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 NH 4 NO 3 : 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 NO 3 test (PSNT) results were obtained at sidedress. The late‐season stalk NO 3 (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 ( R 2 = 0.76), the PSNT ( R 2 = 0.78), relative SPAD ( R 2 = 0.72), and the LSSN test ( R 2 = 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.