IS SULFUR A LIMITING FACTOR OF CROP PRODUCTION IN SOME UTAH SOILS?

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Abstract
An analysis of the Cache Valley soils shows them to contain from 252-1764 lb. and to average 903 lb. of sulphur per acre-foot of 3,600,000 lb. On the basis of certain simplifying assumptions, a mathematical equation is developed indicating the general form of the relationship between the crop yield and the time where no sulphur is added from outside sources. On the basis of this equation, and by means of the law of diminishing returns, a method of determining the critical sulphur content in terms of soil and crop characteristics and economic constants is illustrated. The quantity of sulphur carried from the soil varies with the crop, the quantity of water applied and the composition of the soil. Analyses of the water of 45 streams, the waters of which are used for irrigation purposes, showed them to carry from 3-676 lb. of sulphur per acre-foot of water. Six streams carried over 200 lb. and 34 streams carried less than 100 lb. Thus the quantity of sulphur carried to the soil by irrigation water is often appreciable. The waters used on the soils of Cache Valley contain only small quantities of sulphur. The precipitation was collected in 10 localities in the valley. The average annual quantity of sulphur brought to the soil over a period of 4 yr. at the different stations varied from 0.4-12.1 lb. with an average of 9.5 lb. The precipitation collected near the college campus had an average annual sulphur content of 32.7 lb. Sulphur-carrying salts increase the bacterial activity of the soil, especially nitrogen fixation. This may be due either to the direct action of the sulphur as food for the microorganisms, or to an indirect action upon insoluble nutrients. The conclusion is reached that sulphur may become a limiting factor of crop production in some Cache Valley soils. The time required for this to manifest itself in diminished crop returns will vary with the soil, the specific irrigation water used, and the crop grown.