Biochar rate-dependent regulation of extended nitrogen supply by modifying stable aggregates-N and microbial responses
Muhammed Mustapha Ibrahim, Zhaofeng Chang, Zhimin Li, Jerry Joseph, Ado Adamu Yusuf, Xianzhen Luo, Enqing Hou
Abstract
Abstract Besides carbon sequestration, biochar amendment in soils can regulate the loss of applied fertilizer-nitrogen (N) into the environment. Soil aggregates are essential in controlling soil N stocks' stabilization and supply. However, unraveling the rate-dependent impact of biochar on stable soil aggregates and their associated N in fertilized soils over an extended period is a prerequisite to understanding its implications on soil-N dynamics. We unraveled how high and low biochar application rates combined with inorganic fertilizer (20- and 40-tons ha −1 [FB1 and FB2]) affected soil N fractions, stable soil aggregates, aggregates associated-N, and microbial responses to regulate N supply for Nageia nagi after one year. Results revealed that biochar amendment, especially at higher rate, increased the concentration of inorganic N and some amino acids compared to sole fertilizer (F). Available N increased by 16.5% ( p = 0.057), 23.8% ( p = 0.033), and 34.8% ( p = 0.028) in F, FB1, and FB2, respectively, compared to the control (C). Also, 28.1% and 32.8% significant increases in the availability of NH 4 + -N were recorded in FB1 and FB2, respectively, compared to F. NO 3 − -N availability was significantly increased by 15.2%, 21.8%, and 20.8% in FB1, FB2, and C, compared to F. Biochar amendment, irrespective of rate, increased stable microaggregates (< 0.25 mm). However, FB2 significantly increased macro- and intermediate-aggregate-N, and urease activity, and hence higher N supply capacity to meet the N need of N. nagi even after one year. Hence, the N content of N. nagi was 41.3%, 28.8%, and 12.2% higher in FB2, FB1, and F, respectively, compared to the control. Biochar amendment decreased bacterial species diversity but increased the proportion of NH 4 + -oxidizers (especially the Betaproteobacteria) to maintain the mineralization and slow release of N. Although a low biochar rate was more beneficial than sole fertilization, higher biochar application rate could sustain higher N supply by stabilizing soil microaggregates and increasing macro- and intermediate-aggregates N, its mineralization, and slow-release over longer periods.