Heat Stress and Cotton Yields in Arizona

Abstract

Yield of upland cotton was related to heat stress in Yuma, LaPaz, Maricopa, and Pinal Counties for the period 1987-1999. Heat stress during the primary fruiting cycle was assessed using heat stress units (HSU) which were derived from mean daily canopy temperatures computed using a canopy temperature model and local AZMET weather data. Mean lint yields were computed for years with low, intermediate and high levels of HSU. Yields in years with low levels of heat stress were always significantly greater than yields in years with high levels of heat stress. Differences in yield between high and low heat stress years ranged from 100 lb/a in Maricopa County to 254 lb/a in Yuma County and averaged 166 lb/a across all counties. Differences in yield between the low and intermediate stress years, and intermediate and high stress years averaged 86 and 80 lb/a, respectively across all counties; however, these differences were not always significant in individual counties.