Soil physical and chemical properties of pure Pinus massoniana and mixed-species tree plantation with different age in south Guangxi area

Six forest stands of 59，34，and 24 years old Pinus massoniana and their mixed forests were selected and 20 m by 20 m plots were set up to analyze the changes of soil nutrients content under different forest stands and forest ages. Soil samples were taken from 0 to 60 cm soil layers. The results showed that soil moisture and the bulk density in the mesophytic forest were higher than those of other forests land. The highest soil porosity value was observed in the early forest land. Soil pH value of different forest ranged from 4.45 to 4.75，indicating the variation was small. It was indicated that the mixed forest was more able to increase the soil fertility than the pure forest because that the trends of soil acidity，organic matter content and total P and K in mixed forests aged 34 and 24 years were higher than those in pure forests of the same year. However，the content of soil available P and K decreased with the increase of soil depth，and varied in terms of forest ages. From the changes of soil parameters in different forest lands，soil nutrients in the 34-year-old P. massoniana forest was superior to that of other forest stands.