FERTILIZER SULFUR EFFECTS ON CORN YIELD AND PLANT SULFUR CONCENTRATION

Concern for S deficiencies of corn (Zea mays L.) is common among producers and fertilizer dealers in the Midwest. This concern results from emphasis on high yields with subsequent large S needs, accompanied by a decreasing S supply from incidental sources. A survey was made of corn response to fertilizer S in Missouri. Sites were selected on the basis of high yield potential and on soils that the farmers and fertilizer dealers suspected needed S, but that had not previously been considered S deficient. During 1991 and 1992, fertilizer S rate studies were conducted at 53 sites throughout Missouri. Sulfur rates of 0, 15, 30, and 60 lb S/acre were used. Ammonium sulfate and ammonium thiosulfate were the S sources that were applied at planting or within 4 wk following planting. Grain yields exceeded 175 bu/acre at 29 of 47 site-years. Grain yield increases from fertilizer S were observed at three of 47 harvested sites, and yield decreases at five sites. However, leaf S concentrations were above previously established critical levels. Leaf S concentrations were increased by fertilizer S at 36% of the sites at the six leaf stage and at 38% of the sites at anthesis. Grain S concentrations were increased by fertilizer S at 15% of the sites. Leaf and grain S concentrations and N:S tissue ratios correlated very poorly with relative yield. Fertilizer S recommendations (none recommended for all but one site) based on soil sulfate measured at planting were incorrect for only three sites. Consequently, this research indicates no change is needed from present S fertilizer recommendations for corn groan in Missouri.