Water stress indicators and stress functions to calculate soil water depletion in deficit irrigated grapevine and kiwi

摘要

In traditional irrigation engineering, the value of average soil water content in the root zone is considered to be allowed to range between field capacity (FC) and the lower limit of the readily accessible water (RAW), a certain threshold above the so-called permanent wilting point (PWP). However, in deficit irrigation conditions, the lower part of the total available water is also explored. The need for a more precise control of soil water depletion requires simple models using stress coefficients(Ks) as refined models are of limited applicability in this context. As empirical models lead to a high level of uncertainty, its adequacy needs adjustments based in locally measured stress indicators, allowing appropriate self-learning routines to be applied. In this direction, we first report experimental results versus outputs from a simple soil water depletion model, using plant water status to obtain Ks and estimate transpiration. The examples concern a grapevine cultivar with isohydric behavior, in SE Portugal (field conditions) and kiwi, in NW Portugal, which displayed an anisohydric behavior, when submitted to water stress under controlled conditions. Different indicators were used, according to the behaviour shown, allowing reasonable T estimations but, for kiwi, this was only possible by considering the effect of ETo variations on Kcb xKs.