Estimation of maize evapotranspiration under water deficits in a semiarid region

A field study was conducted to investigate the response of leaf water potentials (ψl) and stomatal conductance (Cs) of maize crop to soil water availability, and to test and compare the soil water adjustment coefficient (Ks) functions for estimation of actual evapotranspiration (ET) under water deficits. The results showed that correlation coefficients of Ks to Cs and ψl peaked at 09:30 hours, and then decreased, indicating that ψl and Cs at 09:30 hours were better predictors of plant water status. The correlations of Ks to relative leaf water potential (ψl/ψlm) and relative leaf stomatal conductance (Cs/Csm) were better than that of Ks to ψl and Cs directly. Kswas also significantly related to soil water availability (Aw). Correlation with Ks was reduced in the following order: Cs/Csm > Aw > ψl/ψlm. The procedure was used that reference crop evapotranspiration (ET0) was estimated by the modified Penman formula and with a crop coefficient (Kc) and different Ks functions. The results showed that it was the best estimation with Ks function based on the relative stomatal conductance, and at least in the case of maize that the soil water adjustment coefficient Ks based on relative stomatal conductance Cs/Csm provided a means of predicting required adjustments in ET estimation for different soil water status.