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Deficit irrigation (DI) is a key strategy to reduce agricultural water use under increasing water scarcity. To enhance the effectiveness of this approach, soil amendments such as superabsorbent polymers (SAPs), biochar, and bentonite can improve soil hydro-physical properties and help crops withstand drought stress. Following the PRISMA guidelines, we systematically reviewed 107 peer-reviewed studies published between 2000 and 2025. The focus was on crop yield, water productivity, and soil properties under deficit irrigation combined with different soil amendments. Superabsorbent polymers reduced nitrate leaching by over 70% and increased fruit weight by up to 15%. Biochar sustained crop yields while reducing irrigation water use by about 21% and lowering greenhouse gas emissions. Bentonite improved surface irrigation efficiency and enhanced plant-available water. Overall, water savings ranged from 15 to 50%, depending on amendment type, application rate, and soil conditions. Integrating soil amendments with deficit irrigation enhances water productivity, crop resilience, and environmental sustainability. These findings are relevant not only to arid and semi-arid regions such as Iran but also to global agricultural systems facing water scarcity. Long-term, cross-regional studies are recommended to strengthen applicability and guide practical adoption.
Hajirad et al. (Mon,) studied this question.