Seasonal dynamics and operational monitoring of hedgerow olive tree transpiration in response to applied water

Abstract

We used 2012 sap-flow measurements to assess the seasonal dynamics of daily plant transpiration (ETc) in a high-density olive orchard (Olea europaea L. ‘Arbequina’) with a well-watered (HI) control treatment A, to supply 100% of the crop water needs, and a moderately watered (MI) treatment B, which replaced 70% of crop needs. We then tested the hypothesis of indirectly monitoring olive ETc from readily available vegetation index (VI) and ground-based plant water stress indicators. In the process, we used the FAO56 dual crop coefficient (Kc) approach. For the HI olive trees, we defined Kcb as the basal transpiration coefficient, and we related Kcb to the remotely sensed soil-adjusted vegetation index (SAVI) through a Kcb-SAVI functional relationship. For the MI treatment, we defined the actual transpiration ETc as the product of Kcb and the stress reduction coefficient Ks, and we correlated Ks with MI midday stem water potential (ψst) values through a Ks-ψ functional relationship. Operational monitoring of ETc was then implemented with the relationship ETc = Kcb(SAVI) × Ks(ψ) × ET0 derived from the FAO56 approach and validated, taking as inputs collected SAVI and ψst data reporting to year 2011. Low validation error (6%) and high goodness-of-fit of prediction were observed (R2=0.94, RSME=0.2 mm day-1, P=0.0015), allowing us to consider that, under field conditions, it is possible to predict ETc values for our hedgerow olive orchards if SAVI and water potential (ψst) values are known.