Will Sulfur Limit Bioenergy Feedstock Production?.

The short- and long-term effects of striving for higher grain yields and removing crop residues for bioenergy feedstock production must be understood to provide more quantitative crop and soil management 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 minimum-till corn (Zea mays L.) bioenergy 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. Plots established in 2006 on a Clarion loam showed that applying 34 kg S/ha increased mean plant dry weight and whole-plant S concentrations at the V5 growth stage. By mid-silk, however, S concentrations were 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 statistically outperformed the others, although 30 lb S/A applied as 13-33-0-15S increased grain yield 439 kg/ha compared with the control. On a Clarion silt loam in 2007, application of 34 kg S/ha once again increased mean plant dry weight and whole-plant concentrations of S at V5, but by mid-silk, S concentrations were again below the sufficiency range. This time, application of 34 kg S/ha as either 13-33-0-15S or 21-0-0-24S increased yield by more than 627 kg/ha compared with the control, a difference significant at p=0.08. Below-normal precipitation during part of each growing season presumably minimized the statistical response to S fertilizer. However, our results suggest that S may quickly become a limiting nutrient for corn grown to supply bioenergy feedstocks.