Submitted to: Environmental and Experimental Botany
Publication Type: Proceedings
Publication Acceptance Date: 6/17/2002
Publication Date: N/A
Interpretive Summary: Remote sensing techniques, based on measuring the reflected radiation from plant leaves or canopies, have the potential of evaluating crop physiological characteristics and environmental stresses either at a large scale (a region or field) or a small scale (a canopy or leaf). In short, selecting wavelengths sensitive to relatively subtle changes in leaf chlorophyll concentration that may accompany stress will greatly facilitat agricultural uses for remote sensing. This study determined the capability of remote sensing to discriminate differences in cotton growth and physiology due to applications of a commercially available plant growth regulator, mepiquat chloride. As expected, the growth retarding effects of mepiquat chloride decreased plant height, total leaf area, and dry matter accumulation. The three different rates of mepiquat chloride also increased leaf chlorophyll concentration, and reduced leaf spectral reflectance at the specific wavelengths of 515 to 590 nanometers (the gree reflectance peak) and 700 to 945 nm (the region of near infrared reflectance common in all leaves). Leaf reflectance data was used to estimate leaf chlorophyll and separate leaves treated with mepiquat chloride from untreated controls. Results suggest hyperspectral imagery in narrow, 5-nanometer-wide wavebands has potential to delineate sites in the field for Pix applications, and hence lower application costs.
Technical Abstract: Remote sensing has potential to estimate or predict crop physiological characteristics and environmental stresses in both a large scale (a region or field) and a micro scale (a canopy or leaf). A pot-culture experiment was conducted under field conditions to investigate the effects of a plant growth regulator, mepiquat chloride (MC), on cotton (Gossypium hirsutum L.) growth, physiology and leaf reflectance properties. Four MC treatments of 0 (control), 25, 50, and 100 g a.i. MC per hectare, were applied foliarly a week after first square (floral bud) stage. The fourth leaf from the plant terminal was used to measure leaf reflectance, chlorophyll, carotenoids and mineral concentrations. Plants were harvested weekly for growth analysis. Application of MC decreased growth, increased leaf chlorophyll, and decreased leaf reflectance. Leaf chlorophyll could be estimated using reflectance measures at 545, 570, and 930 nm. Leaf carotenoid and K concentrations could also be estimated from three or four wavebands. Reflectance measures at 420, 545, 810, and 935 nm separated MC-treated plants from untreated plants, but were unable to distinguish different application rates of MC. Stepwise linear regression and discriminant analysis suggested MC-induced changes in leaf reflectance were not only due to increased chlorophyll, but also to other as yet unidentified physiological or morphological characteristics in MC-treated leaves.