Yield Response of Irrigated Corn to Landscape Position Under Variable Nitrogen.

Variable nutrient and water supply can result in spatial and temporal variation in crop yield within a given agricultural field.  For the western Corn Belt, irrigated corn accounts for 58% of total annual corn production with the majority grown in Nebraska.  Although irrigation decreases temporal yield variation, significant spatial variability can exist within irrigated fields for a given year.  Objectives were to understand how soil properties and field topography data relate to spatial variation in irrigated corn fields under variable N rates.  Two on-farm study sites located in Hamilton County, NE and Keith County, NE were used to determine landscape position effects on corn yield under variable N rates.  Nitrogen plots (6-m x 15-m) were replicated across fields consisting of 0, 84, 168, 224, and 280 kg N ha^-1.   Fertilization occurred at or near the V4 growth stage using a high clearance sprayer.  Grain yield was determined by hand-harvesting two adjacent rows (3-m length each) at physiological maturity.  Landscape position features (summit, shoulder, backslope, footslope, and toeslope) were derived from publically available 2-m resolution digital elevation models (Hamilton Co.) and real-time kinetic elevation data (Keith Co.).  Apparent electrical conductivity (EC_a) was measured at both locations prior to planting. A corn yield response model will be developed based on soil and landscape position properties and evaluated to access the potential for use as site-specific management units related to N management.