Automated soil water content-based irrigation under high and low water availability scenarios for a nectarine orchard

In a low water availability scenario, as is increasingly frequent in Mediterranean areas threatened by climate change and endemic water scarcity, to achieve the best irrigation water efficiency is of vital importance. This study aimed to assess the feasibility of an automated irrigation scheduling strategy based on real-time threshold volumetric soil water content values (VSWC), monitored with capacitance probes, in adult early-maturing nectarine orchard (Prunus persica (L.) Batsch cv. `Flariba’, on GxN-15 rootstock). Two drip irrigation practices were tested: one control treatment (T-0) based on conventional crop evapotranspiration calculations (ETc, FAO-56), and one automated treatment (T-A) based on management allowed depletion (MAD) threshold values, derived from VSWC data, with a feed-back control system. Furthermore, for both treatments agro-physiological responses were evaluated under two different water availability scenarios (each one comprised of three consecutive growing seasons): no water restrictions (high water availability), and deficit irrigation (low water availability), in which reduced water to irrigate nectarine trees involved regulated deficit irrigation criteria.  In the high water availability scenario, T-A (MAD = 10%) and T-0 (ETc = 100%) irrigation treatments showed no significant differences in the plant-soil water status, vegetative growth, yield, and nectarine fruit quality parameters. The VSWC was not a limiting factor and full irrigating to achieve a maximum yield was a profitable option. In the low water availability scenario, the T-A treatment (subjected to MAD = 10% during pre-harvest and 30% during post-harvest) received 43% less water than the control, which promoted moderate plant and soil water deficits, leading to a decrease in vegetative growth (winter pruning weight and tree canopy cover), without compromising the total yield and nectarine fruit quality parameters (including an increase in the total soluble solid content). The crop water use efficiency increased by an average of 34%. The proposed automated irrigation strategy, based on MAD seasonal threshold values, combined with regulated deficit irrigation phenological criteria could be considered a promising tool that could be eventually extrapolated to other stone fruit orchards under water scarcity conditions. Acknowledgements: This work was funded by Spanish Agencia Estatal de Investigación (PID2019-106226RB-C21/AEI/10.13039/501100011033) and Fundacion Séneca, Región de Murcia (19903/GERM/15) projects.