Effect of winter cover cropping practices on maize yield and nutrient cycling

The Illinois Nutrient Loss Reduction Strategy has set Phase 1 reduction milestones for nitrate-nitrogen and total phosphorus of 15 percent and 25 percent, respectively, to the Mississippi River by the year 2025 with the ultimate goal of a 45 percent reduction for both nutrients when compared to average annual riverine loading for years 1980-1996. With estimated levels of 80 percent and 48 percent of nitrate-N and total-P nutrient loads coming from agriculture, the reduction strategy stresses the importance of farmers’ voluntary implementation of best management strategies in order to reach these goals. The purpose of this study was to compare the differences in nutrient cycling of nitrogen and phosphorus from an annual rye winter cover-cropped treatment to a conventional tillage control (fall chisel and spring field cultivation) by measuring preseason fertility, nutrient flux in subsurface tile lines, end of season soil fertility, and crop yields for each treatment. Best management practices consisted of a no-till cover crop scenario with side-dressed nitrogen application at vegetative growth stage 4 (V4). Soil fertility and crop nutrient uptake was measured prior to cover crop termination and again at crop maturity. Throughout the growing season, tile water was collected and analyzed for nitrate and phosphate concentrations. Cumulative losses from April-July 2015 of nitrate nitrogen were calculated at 10.61 and 11.69 kg ha-1 NO3-N for the annual rye treatment and conventional treatment, respectively. Weighted mean nitrate-nitrite nitrogen concentrations in subsurface drainage tile were 4.41 and 6.10 ppm for annual rye and conventional treatments for the same time period. Soil fertility measures of organic matter, nitrogen, and phosphorus did not have a conclusive impact on the final yields of each representative treatment, however, seven out of the top ten yielding annual rye treatments were on the soil with a higher Illinois Soil Nitrogen Test (ISNT). Nitrogen fertilizer rates and timing had a significant impact on final yields with the highest yield being 16.9 Mg ha-1 (271 bu ac-1) at a nitrogen fertilizer rate of 177 kg ha-1 (158 lb ac-1) for the conventional tillage treatment and 16.4 Mg ha-1 (261 bu ac-1) for the no-till annual rye winter cover treatment at a fertilizer rate of 206 kg ha-1 (184 lb ac-1). These results indicate a higher nitrogen rate is necessary for equal yields when a no till winter cover is compared to a conventional tillage plot if water is not a yield limiting factor