More than 1,600 different grades of mixed fertilizers were sold in the continental United States in the year that ended June 30, 1955.

Thirty grades supplied about 79 percent of the total tonnage of mixtures. Only 15 grades accounted for 63 percent.

Many of the States publish lists of the grades recommended by the respective agricultural experiment stations, and several prohibit the registration and sale of nonrecommended grades. Restriction of the number of grades of mixed fertilizers makes for simplification of manufacturing operations, lower production and marketing costs, and more effective utilization of supplies of fertilizer materials. It also aids regulatory operations and simplifies the choice and use of fertilizers.

PHYSICAL CONDITION is a major problem in the manufacture, distribution, and use of solid fertilizers. The problem has been intensified by the trend toward higher-analysis materials and mixtures, but progress has been made in solving it.

Important factors involved in the physical condition of a fertilizer are its hygroscopicity (proneness to absorb moisture from the atmosphere), caking tendency, and particle size. These factors, often interrelated in their effects, markedly influence the utility of the product as regards its storage, shipping, and application in the field.

Many fertilizers readily absorb moisture from the air, which may cause them to become sticky. This is especially true of calcium nitrate, ammonium nitrate, sodium nitrate, urea, and their mixtures with other materials.

Among the materials that have little or no tendency to absorb moisture under the atmospheric conditions prevailing in the United States are mono-ammonium phosphate, potassium nitrate, potassium sulfate, and the super-phosphates.

Serious caking may occur when hygroscopic fertilizers are subjected to pressure, as in large piles or high stacks, or when moisture is lost because of changes in atmospheric conditions.

Caking may result, too, from other causes as from chemical reactions among the ingredients of mixed fertilizers and it is encouraged by high proportions of fine particles.

Mixed fertilizers may undergo segregation during shipping and handling because of differences in the specific gravity and the size of the particles of their ingredients.

A solid fertilizer cannot be distributed evenly in the field if it is sticky or caked, if its ingredients undergo segregation, or if its drillability (uniformity of flow) is hindered by its particle size. The drillability of fertilizer is at its best when the particles are dry, uniform in size, spherical in shape, and of such a practical size as to minimize the cohesive forces between them.

Good physical condition in fertilizers is favored by regulation of the initial moisture content; proper curing to insure completion of chemical reactions before shipment; elimination of fine particles; use of the right kind and quantity of conditioning agent to hinder coalescence of the particles; granulation or, with mixtures, use of ingredients having uniform and relatively large particle size; packaging in moisture-resistant containers; protection from extremes of atmospheric temperature and humidity; and storage in low stacks or piles.

Granulation of fertilizers, whereby the particles are converted into spheroids of substantially uniform size, is an especially effective way of promoting good physical condition. Several fertilizer materials, including ammonium nitrate, ammonium phosphate, calcium cyanamide, calcium nitrate sodium nitrate, the normal and triple super-phosphates, and urea, are marketed wholly or partly in granular form, and granulation of mixed fertilizers is practiced extensively.

FERTILIZER-CONTROL LAWS have been enacted by all States, but the Federal Government does not exercise similar authority in this field. The laws are revised from time to time as may be necessitated by changed conditions and practices.

In the interest of more uniform legislation among the States, recent revisions have been based largely on a model fertilizer bill developed by the Association of American Fertilizer Control Officials (Proposed Model State Fertilizer Bill (11th draft), Association of American Fertilizer Control Officials, Official Publication No. 10, 66-77, 1956).

All the State laws require registration of the various brands and grades of fertilizers before they are offered for sale, sold, or distributed. They also require guarantees of the minimum percentages of each of the three primary nutrient elements expressed in terms of total nitrogen (N), available phosphoric oxide (P₂O₅), and soluble potash (K₂O) and they provide penalties for failure to meet the guarantees and for other violations. Guarantees of other constituents are required or permitted in some instances, and it may be necessary for the container or tag to carry certain information relating to filler and to the character of the fertilizer.

Many of the State laws designate the minimum percentage of total plant nutrients that may be guaranteed in a fertilizer. Some States limit the sale of mixed fertilizers to certain specified grades approved by the appropriate agricultural experiment station.

The laws or the accompanying regulations generally include provision for registration and inspection fees; the labeling and identification of packaged fertilizers and of fertilizers distributed in bulk; the periodic reporting (to the control authority by the manufacturer or the distributor) of the quantities of fertilizer distributed; and the inspection, sampling, and analysis of fertilizers and the publication of the data.

Satisfactory operation of fertilizer-control laws necessitates, among other things, the use of standardized methods of sampling and chemical analysis. The development and publication of such methods is a function of the Association of Official Agricultural Chemists. The State laws or the accompanying regulations generally specify the use of the A.O.A.C. methods in official fertilizer inspections.

Variations in certain phases of the fertilizer-control laws among the individual States or groups of States reflect largely the differences in the character of the agriculture and in the soil and crop requirements for plant nutrients. The laws generally afford protection to the consumer as well as to the manufacturer.

IT MAY BE SAID with confidence that fertilizers will play an increasingly significant role in the Nation's agricultural economy and that in the years to come the trend in their production and use will continue markedly upward.

The country is richly endowed with resources of fertilizer raw materials and of their requisites for processing, which are economically usable under present conditions, and far larger resources reside in less favorable situations.

We have extensive facilities for winning and processing the raw materials by modern methods and techniques, all of which constantly are undergoing improvement. For the most part, those facilities are widely distributed over the country.

For the foreseeable future, the problem of adequate supplies of fertilizer for the American farmer appears to be largely one of continuing to expand the productive capacity to keep pace with the demand. But it should be emphasized that great opportunity remains for technological advances in fertilizers and for improving the efficiency of their use in crop production and in other phases of farm management.