Corn Nitrogen Fertilization In a Rye Cover Cropping System.

Concerns about nitrate (NO₃-N) in surface water as a major contributor of nitrogen (N) loading to the Gulf of Mexico leads to increasing need for alternative practices to reduce NO₃-N loss from corn (Zea mays L.) and soybean [Glycine max. (L.) Merr.] fields. The project seeks to determine optimum corn N fertilization requirement and corn-soybean productivity in a no-till corn-soybean rotation system when grown in sequence with winter rye (Secale cereal L.). The study is conducted at four sites in Iowa, with plus/minus post-harvest seeded rye as the main plot and six early sidedress N rates applied to corn as a subplot (UAN). In 2009, low spring temperatures limited rye growth, but warmer temperatures resulted in increased rye production in 2010. An increase in rye biomass production was also observed with the highest prior-year N application to corn in 2010. On average, the rye cover crop reduced corn yield by 0.48 and 1.24 Mg ha^-1 across sites in 2009 and 2010, respectively. Despite these corn yield differences, there was no effect of the rye on the economic optimum N rate (EONR). Reduction in corn yield was associated with larger rye biomass production, which is weather dependable. Soybean yield, on the contrary, was not affected by the rye cover crop in either year indicating no impact of the rye on soybean establishment and growth. Based on the first two years, there is no expectation of rye cover crop effect on soybean yield but in most situations corn yield will be negatively affected. Even with a reduction in corn yield due to rye, results indicate that the corn EONR may not change. This research will continue to confirm findings and to evaluate longer term effects of winter rye in corn-soybean productivity.