The validity of predawn leaf water potential as an irrigation-timing indicator for field-grown wheat in northern Syria

We evaluated the validity of predawn leaf water potential (ψPL) as an irrigation-timing indicator, using five field-grown wheat cultivars in three moisture regimes in northern Syria. The relationships between ψPL and amount of roots, soil water potential (ψSoil), and vapor pressure deficit (VPD) were examined. The effect of the amount of roots on ψPL was only observed before the onset of tillering. The effect of ψSoil was recognized for values below the primary wilting point, and a relationship between nighttime VPD and ψPL was observed above the primary wilting point in some cultivars. However, grain yield decline in the 50% irrigation treatment was not explained by the ψPL change; therefore, the use of ψPL alone is not recommended for determining irrigation timing in the study area.