Tillage, Crop Rotation, and Cover Crop Impacts on Corn Nitrogen Requirements in Southeastern SD.

Nitrogen (N) is the lifeline of corn (Zea mays) production. There is uncertainty whether nitrogen requirements are the same for corn raised under long term no-till versus conventional till production systems. The objective of this study was to evaluate N fertilizer requirements for long term no-till soils in southeastern South Dakota, while considering effects from cover crops and crop rotation. This was a two year study at the SDSU Southeast Research Farm near Beresford, SD on long term no-till plots established in 1991. Treatments included rates of 0, 40, 80, 120, 160, and 200 lbs applied N per acre. Rotations were corn-soybean (Glycine max) (2-year) and corn-soybean-small grain (3-year); the 3-year rotation was split additionally by ‘cover crop’ and ‘no cover crop’ strips. Measured parameters included: spring and fall soil nitrate-nitrogen (0-2 ft), soil plant analysis development (SPAD) meter readings, normalized difference vegetation index (NDVI) readings, ear leaf N content, total plant N uptake, grain yield, test weight, grain moisture, and grain protein. In 2014, small plot results were quite variable due to 13.5” of rainfall in June; the 2015 growing season was mild, producing better yields. Both N rate and tillage showed significant impacts on yield in the 2014 and 2015 3-year rotation. In 2014, spring soil nitrate levels were 50 lbs per acre less in the ‘cover crop’ verses ‘no cover crop’ treatments, but no significant yield differences were seen between cover crop treatments. N that was not available at the beginning of the growing season likely became available later when cover crop residue decomposed. No-till soils did not consistently require more N than conventional till soils in this study. More research should be conducted to further investigate corn N requirements in South Dakota.