Brian Lang, Field Agronomist, Northeast Area and John Sawyer, Professor and Soil Fertility Extension Specialist, Department of Agronomy
Over forty years of prior research in Iowa had rarely noted improved corn yield with sulfur (S) fertilization. Statewide and regional studies conducted in Iowa from 2000 to 2005 had not found corn yield increase from S fertilizer application. However, recently in northeast Iowa, S deficiency was documented in alfalfa production with significant yield responses from applied S fertilizers (Lang et al., 2006). On similar lower organic matter silt loam and coarse textured soils, early corn growth had been exhibiting strong visual S deficiency symptoms. The objective in 2007 through 2008 was to investigate the extent of S deficiency in the northeast Iowa geographic area and the potential economic response of corn production to S fertilization.
The ISU Extension Agronomist initiated 31 on-farm S fertilizer research trials on corn in 2007 and 2008. The Agronomist worked with farmers and agricultural dealerships to select research sites at random across 9 counties with different soil types, tillage systems and crop rotations. The only stipulation was that the sites had no recent manure or sulfur fertilizer applications.
Corn grain yield increase to S fertilization occurred at about 70% of the sites. The frequency was 89% with coarse textured sandy soils and 64% with fine textured loam and silt loam soils. The average yield increase was 24 bu./acre on coarse textured soils and 11 bu./acre on fine textured soils. The net economic return to sulfur was $70 per acre on coarse textured soils and $25 per acre on fine textured soils. This research indicates a change in the need for S fertilization in northeast Iowa, and that S application is an economically viable fertilization practice on many soils. The potential economic impact of this research for corn production in northeast Iowa approximates $15 million. However, the research also shows that corn does not respond to S application in all fields or field areas. Additional research is critically needed regarding plant and soil S tests, plant canopy S stress sensing, site characteristics, and S deposition in order to develop better predictive indices of S deficiency and need for S fertilization. These tools would provide better decision making and enhance positive economic return to S fertilization for producers.
100 Corn and Soybean Production
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March 5, 2009
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