Estimating leaf nitrogen concentration with three-band vegetation indices in rice and wheat

Abstract

Real-time and nondestructive monitoring of crop nitrogen (N) status is of significant importance for precision N management in rice and wheat production. In eight field experiments with different N rates, water regimes and cultivars in rice and wheat crops, a new form of three-band vegetation indices was constructed to reduce saturation in two-band vegetation indices, and the optimal common three-band vegetation index was selected to establish models for canopy leaf N concentration (LNC) monitoring in rice and wheat. The results showed that the linear models for LNC monitoring with (R924−R703+2×R423)/(R924+R703−2×R423) were stable and accurate, with coefficient of determination (R2) of 0.870 and 0.857, and SE of 0.052 and 0.148 in rice and wheat, respectively. Testing of the models with independent data gave R2 of 0.866 and 0.883, RRMSE of 13.1% and 16.9%, and slope of 0.741 and 0.980 in rice and wheat, respectively. Further analysis of the influence of bandwidth change on LNC accuracy indicated that the allowable bandwidths for the central bands were 36nm for 924nm, 15nm for 703nm and 21nm for 423nm. The new three-band vegetation indices with narrow bands and broad bands in the present study are generally more effective for LNC monitoring compared with the other published vegetation indices.