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Nitrogen Management

Remote Sensing-Informed Variable-Rate Nitrogen Management of Wheat and Corn

Agronomic and Groundwater Outcomes

^a Dep. of Agron., 209A Waters Hall, Univ. of Missouri, Columbia, MO 65211
^b Dep. of Soil Science, North Carolina State Univ., Raleigh, NC 27695-7619
^c Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27695-7620
^d Dep. of Statistics, North Carolina State Univ., Raleigh, NC 27695-8203

^* Corresponding author (jeff_white{at}ncsu.edu)

Received for publication May 19, 2005. 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 NO₃–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.

Abbreviations: BMP, best management practice • CIR, color infrared photography • DGPS, differential global positioning system • FA, uniform, field-averaged nitrogen management • GDVI, green difference vegetation index • GNDVI, green normalized difference vegetation index • Go, Goldsboro soil • GS, growth stage • Ly, Lynchburg soil • MCLG, maximum contaminant level goal • NIR, near infrared • No, Norfolk soil • NormNIR, normalized near infrared • NUE, nitrogen use efficiency • RGDVI, relative green difference vegetation index • RS, remote sensing • RYE, uniform, Realistic Yield Expectation nitrogen management • SS, in-season, site-specific, variable-rate nitrogen management

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