Estimation of maize evapotranspiration under water deficits in a semiarid region

A field study was conducted to investigate the response of leaf water potentials (ψ₁) 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 β₁ peaked at 09:30 hours, and then decreased, indicating that ψ₁ and C(s) at 09:30 hours were better predictors of plant water status. The correlations of K(s) to relative leaf water potential (ψ₁/ψ(1m)) and relative leaf stomatal conductance (C(s)/C(sm)) were better than that of K(s) to ψ₁ 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) > ψ₁/ψ(1m). The procedure was used that reference crop evapotranspiration (ET₀) was estimated by the modified Penman formula and with a crop coefficient (K(c)) 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.