Interactive Effects of Honeysuckle Planting and Biochar Amendment on Soil Structure and Hydraulic Properties of Hillslope Farmland

Plant roots and biochar amendment cause changes in soil structure and hydraulic properties; however, their interactive influences are still inadequately understood. A six-year field study was conducted on hillslope farmland in the Sichuan basin, China, to evaluate how honeysuckle planting and biochar application affect soil structure and hydraulic properties. Various parameters related to soil structure (soil organic matter (SOM), soil aggregate stability, bulk density were obtained in the laboratory) and hydraulic (hydraulic conductivity, and soil water retention characteristics by single porosity of van Genuchten 1980 and dual porosity bi-exponential model) properties were determined. The results showed that honeysuckle planting alone increased (SOM) content, honeysuckle planting following biochar amendment could not only enhance SOM content to a greater magnitude in top 20 cm soil but also markedly increase the SOM content in deeper soil layers (20–30 and 30–40 cm), while the application of biochar alone enhanced the SOM content in top 20 cm soil. The combination of honeysuckle planting and biochar amendment could increase soil aggregate stability. Furthermore, It was found that soil pores with size r > 125 µm were the dominant macropores in all treatments. Honeysuckle planting increased saturated soil hydraulic conductivity (Kₛ) significantly (p < 0.05). Biochar amendment also significantly increased Kₛ directly or indirectly through enhancement of SOM content. Results also showed that honeysuckle planting and biochar amendment could lead to a greater increase in saturated soil water content than saturated soil hydraulic conductivity. However, SOM showed lower value in bare land plots suggesting that both honeysuckle planting and biochar could increase SOM in soil, hence improving soil quality. Therefore, our field study demonstrated that the practice of honeysuckle planting and biochar amendment jointly in sloping farmland of purple soil could effectively strengthen soil structure and improve soil water retention.