Deficit Irrigation Strategies in Almond Orchards: A Review of the Effects on Yield, Physiology, Nut Quality, Economics, and Remote Sensing

Sustainable water use is a major challenge in irrigated agriculture, particularly in arid and semi-arid regions where water availability strongly influences crop productivity and quality. Almond (Prunus dulcis (Mill.) D.A. Webb) is an important nut crop cultivated extensively in such environments, making efficient irrigation management essential for sustainable production. A total of 63 studies were included in the review, comprising 62 field studies and one pot experiment, some of which incorporated modelling, remote sensing, physiological monitoring, or sensor-based irrigation-management approaches, to evaluate deficit irrigation (DI) in almond, with particular emphasis on regulated deficit irrigation (RDI), sustained deficit irrigation (SDI), low-frequency deficit irrigation (LFDI), and partial root-zone drying (PRD). The review examines how irrigation strategy, deficit intensity, timing and duration of water restriction, cultivar, tree age, and environmental conditions affect irrigation water savings, yield, kernel quality, water productivity, water-use efficiency, and physiological responses. In addition, the economic implications of DI and recent applications of remote sensing (RS) for detecting water stress and supporting irrigation scheduling are evaluated. Overall, the evidence indicates that DI can substantially reduce irrigation water use while maintaining acceptable yields and, under specific conditions, improving kernel quality. However, responses vary considerably among studies, reflecting interactions among deficit characteristics, environmental conditions, cultivar, and tree age and limiting the development of universally applicable management recommendations. The review further indicates that integrating DI with RS-based monitoring has potential to support site-specific and adaptive irrigation management by improving water allocation, detecting emerging water stress, and enhancing water-use efficiency. Such integrated approaches may become increasingly important in regions experiencing greater drought frequency and competition for water resources. Future research should prioritize multi-environment and multi-cultivar validation of integrated DI–RS approaches, the development of practical decision-support tools and economic thresholds, and the assessment of their transferability from experimental conditions to commercial orchards. Combining physiological indicators, RS technologies, and crop-specific irrigation strategies could contribute to more resilient and sustainable almond production under increasing water scarcity and climate variability.