Misdiagnosis of water and N stress can reduce yields. The objective of this study was to determine the influence of water and N stress in corn (Zea mays L) on yields and crop reflectance. A replicated N and water treatment factorial experiment was conducted in 2002, 2003, and 2004. Yield losses due to water (YLWS) and N (YLNS) were determined using the 13C discrimination (D) approach. Crop reflectance was measured at three growth stages (V8-V9, V11-Vt, and R1-R2). Reflectance measurements indicate that at the V8-V9 growth stage, N and water stress impacted and did not impact reflectance, respectively, while at the R1-R2 growth stage both N and water stress impacted reflectance. A remote sensing model based on YLNS was more accurate at predicting N requirements than yield and yield plus YLWS based models. These findings were attributed to water and N having additive effects on yield, similar optimum N rates for both soil moisture environments, and water stress not impacting reflectance at the V8-V9 growth stage.
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