A Review on Sustainable Slow-Release N, P, K Fertilizer Hydrogels for Smart Agriculture

The agricultural sector of any country plays a pivotal role in its economy. Irrigation and the provision of appropriate nutrient levels in soil are essential for optimizing plant growth and enhancing crop productivity. To support the increasing need for food due to the growing population worldwide, synthetic fertilizers have been widely used in the agricultural sector. These fertilizers could readily dissolve in the irrigation water or soil moisture, causing excessive release of the nutrients that plants cannot uptake from the root zone. The excess nutrients in the soil further harm the environment via surface run-off, leaching, and volatilization. Thus, materials with high water absorption and retention capacity, and precise control over the prolonged fertilizer release offer a potential solution to address these issues. To meet these requirements, the development of slow-release fertilizer hydrogels (SRFHs) represents a promising approach. SRFHs serve as natural agrochemicals to enhance crop growth and yield through controlled and self-sustained delivery of water and nutrients. This review provides a comprehensive study on the recent advancements in SRFHs, including their preparation methods, properties, slow-release behavior, and applications in smart agriculture. The response of soil microbial diversity to slow-release fertilizers is briefly discussed, and the future potential of SRFHs is highlighted herein.