Optimize Side-Dress Nitrogen Application On Corn Using Algorithm and Optical Sensing Technology in South Carolina.

Corn growers consider the reduced or variable nitrogen (N) fertilizer application in order to reduce crop inputs and maximize yields. The objective of this study, initiated in 2007, was to evaluate the potential of using algorithm and N rich strip for estimating a side-dress N application on corn (Zea mays L.). A commercially available soil EC measurement system (Veris Technologies 3100) was used to identify variations in soil texture. Nitrogen was applied at planting. During the corn vegetation, the GreenSeeker optical sensing technology was used to measure the Normalized Difference Vegetation Index (NDVI). For 2007, the grain yield (y) was estimated as y = 0.3511e^375.56x, where x is INSEY calculated as NDVI divided by number of days from planting to sensing (Growing Degree Days>0). The Response Index (RI), calculated by dividing the average NDVI readings from plots with high N applications by the average NDVI readings from the area ready for a side-dress, was estimated at 1.39 for the same year and indicated that we could expect about 39% increase in corn yield potential with additional N application. The maximum calculated rate to which corn could potentially respond would be about 80 kg N ha^-1. In 2008, the NDVI measurements did not show a significant difference between high N rich application and plots with standard N application at planting indicating that there would be very little or no corn yield potential increase with additional (side-dress) N application. The results also indicated that soil EC measurements, in addition to the NDVI readings, may help to determine the optimum side-dress N application rates for corn grown under different soil textures.