Evaluation of nitrogen status in a wheat crop using unmanned aerial vehicle images

The excessive use of N in agriculture has created various environmental and economic problems. Remote sensing and unmanned aerial vehicles (UAV) are feasible solutions to infer the status of a crop and enable a better management during the growing season. The objective of this study was to correlate experimental N content and wheat (Triticum aestivum L.) crop aboveground biomass data with vegetation indices estimated using UAV images. In this study, the N nutrition index and N dilution curve were used as indicators of the state of plant N; input variables to estimate these indicators were the N content and aboveground biomass. Four flight campaigns were conducted at different phenological stages of a wheat crop and seven N doses were evaluated. A linear relationship of blue normalized difference vegetation index (BNDVI) and green normalized difference vegetation index (GNDVI) with aboveground biomass and N content was identified. BNDVI and biomass demonstrated high [R.sup.2] during boots swollen and end of anthesis growth stages (0.62 and 0.68, respectively), while GNDVI showed the highest [R.sup.2] during the ear half emerged and beginning of anthesis growth stages (0.84 and 0.79, respectively). For N content estimation, GNDVI showed a higher correlation than BNDVI, and the adjustment curve showed an [R.sup.2] up to 0.81 only for the last flight (end of anthesis), BNDVI showed an [R.sup.2] of 0.78. Remote sensing and vegetation indices estimated from UAV images can be reliably used to estimate N content and wheat biomass, contributing to knowing the crop N status. Key words: Blue normalized difference vegetation index, critical nitrogen dilution curve, green normalized difference vegetation index, nitrogen nutrition index, Triticum aestivum.