Use of slow-release N fertilizer to control nitrogen losses due to spatial and climatic differences in soil moisture conditions and drainage in claypan soils
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Agricultural soils are a major source of nitrous oxide (N₂O) which has a significant environmental impact on global warming and ozone depletion. However, there is little information on soil N₂O emissions under different drainage and irrigation treatments in claypan soils. The objectives of this research were to determine the relationship between soil N₂O efflux, temperature, soil NO₃ --N, and soil water content and to examine the performance of polymer-coated urea (PCU) compared to conventional urea in relation to crop N uptake and environmental N loss under four drainage/irrigation treatments in a claypan soil in northeast Missouri. The treatments consisted of: 1) no irrigation or drainage (NIN), 2) no irrigation and drainage (NID), 3) subirrigation and drainage (SUB), and 4) overhead irrigation and no drainage (OND). The plots were split into N fertilizer treatments of pre-plant-applied conventional urea or polymer-coated urea at rates of 0, 140, and 280 kg N ha-¹. At the beginning of 2004, significantly lower soil N₂O flux was measured with application of PCU under NIN and OND. However, no consistent differences in soil N₂O efflux between fertilizers were observed in 2005, probably due to the lower precipitation that year. Higher NO₃ --N concentrations were observed under application of urea at the beginning of the 2004 growing season. In contrast, PCU led to higher NO₃ --N concentration later in the growing season. No differences were observed between fertilizers. The results of this study suggest that PCU may be effective in reducing environmental N losses under wet conditions early in the growing season.