Evaluation of Optical Sensing and Clemson Algorithm to Improve Side-Dress N Rate for Corn Under Different Soil Zones in South Carolina.

Optical sensing technology may help to improve nitrogen (N) management in corn (Zea mays L.). The objective of this study was to optimize side-dress N rate for dryland corn under different soil electrical conductivity (EC) zones using GreenSeeker optical sensing technology and Clemson corn algorithm. A commercially available Veris Technologies 3100 was used to identify soil variations in the field and define three zones based on soil EC measurements. Pioneer 31G71 corn was planted at 69,200 seeds ha^-1 in strip-till (ST) on 25 March 2010 and 18 March 2011. Nitrogen was applied to corn at 45 kg ha^-1 after planting (standard practice) and calculated rates as side-dress application at V6 stage. Selected plots in each zone were fertilized with 180 kg ha^-1 at planting (high N rich strips, where N was not a limiting factor). Plant normalized difference vegetation index (NDVI) was recorded in corn plots using GreenSeeker prior to side-dress N application. The side-dress N rates were calculated based on Clemson algorithm and response index (RI) (NDVI high N rich strip / NDVI standard practice) for each zone. The calculated N rates for different EC zones and average across zones with 25% above and below that average were compared with a standard application of 135 kg N ha^-1. The results showed that calculated side-dress N rates of about 35 kg N ha^-1 for zone 1 and 67 kg N ha^-1 (rate 25% lower than the calculated average across zones) for soil zones 2 and 3 did not significantly reduce corn grain yields compared to a standard N application in both years.