Optimum time span for distinguishing little canary grass (Phalaris minor) from wheat (Triticum aestivum) crop based on their spectral reflectance characteristics

Abstract

The study was carried out at Ludhiana during 2006–08 to establish the optimum time span for distinguishing little canary grass (Phalaris minor Retz.) from wheat (Triticum aestivum L. emend. Feori & Paol.) crop based on their spectral signatures. The experiment was laid out in randomized block design with 6 replications and consisting of 12 treatments comprising 0, 10, 15, 25, 50, 75, 100, 125, 150, 200, 250 plants/m2 and a pure P. minor plot (Tmax). Results revealed that irrespective of wheat and weed, the per cent red reflectance values decreased as growth period progressed up to 95 days after sowing and increased sharply thereafter due to increased chlorophyll content. Maximum infrared reflectance value was observed at 95 days after sowing. The highest value of infrared reflectance of 25.20 to 66.49% in 2006–07 and 27.93 to 66.24% in 2007–08 was recorded under pure wheat and the lowest, 18.96 to 54.24% in 2006–07 and 18.17 to 55.46% in 2007–08 in pure P. minor. However, infrared reflectance values declined after 95 days after sowing up to harvesting due to onset of senescence. The highest radiance ratio and normalized difference in vegetation index values were recorded under pure wheat treatment and minimum under pure weed plots due to dark green colour and better vigour of wheat as compared to P. minor. It was observed that by using radiance ratio and normalized difference vegetation index (NDVI), pure wheat can be distinguished from pure populations of P. minor after 34 days after sowing and at different levels of weed populations can be discriminated amongst themselves from 68 days after sowing up to 107 days after sowing.