Tuesday, November 6, 2007
193-8
Evaluation of Optical Canopy Sensors for in-Season N Rate Management in Corn.
Daniel W. Barker and John E. Sawyer. Iowa State University, Department of Agronomy, 2104 Agronomy Hall, Ames, IA 50011-1010
Optical canopy sensors are an emerging technology that can serve as a useful in-season N fertilizer management tool for corn (Zea mays L.) production. The objective of this study is to determine the effectiveness of optical canopy sensors to differentiate N stress in corn for adjustment of N fertilization rates. Nitrogen rate trials were conducted at 21 sites on Iowa State University Research and Demonstration Farms in 2006, with corn following soybean [Glycine max (L.) Merr.] and corn following corn. Fertilizer N rates of 0-270 kg N ha-1 in 45 kg N ha-1 increments were broadcast applied and incorporated urea prior to planting or surface broadcast applied ammonium nitrate shortly after planting. The optical sensors used in the study were the Holland Scientific Crop Circle ACS-210, NTech GreenSeeker Model 505, and Minolta SPAD-502. Corn plants were monitored for N deficiency stress symptoms between the V10-V13 corn growth stages. Numerous vegetative indices were compared and evaluated as indicators of N stress. Indices were also converted to values relative to the reading from the highest N rate applied at each site and correlated to the applied N rate minus economic optimum N rate (dEONR). The normalized difference vegetative index (NDVI) was less variable across N rates when collected with the Crop Circle . The chlorophyll index (Chl) and SPAD were similar, and showed more differentiation to dEONR compared to NDVI. Relative NDVI (rNDVI) provided the highest correlation across all sites to dEONR when collected with the Crop Circle and GreenSeeker sensor units.