Using Optical Sensing Technology to Determine a Site-Specific Nitrogen Application on Corn in Relation to Soil Electric Conductivity.

Due to considerable soil variability in the southeastern United States, nitrogen (N) application to corn should be based on soil zone maps to apply N only where needed at appropriate rate. The objective of this study was to evaluate the site-specific side-dress nitrogen application in corn (Zea mays L.) planted under dryland conditions in relation to soil electric conductivity (EC).The research project was initiated with planting wheat (Triticum aestivum L.) cover crop in the fall of 2006 at Clemson University, Edisto Research and Education Center near Blackville, SC. A commercially available soil EC measurement system (Veris Technologies 3100) was used to identify variations in soil texture across the fields prior to planting corn and create soil zone maps using Global Positioning and Geographical Information Systems. Corn was planted across four different soil zones and under three tillage systems (no-till, conventional, and strip-till), two methods of N application (all at planting and split application), and five N rates (0, 45, 90, 134, and 179 kg N ha^-1). During the corn vegetation, the Green Seeker optical sensing technology was used to measure the Normalized Difference Vegetation Index (NDVI) and correlate this information with the soil EC to help determine optimum side-dress N application for corn. The algorithm procedures for this project were originally developed at Oklahoma State University. The results indicate that recommended N for corn, based on the NDVI readings and algorithm, will change with the soil texture. Therefore, there is a need to use EC, in addition to the NDVI readings, to determine the optimum nitrogen side-dress application rates on corn for different soil textures.