Estimation of maize evapotranspiration under water deficits in a Semiarid Region

A field study was conducted to investigate the response of leaf water potentials (psi(1)) and stomatal conductance (C-s) of maize crop to soil water availability, and to test and compare the soil water adjustment coefficient (K-s) functions for estimation of actual evapotranspiration (ET) under water deficits. The results showed that correlation coefficients of K-s to C-s and psi(1) peaked at 09:30 hours, and then decreased, indicating that psi(1) and C-s at 09:30 hours were better predictors of plant water status. The correlations of K-s to relative leaf water potential (psi(1)/psi(1m)) and relative leaf stomatal conductance (C-s/C-sm) were better than that of K-s to psi(1) and C-s directly. K-s was also significantly related to soil water availability (A(w)). Correlation with K-s was reduced in the following order: C-s/C-sm > A(w) > psi(1)/psi(1m). The procedure was used that reference crop evapotranspiration (ET0) was estimated by the modified Penman formula and with a crop coefficient (K-s) and different K-s functions. The results showed that it was the best estimation with K-s function based on the relative stomatal conductance, and at least in the case of maize that the soil water adjustment coefficient K-s based on relative stomatal conductance C-s/C-sm provided a means of predicting required adjustments in ET estimation for different soil water status. (C) 2000 Elsevier Science B.V. All rights reserved.