Prediction of nitrogen mineralization from novel bio-based fertilizers using chemical extractions

Bio-based fertilizers (BBFs) are an increasingly important source of nutrients in agriculture, promoted by the new EU fertilizer regulation aiming to enable a circular bioeconomy. Predicting the mineralization-dependent nutrient release of BBFs is critical for their appropriate use and to minimize environmental losses. We assessed mineralizable nitrogen (N) and carbon (C) of a representative selection of 32 BBFs and evaluated a set of chemical extraction methods to predict their N mineralization dynamics. In 84-day aerobic incubations, cumulative mineral N release varied between −13 and 100 % of amended N. Mineralized C ranged from 10 % to 117 % of amended C. Based on the dynamics of N and C mineralization, BBFs were classified into five significantly different groups. Among the tested chemical indicators of N mineralization from BBFs, cold and hot water presented the lowest extraction intensities, followed by hot potassium chloride and hot sulfuric acid extractions, while C:N ratio is based on total contents. Mineral N released almost immediately was best predicted by cold water extractable N, while hot sulfuric acid extractable N and C:N ratio predicted N released after the first two weeks and after 84 days, respectively. The combination of these three indicators was able to discriminate BBFs into four out of five mineralization classes. Such a cost-effective yet accurate estimation of N mineralization dynamics from BBFs can therefore be used as a basis to inform farmers on suitable timing and amount of BBF application, improving the synchrony between N release from BBFs and crop N demand.