Differences in Soil Physicochemical Properties in Different-Aged Pinus massoniana Plantations in Southwest China

With increasing age, plants will cause changes in soil physicochemical properties. The objective of this study was to investigate differences in the soil physicochemical properties in different-aged Masson pine forest plantations (i.e., 10, 20, 40, and 60 years old). Soil samples were collected in a pure Masson pine forest plantation in Southwest China. The soil determination indexes included organic carbon, nitrogen, phosphorus and potassium contents, water content, bulk density, and pH. The soil pH of a 20-year-old forest was significantly (p < 0.05) higher than that of a 10, 40, and 60-year-old forest. In addition, soil-available phosphorus in a 60-year-old forest was significantly (p < 0.05) higher than that in the other three age forest groups. With increasing forest age, available phosphorus increased, while available nitrogen decreased at 20 years old and then increased at 40 years old. There was a significant positive correlation (p < 0.05) between total nitrogen and available potassium; no significant correlation (p> 0.05) between total phosphorus and total potassium, organic carbon, bulk density, and pH; and a significant negative correlation (p < 0.05) between available phosphorus and the water content. The availability and utilization efficiency of soil nutrients in young forests were higher than those in old forests and the intermediate forest age was an important time point that affected the soil properties. To improve the availability of soil nutrients and ensure the sustainable utilization of soil resources, it is necessary to increase the input of nitrogen and especially phosphorus. More attention should be given to the phytochemometric response with respect to the age of plantations.