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CROP ECOLOGY, MANAGEMENT & QUALITY

Identification of Optical Spectral Signatures for Detecting Cheat and Ryegrass in Winter Wheat

^a Dep. of Plant and Soil Sciences, Oklahoma State Univ., Stillwater, OK 74078
^b Dep. of Biosystems and Agric. Engineering, Oklahoma State Univ., Stillwater, OK 74078

^* Corresponding author (wrr{at}mail.pss.okstate.edu)

Precision weed management technology has immense potential for treating weed species at a small scale. To this end, however, crop and weeds must be recognized. One approach to this involves identification of reflectance signatures of crops and weeds that differ in the visible and near-infrared (NIR) wavelength region. Reflectance spectra were used for the detection of cheat (Bromus secalinus L.), ryegrass (Lolium multiflorum Lam.), and winter wheat (Triticum aestivum L.) under greenhouse conditions. A total of three experiments (two in December 2002 and one in February 2003) were conducted at the Agronomy Research Station, Stillwater, OK. The three species and two N levels were arranged in a completely randomized design with three replications. Spectral readings were taken at Feekes 3 and 5 winter wheat growth stages with a spectrometer. Two spectral measurements were obtained from each pot. The spectral measurements from the three experiments were combined by the two growth stages because preliminary analysis revealed that date of measurement and N levels were not significant. The spectral readings were measured at 1-nm intervals and averaged into 10-nm bandwidths for the wavelengths from 400 to 865 nm. Data were analyzed using a discriminant analysis procedure. The discriminant function with the band combinations 515/675, 555/675, and 805/815 resulted in the best overall correct classification (94%) of observations at Feekes 3, while for spectral data at Feekes 5 the discriminant function with the band combinations 755 and 855/675 resulted in 66.7% overall correct classification of observations. In several instances, ryegrass was classified as either cheat or winter wheat, while cheat was classified as rye. Cheat was not classified as winter wheat in most instances. This suggests that it is possible to identify cheat in winter wheat using wavelength ratios developed from spectral readings in 10-nm bands between 500 and 860 nm.

Abbreviations: NIR, near-infrared

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