Studies were designed to explore spatial relationships of water and/or heat stress in cotton and soybeans and to assess factors that may influence yield potential. Investigations focused on detecting the onset of water/heat stress in row crops using thermal and multispectral imagery with ancillary physicochemical data such as soil moisture status and photosynthetic pigment concentrations. One cotton field with gradations in soil texture showed distinct patterns in thermal imagery, matching patterns measured by the VERIS 3100 soil EC mapping system. Yield of cotton obtained from 2003 to 2007 also followed mapped soil textures, and this depended to an extent on timing and amounts of precipitation. Thermal images were obtained of a soybean canopy in irrigated and non-irrigated fields, and samples were taken from three leaves at four locations of both fields for pigment analysis using high performance liquid chromatography (HPLC). Although leaf sample size for this preliminary study was rather small, significant differences between leaves sampled from irrigated vs. non-irrigated soybean plants were seen for three pigments at the 0.10 level. For another cotton field, several thermal images acquired over a five-week time interval (July-August 2006) were composited to produce a cumulative thermal map. Changes in canopy cover (derived from intensity-normalized color infrared imagery) were also mapped. Composited thermal imagery combined with tracking canopy cover change at key phenological stages could serve as a useful alternative to vegetative indices (VIs) for the in-season prediction of production potential as well as early senescence
promoted by heat/water stress in highly heterogeneous fields, and foster the development of site-specific applications of insecticides to protect high-yielding areas and cost-effective application of defoliants/harvest aids for cotton. Thermal mapping was seen as a useful tool for characterizing soils to predict yield depending on temporal precipitation patterns and thus could be useful for determining supplemental irrigation needs.
