Primary and Residual Effects of a Bio-based Composite Fertilizer in a Wheat-Barley-Maize Cropping Sequence

Purpose Conventional fertilizer efficiency is generally low, while global fertilizer resources, particularly phosphate reserves, are rapidly being depleted. Rice husk (RH) is an abundant, silicon-rich agricultural by-product with significant potential as a sustainable fertilizer precursor. In this study, a bio-based composite fertilizer (RH-NPK) enriched with nitrogen, phosphorus, potassium, and silicon was developed through alkaline hydrolysis of rice husk, subsequent acidification with phosphoric acid, and nitrogen enrichment using ammonium nitrate. Methods A greenhouse experiment was conducted to evaluate the primary and residual effects of RH-NPK in comparison with a conventional 15–15-15 fertilizer. Wheat was grown as the first crop, followed by barley and maize cultivated sequentially in the same soil without additional fertilizer input. Results The chemical and mineralogical properties of RH-NPK were characterized by FTIR and XRD analyses, which confirmed the presence of silicate, phosphate, and nitrate functional groups and a mixture of amorphous and crystalline mineral phases. The fertilizer contained 9.82% N, 7.66% P, 13.6% K and 2.94% Si, with a near-neutral pH (6.15). RH-NPK produced plant dry weights comparable to or higher than those obtained with 15–15-15 in wheat, even at a 25% reduced application rate. The residual effect was pronounced in maize, where biomass exceeded the conventional fertilizer. Moreover, RH-NPK significantly increased plant nitrogen, phosphorus, potassium, and silicon concentrations, especially in the second and third crops. Conclusion The results demonstrate that RH-NPK is an effective Si-enriched bio-based fertilizer capable of improving nutrient use efficiency and sustaining crop productivity while reducing reliance on conventional mineral fertilizers.