Spatial Patterns And Controlling Factors Of Soil Organic Carbon (SOC) In A Tributary Catchment Of The Nanka River Basin Across The China-mvanmar Border

Soil organic carbon(SOC)plays an important role in global terrestrial ecosystem carbon cycling.However,the relationships between land-use and SOC stocks remain unambiguous and poorly quantified,especially in extremely complex mountainous terrain.This paper addressed to investigate the correlations between SOC stocks and multiple confounding factors(e.g.soil properties,topography and land-use type)in a tribute catchment located in the low-latitude hot and humid valleys across the China-Myanmar border.We used a grid sampling method to locate 73 sampling points,where 219 soil samples were collected at three sampling intervals along the 60cm-depth soil profiles for each sampling point.After air drying and sieving through 2mm mesh and 200-mesh,physical and chemical properties such as soil pH,soil organic matter(SOM)content,total nitrogen content and alkali-hydrolyzable nitrogen(K-N)content,and soil particle-size composition(mechanical composition)were measured in laboratory.Soil organic carbon(SOC)stocks were estimated in the mineral soil up to 60cm depth by the Pedological professional knowledge-based method.Spatial pattern of soil organic carbon(SOC)across the study area was simulated by the Kriging interpolation method.The relationship between environmental factors and soil organic carbon(SOC)was analyzed using Pearson correlation analysis.Variables associated with topography such as elevation,slope and aspect were extracted from the local topographic map with a contour interval of 20m.The results highlighted the importance of environmental conditions such as soil properties and topography rather than land-use types on soil organic carbon(SOC)stocks.(1).The soil organic carbon(SOC)was strongly correlated with soil bulk density(R2=0.42,P<0.01),total nitrogen content(R2=0.45,P<0.01)and topographical variables such as elevation,slope and aspect(P<0.05).(2).Higher soil organic carbon(SOC)mainly occurred in the areas with a slope range of 15°-25° and in sunny slopes.SOC increased with elevation at lower elevations and decreased with elevation at higher elevations.(3).Vertically,topsoil had higher soil organic carbon(SOC)stocks,which accounted for 43%of the total soil organic carbon(SOC)stocks in the whole examined soil layer up to 60cm depth.However,proportion of soil organic carbon(SOC)stocks in topsoil horizons differentiated among land use types.Secondary forests had higher values than planted forests and rain-fed farmlands.Overall,topography has a predominant impact on the horizontal distribution of SOC in the areas of mountainous terrain,whereas land use/cover types were the major determinant of the vertical distribution of SOC.To precisely evualate and simulate the SOC losses caused by land use/cover change,it is therefore necessary to consider the topographical controls of the horizontal distribution of SOC and the effects of land management on the vertical distribution of SOC.This finding presented here can enhance our understanding of the SOC consequence of land use/cover change.