New and Better Fertilizers

E. L. Newman and W. L. Hill.

Better fertilizers have been coming on the market for years.

New fertilizers are rarely new from the chemist's viewpoint. They generally are composed of known chemical compounds, although the proportions of the compounds actually present may be difficult to determine.

Usually a promising new fertilizer undergoes lengthy development before it is offered commercially. Also, a nutrient-bearing compound often is used as a raw or intermediate material in the manufacture of fertilizers for some years before it may become available to the farmer for direct use. Anhydrous ammonia and phosphoric oxide are two of many examples.

Novelty in a fertilizer must then be regarded as newness to the retail market. In this light, our subject demands a discussion of the things that are likely to influence new or improved fertilizers.

The development of a new fertilizer to market status is a response to the need for some particular quality or set of qualities that are expected to lower the cost, provide easier handling, or supply soil and crop requirements better. Examples are the water-soluble phosphorus of ammonium phosphates, the water-insoluble nitrogen of urea-formaldehyde, the noncaking and dust-free character of granular fertilizers, balanced nutrient contents of polynutrient fertilizers, and the low-cost nitrogen afforded by anhydrous ammonia.

Because needs vary from region to region, reflecting a diversity of soils, crops, climates, and farm practices, the nature of the most suitable fertilizer also differs among the regions. Often the fertilizer is expected to do more than supply additional nutrients.

These circumstances are illustrated by the following specifications for an ideal fertilizer, compiled by T. P. Hignett of the Tennessee Valley Authority, from suggestions by agronomists, farmers, and fertilizer manufacturers:

The ideal fertilizer Mr. Hignett was advised should carry high concentrations of the three primary plant nutrients (nitrogen, phosphorus, and potassium), generous amounts of the secondary nutrients (calcium, magnesium, and sulfur), and small amounts of several micronutrients. It should be in the form of hard, round granules, about 0.1 inch in diameter, that are impervious to moisture until placed in the soil, whereupon the nutrients should dissolve immediately, even though the soil be dry, and become completely utilizable by short-season crops. At the same time the nutrients should neither be fixed by the soil nor leached from it, so that a residual effect will extend over a period of years. It should have an alkaline reaction on acid soil, and an acid reaction on alkaline soil. It should be adaptable to manufacture by unskilled labor in whatever equipment happens to be available in the factory. Finally, it should kill weeds and bugs and condition the soil.

Obviously this is an absurd specification and was meant to show the impossibility of achieving the perfect fertilizer. Nevertheless the respective specifications are desirable under certain conditions and must be given proper consideration in the design of improved fertilizers. The specifications can be used also as factors in judging the possibilities of materials yet to come. The several elements of value arise in one or more of three avenues of approach to fertilizer appraisal--character, effectiveness, and cost.

THE CHARACTER OF A FERTILIZER depends largely on such chemical properties as concentration and reactivity of the major nutrients.

Reactivity, as we use the word here, means the tendency of the fertilizer substance to dissolve and become available to plant roots. It can be measured reasonably accurately as solubility.

Among the factors that influence the character of fertilizer are certain physical properties that facilitate handling in storage, transportation, and application to the soil. Emphasis on physical character has increased notably in recent years. Farmers no longer tolerate caked fertilizers. Powdery materials are becoming less acceptable.

The benefits of some high-analysis products have been gaining recognition over a very much longer period. These trends are especially marked in the regions where the use of fertilizer is relatively new. Considerable attention also has been given to the reactivity or solubility of nutrients. Some results along this line are the development of urea-form, a synthetic nitrogen fertilizer of controlled solubility, and recognition of the importance of water-soluble, phosphorus-bearing fertilizers for fast-growing crops.

THE EFFECTIVENESS OF A FERTILIZER is measured in terms of crop response to its use. Responses are determined to a large extent by environmental factors peculiar to the farming region soil type, climate, and water supply. These conditions must be accepted much as they are, and farming is thereby regionalized. Response is also influenced by cultural practice, in which some noteworthy factors are kind of crop, crop rotation, kind and amount of fertilizer, placement of fertilizer in soil, and time of application. Effectiveness of a fertilizer thus depends not only on its character but also on where it is used and the way it is used.

