New tools for regulated deficit irrigation scheduling in early maturing peach trees

Abstract

Regulated deficit irrigation (RDI) is an irrigation strategy designed to save water with a minimum impact on yield and fruit quality (Chalmers, 1989). In stone fruits trees two critical periods have been defined. The first one corresponds to the second rapid fruit growth period (stage III), when water stress induces a reduction in yield due to the smaller fruit size at harvest. The second critical period is the early postharvest period, in which water stress affects flower bud induction and/or the floral differentiation processes that occur at this time (Ruiz-Sánchez et al., 1999). It is important to bear in mind that in peach trees RDI can reduce yield if the recovery of tree water status is delayed after deficit irrigation, particularly when the water stress extends into the stage III of fruit development (Girona et al., 1993). For this reason, in early maturing peach trees, with their very short period from fruit set to harvest and a very long post-harvest phenological period, deficit irrigation should be applied only during the post-harvest period in order to avoid any effect on yield and fruit quality. Under deficit irrigation conditions, the continuous control of tree water status is crucial in order to prevent a moderate, potentially beneficial, water stress from becoming too severe and ending in a reduction of yield (Domingo et al., 1996). In this sense, LVDT sensors are able to measure daily trunk diameter fluctuations (TDF) with great precision, generating sensitive parameters which strongly correlate with established plant water status parameters (Ortuño et al., 2010). The most common TDF parameter for the irrigation scheduling is the maximum daily trunk shrinkage (MDS). Absolute MDS values registered without considering the evaporative demand might be meaningless, and for irrigation scheduling it is better to use the concept of signal intensity (SI) (actual MDS/reference MDS) (Goldhamer and Fereres, 2001). MDS SI values above unity indicate water stress levels, while SI values of unity indicate the absence of irrigation-related stress (Ortuño et al., 2010). The research reported in this paper was conducted to test the hypothesises that RDI scheduling can be based exclusively on MDS measurements, and that by maintaining MDS SI values close to unity during fruit growth, a moderate water deficit during early postharvest X Simposium Hispano-Portugués de Relaciones Hídricas en las Plantas Sesión 1.4 68 period and a more severe water stress during late postharvest period, it is possible to save water without affecting yield and fruit components