Influence Factors Of Soil Organic Carbon At Middle Reaches Of Heihe River In Northwest Arid Area

Soil organic carbon pool plays an important role in global carbon cycle.It is necessary to investigate the mechanisms of soil organic carbon and its influence factors.The thesis is discussed the main influence factors of soil organic carbon in Middle reaches of Heihe River,in Arid area of Northwest China.The effects like climate,land use and soil physical and chemical characteristic to soil organic carbon's decaying were observed briefly.The main conclusions are as follow:1.From southeast to northwest,the soil organic carbon decay gradually with the increasing of temperature and the decreasing of precipitation.The deserts are quite affected by the climates.Its organic carbon has distinguished evidently.The organic carbon content of soil profiles have great positive relations with temperatures at P＜0.05,and have great negative relations with precipitation at the same time.The climate factors also affect on the background of farmlands to some degree.The climate factors' influences have reduced while the cultivations have reacted chiefly from southeast to northwest.2.The organic carbon contents of high density grasslands,the middle density grasslands,the dry lands,paddy fields and the deserts have distinctions at P＜0.01. The distinctions between desert and other land uses are evidently.The distinctions between high density grasslands and the dry lands,middle density grasslands and paddy fields are not evidently.3.Soil profile organic carbon distributions gradually decrease with the depth increasing at the depth of 100cm.The organic carbon contents of grasslands are more than farmlands in 40cm depth,and it is reverse under 40cm depth.Just because of the eluviations caused by the cultivations.The organic carbon contents of the deserts are very low.About a half above organic carbon preserved in 40cm soil body.4.The properties of soil show some differences because of different land use.The lawn soil has higher water content,CEC,C/N and the clay content,at the meanwhile, its volume weight and pH are lower.All of these are advantageous to the organic carbon accumulation.Cultivation may increase the input of organic materials. Eluviations may reduce the pH of soil profile in the certain degree,and increase clay depositions of subsoil.But mechanized farming may lead to elevating of soil volume weight,and reduce C/N,which will break the organic carbon stability.The soil profile organic carbon contents are connected remarkably with the moisture content,CEC and volume weight(P＜0.01).The organic carbon contents of topsoil have great negative relations with pH at P＜0.01,and have positive relations with clay at P＜0.05.Under 20cm depth,the relations of organic carbon contents,pH and the clay contents are not remarkable.