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Monitoring long-term impacts of fertilizer N and the fate of N sources in production fields are needed. The objective of this study was to determine total soil N temporal and spatial changes over an 8 year period in a ¼ section. The site was located in east-central South Dakota in a 65-ha field. Crop rotation was corn and soybean. During the study corn was grown for 5 years (1995, 1997, 1999, 2001, and 2002) and soybeans were grown for 3 years (1996, 1998, and 2000). Two tillage methods were used; no-till between 1995 and 1999 and strip-till between 2000 and 2002. More than 600 soil samples from the 0- to 15-cm soil depth were collected from a 30- by 30-m offset grid in May, 1995 and between May and June, 2003 and were aggregated to a common 40- by 40-m grid cell. Soil samples were air dried (35 ºC), ground, sieved, and analyzed for total N, total C, 13C discrimination (∆), and δ15N on a ratio mass spectrometer. Findings from this study can be used to an improved understanding of N cycling in production fields.

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Proceedings of the South Dakota Academy of Science