Reuse of biogas sludge for the slow-release fertilizer production to improve fertilizer use efficiency and soil fertility

Fertilizer overuse causes negative impacts on the environment and crop yields. Therefore, the production of slow-release fertilizers from biogas sludge is a potential solution for waste reuse and sustainable use of fertilizers. Granular fertilizers containing primary macronutrients (N, P and K) were formulated using biogas sludge and supplementary chemical compounds before coating with a thin film of glutaraldehyde cross-linked gelatin. The coating films reduced the release rates of N and P effectively. The application of formulated biogas fertilizers resulted in the competitive yield and growth rate of mustard greens over the 45-days cultivation compared to the application of commercial fertilizers. Particularly, the application of coated biogas fertilizers led to less nutrient losses in drainage water while maintained a balanced supply of available nutrients and beneficial bacteria in soils. This study emphasizes the feasibility to reuse biogas sludge for slow-release fertilizers production in improving fertilizer use efficiency and soil fertility. [Display omitted] •Hybrid fertilizer was produced with biogas sludge and supplementary chemicals.•Glutaraldehyde cross-linked gelatin was used as the slow-release coating film.•N and P release from hybrid biogas fertilizers in water reduced after coating.•Hybrid biogas fertilizers achieved the competitive yield and plant growth rate.•Fertilizer use efficiency and soil fertility increased with the coated fertilizer.