The difference of soil properties between pure and mixed Chinese fir (Cunninghamia lanceolata) plantations depends on tree species

Second generation Chinese fir plantation has occurred the problem of site deterioration, which is usually supposed to be solved by mixed plantation. Here, we determined the physicochemical properties of six soil layers in pure and three types of mixed Chinese fir plantation stands (admixed species: Michelia macclurei, Pinus massoniana, and Phyllostachys heterocycla) in southeast China. The Ph. heterocycla is a bamboo. The effects of plantation type and depth on soil properties and variations among different depths were analyzed by two-way ANOVA with Tukey’s test. Non-parametric Wilcoxon rank sum test was used to analyze the soil property differences between pure and mixed plantations. The soil organic matter and alkaline hydrolysis nitrogen of mixture of Chinese fir and Ph. heterocycla were significantly higher than those of other plantation types (p < 0.05). The variations of soil chemical properties in pure plantation were significantly greater than these in mixed plantation. The soil organic matter in 10–20 cm soil layer, alkaline hydrolysis nitrogen in 10–40 cm, total phosphorus in 0–40 cm, available phosphorus and rapidly available potassium in nearly all soil layers were significantly lower in pure plantation than that in mixed plantation. In general, the mixed Chinese fir plantation could improve the soil quality, especially for chemical properties. Further investigations into the effects of mixing proportions of tree species on soil properties are needed to explore the effect of tree species on soil quality.