Impacts of adding biochar on nitrogen retention and bioavailability in agricultural soil

Interest in the use of biochar to improve soil productivity has rapidly increased. Nitrogen (N) loss, retention and bioavailability in biochar-amended soils fertilized with NH4+–N and NO3−–N were studied using leaching and pot experiments. NO3−–N leaching from the soils fertilized with NH4+–N and NO3−–N was significantly reduced by biochar addition. NH4+–N leaching from the NO3−–N fertilized soil was also significantly reduced by biochar, while no significant effect was observed for the NH4+–N fertilized soil. Also lower NH4+–N and NO3−–N were leached from NO3−–N fertilized soil with maize (Zea mays L.) grown. Mitigation of N leaching loss following biochar addition is mainly attributed to the increase in soil water holding capacity (WHC), NH4+ adsorption and enhanced N immobilization. Biochar addition stimulated maize growth, both above and below ground. Biochar also increased N utilization efficiency (NUE) of maize but decreased N accumulation efficiency (NAE), indicating that biochar addition may improve N bioavailability in agricultural soils. Therefore, reduction of N leaching, and increase of N retention and bioavailability in agricultural soils can potentially decrease the N fertilizer demand for crop growth. •Biochar reduced NO3−–N and/or NH4+–N leaching from soils.•Biochar addition improved maize growth including biomass and root morphology.•Biochar increased N utilization efficiency, but reduced N accumulation efficiency.•Biochar could increase N retention and bioavailability in agricultural soils.