SPECTRAL RESPONSE OF WHEAT AND ITS RELATIONSHIP TO AGRONOMIC VARIABLES IN THE TROPICAL REGION

The spectral behavior of three varieties if wheat (Anahuac, IAC-24, and BH-1146) was analyzed using field radiometry throughout the 1988 growing season, in the region of Assis, SP. Reflectance factors were measured in the visible and near infrared portion of the electromagnetic spectrum for 30 sampled fields from four commercial farms and transformed into vegetation indices. These indices were related to agronomic variables (grain yield, green phytomass, dry phytomass, canopy height, etc.) after 10 measurement missions conducted weekly from 30 days after planting until harvest. The main objective of this work was to verify the potential of spectral data to estimate grain yield of wheat growing in tropical region. The vegetation index obtained at booting to beginning of flowering stages related quite well to the final grain yield (correlation coefficients of 0.82-0.93). The radiometric data were analyzed multitemporally also, where the vegetation indices were integrated throughout the growing cycle and related to grain yield. Results clearly indicated that the reflected energy at certain stages of the crop development and at certain wavelength bands are well related to the final grain yield. Therefore, spectral data, transformed into vegetation indices, have great potential to be used in yield predicting models for wheat growing in tropical regions. © 1990.