Remote Sensing‐Informed Variable‐Rate Nitrogen Management of Wheat and Corn: Agronomic and Groundwater Outcomes

In‐season, site‐specific, variable‐rate (SS) N management based on remote sensing (RS) may reduce N losses to groundwater while maintaining or increasing yield and N fertilizer‐use efficiency. We compared in‐season, RS‐informed N management applied on a uniform, field‐average (FA) or SS basis with the current uniform best management practice (BMP) based on “Realistic Yield Expectations” (RYE) in a typical 2‐yr southeastern U.S. coastal plain rotation: winter wheat ( Triticum aestivum L.)–double‐crop soybean [ Glycine max (L.) Merr.]–corn ( Zea mays L.). Compared with the RYE‐based BMP, RS‐informed SS management achieved: (i) a maximum of 2.3 mg L −1 less groundwater NO 3 –N after 2001 wheat due to 39 kg ha −1 less fertilizer N and a 25% greater harvest N ratio (N in grain or forage/total N applied); (ii) 370 kg ha −1 more 2002 corn grain with 32 kg ha −1 greater N applied, similar harvest N ratio, and 37 kg ha −1 greater surplus N; (iii) 670 kg ha −1 more 2003 wheat grain associated with 14 kg ha −1 greater fertilizer N, 27% greater harvest N ratio, and 9 kg ha −1 less surplus N. Excepting one corn FA treatment that received excessive N, RS‐informed management produced equal or greater economic returns to N than RYE, and less surplus N for wheat. Treatments produced enduring effects on groundwater [NO 3 –N] consistent with agronomic results, but small relative to temporal [NO 3 –N] fluctuations that were positively correlated with water table elevation. To assess N management in leaching‐prone soils, frequent, periodic groundwater monitoring during and after the cropping season appears essential.