Cotton Leaf Reflectance Changes after Removal from the Plant
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It is important in precision agriculture research, particularly in projects involving remote sensing, to collect a large number of field measurements on the optical properties of agricultural materials such as plant leaves. In making these measurements, maintaining a high level of accuracy and at the same time being expeditious are critical. A reasonable compromise would be to quickly collect a large number of field samples, store them appropriately during transit to the lab, and then make measurements with a laboratorygrade spectrophotometer. Concern arises, however, on the possibility that several hours of storage could significantly change the reflectance spectra of living plant material after removal from plants. Therefore, a study was conducted to quantify the change in reflectance spectra of cotton leaves over a period of time after picking. Cotton leaf samples were picked from cotton plants and then bagged in plastic zipper bags and stored in a cooler with ice underneath the samples. Reflectance spectra of cotton leaf samples were collected at 15, 180, 360, and 840 minutes after the leaves were picked with a UV/Vis/NIR (ultraviolet, visible, and nearinfrared) spectrophotometer in the wavelength region from 250 to 2000 nm. Spectral data were analyzed with SAS software to evaluate spectral changes of the leaf samples with time. It was concluded that, while certain cotton leaf reflectance spectra can be expected to change to a statistically significant degree within the first 14 h after removal from the plant, the changes are not large over that period of time. It is apparently reasonable to use a laboratory-grade spectrophotometer to measure cotton leaf spectral reflectance from 250 to 2000 nm within the first 14 h after having removed the leaves from the plant, assuming the leaves are properly stored. The Cotton Foundation 2009.