Biochar effects on aggregation and carbon-nitrogen retention in different-sized aggregates of clay and loam soils: A meta-analysis

Abstract

Biochar offers environmental benefits, such as enhanced soil aggregation and carbon sequestration. However, its effect on soil aggregation and organic carbon and nitrogen sequestration across soil textures remains unclear. In this systematic review, the results of 534 experiments reported in 100 peer-reviewed articles were analyzed. The results show that biochar addition enhances macroaggregate formation, improves aggregate water stability, and enriches organic carbon and nitrogen in different-sized aggregates compared with un-amended controls. When comparing clay and loam soils to biochar, clay soils respond more effectively to biochar than did loam soils. Specifically, the size distribution of clay aggregates responded to biochar input, whereas the organic carbon within different-sized aggregates of loam soil significantly increased. The benefits of biochar are attributed to the reduction in clay bulk density (−10.9 %) and the increase in microbial biomass carbon (+32.4 %), as well as enhanced organic matter input from plant biomass (+28.3 %) in loam. Long-term experiments (> 3 yr) revealed more macroaggregate-associated organic carbon in both loam and clay soils. Based on the results of this assessment, the optimal application conditions of biochar in loam and clay soils are as follows: in loam soils with initial organic carbon levels of 5–10 g·kg⁻¹, biochar should be applied at a rate of 10–20 t·ha⁻¹ to maximize large macroaggregate formation; in clay soils, an application rate of 20–40 t·ha⁻¹ of biochar is recommended. Overall, biochar improves aggregate stability and carbon and nitrogen contents, with distinct responses in clay and loam soils.