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Updated: Jan 17, 2026

Assessment of Labile Organic Carbon in Soil Using Sequential Fumigation Incubation Procedures
Published on: October 29, 2016
Microbial assimilation-mediated organic nitrogen accumulation after seven-year biochar-based fertilizer application
Jun Wang1, Qin Qin2, Yafei Sun2
1Eco-Environmental Protection Research Institute, Shanghai Academy of Agricultural Sciences, Shanghai 201403, China; Shanghai Key Laboratory of Protected Horticultural Technology, Horticultural Research Institute, Shanghai Academy of Agricultural Sciences, Shanghai 201403, China; Shanghai Engineering Research Centre of Low-Carbon Agriculture, Shanghai 201403, China; Key Laboratory of Low-carbon Green Agriculture in Southeastern China, Ministry of Agriculture and Rural Affairs, Shanghai 201403, China.
Abstract:
The microbial processes engaged in nitrogen (N) assimilation regulate both the stability of soil N pools and the sustained N supply required for crops. Nevertheless, current understanding is limited regarding how biochar-based fertilizer influences organic N accumulation through microbial assimilation. This study investigates the role of microbial assimilation in the accumulation of organic N in a fluvo-aquic soil when chemical fertilizers are partially replaced with biochar-based fertilizer by quantifying microbial N in living biomass and necromass. Topsoil samples were collected from a 7-year field trial with four treatments: no fertilization (CK), chemical fertilizer only (CF), 30 % substitution of chemical N with biochar-based fertilizer (LBF), and 60 % substitution of chemical N with biochar-based fertilizer (HBF). Biochar-based fertilizer application demonstrated significantly increased soil organic N (SON) by 11.89 %-24.74 % compared to traditional chemical fertilization, with HBF exhibiting 11.49 % greater efficacy than LBF. Microbial necromass N accounted for 24.85 %-57.01 % of SON enhancement, dominated by fungal sources (19.25 %-37.45 %) over bacterial (5.60 %-19.56 %). Structural equation modeling revealed direct positive effects of biochar-based fertilizer on fungal and bacterial necromass N, while microbial biomass N (MBN) negatively regulated SON. Random forest analysis identified MBN, microbial necromass N, and microbial abundance as strong predictors of SON variation. Fungal necromass emerged as the primary driver of SON accumulation under biochar-based fertilizer fertilization. These results clarify the microbial pathways supporting enhanced soil N retention with biochar-based amendments and underscore the potential of fungal-mediated processes for sustainable soil fertility management.
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