Thursday, November 16, 2006 - 9:15 AM
327-4
Mitigation of N Export from Conventional Agriculture Using Cover Crops.
Changes in agricultural practices have been proposed as a means for more efficient use of N in cropping systems, for example using cover crops as slow release fertilizers and as a means for locking up N during periods of high leaching potential. A past study at the W.K. Kellogg Biological Station (KBS) in southwestern Michigan has demonstrated that a threshold for N2O flux, one measure of N export, occurred at 134 kg N ha-1 yr-1, which is the recommended N rate for corn in Kalamazoo County, where KBS is located. Grain yields reached an asymptote at N additions of ~101 kg N ha-1 yr-1. In this study, we assessed N export as N2O surface fluxes and NO3- leaching across an N gradient in a corn-soybean rotation grown with and without cover crops to determine whether we can use cover crops to provide N in the spring and to take up residual N in the fall. We measured N2O fluxes using a static chamber technique at seven N rates (0, 34, 67, 101, 134, 168, and 202 kg N ha-1 yr-1) and NO3- leaching with zero tension lysimeters at the 0, 101, and 202 kg N ha-1 yr-1 levels in our corn plots. N2O fluxes increased precipitously at 134 kg N ha-1 yr-1, as they did in the previous study at KBS and NO3- leaching did not increase until 202 kg N ha-1 yr-1. Cover crop incorporated before planting provided some N to the growing corn crop and cereal rye (Secale cereale L.) planted after corn harvest reduced NO3- leaching at the 202 kg N ha-1 yr-1 level of N addition. Our results suggest the potential for improved N management achieved by integrating a winter annual cereal into corn-soybean rotations that are otherwise managed conventionally.
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