Experimental evaluation of a fertilizer can be approached from two basic viewpoints. A fertilizer of known character may be tested to find the region and cultural practice that provides the conditions for best performance, or a particular cultural practice may be studied to determine fertilizer characteristics that will induce the greatest response. The sets of conditions under which present-day fertilizers prove effective have been broadly demonstrated experimentally, although in farming practice the choice of fertilizers is not always in line with experiment.

COST is probably the most important consideration in the consumer's choice of a fertilizer. The farmer's first thought is usually, "How much does it cost?" Only so much can be spent for fertilizer, and he wants the most for his money. This is a proper view, provided he measures cost in terms of the quantity of plant nutrients purchased rather than on the basis of the weight of material received. For example, the Illinois farmer who chooses a 5-10-10 (the numbers indicate percentages of nitrogen, phosphate, and potash, in that order) fertilizer at 59 dollars a ton may not realize that a 10-20-20 fertilizer at 104 dollars a ton is the better bargain. Adding the costs of distribution and application to the purchase price widens the margin, because the same amount of nutrients can be handled and applied more cheaply in the concentrated material.

PROSPECTS for better fertilizers may be gaged on the basis of the criteria for appraisal character, effectiveness, and cost.

The manufacturer alone can make alterations in fertilizer character, but both manufacturer and consumer can make contributions to effectiveness and lower the cost, especially the cost after application to the soil. The farmer who uses a fertilizer of low reactivity as a starter fertilizer for a fast-growing crop is not getting the best out of the fertilizer. Conversely, a farmer sometimes may integrate fertilizer application with crop rotation in such a way that application of one low-cost major nutrient is required only once in several years. He thus achieves economies in tonnage and cost greater than any price advantage that the manufacturer could provide.

IMPROVED PHYSICAL CHARACTER of fertilizers, particularly the polynutrient goods, has been a subject of much research. Great strides have been made toward the development of noncaking, free-flowing fertilizers. Much remains to be done, of course.

For years diluents known as conditioners have been incorporated into fertilizers, either deliberately or incidentally, to prevent caking by formation of a coating on the fertilizer particles or by simple mechanical separation of the particles. The trend to goods of higher analysis has squeezed out diluents to a marked extent and thus has necessitated a search for other ways to keep fertilizers free-flowing.

Physical nature is controlled by one or more procedures choosing the best-adapted ingredients, selecting favorable proportions of ingredients, granulating the fertilizer, reducing the moisture content, coating the granules with suitable agents, and packaging in moisture-resistant bags.

Each nutrient combination usually presents a special problem, so that considerable research is nearly always required for the development of an economic technique that permits production of the fertilizer in free-flowing form. Despite the many obstacles, the current effort to better the physical character of fertilizers is improving the marketed products.

The difficulty of maintaining a fertilizer in good condition usually increases with the solubility of the nutrients. Highly soluble and concentrated forms of nutrients frequently present major problems. In such cases, one answer to the question of poor physical condition is direct use in solution form. The direct application of liquid fertilizers is a growing practice. The problem here is transferred from the physical condition of a solid to the nutrient level in a liquid. Poor condition is nicely avoided at the expense of nutrient concentration. At the same time, the cost of storage and transportation is increased. Because liquids of higher nutrient content thus become a chief objective of improvement, the problem in this case shifts from physical to chemical character.

CHEMICAL CHARACTER, which includes such properties as concentration and reactivity, is an avenue for the further improvement of fertilizers. The trend toward high-analysis goods persists. It has perhaps approached the practical limit in a few of the newer market areas, but in the old and at the same time heavy-consuming regions the acceptance of higher concentrations is slow. Progress can be made as rapidly as the consumer is convinced of the advantages of higher grades.

Adjustment of nutrient proportions in polynutrient fertilizers, to reach proper balance for crop needs, provides another opportunity for betterment. The manufacturer must look to the agronomist for guidance here.

Continued expansion of the use of anhydrous ammonia and nitrogen solutions for side and top dressings could have a pronounced effect on the formulation of solid fertilizers. Because this practice relieves the need for nitrogen-rich fertilizer at planting time, a part of the nitrogen will likely be dropped from the starter fertilizer and, in the interest of economy and effectiveness, transferred to later applications. The lowered content of nitrogen compounds would alter somewhat the physical and chemical nature of the fertilizer used at planting time. The net effect would probably be improvement.