Estimation of sugarcane leaf nitrogen concentration using in situ spectroscopy

The aim of this study was to explore the use of in situ spectroscopy for estimating sugarcane leaf nitrogen (N) concentration. Leaf spectral reflectance was measured using a field spectroradiometer in the 350–2500 nm range from sugarcane variety N19 crops of 6–7 months old under on-farm conditions. Lab-determined leaf N concentrations of the samples taken ranged from 1.00% to 1.55%. Vegetation indices based on simple ratio (SR); viz. SR (743, 1316), SR (743, 1317) and SR (741, 1323) generated from first-order derivatives of leaf reflectance showed the best correlation with leaf N concentration, with r2 values of 0.76 (P < 0.01), 0.75 (P < 0.01) and 0.74 (P < 0.01), respectively. The root mean square errors of prediction (RMSEP) using a leave-one-out cross validation method were 0.089% (P < 0.01) for SR (743, 1316), 0.092% (P < 0.01) for SR (743, 317) and 0.084% (P < 0.01) for SR (741, 1323). These results suggest that the in situ spectroscopy has potential use in predicting sugarcane leaf N.