Introduction of cover crops in a maize–soybean rotation of the Humid Pampas: Effect on nitrogen and water dynamics

The continuous cropping system of maize-soybean rotation in the Humid Pampas poses a risk for the leaching of nitrogen. The purpose of this study is to determine the effect of fall-winter cover crops and a mixture of oats and vetch on water use, yields of main crops, and the potential for nitrogen losses. Trials took place between 2006-2011. Generally, cover crops reduced risk of spring nitrate leaching, though vetch and rape increased the risk of nitrogen leaching when preceeding maize. Low carbon to nitrogen ratios of cover crops were associated with increased nitrogen availability and higher maize yields. Oats and vetch before maize and grasses before soybeans resulted in the best alignment between nitrogen release from degrading cover crops and main crop nitrogen needs. Water use did not affect main crop yield except during an unusually dry season. This study supports the use of cover crops to enhance water use efficiency and nitrogen recycling while maintaining or raising yields of main crops in the Humid Pampas region of Argentina.