Abstract
A field study was conducted to investigate the response of leaf water potentials ( ψ l) 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 ψ l peaked at 09:30 hours, and then decreased, indicating that ψ l and C s at 09:30 hours were better predictors of plant water status. The correlations of K s to relative leaf water potential ( ψ l/ ψ lm) and relative leaf stomatal conductance ( C s/ C sm) were better than that of K s to ψ l and C s directly. K swas 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 > ψ l/ ψ lm. The procedure was used that reference crop evapotranspiration (ET 0) 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.
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