Almond responses to a single season of severe irrigation water restrictions

A substantial area of the new almond plantations in Spain is under irrigation, but due to recurring severe droughts, the irrigation water allocation for agriculture can be drastically reduced eventually. This study assesses the physiological and yields effects of a single-season water deprivation (2017) over three seasons (2017–2019) on a previously well-irrigated mature almond [Prunus dulcis (Mill) D.A. Web, cv. Guara] orchard in southern Spain. Three irrigation treatments were imposed during 2017: full irrigation, applying the amount required to match maximum crop evapotranspiration (FI); sustained deficit irrigation applying 25% of FI (DI); and rain-fed which received no irrigation at all (RF). During 2018 and 2019, all treatments were irrigated as FI. The results document the vulnerability of irrigated almond orchards to severe water stress, as the rainfed treatment resulted in 92% tree mortality. In relation to FI, yield and quality were reduced in RF and DI by the negative impact of water stress on kernel weight and the formation of hull tights in the season of water deprivation. In the two following years, the negative impact on yields persisted due to reductions in fruit load (carry-over effects) even though trees in DI and RF were restored to full-irrigation levels. The three-year average yields of DI and RF treatments were less than what could be predicted from an almond production function obtained in the same orchard. This highlights the long-term negative impacts that severe water stress resulting from suspending or reducing drastically irrigation in a single season has on almond trees.