Recycling agricultural waste into controlled-release fertilizer: Integrating rice husk biochar with NPK fertilizer for efficient okra growth

Abstract

The development of sustainable and efficient fertilizers is crucial for improving agricultural productivity while minimizing environmental impact. In this study, we introduce an efficient impregnation method for producing rice husk biochar (RHB)-based NPK fertilizers, aimed at enhancing nutrient use efficiency (NUE) and plant growth of okra at the small scale. Physicochemical characterization confirmed successful NPK impregnation into the biochar matrix, as evidenced by X-ray diffraction (XRD) analysis, nitrogen sorption analysis, and Energy Dispersive X-ray Spectroscopy (EDX). XRD results revealed distinct crystalline phases of NPK compounds within the biochar structure, while nitrogen sorption analysis indicated a significant reduction in surface area from 88.512 m²/g (RHB) to 0.485 m²/g (NPK-impregnated RHB; NPK-iRHB), confirming nutrient occupation within biochar pores. Elution studies confirmed a more controlled and sustained nutrient release in NPK-iRHB, leading to superior NUE (38%), compared to RHB (0%; p=0.000), NPK fertilizer (19%; p=0.048) and physically mixed NPK-RHB (24%; p=0.999) towards the final stage. Additionally, NPK-iRHB reduced fertilizer input by 50% compared to NPK fertilizer (p=0.004), demonstrating significant cost savings. The enhanced performance of NPK-iRHB was attributed to stronger nutrient binding and controlled release properties, which were absent in the physically mixed NPK-RHB (pm-NPK-RHB). These findings underscore the importance of biochar impregnation over simple mixing, providing a more effective and environmentally friendly fertilizer alternative. The proposed impregnation technique is not only simpler, requiring fewer processing steps, and more cost-effective but also offers a promising solution for sustainable nutrient management in agriculture while repurposing agricultural waste into high-value fertilizers.