Development Of Slow Release Nano Composite Fertilizer Using Biodegradable Super absorbent Polymer

Abstract

This work aimed at developing a slow release nano-composite fertilizer (SRF) for improved nutrient use efficiency in soil using a biodegradable superabsorbent polymer. Partially neutralized acrylic acid was grafted onto cellulose isolated from water hyacinth by radical polymerization reaction. The reaction conditions were optimized through assessment of grafting parameters namely, grafting cross-linking percentage (GCP), percentage grafting cross-linking efficiency (%GCE) and water absorption tests. The copolymer was characterized by Fourier transform infra-red (FTIR) spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Energy dispersive X-ray (EDX) spectroscopy. Water absorbency of the copolymer hydrogel was assessed in saline solutions and in solutions of various pH values. Degradation of the copolymer was tested by soil burial test and microbial culture isolated from agricultural soil. The optimized product exhibited superabsorbent qualities in distilled water and the water absorbency was influenced by pH and by the presence, nature and concentration of ions. The copolymer revealed the capacity to retain moisture in soil and degradation both in soil and microbial culture. A SRF was formulated by incorporating nano-hydroxyapatite (nano-HA), urea, (NH4)2HPO4 and K2SO4 into the cellulose grafted copolymer, and the release of nutrients was assessed using laboratory incubation experiment. Significantly higher (p≤0.05) content of mineral nitrogen (mineral-N) was observed in the first 4 weeks in conventional fertilizer (CF) compared to SRF treatments and the control. Mineral-N content in SRF treatments increased considerably between the 8th and 12th week, and declined in the 16th week. The values of potentially mineralizable N estimated using single first-order kinetics model related well to the observed cumulative mineral-N at 16th week. Significantly higher P content was observed in CF compared to SRF treatment in the 4th week, whereas in the 8th week, some SRFs released significantly higher content than CF. The data revealed reduced chances of leaching losses and toxic effect to the plant roots, as well as synchronized nutrient release to cater for the requirement by crops. Effect of the formulated SRF on the performance and yield of maize, kale and capsicum was evaluated in a greenhouse experiment. SRF recorded higher dry matter and yields relative to CF with similar application rates, though statistically insignificant. The agronomic optimal application rates of SRF determined by quadratic function were higher than that of CF. SRF enhance growth and yields of crops just like CF and could potentially have greater benefits such as improving soil health and resilience. Therefore, a slow release nano-composite fertilizer has been fabricated and investigated under laboratory and greenhouse (controlled) conditions. It is recommended that the formulated SRF be tested under field conditions.