Rye cover crop retains nitrogen and doesn't reduce corn yields

Intensive nitrogen (N) fertilization is often associated with corn (Zea mays L.) production, and winter cover in the form of rye (Secale cereale L.) is proposed as a means to conserve inorganic N and soil carbon (C). Yet the seasonal niche for cover crop in field crop rotation in North Central USA is highly variable, leading to uncertainty regarding cover crop benefits. An 8-year study in SW Michigan examined winter rye cover vs fallow in a corn-corn-soybean (Glycine max) sequence, and interaction with a 7-rate N fertilizer gradient. Soil C, water retention, pH and nutrient status were negatively affected by high N fertilizer. Rye cover had almost no detectable soil amelioration, but did maintain mid-season N availability relative to fallow plots, as indicated by soil inorganic N (90 kg ha(-1) vs 57 kg ha(-1)) and consistently high corn SPAD readings by 1.5 units. Soil aggregation, porosity and soil C pools were not influenced by the presence of a rye cover crop, with the exception of large particulate organic matter C. Over 8 years corn yields were not reduced in plots with a winter rye cover, under widely variable weather conditions. Overall, a rye cover crop had minimal impact on soil C but was an effective N management tool with no corn yield penalty.