The Research Of Soil Organic Carbon Sequeatration Under Conservation Tillage In Maize Land

Nowadays the conservation tillage is emphasized as a method of decreasing the emission of CO2 directly. The decomposing rate of soil organic carbon (SOC) can be influenced by changing the soil physical, chemical properties and the inputs of organic matters. The research of soil organic carbon sequestration under conservation tillage is very important to increase the storage of SOC in farmland and mitigate the greenhouse effect and global climate changes. However, there was little research about SOC sequestration under conservation tillage in northern China. Based on the long-term conservation tillage experiment in Shou yang county, Shan xi province, the storage of SOC, soil aggregate and the physical fractions of the SOC in aggregates, and the impact-factors of SOC under conservation tillage were studied to provide the a theoretical basis to understand the process of the accumulation and turnover of the SOC, and choose the better tillage method to increase the SOC in farmland soils. The main results were as follow:(1) The distribution of the content and the storage of the SOC were affected by different tillage treatments, namely all straw return tillage (ASRT), no-till with straw mulching (NTSM), no-till with leaving stubbles (NTLS) and conventional tillage (CT). The content and the storage of the SOC in ASRT and CT treatments were evenly distributed at the depth of 0 to 20cm and decreased from 20 to 100cm, while gradually decreased in NTSM and NTLS treatments from soil surface to deep soil layers. The storage of the SOC under different tillage showed the order:NTSM> NTLS> ASRT>CT. ASRT, NTSM and NTLS treatments increased the content of SOC in the top layer of soil, while compared with CT treatment, the NTSM treatment can significant improve the content and the storage of the SOC, increased by 14.5% and 35.7% respectively.(2) The composition and the quantity of soil water stable aggregates and their organic carbon were affected by different tillage treatments. Compared with CT treatment, ASRT, NTSM and NTLS treatments can improve the quantity of soil water stable aggregates, the content of the aggregate organic carbon and the mean weight diameter. Improvement under NTSM treatment showed more significant than others. There was a significant positive correlation between the quantity of the macro-aggregate and the content of SOC in 0 to20cm soil depth.(3) There were three physical fractions of SOC in aggregate which were free light fraction (LF), intra-aggregate particulate organic matter (iPOM) and mineral associated SOC (mSOC). And the organic carbons of them were LFOC, iPOC and mSOC respectively. The result showed that the highest quantity of LF and iPOM were in 250 to2000μm water stable aggregate and the lowest were in 53 to 250μm water stable aggregate among three aggregate-size classes. The content of LFOC and iPOC showed the same trends. ASRT, NTSM and NTLS treatments improved the quantity of LF and iPOM and the content of LFOC and iPOC in macro-aggregates (>2000μm and250-2000μm), NTSM treatment effect was the most significant There were no significant differences of content of mSOC under the four treatments. The content of SOC was significant positively correlated with the content of LFOC, iPOC and mSOC in 0 to 20cm depth soil. And the contribution rate of the physical organic matter fractions to SOC showed order:LFOC>iPOC>mSOC.(4) Soil temperature, moisture, bulk density, compaction, pH and enzyme activity were the impact-factors of the content of SOC. these impact-factors in 0～10cm soil depth were mainly influenced by different tillage. Compared with CT treatment, soil temperature decreased by 1.6 to 2.0℃, soil moisture increased by 20.2% to 30.6%, soil compaction increased by 98.6% to 194.4%, soil pH decreased by 0.2 to 0.4, and the activities of dehydrogenase, urease,β-glucosidase and alkaline phosphatase increased under NTSM and NTLS treatments. The SOC was significant negatively correlated with soil temperature and compaction, whereas was positively correlated with the activities of dehydrogenase, urease,β-glucosidase and alkaline phosphatase. The soil temperature was negatively correlated with the content of LFOC, iPOC and mSOC.