Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2012
Publication Date: July 12, 2012
Citation: Zhang, H., Lan, Y., Suh, C.P., Westbrook, J.K., Lacey, R., Hoffmann, W.C. 2012. Spectral properties of crops at different growth stages. Transactions of the ASABE. 55:1-8. Interpretive Summary: Detection and elimination of volunteer cotton plants is deemed necessary to complete boll weevil eradication efforts in Texas. However, timely detection of volunteer cotton plants over large areas and diverse habitats is a challenging process. We used a ground-based hyperspectral sensor to examine the spectral reflectance properties of cotton, corn, sorghum, and soybean during different growth stages. The results showed that the reflectance spectra of plants could be used to readily differentiate among crop types at the early vegetative and late growth stages. Based on these promising results, remote sensing technologies show considerable potential as a tool for detecting volunteer cotton plants and future evaluations using air-based spectral sensors are warranted.
Technical Abstract: 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. The spectral reflectance properties of cotton, corn, soybean, and sorghum during different growth stages were examined to determine whether the spectral properties of plants could be used to distinguish cotton from other crops. Two field blocks with two different soil types (Belk clay [BaA] and Ships clay [ShA]) were set up with cotton, corn, soybean, and sorghum in each block and grown 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.