FIELD-SCALE VARIABILITY OF NITROGEN AND DELTA-N-15 IN SOIL AND PLANTS

Understanding the factors that influence soil and plant nitrogen (N) s patial variability may improve our ability to develop management syste ms that maximize productivity and minimize environmental hazards. The objective of this study was to determine the field (65 ha) scale spati al variability of N and delta(15)N in soil and corn (Zea mays). Soil, grain, and stover samples were collected from grids that ranged in siz e from 30 by 30 m to 60 by 60 m. Plant samples, collected following ph ysiological maturity in 1995, were analyzed for total N and delta(15)N . Soil samples, collected prior to planting in the spring of 1995 and 1996, were analyzed for inorganic-N, total N, and delta(15)N. All para meters showed strong spatial relationships. In an undrained portion of the field containing somewhat poorly and poorly drained soils there w as a net loss of 95 kg N ha(-1), while in an adjacent area that was ti le drained there was a net gain of 98 kg N ha(-1). Denitrification and N mineralization most likely were responsible for losses and gains, r espectively. Differences between the N balances of these areas (193 kg N ha(-1)) provide a relative measure of the impact of tile drainage o n plant N availability and greenhouse gas production in a wet year.