Nitrogen Recommendations for Corn: An On‐The‐Go Sensor Compared with Current Recommendation Methods

Abstract

Precision agriculture technologies provide the capability to spatially vary N fertilizer applied to corn (Zea mays L.), potentially improving N use efficiency. The focus of this study was to evaluate the potential of improving N recommendations based on crop canopy reflectance. Corn was grown at four field sites in each of 2 yr in Centre County, Pennsylvania. Preplant treatments included: zero fertilizer, 56 kg N ha−1, and manure. Split‐plot treatments included the following N sidedress rates as NH4NO3: 0, 22, 45, 90, 135, 180, and 280 kg N ha−1, and one at‐planting N rate of 280 kg N ha−1. Light energy reflectance (590 and 880 nm), chlorophyll meter (SPAD) measurements, and the presidedress NO3 test (PSNT) results were obtained at sidedress. The late‐season stalk NO3 (LSSN) test was determined. The economic optimum nitrogen rate (EONR) was determined based on grain yield response to sidedress N rates. Relative green normalized difference vegetation index (GNDVI) and relative SPAD were based on relative measurements from the zero sidedress treatment to the 280 kg N ha−1 at‐planting treatment. The EONR from 24 preplant treatment–site combinations was related to relative GNDVI (R2 = 0.76), the PSNT (R2 = 0.78), relative SPAD (R2 = 0.72), and the LSSN test (R2 = 0.64), suggesting that relative GNDVI was as good an indicator of EONR as these other, more conventional tests. Because relative GNDVI can be obtained simultaneously with a sidedress N fertilizer application, the potential to accommodate within‐field spatial and season‐to‐season temporal variability in N availability should improve N management decisions for corn production.