Mixed with Broadleaf Tree Species Improved Soil Aggregate Stability in Chinese Fir (Cunninghamia lanceolata) Plantations: Based on the Le Bissonnais Method

Soil aggregate stability is an integrated parameter related to soil structure, soil quality, and erodibility. Although mixed stands have been proven to improve soil quality and productivity, there is limited knowledge regarding how mixed with broadleaf tree species affects soil aggregate stability in Chinese fir (Cunninghamia lanceolata) plantations in the subtropical region of China. In this study, soil samples were selected at the 0-20 cm and 20-40 cm depths from the three plantations of Chinese fir, including C. lanceolata x Michelia macclurei (stand type I), C. lanceolata x Mytilaria laosensis (stand type II), and pure stand of C. lanceolata (stand type III). The Le Bissonnais method was chosen to determine the soil aggregate stability, which included fast wetting (FW), slow wetting (SW), and wet stirring (WS) disruptive treatments. Our findings showed that compared to pure stand, mixed stands had higher levels of soil chemical properties (including organic carbon (OC), total nitrogen (TN), and free aluminum oxides (Al-d)) and more stable soil structure, especially stand type I. Soil OC and TN contents were significantly positively correlated with soil mean weight diameter (MWD) and geometric mean diameter (GMD) and were significantly negatively correlated with the soil erodibility K values, which are the key indicators reflecting the stability of soil aggregates. The FW treatment simulates the slaking of soil under heavy rains, which caused the greatest damage to the soil aggregate structure, regardless of the stand type. Appropriate development of mixed forests can play a vital role in stabilizing soil structure in Chinese fir plantations, thereby promoting soil resources to be sustainably utilized in the subtropical red soil area in China.

Automated summary

Soil aggregate stability is an important factor for soil structure, quality and erosion. This study focused on how the inclusion of broadleaf tree species affects soil aggregate stability in Chinese fir plantations. The results showed that mixed stands of Chinese fir with broadleaf trees had higher soil chemical properties and more stable soil structure, especially when mixed with Michelia macclurei and Mytilaria laosensis. Soil organic carbon and nitrogen contents were positively correlated with soil aggregate stability, while soil erodibility had a negative correlation.