Hydrogel-biochar composite for agricultural applications and controlled release fertilizer: A step towards pollution free environment

With the aim to develop superabsorbent and moisture retaining hydrogel-biochar composite for agricultural applications and as a controlled released fertilizer it was synthesized through graft-polymerization onto pine resin backbone. The biochar produced at 600 °C and morpho-mineralogically characterized. The N–P–K nutrient impregnated biochar was polymerized with hydrogels. The cross-linking of the composite was characterized by scanning electron microscope, transmission electron microscope, FT-IR, thermogravimetric analysis and water absorption capacity. The developed composite was able to increase water retention capacity (57.20–67.61%), porosity (6.25–21.05%); and decrease bulk density (5.26–9.02%) significantly. The degree of swelling varied 37–86 mL/g (swelling index) times of its own weight due to existence of numerous hydrophilic functional groups. The swelling index was more at pH 9.2 followed by 7.00 and lowest at 4.01. In the composite the N–P–K ratio was significant and rate of release of N–P–K in water and soil decreased with increasing acrylamide, monomer and cross-linker. After 288 h of incubation the N–P–K nutrient release from hydrogel-biochar composite varied 36.49–81.37%. Similarly, it exhibited 35.46–90.83% release of N–P–K in soil after 45 days study. The release kinetics fitted by Korsmeyer-Peppas model illustrates that the n values were 0.5–1.0 (anomalous transport). After 180 days in buried study the weight loss was 59.4–72.9% and validated to be biodegradable with 138.6–162.4 days half-life. Such powerful and multifunctional hydrogel-biochar composite might be a gifted substance as soil conditioners, controlled release fertilizer carrier and water preserving mediator (drought-prone areas) for sustainable green and pollution free environment.