Cotton Leaf Reflectance Changes after Removal from the Plant

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.