This study compares nitrogen use in field corn between a conventionally managed farming system (CONV), a low-input system with a winter legume cover crop (WLCC), and a system receiving organic inputs with a winter legume cover crop (ORG), each under either standard (ST) or conservation tillage (CT). To evaluate seasonal soil N availability and crop N status, and to link this to crop yield, soil and plant samples were taken at four stages in 2003 and 2004: five-leaf (V5), eight-leaf (V8), silking, and harvest. Up until the V8 stage, leaf nitrogen in the ORG and WLCC systems remained similar to that of the CONV system. However, by the silking stage, plant N content was clearly lower in the ORG and WLCC systems. The tillage regime had a relatively small influence compared to main management. Grain yield across systems was consistent in both years, with the CONV system yielding more than the other two; within each system, yields were not different between tillage practices (ST vs. CT). Soil nitrate was consistently quite high in the ORG and WLCC plots throughout the season, suggesting that the low plant N status of these two systems observed at maturity might not have been due to a lack of available N, but instead to some kind of physiological impediment to uptake in the later part of the season resulting in reduced yield.
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