The so-called stress functions, allowing quantification of transpiration or
evapotranspiration reduction, as an answer to water deficit stress (stress coefficient,
Ks), are useful tools for irrigation scheduling. It is known that this coefficient depends
on several variables and parameters, such as evapotranspiration rate, root
patterns/density and soil properties. However, the most common Ks models with
practical applicability do not include some of these factors and the experimental work
on this matter is not abundant. A well-known model proposed in the FAO 56 manual
uses two parameters: the allowable depletion (p) and the total available soil water
(TAW) in the root zone, the input variable being the soil water depletion (SWD). We
discuss the application of this model in olive trees under specific natural conditions.
Two studies were conducted in Alentejo, South Portugal (2011 and 2017), in one
intensive and one super intensive drip irrigated olive orchards (Olea europaea
'Arbequina'). Transpiration reduction was obtained from sap flow measurements. For
both experiments, Ks was related to the estimated SWD. The experimental relationship
was compared with modelling outputs. Experimental results show that, in both
experiments, the Ks FAO 56 model only fits using parameters such as p= 0.05 and TAW
= 350 mm. The suggested p in that manual is 0.7. Furthermore, for such soils,
anisotropic canopy and small wetted area (drippers), 350 mm is much more than first
approach estimates would suggest. The results can be related with the root system
functioning and resilience of olive treesinfo:eu-repo/semantics/publishedVersio
