Leaf Area, Light Interception, and Yield Estimates from Spectral Components Analysis

Plants integrate the soil and aerial environments and express their development, stress response, and yield capabilities through the canopies achieved. The identities (1n LAI)/VI × Yield/(ln LAI) = Yield/VI [1] (1n LAI)/VI × IPAR/(ln LAI) = IPAR/VI, [2] where VI denotes any one of several spectral vegetation indices available; LAI is leaf area index; IPAR is intercepted photosynthetically active radiation; and yield is grain yield help interpret the information conveyed by canopies. Our objective herein was to test Eq. [l] and [2] term by term. LANDSAT multispectral scanner (MSS) spectral and field-measured LAI data for 32 grain sorghum (Sorghum bicolor L. Moench) fields in Hidalgo County, Tex., for the years 1973,1975, and 1976 are the exemplary data used. The predominant soil types at the nonirrigated sites were McAllen (fine-loamy, mixed, hyperthermic Aridic Ustochrepts) and Brennan (fine loamy, mixed, hyperthermic Aridic Haplustalfs) fine sandy loams, whereas the irrigated sites were typified by Hidalgo (fine-loamy, mixed, hyperthermic Typic Calciustolls) sandy clay loam and Raymondville (fine, mixed, hyperthermic Vertic Calciustolls) clay loam. The IPAR vs LAI relation used was from the latest version of the sorghum growth and yield crop (SORGF) model. Each of the equation terms as well as the relation between yield and IPAR is illustrated. All were highly significant with coefficients of determination, r², that ranged from 0.53 C 0.83. The IPAR vs LAI relations from the literature can be used in Eq. [l] to estimate IPAR from VI if LAI and VI were observed. The right hand side of Eq. [1] and [2] imply that even though the instantaneous VI relate to IPAR and yield, cumulative IPAR or cumulative VI for the season or for a period around maximum canopy development might relate even better. The fit of the relations to data from multiple weather years, irrigated and dryland plantings, across genotypes, and for differing planting configurations helps underscore the generality of the relationships and emphasizes the imformation inherent in crop canopy observations. Such spectral observations provide at alternative way of acquiring LAI or IPAR needed for large-scale use of agrometeorological crop models and for independent estimates of phytomass and grain yield.