FIG. 162.—One of the experimental fields used by the department to test the effect of new nitrogen fertilizers on cotton
NITROGEN From the Air Makes Good Fertilizer
Nitrate of soda from the Chilean fields and small deposits of potassium nitrate are the only natural supplies of nitrogen in a form available for fertilizers.
Other available forms are by-products; ammonium sulphate from coke ovens, gas works, etc., cottonseed meal from cotton, animal tankage and dried blood from slaughterhouses, fish scrap from nonedible fish and small quantities of material from other sources. The by-products containing organic nitrogen are being used more and more for feeding purposes and the supply available for fertilizers is becoming smaller and smaller. As a result of this condition the attention of investigators in recent years has turned to the production of nitrogen salts by obtaining nitrogen from the atmosphere through chemical methods. The effect of air-derived nitrogen salts in commercial fertilizers on crop production is now a much discussed subject by farmers, fertilizer manufacturers, and investigators.
The development of nitrogen-fixation processes and the operation of nitrogen-fixation plants is making available to agriculture a large supply of high-analysis nitrogen salts. Information concerning their effect on crops and suitability for use as fertilizers is of considerable interest.
The materials which have received most attention by manufacturers and investigators are ammonium chloride, which contains 31.8 per cent ammonia; ammonium nitrate containing 42.5 per cent ammonia; urea containing 55.6 per cent ammonia; urea phosphate containing 21.5 per cent ammonia and 45 per cent phosphoric acid; ammonium phosphate containing 14.7 per cent ammonia and 61.7 per cent phosphoric acid. All of these materials possess a high plant food content, as is evidenced by a comparison with nitrate of soda, which contains 18 to 19 per cent ammonia. That the greater use of chemical salts in the manufacture of fertilizers possesses a marked trend is shown by the much greater production of air-derived nitrogen salts, especially in Europe.
It is estimated at present that at least one-half of the world’s inorganic nitrogen comes from the atmosphere through nitrogen-fixation methods, as against only 7 to 8 per cent in 1913.
Experiments to determine the effect of these concentrated air- derived nitrogen salts under American farm conditions have been made covering a period of several years with cotton, potatoes, corn, garden, and truck crops. These have been located on official test farms and on commercial farms on some of the principal soil types in the Eastern States. (Fig 162.) The effect of the air-derived nitro-salts, when used in mixed fertilizers with acid phosphate and potash, has generally been good, and compares favorably with nitrate of soda and sulphate of ammonia.
In the fertilization of cotton, ammonium nitrate and urea have proven to be very good forms of plant food and have produced larger yields than did ammonium chloride, which has given a relatively smaller production than other nitrogen materials. The use of these air-derived nitrogen salts containing relatively high concentrations of ammonia when used in mixed fertilizers under cotton has not produced any injurious effect on germination or on the plants in the early stages of growth. Neither has there been any indication of unusual leaching from the soil.
With potatoes, a crop requiring large quantities of fertilizers, the air-derived nitrogen salts have shown up well. Fertilizers having their nitrogen derived from these concentrated materials have produced as large yields as those having their nitrogen derived from nitrate of soda or sulphate of ammonia. This has proven true in all the large potato-growing sections of the Atlantic seaboard.
These new fertilizer salts have also been successfully used with garden and small truck crops, which make a rapid growth, fruit, and mature in a relatively short period. Their effect on garden peas, Lima beans, snap beans, and sweet corn has been good, producing somewhat larger yields than has nitrate of soda or sulphate of ammonia.
Although the effect of air-derived nitrogen salts, most of which are highly concentrated, on crop growth and production, are generally good when used in mixed fertilizers, there are difficulties to overcome. The keeping qualities of fertilizers as to caking, moisture, etc., and the ease with which they can be distributed in the field are important factors. Some of them, like ammonium nitrate, may have undesirable physical features in bulk mixtures or in storage and require that methods of preparation, mixing, storage, and application may have to be worked out, as had to be done with some of our ordinary fertilizer salts and their mixtures.
Small quantities of nitrogen-fixation products are now being used in commercial fertilizer mixtures, but their introduction into general use will no doubt be gradual, as it should be, in order to allow sufficient time to overcome the difficulties which may arise in commercial mixing and farm application.