Abstract
The response of transpiration (Tr) and stomatal resistanse (rs) to extractable soil water and the vapor pressure dificit of the air was investigated over three differentially irrigated wheat plots for an entire growing season. The objective was to devolop a physiological basis for remote monitoring of crop and soil water status. The results indicated that Tr was closely correlated with the extractable soil water (ESW) remaining in the soil when the ESW was less than 40%. When the ESW was greater than 40%, Tr was propotional to the vapor pressure deficit of the air (VPDa). Stomatal resistance (rs) was found to increase hyperbolically with decreasing ESW (r=0.82), although rs was small and independent of ESW at high ESW. No relationship was found between rs and VPDa. The correlation between the ratio Tr/VPDa and ESW was higher (r=0.75) than the correlation between Tr and ESW. Normalizing Tr and ESW values for the water stressed plots to those observed in the well watered plot improved this correlation to r=0.91. Multiple regression analysis showed that rs1 and VPDa were highly correlated with ESW (r=0.92-0.97).
