Synergistic incorporation of calcium and zinc fertilizers in superabsorbent polymers

Abstract

Mineral fertilizers and water are essential for food production, and their sustained delivery is imperative to maximize crop yields. During heavy rainfalls, fertilizers can leach into the environment. During drought, fertilizers cannot dissolve in the soil. Superabsorbent polymers (SAP) can improve soil water retention capacity, by absorbing water during rainfall and releasing it during dry periods. In this study, we have integrated varying levels of calcium nitrate and zinc sulfate in an SAP to achieve fertilizer-SAP composites. Fertilizer-SAP composites can both help alleviate fertilizer leaching during heavy rainfall and facilitate their dissolution during dry periods, thank to moisture they absorb from the soil. SAP composites can also slow down the release of nutrients and keep them closer to the root area, for optimum plant uptake. Furthermore, we have observed a synergistic effect of nutrient incorporation in SAP, manifested by the enhanced water uptake of composites compared to pure SAP. For instance, SAP composites with 17 wt% zinc sulfate and calcium nitrate achieved superior water absorptions of 1462 and 1626 g/g, respectively. In comparison, pure SAP in this study reached approximately 800 g/g, and most commercial SAPs have water absorption capacities of 500 g/g. Suggested SAP application is often reported as 15–45 kg per hectare, in the literature. In comparison, the recommended zinc and calcium doses are as low as 3–5 kg/ha. Therefore, by a single fertilizer-SAP application, farmers can cover both the SAP and zinc, or calcium demands of their fields.