Analysis of crop and weed leaf diffuse reflectance spectra

Diffuse leaf reflectance at the three- to five-leaf stage was measured for six species common to agriculture in Saskatchewan, Canada. The three crop species were wheat (Triticum aestivum), canola (Brassica napus L.), and field pea (Pisum sativum L.). The three weed species were wild oat (Avena fatua L.), wild buckwheat (Polygonum convolvulus L.) and Canada thistle (Cirsium arvense (L.) Scop.). Plants were grown in regulated environmental chambers. For each plant, the leaf reflectance of two different leaves or leaf segments was measured, with between 40 and 50 plants for each species. Measurements were recorded between 270 and 2500 nm with a maximum data interval of 2 nm. Reflectance measurements were recorded with leaves against black and white backgrounds. These reflectance spectra corresponded to the expected green-plant profile. Distribution of the data was investigated numerically using the Anderson-Darling and Shapiro-Wilks goodness-of-fit statistics, standard deviation, skewness, and kurtosis, and qualitatively with histograms. Large deviations from the generally assumed normal distribution were observed, and these deviations were dependent on both wavelength and species.