The Characteristics Of Soil Physical And Chemical Properties Of Pinus Massoniana Plantations At Different Age Stages In Southern Sichuan Province

Pinus massoniana plantation is the main plantation tree species in south China, in recent years, due to the lack of scientific theoretical guidance and practical sustainable management technology, too much emphasis on short-term productivity and economic interests, but don’t respect soil nutrient supply capacity and its own growth and development of pinus massoniana plantation at different age stages, result in the consequences of plantation area though expanding quickly, however, quality significantly decreased. Nowdays there are many plantation problems such as soil fertility declines, biodiversity declines,etc.In this paper, by using the method of spatial sequence instead of time successional sequence, seven different plantation ages (3 years,5 years,8 years,14 years,31 years,37 years,40 years) pinus massoniana plantations in central and southern regions of yibin city of sichuan province, were selected for studying on the soil physical properties and chemical properties, through the significant difference of the physical and chemical properties as the basis of forest age and soil depth to reveal soil nutrient status of pinus massoniana in southern Sichuan Province, and provide theoretical basis for scientific management of soil nutrient resources.The main results were as follows:(1) In the same soil layer, the basic rule of the soil physical properties of pinus massoniana plantations at different ages shows that:with the growth of pinus massoniana plantation age, significant difference was found in the soil bulk density, and there showed a upside down "N" type growth rule with the growth of forest age;With the growth of pinus massoniana plantation age, significant difference was found in the soil porosity, and there showed a erected "N" type growth rule with the growth of forest age; With the growth of pinus massoniana plantation age, significant difference was found in the soil moisture percentage, and there showed a "W" type growth rule with the growth of forest age. However, with the increase of soil depth, significant difference was found in soil physical properties, and the soil bulk density increased, the soil porosity and the soil moisture percentage decreased.(2) In the same soil layer, the basic rule of the soil chemical properties of pinus massoniana plantations at different ages showed that:significant difference was found of the content of soil organic matter, total nitrogen, available nitrogen, total phosphorus, available phosphorus, total potassium and available kalium with the growth of forest age. Among them, the rule was consistent of the content of soil organic matter, total nitrogen, available nitrogen, and available kalium with the growth of forest age, all showed a erected "N" type growth rule, that was from 3 year to 8 year, the content increased with the growth of forest age, from 8 year to 31 year, the content reduced with the growth of forest age, from 31 year to 40 year, the content increased with the growth of forest age again;The content of total phosphorus and available phosphorus with the growth of forest age showed a trend of "W" type growth rule, from 3year to 5 year, the content decreased with the growth of forest age, from 5year to 8 year, the content increased with the growth of forest age, from 8 year to 31 year, the content decreased with the growth of forest age again; from 31 year to 40 year, the content increased with the growth of forest age once again;The content of total potassium with the growth of forest age also showed a trend of "W" type, but there was slightly different with the total phosphorus and available phosphorus wave stage, that was, from 3year to 5 year, the content decreased with the growth of forest age; from 5 year to 8 year, the content increased with the growth of forest age, from8 year to 14 year, the content decreased with the growth of forest age again; from14 year to 40 year, the content increased with the growth of forest age once again.With the increase of soil depth, except total potassium content was increased gradually, and other nutrients were gradually reduced, and significant difference was showed basically in soil nutrient content of the same age stages but different soil layer.At the same time, analysis the correlation among soil nutrients showed that, except total potassium and soil PH value, there was significant positive correlation basically among other nutrients.(3) The sample area soil PH value of pinus massoniana plantations at different ages between 3.96～4.51, the overall trend was acid, wavy, but with the growth of the forest age or the increase of soil depth, soil PH value had no obvious change rule, so this study considered that, although soil PH value will affect the effectiveness of the soil nutrient, there was no obvious correlation among soil nutrients.(4) According to the soil physical and chemical properties changing with the forest age and soil depth, analysising its reason, mainly related to the following reasons:the pinus massoniana forest soil background value before pinus massoniana plantations at different ages were planted, young forest grow fast and nutrient demand big but forest litter content high, the interference of middle people pick up litter seriously, late mature forest grow with decreased nutrient demand, soil nutrient with the characteristics of the surface.