Characteristics Of Soil Organic Carbon And Its Active Components In Different Land Use Type

The parallel mountain ridge and valley of east Sichuan is vast with a large population. Parallel mountain ridge and valley mainly focuses on traditional agriculture. In recent years, the land use type of agricultural land in the region witnesses a number of changes with the steady progress of agricultural structure adjustment, which thus leads to a major change of soil carbon pool in the soil. Therefore, it is quite necessary to probe into the change characteristics of the contents of soil organic carbon and its active components under the condition of different agricultural land use types. Through field investigations, soil sampling and indoor test analysis and with the support of SPSS 17.0 software platform, the paper analyzes the change characteristics of total organic carbon (TOC), dissolved organic carbon (DOC), readily oxidized organic carbon (ROC) and microbial biomass carbon (MBC) in the case of vegetable plots, orchards, paddy fields and dry fields in the region, the change features of allocation proportion of active components and the correlation of the physical and chemical properties of soil. The research results are as follows:(1) The particles in Four types of land use soil are component mainly of silt and clay, the soil pH is weakly alkaline, the value of pH is 7.24～7.89. Soil total nitrogen content is between 0.43-1.06g/kg, In each soil layer showed a characteristic that paddy fields> orchards> vegetable plots> dry fields, The content of soil available nitrogen in surface showed a characteristic that paddy fields(73.11mg/kg)>orchards (53.77mg/kg)> vegetable plots(52.29mg/kg)>dry fields(46.41mg/kg) (P<0.01).The content of soil total phosphorus is between 0.54～0.87g/kg, The highest content of surface is vegetable plots for 0.84g/kg,the paddy fields was the lowest for 0.71g/kg (P<0.05), The content of soil available phosphorus in surface showed a characteristic that vegetable plots(22.43mg/kg) >orchards (14.71mg/kg)>paddy fields(10.89mg/kg)>dry fields(7.53mg/kg) (P<0.01). The content of soil total potassium showed a characteristic that orchards> vegetable plots >dry fields> paddy fields, The lowest content of soil total potassium was the paddy fields for 15.66g/kg lower than other land use types significantly(P<0.05),The content of soil available potassium in surface showed a characteristic that vegetable plots(116.98mg/kg) >dry fields(104.95mg/kg)>orchards (102.00mg/kg)>paddy fields(82.18mg/kg) (P<0.05).(2)In the soil layer from 0 to 20cm, the contents of TOC in the soil are characterized by the change from more to less, namely paddy fields (18.00g/kg), orchards (15.49g/kg), vegetable plots (9.43g/kg) and dry fields (7.57g/kg) respectively and content differences reach a remarkably significant level (P<0.01). In the vertical distribution of the content of TOC, the contents of TOC in the soil all take on the characteristic of decreasing with the increase of soil depth according to four land use types.(3)In the soil layer from 0 to 20cm, the contents of DOC in the soil are characterized by the change from more to less, namely paddy fields, orchards and dry fields respectively and its differences reach a significant level (P<0.01). The contents of DOC in paddy fields (53.45mg/kg) and orchards (52.21mg/kg) are remarkably higher than that of vegetable plots (31.88mg/kg) and dry fields (24.38mg/kg). In the vertical section, the contents of DOC in the soil all take on the characteristic of decreasing with the increase of soil depth. The allocation proportion of DOC varies from 0.28% to 0.47% and takes on the characteristic of the change in various layers from more to less, namely vegetable plots, orchards, paddy fields and dry fields respectively. The allocation proportion of DOC in the soil of vegetable plots is obviously higher than that of other three land use types. The difference between paddy fields and dry fields is not remarkable. In the case of different land use types, the allocation proportion of DOC takes on the trend of increasing with the increase of soil depth.(4)In the soil layer from 0 to 20cm, the contents of ROC in the soil are characterized by the change from more to less, namely orchards (4.63g/kg), paddy fields (3.78g/kg), vegetable plots (2.90g/kg) and dry fields (2.25g/kg) respectively and its differences reach a remarkably significant level (P<0.01). The content of ROC in the soil of orchards is markedly higher than that of vegetable plots and dry fields. In the vertical section, the contents of ROC in the soil take on the characteristic of decreasing with the increase of soil depth. The allocation proportion of ROC is between 13.97% and 31.33% which is considerably higher than that of the active organic carbon of other components. In the soil layer from 0 to 20cm, the allocation proportion of ROC in the soil in the case of four land use types is characterized by the change from more to less, namely vegetable plots (31.33%), dry fields (30.05%), orchards (30.01%) and paddy fields (21.63%) respectively and its differences reach a notably significant level (P<0.01).(5)In the soil layer from 0 to 20cm, the contents of MBC in the soil take on the characteristic of the change from more to less, namely orchards (440.78mg/kg), paddy fields (414.86mg/kg), vegetable plots (291.42mg/kg) and dry fields (183.60mg/kg) respectively and its content differences do not reach a markedly significant level (P<0.01). In the vertical section, the contents of MBC in the soil take on the characteristic of decreasing with the increase of soil depth. The allocation proportion of MBC varies from 1.51% to 3.14%. In the soil layer from 0 to 20cm, the allocation proportion of MBC takes on the characteristic of the change from more to less, namely vegetable plots (3.14%), orchards (2.86%), paddy fields (2.37%) and dry fields (2.45%) respectively and its differences reach a significant level (P<0.05).(6)Among different land use types, the correlation among DOC, ROC, MBC and TOC has reached a markedly significant level. Among vegetable plots, orchards and paddy fields, a significantly positive correlation can be found in TOC and ROC, DOC and MBC, ROC and MBC. However, TOC and ROC, TOC and DOC in paddy fields do not reach the level of significant correlation. The correlation among other components is not significant. A significantly positive correlation can be seen between soil clay content and TOC in the soil. A positive correlation can be noticed between soil silt content and TOC. A significantly negative correlation can be found between soil sand content and TOC. TOC in the soil is positively related to total nitrogen (TN), alkali hydrolysable nitrogen (AN), available phosphorus (AP) and available potassium (AK) and is not significantly related to pH, total phosphorus (TP) and total potassium (TK).