Variation of Contents of Organic Carbon and Physic-chemical Properties of Soil and Path Analysis for Their Relations in Different Age-group Chinese Fir Plantations

Organic carbon and physic-chemical properties of soil at different depths(15,30,45,60cm)in Chinese fir plantations in Fushou forest farm of Hunan Province were analyzed for the variation characteristics of organic carbon content and physic-chemical properties of soil in three age-group Chinese fir plantations,and their relations were studied through path analysis.Results showed that the contents of soil organic carbon(SOC)declined along with the increase of soil depths in three forest soil.The contents of SOC of juvenile,medium and mature in 0-15 cm soil layer was 2.0,2.2 and 2.2 times as much as those in 15-30 cm,4.0,3.6 and 3.2 times as much as those in 30-45 cm and 6.1,3.9 and 3.6 times as much as those in 45-60 cm,respectively.The coefficient variation of SOC contents among different soil layer was more than 65% in each forest soil and that of juvenile was highest.And there was a significant difference of SOC contents in between 0-15 cm layer and other layers whose depth was more than 15 cm in same forest soil(P0.05).Changes of SOC contents varied in the order of maturejuvenilemedium in 0-45 cm soil layer with increasing age of Chinese fir plantations.Significant variation characteristics of SOC contents among different forest soil were found in each soil layer.The coefficient variation of SOC contents in 45-60 cm was highest(57.67%),but lowest(25.42%)in 0-15 cm and varied in the order of 45-60cm30-45cm15-30cm0-15 cm,but significant difference of SOC contents among forest soil in each soil layer was not found(P0.05).With the increasing depths of soil,the contents of total nitrogen(N)and total phosphorous(P)declined along with increasing soil depths in three forest soil.However,soil bulk density and soil N and P contents had opposite variation trend,and soil pH value and total potassium(K)had no regular variation.With increasing age of Chinese fir plantations,content of N,P and K of soil showed higher value in juvenile,a minimum in medium and significant increased in mature.Soil bulk density increased first and then decreased,soil pH value was higher in juvenile,then decreased in medium,and remained stable or decreased slightly.Results showed that the contents of N,P and C/N were leading factors influencing SOC content variation by path analysis between soil organic carbon content and soil physic-chemical properties,but their influence mechanism were different.