No abstract

The availability of nutrients from inorganic fertilizer salts can be regulated through coating such materials. The release rate was investigated in several elution and leaching experiments. The release approached linearity for a considerable period; thereafter the rate dropped off. The release rate was largely independent of the pH of the elutant and of the soil pH. An increase in temperature from 10° to 20°C. almost doubled the initial release rate. The release could be regulated very efficiently through the coating thickness. There was an effect of ionic species, nitrate and ammonia being given off more rapidly than potassium or phosphates. The release was only slightly reduced under sterile conditions. It was concluded that diffusion is the most likely release mechanism and proposed that discrepancies such as the high Q10 value could be explained through possible changes in membrane properties. Coated fertilizers thus possess the properties required for regulation of the availability of nutrients: they may reduce leaching losses and provide a steady prolonged nutrient supply to plants.

Shrubs of Artemisia tridentata and Larrea tridentata have unusually high oxygen requirements for root growth. Roots of Franseria dumosa, like many economic plants, need lesser amounts of oxygen. An oxygen diffusion rate of about 0.30 mg cm-2 min-1 is required by Franseria to achieve a root growth rate that is 50% of maximum at the experimental temperatures. The corresponding figures for Artemisia and Larrea are about 0.50 and 0.43, respectively. It is concluded that the general exclusion of Larrea and Artemisia from fine-textured and poorly drained soils in the desert is a reflection of their relatively high oxygen requirements for root growth.

It was shown using membrane‐coated granular fertilizer, in which the membrane constituted 11 or 12.5% of the weight of the granules, that: (a) moisture levels, exceeding the range of permanent wilting percentage to field capacity in a loam soil, did not appreciably affect the rate of transfer of minerals through the membrane of coated fertilizer mixed in the soil, (b) the time for transfer of a given fraction of fertilizer through membranes is substantially extended if the fertilizer is topdressed on a soil as compared to incorporated (presumably due to intermittent drying between leachings), and (c) an efficiency of recovery ranging from about 25 to 45% was obtained from a single application, incorporated in the sand, of coated ammonium nitrate by corn during a 3‐month growing period. In the latter study a sand was used containing < 1% of clay and as much as 7 feet of water passed through the root zone during the period of the study. Implications of the coating technique for controlling fertilizer availability are briefly considered.

No abstract