Application of superabsorbent natural polymers in agriculture

To meet global food demand, reduce waste, and minimise environmental impact, the agricultural sector must improve its current practices on soil amendment, fertiliser encapsulation, and seed and crop protection. Super absorbent polymers (SAPs) are a class of polymeric materials that can absorb and retain large quantities of liquids/aqueous solutions compared to their own mass. Typically, SAPs are cross-linked to form three-dimensional hydrophilic networks, commonly known as hydrogels. Although SAPs can be synthesised from both synthetic and naturally sourced materials, for agricultural applications they are generally composed of synthetic polymers, due to their advantageous properties. These include higher water absorption rate and capacity, low cost, availability, durability, and mechanical performance. However, many of these systems utilise polyacrylic acid (PAA) and polyacrylamide (PAM) monomers which may have toxic effects on the nervous and respiratory systems of humans and animals. To ensure sustainable agricultural practices and maintain healthy long-term crop output, synthetic SAP usage must be greatly reduced. This review article aims to investigate alternative natural SAPs for agriculture and critically rationalise their adoption into the industry. Specific applications investigated include (i) soil amendment, (ii) fertiliser encapsulation, (iii) seed coating, and (iv) crop protection.