Determining in-season nitrogen requirements for corn using aerial color-infrared photography

Fast, accurate methods to determine in-season corn (Zea mays L.) nitrogen (N) requirements are needed to provide more precise and economical management and potentially decrease groundwater N contamination. The objectives of this study were to: (i) develop a methodology for predicting in-season N requirement for corn at the V7 and VT stages using aerial color infrared (CIR) photography; (ii) validate the RGDVI-based remote sensing technique for determining in-season N requirements for corn at VT; (iii) determine the relationships between corn agronomic parameters and spectral parameters that influence the prediction of optimum NV7 and NVT rates. Field studies were conducted for four years over a wide range of soil conditions and water regimes in the North Carolina Coastal Plain. A two-way factorial experimental design was implemented as a split-plot in randomized complete blocks with NPL as the main plot factor and NV7 or NVT as the sub-plot factor. Corn agronomic parameters were measured and aerial CIR photographs were obtained for each site at V7 or VT prior to N application. Spectral radiation of corn measured using the Green Difference Vegetation Index (GDVI) relative to high-N reference strips using a linear-plateau model was the best predictor of optimum NVT (R2 = 0.67). Very weak correlations were observed between optimum rates of N V7 and band combinations with significant correlations for relative G, RGDVI, and relative difference vegetation index (RDVI). In the VT validation study, the difference between predicted and observed optimum NVT rates ranged from -30 to 90 kg N ha-1. Overall, the remote sensing technique was successful (r2 = 0.85) in predicting optimum NVT rates despite the inherent constraints of predicting yield potential in any particular year. The spectral index RGDVI showed consistently significant relationships with corn agronomic parameters measured at VT. By assessing corn N requirements late in the season during the period of maximum N uptake and applying fertilizer appropriately, application of large amounts of N early in the season when corn uptake is low and leaching potential high might be avoided, thus minimizing groundwater pollution.