Deficiency in corn causes a shortening of the internodes of corn and a severe stunting.A typical zinc-deficient plant is shown in Figure 9. When the deficiency is severe, many corn plants will die in the seedling stage, with those recovering exhibiting several different colorations and symptoms ranging from a lack of green color in the upper leaves to interveinal striping in the upper leaves. Severe zinc deficiency in corn is known as "white bud."Zinc deficiencies are corrected by soil applications of zinc sulfate and zinc chelates in the case of row crops, and by spray as well as soil applica-

A considerable part of the phosphorus in most mixed ferti lizers is carried as dicalcium phosphate produced as a conse quence of ammonia neutralization of the mixture. Agronomic experience with such mixtures suggests that the phosphate pro duced in situ has a higher nutritive value than separate prepara tions of dicalcium phosphate. Any increased nutritive value of the dicalcium phosphate must, it would seem, stem mainly from enhancement of phosphorus solubility in the presence of soluble salts. Accordingly, the solubility of a laboratory preparation of dicalcium phosphate was measured in water and several salt solutions. Greenhouse techniques were designed to minimize re sponses to nutrient constitutents of the salts, change in available soil phosphorus status and physiological effects due to the salts, so that differences in plant response to binary mixtures of di calcium phosphate and several salts were indicative of differences in solubility of dicalcium phosphate. Alfalfa was used as the test crop on Nunn, Carrington, and Chester soils. In general, salts such as ammonium sulfate, which in laboratory tests markedly increase the solubility of dicalcium phosphate with increasing ionic strength, also gave the greatest crop responses in the greenhouse. Those salts such as the ammonium nitrate type, which increase the solubility only moderately and level off at ionic strengths between 2 and 4, only occasionally gave increased crop response, while salts such as the calcium nitrate type, which decrease the solubility sharply with increasing ionic strengths, usually gave a negative crop response.

A greenhouse test to measure the effect of placement, granule size, and the relative phosphate fixing capacity of the soil upon the efficiency of superphosphate and dicalcium phosphate was performed. The materials, labeled with P32, granulated, and sized to 4–6, 8–10, 14–20, 28–35, and −35 mesh were used in band and mixed placements on Evesboro and Davidson soils. A major difficulty encountered in greenhouse experimentation with granulated fertilizers stems from the problem of securing small samples for pot application that truly represent the test materials. Even with close‐sized materials the minimum representative sample of coarse granules is several‐fold larger than the quantity required for pot application. The test crop was wheat. Using increased yields, total phosphorus uptake, and percentage of the plant phosphorus derived from the fertilizer as criteria of agronomic value, the 14–20 mesh granules of superphosphate were the best size tested with this material while the 28–35 and −35 were the best sizes tested with dicalcium phosphate.

Processes for producing nitric phosphate offer a means for utilizing low grade phosphate material, called leached-zone ore, that occurs in Florida land-pebble deposits. Because the nitric phosphate produced therefrom carries a much larger amount of aluminum than that made from commercial Florida land pebble, nutritive tests were made in the greenhouse, in order to determine the relative value of the high-alumina nitric phosphate.Crop yields and phosphorus uptakes showed that the leached-zone nitric phosphate had a lower agronomic value than the land-pebble material, when both had a low proportion of phosphorus in the water-soluble form. At medium levels of water solubilities, however, both products and triple superphosphate gave comparable yields.

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