Effects of optical sensing based variable rate nitrogen management on yields, nitrogen use and profitability for cotton

This research evaluated the profitability and nitrogen (N) efficiency of real time on-the-go optical sensing measurements (OPM) for variable-rate (VRT) N management for cotton. Two forms of OPM-based VRT N management and the existing farmer practice (FP) were used to determine N rates applied to cotton on 21 farm fields in the lower Mississippi River Basin states of Louisiana, Mississippi, Missouri and Tennessee, USA. A modified version of the Schabenberger and Pierce on-farm experimentation model was used to evaluate VRT N management and landscape, soil and weather factors on lint yields, N rates, N efficiency (lint yield divided by N rate) and net returns. Field level mean lint yields were not different between VRT and FP. VRT decreased N rates applied on four fields and increased N rates applied on four other fields. However, landscape, soil and weather attributes specific to fields influenced VRT N rates. VRT N rates were similar to FP N rates on the other fields in the study. N efficiency was not improved with VRT N management. N rates were not low enough to increase N efficiency. Changes in lint yields and N rates due to VRT coupled with USDA NRCS Environmental Quality Incentive Program cost-share payments were not sufficient to produce higher net returns relative to FP N management at the field level. In this multi-site, multi-year study, yields and net returns from VRT were not different from FPs which did not utilize variable rate N management.