The Impact of Rye Cover Crop on Runoff Losses of Nutrients and Earthworm Populations.

Corn (Zea mays L.) silage and soybean [Glycine max (L.) Merr.] rotations in the upper Midwest leave minimal amounts of surface residues and this can contribute to soil degradation and a reduction in water quality. Planting cover crops after harvest can reduce these concerns, but their effectiveness has not been thoroughly investigated. Therefore, we applied 70 mm of simulated rainfall in 60 min to five replicate, 1.5 by 3.0 m, plots in a no-till, corn silage-soybean rotation that were planted with a rye (Secale cereale L.) cover crop each of the last 14 years and to five plots with no cover. The simulations were conducted in October 2014 about a month after corn harvest and rye planting and shortly (< 1hr) after broadcast application of monoammonium phosphate and potash fertilizers. It took significantly longer (5.9 min, P < 0.05) for the plots with living rye cover crops to produce surface runoff and total runoff volume was 65% less than that from the plots without a cover crop. This reduction in runoff volume resulted in similar significant reductions in sediment (68%) and NO₃-N (66%) losses. Even greater reductions in total P (83%), total dissolved P (84%), K (89%), and NH₄-N (84%) were noted due to slight reductions in their average concentrations. Earthworm populations and biomass, measured using electrical extraction after rainfall simulation and again the following spring, were 1.2 and 1.4 times greater in the cover crop plots than in the no cover plots in the fall and 3.2 and 2.5 times greater in the spring. Our results suggested that a living cover crop and the long-term use of cover crops can contribute to improvements in soil structure and increased earthworm populations that can reduce sediment and nutrient losses in surface runoff due to a severe storm shortly after fertilizer application.