops to ammonia is about the same as to other nitrogen carriers Usually most of the ammonia is absorbed in a zone of about 2

inches from the point of injection within which the soil p H is increased

to a relatively high level

6 Aqua Ammonia for Direct Application

About 113,000 tons of N as aqua ammonia was consumed for direct application in the United States in 1962-1963; of this, about 59 per cent was used in the Pacific States (Scholl et al., 1964) Use of aqua ammonia

is increasing in the U.S.S.R., Denmark, West Germany, Czechoslovakia, Taiwan, Israel, and Poland (FAO, 1963)

According to Baranov (1963), aqua ammonia is the sole form of liquid nitrogen fertilizer used in the U.S.S.R Consumption has increased rapidly-21,000 short tons in 1957; 172,000 tons in 1961; and 294,000

tons in 1962 Aqua ammonia use is concentrated around plants which produce nitrogenous fertilizers and have an excess of ammonia

Aqua ammonia is made by dissolving anhydrous ammonia in water

It is usually produced in the small plants of mixers and distributors, but some is made at the locations of ammonia plants Aqua ammonia is stored under low pressure and distributed directly to farmers in the im- mediate area Its low nitrogen content (usually 20.5 per cent N ) does not encourage transportation over very great distances The main ad- vantages of aqua over anhydrous ammonia are less hazard and lower cost handling equipment Aqua ammonia must be injected beneath the soil surface, usually at depths of at least 4 inches, and the furrows im- mediately closed in order to minimize volatilization In contrast to the application of anhydrous ammonia, some type of pump, usually working from the power takeoff of the tractor, is required for application Aqua ammonia is applied also by ditch and flood irrigation

7 Nitrogen Solutions for Direct Application

Nitrogen solutions for direct application to the soil are aqueous solu- tions, usually of the nonpressure type, which contain their nitrogen in compounds other than ammonia, usually ammonium nitrate or urea, or both (Adams, 1961; Adams et al., 1961)

The highest feasible concentration for nonpressure solutions is 32

In some cases ammonium bisulfate, ammonium sulfate, calcium nitrate,

or sodium nitrate may supply part of the nitrogen, although a solution made u p solely of calcium nitrate has been used in California The absence of free ammonia makes it possible to apply such solutions on the surface of the soil without excessive loss of ammonia

Pressure type solutions such as are used in ammoniation of super- phosphates (see Section 111, C, 8 ) are seldom used for direct application ( Adams, 1961) Recently some low-pressure solutions have been manu- factured specifically for direct application These contain either 37 or

41 per cent total N and are formulated with ammonia and urea or am- monia, urea, and ammonium nitrate

Solutions for direct application have certain advantages over solids The liquids cost less per pound of N, and many have higher nitrogen contents They can be metered accurately into the soil, are easy to in- corporate in irrigation water, and are handled mechanically, which re- duces labor requirements Compared with anhydrous ammonia, nitrogen solutions are safer to handle and the application equipment is simpler and less costly

Nitrogen solutions are used in all parts of the United States, but the greatest use is in the West North Central, the East North Central, and the South Atlantic regions Although solutions for direct application are limited largely to the United States, they are gaining a foothold in France and the United Kingdom (Anonymous, 1 9 6 2 ~ ) The convenience of handling the solutions apparently has led to the rapid increase in usage Nitrogen solutions are corrosive, particularly when they contain am- monium nitrate The preferred construction material for storage is aluminum However, addition of ammonium thiocyanate as a corrosion inhibitor will permit use of carbon steel containers Ammonia-urea and urea solutions are less corrosive than those containing ammonium nitrate and are usually stored in carbon steel

Custom application is a major factor in distribution of all types of nitrogen solutions Many farmers, because of high and rising costs of machinery and labor, prefer to have the materials custom-applied rather than invest in labor and application equipment Farmers with small acreages especially cannot justify investments in application equipment Although nonpressure solutions usually are surface-applied, solutions

containing free ammonia must be injected into the soil to depths of 2

inches or more; otherwise serious volatilization losses occur In the west-

ADVANCES IN FERTILIZERS 25

ern irrigated areas, nitrogen solutions are applied extensively in irriga- tion water by the flood and furrow methods Nonpressure solutions also can be added to water applied by sprinkler systems; however, the prac- tice is not widespread Application methods are described by Adams

et al (1961)

Combining herbicides with nitrogen solutions is a recently developed practice that appears to offer promise (Gibbs, 1964; Klingman, 1964) Klingman combined herbicides with a nonpressure solution and obtained

95 to 98 per cent weed control by surface spraying in corn Approxi- mately 250,000 acres were sprayed in this manner in 1963 and an esti- mated 1.5 million acres was expected to be treated in 1964 Herbicides used have included 2-4D, Atrazine, Simazine, Lorox, and Karmex; how- ever, not all herbicides are compatible with liquid nitrogen

8 Nitrogen Solutions for Fertilizer Manufacture

Over 80 ammoniating solutions, in addition to anhydrous ammonia, are available in the United States for use in the ammoniation of mixed fertilizers They usually consist of a mixture of free ammonia, ammonium nitrate, and/or urea and water in various combinations Formaldehyde sometimes is included with urea to provide slow-release nitrogen- mostly for use in manufacture of lawn and garden fertilizers (see Sec- tion 111, C, 9 ) Occasionally, small amounts of ammonium sulfate and sodium nitrate are included In contrast to solutions used for direct ap- plication, ammoniating solutions always contain free ammonia and hence are always pressure solutions Discussion of their use in ammoniation is given in Section VI, A Descriptions of ammoniating solutions and their manufacture are given by Sauchelli (1963) and Crittendon (1964a) Ammoniating solutions contain from about 37 to 58 per cent N; how- ever, most are in the 37 to 49 per cent range Water, except where only

anhydrous ammonia is used, is an important component and varies from below 1 per cent to around 40 per cent A typical solution containing

