Active canopy sensing of winter wheat nitrogen status: An evaluation of two sensor systems

• This paper systematically evaluated a three band active sensor, Crop Circle ACS-470.
• The GDVI index (R2 = 0.60) performed best for estimating plant N concentration.
• The CIG index (R2 = 0.89) performed best for estimating plant N uptake.
• The GRDVI and MGSAVI indices (R2 = 0.78 and 0.77) performed best for estimating NNI.

Crop canopy sensor based in-season site-specific nitrogen (N) management is a promising approach to precision N management. GreenSeeker sensor has previously been evaluated in North China Plain (NCP) for improving winter wheat (Triticum aestivum L.) N management. The Crop Circle ACS-470 is an active canopy sensor with three user-configurable wavebands. This study identified important vegetation indices that can be calculated from Crop Circle green, red edge and near infrared (NIR) wavebands for estimating winter wheat N status and evaluated their potential improvements over GreenSeeker normalized difference vegetation index (NDVI) and ratio vegetation index (RVI). Six field experiments involving different N rates and varieties were conducted in the Quzhou Experiment Station of the China Agricultural University from 2009 to 2012. The results indicated that best Crop Circle ACS-470 sensor vegetation indices could explain similar amounts of aboveground biomass variability in comparison with GreenSeeker sensor NDVI, but Crop Circle normalized difference red edge/green optimized soil adjusted vegetation index (NDRE/GOSAVI) and red edge chlorophyll index (CIRE) were more sensitive to aboveground biomass (having lower noise equivalent) than GreenSeeker NDVI before and after biomass reached about 5000 kg ha−1, respectively. The Crop Circle green difference vegetation index (GDVI) (R2 = 0.60) and chlorophyll index (CIG) (R2 = 0.89) explained 53% and 7–11% more variability in plant N concentration and uptake than GreenSeeker indices, respectively. The Crop Circle green re-normalized difference vegetation index (GRDVI) (R2 = 0.78) and modified green soil adjusted vegetation index (MGSAVI) (R2 = 0.77) performed consistently better than GreenSeeker NDVI (R2 = 0.47) and RVI (R2 = 0.44) for estimating N nutrition index (NNI). We conclude that the three band user configurable Crop Circle ACS-470 sensor can improve the estimation of winter wheat N status as compared with two fixed band GreenSeeker sensor.