Transpiration reduction as an answer to water stress: models versus measurements for irrigated olive trees in South Portugal

S. Lourenço, N. Conceição, H.P. Losada, J. Silvestre, J. Siqueira, F. Santos, J. Rolim, M.I. Ferreira
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 modeling 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 trees.
Lourenço, S., Conceição, N., Losada, H.P., Silvestre, J., Siqueira, J., Santos, F., Rolim, J. and Ferreira, M.I. (2022). Transpiration reduction as an answer to water stress: models versus measurements for irrigated olive trees in South Portugal. Acta Hortic. 1335, 205-210
DOI: 10.17660/ActaHortic.2022.1335.24
https://doi.org/10.17660/ActaHortic.2022.1335.24
Olea europaea, modeling, Alentejo, roots, irrigation scheduling
English

Acta Horticulturae