Soil and plant water indicators for deficit irrigation management of field-grown sweet cherry trees

Abstract

A two-year experiment with sweet cherry (P. avium L. cv Prime Giant) trees was carried out to ascertain which of the following commonly used soil and plant water indicators is most effective for deficit irrigation scheduling: Ψstem (midday stem water potential), MDS (maximum daily branch shrinkage), gs (stomatal conductance), θv (soil volumetric water content), Ψm (soil matric potential). For this, soil and plant water relations, as well as the physiological and agricultural responses of trees to three different irrigation treatments, were evaluated. The irrigation treatments imposed were: i) a control treatment (CTL) irrigated at 110% of crop evapotranspiration (ETc) throughout the growing season, ii) a regulated deficit irrigation treatment (RDI), which met 100% ETc at preharvest and during floral differentiation and 55% ETc during the postharvest period and iii) a treatment based on normal farming practices (FRM).MDS was the first indicator to detect water stress, while Ψm showed the highest sensitivity postharvest, when it was closely related with Ψstem. Consequently, a multiple linear regression equation based on average Ψm at a depth of 25 and 50 cm, and mean daily air vapor pressure deficit (VPD) was established to estimate Ψstem. The estimated Ψstem explained 84% of the variance in the measured Ψstem. Hence, the equation proposed can be used as a tool to estimate Ψstem and for irrigation scheduling. Based on the relation MDS vs. Ψstem and the observed agronomic response, a postharvest threshold value of −1.3 MPa is proposed for deficit irrigation management in ‘Prime Giant’ cherry trees.