Abstract:

In the Three Gorges Reservoir areas,the typical forest types were selected to study the soil organic carbon (SOC) and its effects on soil physical properties, soil structure,and soil nutrients,which will benefit the ecoenvironment protection.The forest soil samples were collected according to soil genetic horizons.The content of SOC in A horizon(12.06～45.18 g/kg) was obviously larger than that in the lower horizons,over one quantitative grade.The content of SOC from top soil layer to bottom layer descended quickly.The arable land was reconstructed from shrub forest.Though the arable land has the same site with shrub forest,the content of SOC was less than that in shrub forest land after eight years cropping management.The content of SOC in A horizon in arable land decreased 10% compared to shrub forest soil,and the average content of SOC only accounted for 66% of shrub forest soil.The content of SOC had the direct effects on soil physical properties. There were obvious positive linear correlation between content of SOC and soil density and soil capillary porosity〖WTBX〗(R2=0.83,0.83,n=19，p<0.01)〖WTBZ〗.SOC also promote the soil aggregation.The content of SOC positively related to soil aggregation degree and aggregation 〖WTBX〗(R2=0.62,0.76，n=19，p<0.01)〖WTBZ〗.The content of N element was the highest in forest soil in the study area.The content of effective N was six times as large as content of effective P,and 2.5 times of effective K.In soil nutrient elements of N,P,K,the content of SOC had significant relationship with content of N,especially with effective N〖WTBX〗(R2=0.66,n=19，p<0.01)〖WTBZ〗,but not obvious with contents of P and K.The SOC played the dominant role in the N and P mineralization.From top layer to bottom layer,the C/N also descended.The C/P was about six times as great as C/N.Cation exchange capacity (CEC) was closely related to soil aggregation degree(〖WTBX〗R2=0.49,n=19，p<0.01〖WTBZ〗),which means the effect of SOC on CED was practiced by improving soil structure.