Management of small grain residues to retain legume-derived nitrogen in corn cropping systems

Minimizing N pollution from nonpoint agricultural sources is a management challenge in U.S. agriculture and in the Chesapeake Bay watershed. This 2-yr field study examined the impact of C/N ratios, through modification of straw residue, on the availability of small grain-hairy vetch (Vicia villosa Roth) derived N in a corn (Zea mays L.) cropping system. Treatments consisted of three levels of straw retention (0, 1, and 2 Mg ha^-1), with and without a hairy vetch cover crop. Soils were sampled for inorganic N from 0 to 15 cm every 10 d during the growing season, and less frequently at deeper soil depths. Residue decomposition was measured each year using litterbags with residues representative of residue composition in each treatment. Corn productivity was also measured and a partial economic analysis was conducted. On average across sampling dates, soil inorganic N was 7.3% lower in the 1 and 2 Mg ha^-1 straw treatments compared to the zero Mg ha^-1 straw treatment, although this effect was only significant in one of the two study years. Likewise, the 2 Mg ha^-1 straw treatment had 16% more N retained in the residues compared to the other two treatments. Results indicate that simple alterations to common management practices, such as the retention of 1 to 2 Mg ha^-1 of straw from a small grain crop that precedes a no-till vetch cover crop may reduce the potential for off-site N movement, via leaching, but it may also compromise crop yields and net economic returns.