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The in-field site-specific nitrogen (N) management increases crop yield, reduce nitrogen application to minimize the risk of nitrate contamination of ground water, and thus reduce farming cost. Real-time N sensing and fertilization is required for efficient N management. A multi-spectral imaging sensor (MSIS) associated with a variable rate application system was evaluated for application of supplemental N to corn (Zea mays L.) crops based on real-time N and chlorophyll estimates derived from the MSIS reflectance responses of crop canopies. Sensing inputs included ambient illumination, camera parameters, and image histogram of three spectral regions (R, G, NIR). According to the estimated level of chlorophyll contents, the amount of fertilization was determined using a nitrogen recommendation model.

The MSIS-based supplemental N treatment improved the crop N status and increased the yield over most of plots. The yield increase was best achieved in the plot with small amount of initial N-treatments followed by the supplemental variable rate application. Yield data obtained from the plots where N applied on a later season resulted in weak impact of the supplemental N, because of a poor relationship for the N recommendations. For plots with no additional N, the yield increased gradually along with the amount of initial N-treatments, but any application of N more than 101 [kg/ha] (90 [lb/acre]) had minimal impact on yield.