The Distribution Characteristics Of Content And Morphology Of Organic Carbon In Typical Terraces Of Loess Hilly Region

In order to reveal the content,main forms and sequestration mechanism of soil organic carbon?SOC?,we choice typical terraces?corn,wheat,potato,soybean,apple,vegetable greenhouse et al.?in Gansu Zhuanglang Baozigou watershed and Shanxi Ansai Fangta and Majiagou watersheds as study objects.We measured the content of SOC in five the 1 meter soil depth which divided into five soil layer average,the components of SOC and the distribution of SOC in the aggregate under the 0⁴0cm soil depth,in order to uncover the effects of the planting types on the distribution,storage,speciation and sequestration mechanism of SOC and for the rich of SOC sequestration mechanism and theory of organic carbon turnover and establish a scientific and effective ecological effect of soil and water conservation monitoring and evaluation system to provide date support and theoretical basis in loess area.The mainly conclusions as follows:?1?The range of SOC content in 0¹00cm soil layer was 2.63⁸.36 g·kg^-1in Zhuanglang and 1.31⁵.98 g·kg^-1 in Ansai;The content of SOC were significantly higher in intercropping,apple,potato than that of in corn,wheat?P<0.05?,the SOC average content in the soil of terrace was higher than that of slope farmland in every layers of 0⁶0 cm soil;the content of SOC were significantly higher in intercropping and corn than that of in abandoned land,apple and potato.The content of SOC in the soil layer of 0¹00cm showed an obvious hierarchy,the 0⁴0 cm soil layer SOC decreased significantly but in 40 ¹00 cm did not change much.?2?The carbon storage capacity in 1m soil depth in Zhuanglang was 1.02×106 t,3.5×105t in Majiagou,1.53×105 t in Fangta.The distribution of SOC storage showed the same tendency as the distribution of SOC content and the differences were more significant: in Zhuanglang,still remained in apple and intercropping were significantly higher than corn and wheat but in Ansai,it was in corn and intercropping were significantly higher than other planting types.As a whole,the differences among different soil layers of the proportion of SOC storage were significantly.There were effects of planting types on the stability of SOC distribution in 0¹00 cm soil layer.These years,the content of SOC in terrace soil has been imporved which owed to the prioritize of apple orchard in the Loess Plateau.There were highly significantly and significantly positive correlations between the content of SOC andsoil water content.?3?The main soil aggregate compose in was > 5 mm and accounted for the total aggregate 35.11% and 42.75% in 0²0 cm and 20⁴0 cm respectively in Zhuanglang,54.29% and 47.54% in 0²0 cm and 20⁴0 cm respectively in Ansai.The differences of the rate of contribution of macro aggregate among different planting types were significantly,planting fruiter would improve the content of macro aggregate,improve the stability of aggregate and perfect the soil soil quality.The SOC content in 0.5⁰.25 mm aggregate was the biggest and the content of SOC were increased with the decreased of particle size.The contents of SOC in 0.5¹ mm and 0.5⁰.25 mm were higher than other aggregate sizes and showed the?type distribution.The effects of planting types on the proportion of the SOC content in soil aggregate were obviously in > 5 mm macro aggregate <0.25 mm micro aggregate,the 0.25⁵ mm was relatively stable.?4?As a whole,the content of MBC showed the trend of wheat,corn,potatoes,corn and abandoned land significantly higher than intercropping and corn?P<0.05?.The content of MBC in Zhuanglang terrace was higher than Ansai terrace but the content of DOC was on the contrary.The distribution of DOC among different planting types was different with the distribution of DOC.The contents of DOC in apple and intercropping were higher than other planting types.The contents of MBC and DOC were decreased with the increased of soil layer.?5?The planting types had effects on the distribution of humic acid.The content of humic acid in corn soil was significantly higher than potato soil in Zhuanglang,in corn soil it was significantly higher than abandoned land,soybean and greenhouse in Majiagou,Ansai.The effect of soil layer on the distribution of humic acid was not obviously.The content of humic acid in Zhuanglang terrace soil was significantly higher than Ansai and it was higher in corn soil than other planting types.The content of humin carbon accounted for the vast majority of humus carbon.