Combined effects of deficit irrigation and crop level on early nectarine trees

Abstract

A three-year long experiment was implemented in an early nectarine (Prunus persica L. Batsch cv. Flanoba) commercial orchard to evaluate the effects of deficit irrigation and different crop levels on vegetative growth, plant water status, and fruit yield and quality. Three irrigation treatments were assessed: (i) control, full irrigation (TCTL); (ii) normal practice of the farmer (TFRM); and (iii) regulated deficit irrigation (TRDI), which involved irrigating the crop at the same level as the control (TCTL) during the critical periods of the first year and at 60% TCTL during postharvest. In the last two growing seasons the irrigation was scheduled to maintain the signal intensity (SI) of maximum daily trunk shrinkage (SIMDS=MDSTRDI/MDSTCTL) at different water stress levels depending on the phenological stage: SI=1.0 (non-water stress) and SI=1.4 (moderate water stress). Besides, during the last two seasons, the interactions between TCTL and TRDI were studied at five different crop levels, which were obtained by controlling the distance between fruits left on the branches: from very low (16cm between fruits) to very high (8cm between fruits). Crop water use efficiency (WUE) of TRDI was higher than in TCTL and TFRM, increasing by around 25% in 2010 and 2011, and around 74% the final year. Interestingly, TFRM increased the WUE from the first year by more than 30%. The yield/annual increase in trunk-cross-sectional area (ΔTCSA) ratio increased in TRDI with respect to the other treatments as the experiment progressed, reaching differences of 53%. Vegetative growth was clearly sensitive to deficit irrigation with a strong correlation between the increase in the water stress integral obtained by midday stem water potential (Ψstem) and the reduction in TSCA. In contrast, fruit production and quality were not affected by water deficit. As regards the interaction between crop level and water deficit, fruit firmness was the only fruit quality parameter studied that presented significant differences, the highest values corresponding to the fruits from TRDI trees and the lowest crop level. In early nectarine trees, the postharvest period can be considered as a non-critical period for applying RDI strategies but only when the water stress integral applied is of low intensity in May and June (much lower than 9MPa day), in order to limit the decrease in vegetative growth and so not affect the following harvests.