A systematic review on the combined effects of deficit irrigation and soil amendment with super-absorbent polymer on crop yield and water productivity

Deficit irrigation (DI) and soil amendment with super-absorbent polymer (SAP) are viable strategies to reduce agricultural water demand. This review paper aims to discuss the status quo of research studies on this topic focusing on their effects on yield and water productivity (WP). Publications were retrieved from Scopus® database and relevant studies used for the analysis were selected following the PRISMA protocol. Findings indicate that SAP effectively increased yield and WP, particularly under field conditions and various levels of DI. Soil type with high water holding capacity (e.g. clay) showed higher WP when SAP was added in the soil while minimal effect was observed in soil types with lower water retention capacity (e.g. sandy, sandy clay, and sandy loam). The amount of SAP applied varied by crop type but not by irrigation strategy. In conclusion, crop yield and WP is affected by the amount of SAP and DI with some crop- and soil-specific responses. To maximize SAP effectiveness, it is recommended to apply it directly within the plant rooting depth, considering also the specific crop type. Furthermore, future research should adopt systematic irrigation scheduling and appropriate irrigation regimes to enhance SAP and DI efficiency.