Quantifying leaf water potential for scheduling irrigation of wheat under specific soil-climate conditions

The relationship between soil water deficit (SWD), potential evapotranspiration (PET) and midday leaf water potential (LWP) of irrigated spring wheat was studied at Roodeplaat to determine if LWP can easily be estimated from SWD and PET so that it can be used for irrigation timing. A highly significant linear relationship between LWP of a well-watered control and PET for the daylight period was found. The difference between LWP of a stressed plot and that of the well-watered control was linearly related to SWD of the stressed plot. After combining these two linear relationships the resulting equation links LWP to SWD and PET during the day of measurement. This equation may be used to time irrigations at Roodeplaat, provided the critical LWP is known. SWD can be monitored and PET can be computed from routinely measured weather variables.