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Hong, N, White, JG, Weisz, R, Crozier, CR, Gumpertz, ML, Cassel, DK (2006). Remote sensing-informed variable-rate nitrogen management of wheat and corn: Agronomic and groundwater outcomes. AGRONOMY JOURNAL, 98(2), 327-338.

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,,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 [NO3-N] consistent with agronomic results, but small relative to temporal [NO3-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.



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