This study focused on the soil nutrient characteristics of the mixed forest of Cunninghamia lanceolata/Sassafras tzumu with Chimonobambusa quadrangularis planted under the canopy in the state-owned forest farm of Junlian County, Sichuan Province. By comparing the soil nutrient features of the mixed forests of Cunninghamia lanceolata + Chimonobambusa quadrangularis and Sassafras tzumu+Chimonobambusa quadrangularis with those of the pure forests of Cunninghamia lanceolata, Sassafras tzumu and Chimonobambusa quadrangularis, the study aimed to explore the effect of forest and bamboo compound management on soil nutrients, and to provide a scientific basis for improving soil quality and efficiency in the hilly areas of southern Sichuan.

By analyzing and determining the soil chemical properties of the compound forest stands of Cunninghamia lanceolata + Chimonobambusa quadrangularis, Sassafras tzumu + Chimonobambusa quadrangularis, the pure forest stands of Cunninghamia lanceolata, Sassafras tzumu and Chimonobambusa quadrangularis, using the Nemerow method for comprehensive evaluation of soil, the influence of mixed management on forest soil was explored.

1) The mixed management significantly increased soil nutrient content. In terms of basic nutrients, the soil organic matter content of the mixed forests of Cunninghamia lanceolata+Chimonobambusa quadrangularis and Sassafras tzumu+Chimonobambusa quadrangularis was 77.20±3.07 g/kg and 82.57±16.43 g/kg, respectively, which was 43.1% and 14.4% higher than that of the pure forests of Cunninghamia lanceolata (53.97±6.08 g/kg) and Sassafras tzumu (72.17±7.40 g/kg); 2) In terms of available nutrients, the contents of water-soluble nitrogen, available phosphorus and available potassium in the mixed forest of Sassafras tzumu+Chimonobambusa quadrangularis were 268.00 ± 43.21 mg/kg, 3.42 ± 1.16 mg/kg and 145.67 ± 20.67 mg/kg, respectively, which were 16.0%, 10.7% and 20.7% higher than those of the pure forest of Sassafras tzumu; 3) The comprehensive evaluation of soil showed that the Nemerow comprehensive index of the mixed forest of Sassafras tzumu+Chimonobambusa quadrangularis was 1.46, and the forest soil nutrient grade was improved from medium to good.

The mixed management of forest and bamboo effectively improved the soil nutrient status through the ecological complementary effect among speciess compared with pure forest management. Among them, the compound forest of Sassafras tzumu+Chimonobambusa quadrangularis performed best in increasing soil organic matter content, promoting the accumulation of nitrogen, phosphorus and potassium nutrients and improving the proportion of available nutrients. The research results not only enriched the soil ecological theory of forest-bamboo mixed management, but also provided practical references for the ecological restoration and sustainable management of degraded forest land in the hilly areas of southern Sichuan.