Determination of optimal narrow bands for vegetation indices to discriminate nitrogen status in wheat crop

Abstract

Nitrogen stress sensors are based on reflectance measurement controlled by the chlorophyll content. Reflectance of canopy is spectral dependent and more sensitive narrow spectral band can be exploited for reflectance measurement sensors.The experiments for present study were conducted in split plot design on two widely grown wheat (Triticumaestivum L.) cultivars (GW 496 and LOK 1) during rabi seasons of three consecutive years 2007-08 to 2009-10 at Anand. The two cultivars viz; GW 496 and LOK 1 were taken as the main treatments and five nitrogen fertilizer application rates 120, 90, 60, 30 and 0 kg N ha-1 as sub-treatments were randomized in four replications. Spectral reflectance measurements were taken over wheat canopy at different crop growth stages with a dual channel spectroradiometer.The ratio based and soil based indices (viz; RVI, DVI, NRI, RDVI, OSAVI,SAVI2,TSAVI and PVI) were used to find optimal wavebands.The optimum wavebands were explored using contours of R2 values of all possible two band combination for each vegetation index on 2D matrix plots. Except PVI, all indices revealed that red edge inflection point at 733-736 nm was the most sensitive to nitrogen status. The sensitivity of red edge inflection point also explored with first derivatives.

Keywords

• Nitrogen stress
• vegetation index
• red edge
• wheat