43 per cent N might be composed of 20 per cent ammonia, 68 per cent

ammonium nitrate, 6 per cent urea, and 6 per cent water Each solution has its own characteristics which make it desirable or undesirable for a specific mixed fertilizer formulation For example, it is desirable to use

a solution with high free-ammonia content in mixed fertilizers having

a high phosphorus content derived from superphosphate and phosphoric acid For a high-nitrogen, low-phosphorus mixture, a low free-ammonia, high ammonium-nitrate solution is needed

There is a general trend toward solutions having a higher nitrogen content, lower water content, and more components to meet special re- quirements Fewer separate compositions than now exist, however, would

26 LEWIS B NELSON

meet the various needs Ammoniating solutions usually are made at ammonia plants and shipped by tank car and truck to points of mixed fertilizer manufacture

9 Slow-Releuse Nitrogens

Agronomists and the fertilizer industry have long been interested in developing a nitrogen fertilizer that would gradually release its nitrogen throughout the growing season, or preferably, over a longer period Such a fertilizer should result in increased efficiency of uptake by plants, minimize gaseous and leaching losses, and reduce application costs Unfortunately, while certain nitrogen compounds meet the slow-release criteria, their molecules are complex, and high production costs limit their use to lawns, gardens, ornamentals, and specialty crops So far, three nitrogen materials, the urea-formaldehydes, crotonylidenediurea ( Floranid ) , and magnesium ammonium phosphate, have been produced commercially Mitsubishi Chemical Industries in Japan is reported to be planning production of isobutyridene diurea, IBDU, by reacting butyl aldehyde with urea (Anonymous, 1964g) Also, Monsanto Chemical Company in 1962 received a patent on the use of glycoluril as a slow- release nitrogen fertilizer ( U s Patent No 3,061,423) Possibilities may exist, however, for achieving slow release through low-cost coatings and for use of biochemical inhibitors

Urea-formaldehyde is produced by reaction of urea with formalde- hyde in aqueous solution One mole of urea reacts with one mole of formaldehyde to form monomethylol urea, NH2 * CO NH - CH, - OH,

which further reacts to form a series of condensation products The pro- portions of the various compounds formed vary with the mole ratio

of urea to formaldehyde used and the reaction temperature, Thus the material is a mixture of inethylene urea polymers having a range of molecular weights and a range of solubilities in water solutions The marketed product usually contains 38 per cent N, of which 28 per cent

is in a slowly available (cold-water-insoluble) form A small amount of unreacted urea usually remains in the final product Its main advantage

is in its slow rate of nitrification; however, the rate of release is often too slow to meet the needs of the crop

Although the use of urea-formaldehyde is limited largely to the United States where it has been produced for a number of years, it is manufactured in France and the U.S.S.R A reported 15,000 tons was consumed in the United States during 1961, largely in specialty lawn, garden, and turf fertilizers Comprehensive discussions of the manufac-

ture and use of urea-formaldehyde are given by Clark (1963) and

Church (1964)

ADVANCES IN FERTILIZERS 27 Crotonylidenediurea is manufactured commercially by Badische Anilin- and Soda-Fabrik, AG, under the trade name Floranid (Anony- mous, 1963f) The product contains 28 per cent N, of which about nine- tenths is in the form of crotonylidenediurea ( 2-OXO-4 methyl-6-urido- hexahydropyrimidine ) and one-tenth is nitrate The product decomposes slowly in the soil and the nitrogen requirement o17er a growing season reportedly can be met by a single application Increasing the particle size also increases the length of the residual effect Rates as high as 500

to 700 pounds of N per acre have been applied without injuring plants High production costs have limited its use to horticultural crops, lawns, and turfs

Magnesium ammonium phosphate, MgNH4P04 HsO, which exhibits slow nitrogen solubility characteristics, is now in limited commercial

production in the United States by W R Grace & Company (Bridger

et at!., 1962) The commercial product contains 8 per cent N, 17.5 per cent P (40 per cent PzOn), and 14 per cent Mg Magnesium ammonium phosphate in small particle size is reported to nitrify at a rate com- parable with ammonium sulfate However, nitrification decreases as

particle size increases Large-sized particles minus 3 plus 6 mesh are expected to last over a year in the soil Finely pulverized material is used for foliar application The product is said to be nonburning even

at high rates of application

An experimental product, oxamide, ( CONH2)s, has received con- siderable attention by TVA and others in recent years (DeMent et al.,

1961) The product contains 31.8 per cent N in which the rate of hy- drolysis and nitrification is governed by particle size (surface area) Fine oxamide is as available to plants as soiuble sources of nitrogen, while

increasing the particle size reduces the rate of solution Oxamide is not

now produced commercially; however, efforts continue on development

of a low-cost process that will permit its use as a fertilizer

Considerable research has been under way for some time to enclose the fertilizer particle in a suitable coating which would endow slow- release properties (Army, 1963) Various substances have been tried including polyethylene, acrylic resins, vinyl acetate, waxes, paraffin com- pounds, asphaltic mixtures, and sulfur Experimental data are sufficient

to show that fertilizers can be successfully coated to slow the rate of nitrogen release However, most coating materials increase the cost of the fertilizer and present manufacturing problems Uniformity of coating

is essential, but difficult to achieve in large-scale production

T\TA has investigated the coating of urea and other soluble nitrogen

carriers with sulfur which is relatively inexpensive and is a plant nu-

trient in itself Sulfur coating equaling 15 per cent of the weight of