Long-period management and cultivation of Cunninghamia lanceolata large-diameter timber is a new technology and mode of cultivation of C. lanceolata forests. This study aims to investigate the changes of soil physicochemical properties and soil enzyme activities with the age of long-period C. lanceolata forests, so as to provide a theoretical basis for the long-period sustainable management of C. lanceolata as well as the cultivation of large-diameter timber.

Soil physicochemical properties (density, water content, pH, organic matter, TN, TP, TK, Ca and Mg content) and soil enzyme activities (CAT, UE, SC and S-ACP) were analysed in the 0-20, 20-40 and 40-60 cm layers of the C. lanceolata plantation in Lanshan county, Yongzhou city, Hunan province, China, using different forest ages of C. lanceolata plantation forests (30 a and 40 a) as the study object.

1) As the age of C. lanceolata plantation forests increased, the soil bulk density and water content decreased, while the soil organic matter, TN, TP, TK and Ca content increased, and the organic matter, TN, TP, TK and Ca content of 40-year-old C. lanceolata soils were significantly higher than that of 30-year-old C. lanceolata soils in the layer of 0-40 cm. Between 30 and 40 years, soil structure improved and soil nutrients accumulated more than they were consumed. 2) Soil bulk weight increased with the depth of the soil layer in the C. lanceolata plantation forest; water content, organic matter, TN, TP, TK, Ca and Mg content decreased with the depth of the soil layer. 3) Soil CAT, UE, and S-ACP activities showed a decreasing trend with increasing age of C. lanceolata plantation forests, whereas S-ACP activities showed an overall increasing trend; soil CAT, UE, SC, and S-ACP activities in C. lanceolata forests of the same age decreased significantly with increasing depth of the soil layer, and the enzyme activities differed significantly between soil layers.

As C. lanceolata plantation forests age, soil structure improves, soil enzyme activity decreases, and soil nutrients gradually accumulate and increase their content, resulting in the maintenance and improvement of soil fertility.