Integrated agronomic management to alleviate water stress in adult almond trees under Mediterranean conditions

Water scarcity has intensified in recent years, becoming an almost permanent constraint on competitiveness in Mediterranean irrigated agricultural systems. In this context, agronomic practices such as regulated deficit irrigation (RDI) and digitalization allow these systems to maintain productivity. Nevertheless, increasing pressure on water resources with climate change projections has driven the search for complementary solutions to alleviate crop water stress. Among these, reducing leaf area through pruning or using biostimulants based on seaweed has shown to be effective in increasing irrigation water productivity (WP_i) in agriculture. For this reason, the aim of this study was to evaluate the impact of these combined practices over the agronomic response and WP_i of adult almond trees in SE Spain under semiarid conditions. We established a completely randomized factorial experimental design with three factors (Irrigation × Pruning × Biostimulation) and two levels each. For the irrigation factor, we established two levels: precision irrigation (PI), in which irrigation was based on an irrigation threshold of soil water depletion of up to 20% of field capacity during the entire season (0-60 cm depth); and regulated deficit irrigation (RDI) in which the trees were irrigated like PI until phase IV, when the water applied was reduced by 25% during May and June and by 50% during July and August with respect to PI. For the pruning factor, we established two levels based on the intensity: normal pruning (NP) was performed according to the criteria for adult almond trees, removing around 42.8 kg fresh weight per tree, and severe pruning (SP) removing up 76.7 kg fresh weight per tree. Finally, the biostimulation factor was defined according to its application or not: trees without application (NB), while biostimulated trees (BIO) were treated with seaweed-based extracts through foliar spraying and drip irrigation during flowering and fruit set. The results obtained showed that yield were only affected by severe pruning, decreasing by 18.2% in comparison to NP. Even though irrigation water was reduced by 21.4% in trees under RDI with respect to PI (2870 m³ ha⁻¹), yield was not reduced, increasing the WP_i in 46.8%. Under PI conditions, WP_i increased significantly in biostimulated (BIO) trees under NP. In contrast, SP tended to decrease WP_i because of reduced yield compared with NP. The interaction between factors did not show significant differences in WP_i. Biostimulation alleviated water stress, leading to an increase in almond size, particularly under severe pruning. The total amount of biomass removed in SP significantly reduced yield due to a lower number of fruits. Consequently, severe pruning may be considered under extreme water scarcity conditions, provided it is complemented with biostimulation, as seaweed-based extracts also enhanced the photosynthetic rate and reduced the intensity of water stress in the trees.

Funding: Laura Marín is thankful for her Research Staff Training contract funded by the Regional Agency for Science and Technology of the Region of Murcia (Fundación Séneca 22340/FPI/23) and co-funded by the company FMC through the FMC Agricultural Sciences Chair at the Technical University of Cartagena.