To study the ability of different plantation types to enhance the physical and chemical properties of soil, soil physical and chemical properties at layer depths of 0-80 cm under five typical plantations-Platycladus orientalis plantation, Robinia pseudoacacia plantation, Populus alba var pyramidalis plantation, P. orientalis-R. pseudoacacia mixed plantation, and P. alba var pyramidalis-R. pseudoacacia mixed plantation-were analyzed based on the results of field sampling and laboratory testing. The study revealed that (1) In mixed plantations, the bulk density and the physical properties of the soil, including soil maximum water holding capacity, capillary water holding capacity, field water holding capacity, soil total porosity, capillary porosity, noncapillary porosity, soil water content, and soil penetrability, were clearly better than those in the pure plantations. The pH values in mixed plantations and the P. orientalis plantation were lower than those in the R. pseudoacacia plantation and the P. alba var pyramidalis plantation. In mixed plantations, the soil organic matter, total nitrogen, mineral nitrogen, and total phosphorus contents were significantly greater than those in the pure plantations, whereas there was no significant difference in total potassium and available potassium among the various plantations. (2) The bulk density increased as soil depth increased in the 0-80 cm soil layers, whereas the other soil physical properties soil maximum water holding capacity, capillary water holding capacity, field water holding capacity, soil total porosity, capillary porosity, and noncapillary porosity decreased as the soil depth increased: however, there were no obvious differences in soil water content related to soil depth. The soil chemical properties including soil organic matter, total nitrogen, mineral nitrogen, available phosphorus, and available potassium, all decreased as the soil depth increased, though there were no significant differences in the pH values and soil total phosphorus and total potassium contents with soil depth. (3) Correlation analysis of the physical and chemical properties of the soil revealed significant correlations between soil organic matter and soil nitrogen, mineral nitrogen, total phosphorus, soil maximum water holding capacity, capillary water holding capacity, field water holding capacity, soil total porosity, capillary porosity, and noncapillary porosity, whereas there was significant negative correlation with soil bulk density; There was significant correlation between total nitrogen and soil mineral nitrogen, soil maximum water holding capacity, capillary water holding capacity, field water holding capacity, soil total porosity, capillary porosity, noncapillary porosity, but had significant negative correlation with soil bulk density. There was significant negative correlation between soil bulk density and soil maximum water holding capacity, capillary water holding capacity, field water holding capacity, soil total porosity, capillary porosity, and noncapillary porosity. The findings revealed that mixed plantation improved soil physical and chemical properties to a greater extent than did pure plantation. Therefore, this study implies that mixed plantation should be the main part of plantation management in this area in the future and that managers of pure plantations should considered transforming them into mixed plantations.
