New spectral indicator assessing the efficiency of crop nitrogen treatment in corn and wheat

To reduce environment pollution from cropping activities, a reliable indicator of crop N status is needed for site-specific N management in agricultural fields Nitrogen Nutrition Index (NNI) can be a valuable candidate, but its measurement relies on tedious sampling and laboratory analysis This study proposes a new spectral index to estimate plant nitrogen (N) concentration, which is a critical component of NNI calculation. Hyperspectral reflectance data, covering bands from 325 to 1075 nm, were collected using a ground-based spectroradiometer on corn and wheat crops at different growth stages from 2005 to 2008 Data from 2006 to 2008 was used for new index development and the comparison of the new index with some existing indices. Data from 2005 was used to validate the best index for predicting plant N concentration. Additionally, a hyperspectral image of corn field in 2005 was acquired using an airborne Compact Airborne Spectrographic Imager (CASI). and the corresponding plant N concentration was obtained by conventional laboratory methods on selected area. These data were also used for validation. A new N index, named Double-peak Canopy Nitrogen Index (DCNI), was developed and compared to the existing indices that were used for N detection In this study, DCNI was the best spectral index for predicting plant N concentration, with R-2 values of 072 for corn, 044 for wheat, and 0.64 for both species combined, respectively. The validation using an independent ground-based spectral database of corn acquired in 2005, yielded an R-2 value of 062 and a root-mean-square-error (RMSE) of 2.7 mg N g(-1) d m The validation using the CASI spectral information, DCNI calculation was related to actual corn N concentration with a R-2 value of 051 and a RMSE value of 3 1 mg N g(-1) d m. It is concluded that DCNI. in association with indices related to biomass, has a good potential for remote assessment of NNI Crown Copyright (C) 2010 Published by Elsevier Inc. All rights reserved