John L. Kovar, USDA-ARS, USDA-ARS Natl. Soil Tilth Lab., 2110 University Blvd., Ames, IA 50011-3120 and Douglas Karlen, National Soil Tilth Laboratory, USDA-ARS, 2110 University Blvd., Ames, IA 50011-3120.
The short- and long-term effects of striving for higher grain yields and removing crop residues for bio-fuels production on soil-nutrient cycling, physical properties and biological activity must be understood. To provide more quantitative guidelines, soil management studies focusing on tillage, fertilizer rates and placement, cover crops, and controlled wheel traffic are needed. Because it would be difficult to address all of these variables in a single project, our study focused on the sulfur (S) requirements of no-till corn (Zea mays L.) bio-fuel production systems. Our objective was to evaluate the performance characteristics of three S sources (13-33-0-15S, 21-0-0-24S, and 12-0-0-26S) for corn grown on low organic matter soils in Iowa. In 2006, field plots were established on a Clarion loam. At this location, application of 34 kg S/ha increased mean plant dry weight and whole-plant concentrations of S at the V5 growth stage. At the mid-silk growth stage, however, S concentration in the tissue was below the sufficiency range of 0.21% to 0.50%, even when S fertilizer had been applied. Consequently, corn yield was not increased and grain moisture at harvest was not reduced by S fertilizer application. No one S fertilizer source outperformed the others, although 34 kg S/ha as 13-33-0-15S added 439 kg grain/ha compared with the control treatment. Below-normal precipitation during part of the growing season and significant soil variability at this site likely affected the response to S fertilizer.