Characterization Of The Potential Of Organic Carbon Sequestration In Typical Arable Soil And Its Environmental Significance

This paper studied water stable aggregates and its organic carbon together with heavy metals distribution in nine typical arable soils from different temperature zones. The corresponding uncultivated soil was studied too. The main conclusions were listed as follows:(1) The dominated aggregates of arable soils are1000-250μm and250-53μm or>2000μm aggregates. Influence of cultivation on soil water stable aggregates content is affected by soil types. The dispersion degree of soil particles was increased due to the cultivation disturbance and the smaller aggregates resisted the water erosion.(2) soil organic carbon content and organic carbon density of swampy soil in Heilongjiang, dark brown soil in Jilin, black soil in Heilongjiang and red soil in Jiangxi was high,while that of brick red soils in Hainan and chestnut soil in Qinghai and brown soil in Shandong was low. The distribution form of soil organic carbon in water stable aggregate varies with soil types and land use patterns, which was constrained by the allocation of aggregates. The distribution form of organic carbon in uncultivated soils was similar with that of arable soils. Influence of cultivation on soil organic carbon is affected by initial content of soil organic carbon and climatic conditions.(3) Fourier transform infrared spectroscopy (FTIR) resolve showed that organic carbon in microaggregates predominately consisted of aromatic and carbohydrate carbon; spectroscopy of brick red soils and red soil belongs to the spectral characteristic of kaolinite,while that of others belongs to the spectral characteristic of montmorillonite. Organic carbon in macroaggregates of cinnamon soil was mainly composed of labile carbon such as aliphatic carbon and carbohydrate carbon, et al. The stable aromatic carbon tend to be protected in microaggregates.(4) Scanning electron microscope (SEM) showed that the morphology of aggregates varies with soil types, the surface was rough and covered with organic matter, while the multilayer structure of microaggregates favored organic carbon storage and adsorption. X-ray diffraction(XRD) showed that, clay minerals of brown soil, cinnamon soil and dark brown soil were dominated by quartz. (5) Cd pollution was serious and that of Zn、Pb、Cu and As was mild of swampy soil in Heilongjiang, dark brown soil in Jilin, black soil in Heilongjiang and red soil in Jiangxi. For metals except for Pb, the distribution pattern among heavy metals in water stable aggregate was similar in the same type soil, but the distribution form for the same metal varies with soil types, which was constrained by the allocation of aggregates. Pb was enriched in<20μm silt-clay microaggregates. Due to the effect of water flow, Cr, Cd and As in black soil was transferred to250-53μm water-stable aggregates, and in the Cr, Cd and As in the swampy soil had little change; Pb in both black soil and swampy soil was transferred to<20μm silt-clay microaggregates.. The transformation difference of heavy metal was related to soil type and fixed combination mechanism of heavy metals on aggregate. In order to reveal the enrichment law of heavy metals, further research is still needed. There was a strong positive correlation relationship between heavy metal elements and Fe in soil aggregates, which was similar between different soil types. While the correlation between heavy metals and organic carbon varied with soil types. Heavy metals in the whole and were positively correlated to organic carbon in black soil and red soil (except for Cd, Pb in black soil and Cr in red soil), while the relationship in swampy soil and dark brown soil was negative. Cr, Ni, Cu and Zn had strong positive correlation with Fe. Pb didn’t have too much relationship with Fe and organic carbon.