Estimating rice nitrogen status using active canopy sensor crop circle 430 in Northeast China

Active crop canopy sensors are commonly used to estimate crop nitrogen (N) status in precision N management to improve N use efficiency and reduce negative environmental impacts caused by over-application of N. However, traditional vegetation indices (VI) like normalized difference vegetation index (NDVI) obtained from GreenSeeker sensor can become saturated under medium to high crop biomass conditions, making it unsuitable for application in high yield crop management systems. Crop Circle ACS-430 (CC-430) is a newly developed active crop canopy sensor with 3 fixe wavebands covering red (670nm), red-edge (730nm), and near infrared (780nm) regions. The objective of this study is to identify optimum VIs obtained with the CC-430 sensor for estimating rice N status in Northeast China. A total of four field experiments involving five N rates (0, 70, 100, 130 and 160 kg ha^-1) and two rice varieties (Kongyu 131 and Longjing 21) were conducted in 2012 and 2013 in Jiansanjiang Experimental Station of China Agriculture University in Heilongjiang Province, Northeast China. The preliminary results indicated that among 16 different VIs evaluated, red edge-based indices, normalized difference red edge (NDRE) and red edge ratio vegetation index (RERVI) had consistent better correlations with rice plant N uptake (R²=0.8-0.81) and NNI (R²=0.71) across different growth stages, varieties, and years, which have better performance than red light based VI (NDVI, RVI) (R²=0.57-0.66). These results indicated that red edge-based VIs have better potential for estimating rice N status than red radiation-based VIs. More studies are needed to further evaluate this sensor and develop corresponding precision N management strategies to achieve high crop yield and high N use efficiency using this new red edge-based active crop canopy sensor.