Synthesis and characterization of double-network beads based on sodium alginate grafted polyacrylamide as nitrogen,...

The use of conventional water-soluble mineral fertilizers in modern agriculture brings about serious economic and environmental issues related to the loss of nutrients, the contamination of underground water and the contribution to greenhouse gas emissions. To mitigate these issues, both researchers and industrials are turning to alternative solutions such as slow-release fertilizers. In line with this trend, here we report on the formulation of a novel sodium alginate based slow-release NPK fertilizer beads using sodium alginate as a biopolymer, polyacrylamide as a graft polymer, complex NPK fertilizer as a source of nutrient and calcium (Ca²⁺) as a crosslinking cation. Five NPK-rich sodium alginate-based slow-release beads were formulated and then extensively characterized by FTIR, XRD and SEM. The swelling capacity in water was also evaluated and was found to be a function of the grafting percentage. The nutrients release profiles were evaluated in water as well as in sandy loamy soil. The release experiments showed that the formulated hydrogel beads displayed a delayed nutrient release profile compared to water-soluble NPK fertilizer. The magnitude of the release was significantly slow down as the grafting rate increased with the graft copolymer at 20 wt% exhibiting the prolonged longevity as compared to the other formulations The cumulative release of nitrogen, phosphorus and potassium from the NPK-rich SA-g-PAM 20 % were 65 52, and 43 % during the first 56 days of release in water and were 23, 16, and 15 % during the first 35 days of release in a sandy loamy soil, respectively. The study of nutrients release kinetics indicated the release behavior of N, P and K in water and soil was controlled by a non-Fickian diffusion mechanism. These performances highlight that the fabricated fertilizer beads could be a promising alternative to water soluble fertilizer in the moder agriculture.