| Summary: | Valorization of agro-municipal solid wastes into value-added nutrient-enriched slow-release organic amendments (OAs) for ameliorating soil fertility constraint has been proposed as an environmentally friendly and sustainable approach to managing challenges associated with disposal of organic wastes. However, for soils receiving OAs of complex composition, such as biochar-manure-compost (BMC), the predictive knowledge needed to synchronize amount and timing of nitrogen (N) release with plant demand, thereby minimizing environmental pollution, is still lacking. This study validated results from an alkaline hydrolysis method for estimating N mineralization potential with: (i) the standard long-term N mineralization procedure and (ii) actual N uptake from soils amended with BMCs of varied C/N ratios. The alkaline hydrolysis procedure involves direct steam-distillation of BMC-soil mixtures, requiring only 40-min for estimating N mineralization potential, whereas the standard N mineralization procedure followed 26-week laboratory incubation. For both procedures, cumulative N mineralized or hydrolyzed was fitted to the first-order exponential equation to determine the potentially mineralizable N (No) and an analogous “potentially hydrolyzable N (Nmax)” for the BMCs. Nitrogen uptake by maize was evaluated in a six-week pot experiment. The results showed that Nmax and No values differed among the BMCs, indicating differences in chemical composition, and potential mineralizabilities of the BMCs. Increasing biochar content of the BMCs decreased kinetic parameters of N mineralization compared to compost alone. Estimated Nmax values significantly correlated with No (p = 0.023) and N uptake (p = 0.005), suggesting that alkaline hydrolyzable ON can replace the long-term procedure for estimating No in BMC-amended soils, reducing experimental cost and time.
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