Effects of Biochar and Manure Co-Application on Aggregate Stability and Pore Size Distribution of Vertisols

Background: The combination of biochar and organic manure has substantial local impacts on soil properties, greenhouse gas emissions, and crop yield. However, the research on soil health or quality is still in its early stages. Four pot experiments were carried out: C (30 g biochar (kg soil)(−1)), M (10 g manure (kg soil)(−1)), CM (15 g biochar (kg soil)(−1) + 5 g manure (kg soil)(−1)), and the control (without any amendments). Results: When compared to C and M treatments, the MWD of CM was reduced by 5.5% and increased by 4.9%, respectively, and the micropore volume (5–30 m) was increased by 17.6% and 89.6%. The structural equation model shows that soil structural parameters and physical properties regulate the distribution of micropores (5–30 μm) in amended soil. Conclusion: Our studies discovered that biochar mixed with poultry manure had antagonistic and synergistic effects on soil aggregate stability and micropore volume in vertisol, respectively, and thus enhanced crop yield by 71.1%, which might be used as a technological model for farmers in China’s Huang-Huai-Hai region to improve low- and medium-yielding soil and maintain soil health.