Using Early-Season Dark Green Color Index (DGCI) and SPAD to Predict Corn Yield.

Crop sensors may help growers manage in-season N applications in corn (Zea mays L.) to help minimize environmental losses and improve N utilization. However, limited research is available on this technology and its relationship to yield at early-season growth stages (V4-7) when sidedress application is most likely in the Eastern Corn Belt. Field studies in six field environments in Ohio (four site-years) and Michigan (two site-years) were conducted to evaluate the dark green color index (DGCI) and soil plant analysis development (SPAD) as well as their relationship to grain yield at V4, V6, and R1 to R2. Five N rates (0-269 kg ha^-1) were evaluated in Ohio, and six N rates (0-280 kg N ha^-1) were evaluated in Michigan. Significant linear relationships were observed between DGCI and SPAD in all but one environment at V4 and at V6. At both the V4 and V6 growth stages, DGCI detected N application in two of the six site-years, and SPAD was able to detected N application in four of the six site-years. At the R1 to R2 stage, both DGCI and SPAD detected treatment differences in all site-years. Across all site-years, both DGCI and SPAD exhibited a linear relationship to yield at both V6 and R1 to R2 (P<0.01), but the r² values were consistently greater for SPAD. These results suggest that early-season detection of N application with these sensors is variable, but was more frequent using the SPAD meter as compared to the DGCI method.