Optimizing Nitrogen Fertilizer Application in Corn Using Green Technology.

The utilization of active canopy sensors in corn (Zea Mays L.) for in-season N fertilizer management has the potential to maintain optimal production and conserve N fertilizer resources. Canopy sensors can be considered a green technology in production agriculture by attempting equitable land stewardship and providing an economically viable N management practice. The objective of the study was to develop N rate algorithms using active canopy sensors which can prescribe in-season N application to corn. Nitrogen rate trials conducted across Iowa in 2006-2008 were monitored with active canopy sensors. All N rates were applied prior to or shortly after corn planting. The Holland Scientific Crop Circle ACS-210 and NTech GreenSeeker Green Model 505 active canopy sensors were evaluated, with readings collected at the V10-V12 corn growth stages. The sensors were positioned at nadir (0° plane angle) above the inter-row at a distance of approximately 75-cm above the canopy. Many of the calculated sensor indices produced similar relationships with the N rate differential from the economic optimum rate (dEONR), but had considerably different ranges in relative index values from most deficit to adequate N. The canopy indices with the most precision across sites and years (highest adjusted R2 value when regressed with dEONR) were relative normalized difference vegetative index (rNDVI) for the Crop Circle ACS-210 (adjusted R2=0.73), and relative simple ratio index (rSRI) for the NTech GreenSeeker Green (adjusted R2=0.66). The calculated critical index value where no N fertilizer would be applied (plateau index value) was 1.00 and 1.01 for the respective index with the Crop Circle and GreenSeeker Green sensors. The regression model parameters for each sensor can be used to construct a N rate algorithm capable of adjusting N fertilizer rates in-season at the V10-12 corn stages.