Spectral properties of crops at different growth stages
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Timely detection and remediation of volunteer cotton plants in both cultivated and non-cultivated habitats is critical for completing boll weevil eradication in Central and South Texas. However, timely detection of cotton plants over large areas and habitats is a challenging process. We examined the spectral reflectance properties of cotton, corn, soybean, and grain sorghum during different growth stages in 2009 to determine whether the spectral properties of plants could be used to distinguish cotton from other crops. Two blocks were set up according to the soil types in the TAMU farm, which are Belk clay (BaA) and Ships clay (ShA). Cotton, corn, soybean and sorghum were planted and managed in each block using conventional production practices for the area. Spectral information was collected from all crops at different growth stages from May to July. Reflectance spectra and the first derivative of the spectra were analyzed to characterize the spectral properties of crop varieties and compare the crops grown in different soil types. The results showed that the reflectance spectra of different crops could be differentiated at the early vegetative and late growth stages. At the vegetative stage, cotton could be distinguished from other crops; however, the reflectance spectra of soybean and sorghum were not significantly different between 410 and 560 nm. At the reproductive stage, cotton could be distinguished from soybean and sorghum between 510 and 590 nm and 650 and 900 nm. The red edge position could also be used to distinguish cotton, corn, soybean and sorghum at the vegetative growth stage and cotton, soybean and sorghum at the reproductive growth stage. The red edge points of cotton, soybean and sorghum shifted with the growth stages of development. No correlation was found between crop height and individual wavelength, but the difference of the heights of cotton plants grown in two blocks may explain that the reflectance of cotton plants in block BaA was more than those in block ShA.
