Aggregates Distribution Of Typical Soil In Eastern Hunan Province And Analysis Of Influencing Factors On Their Stability

Soil structure is composed of solid,liquid and vapor phases.Soil aggregates,as the basic unit of soil structure,directly affect the physical properties of soil,indirectly control the physical,chemical and biological processes of soil,and control the conservation and movement of water,fertilizer,gas and heat in soil.Good aggregate structure can effectively improve soil fertility.Red soils in southern China suffer from strong weathering and leaching.Soils are rich in iron and aluminium oxides.The main cementing materials are soil organic carbon and iron and aluminium oxides.Studies on the cementing mechanism have been reported,but the existing studies mostly analyze the formation and stability of red soils by single factor,while the multi-factor studies are relatively few.Therefore,more theoretical support is needed to determine whether organic carbon and iron-aluminum oxides,the main cementing materials of soil aggregates,will change under the influence of multiple factors.In this paper,the typical natural woodland,paddy field and dry land developed on three kinds of soil-forming parent materials of Quaternary laterite,granite weathering and slate weathering in eastern Hunan are selected,and the surface and bottom soils are collected separately.The effects of soil-forming parent materials,utilization modes and soil location on the stability of aggregates are discussed,and the related cementing materials are determined and the cementing mechanism is analyzed,so as to further explore China.Formation theory,stabilization mechanism and main controlling factors of soil aggregates in South China.In order to provide a theoretical basis for the improvement of soil structure,fertility cultivation,ecological function restoration and sustainable development of agriculture in the region.The main results are as follows:(1)In the typical soils of Eastern Hunan,the aggregates mainly consist of large aggregates(>2mm),accounting for 66.6% on average,of which the coarse aggregates(>2mm)are 23.6% and the fine aggregates(2-0.25mm)are 43.2%.The coefficient of variation of coarse aggregates is the largest(97.2%)among all grain classes,which indicates that they are the most unstable and vulnerable to the influence of parent material,utilization mode and soil location.The average weight diameter of soil aggregates under differentutilization modes is generally paddy field > woodland > dry land,but the influence of utilization modes on the stability of soil aggregates is limited to surface soil,and its influence on bottom soil is relatively limited.In addition,the average weight diameter of soil aggregates among three utilization modes is significantly different in soils with relatively clay Quaternary laterite.In soils with different parent materials,the average weight diameter of aggregates shows that the texture of aggregates is more sticky and the stability of aggregates is stronger.However,there is no significant difference among the three parent materials in surface soils due to the influence of soil layers.However,the influence of parent materials on the average weight diameter of aggregates is weakened in Dryland or woodland with abundant organic matter,which is characterized by long-term stagnation of water and alternation of dry and wet.Paddy field will obviously strengthen the influence of parent material on the average weight and diameter of aggregates.The average weight diameter of soil aggregates in different soil layers was surface layer > bottom layer,but there was no significant difference in the clayey Quaternary laterite soils.(2)Distribution characteristics of factors affecting the stability of typical soil aggregates in eastern Hunan are as follows: under different parent materials,utilization modes and soil layers,soil physical and chemical properties are different.Organic matter in surface soil is higher than that in bottom soil,and clay content in soil is Quaternary.The soil developed from laterite is the most sticky,and the soil developed from granite weathering is the most sandy.In the soils with different parent materials,the content of free iron oxide is generally as follows: slate weathering > Quaternary laterite > granite weathering,and it is not affected by the way of utilization and the location of soil layer.Amorphous iron oxide content of the three parent materials had no significant difference,but affected by the utilization mode,the soil developed in Quaternary laterite was 84.62% and 106.25% higher than that developed in slate weathered soil in woodlands with higher organic matter and soils with more frequent human disturbance.The content of organic matter will increase with the increase of soil clay,and is restricted by the way of utilization and the location of soil layer.There was no significant difference in the content of free iron oxide among the three utilization modes,and it was not affected by the location of soil layer,but only by the texture.The content of amorphous iron oxide in paddy field > dry land > woodland was 59.62% higher than that in dry land.The content of amorphous iron oxide in paddy field in surface soil increased by123.91% compared with that in woodland due to the control of parent material and soil layer.Land use pattern had no obvious effect on the content of soil organic matter,the limitation of soil layer was lower,and the influence of parent material was greater.The content of organic matter in paddy field in Quaternary laterite soil was higher than that in dry land and woodland,and increased by 180.25% and 109.93%.Under different soil layers,the content of free iron oxide in the surface layer is lower than that in the bottom layer,but there is no significant difference between them in the soil developed in Quaternary laterite;due to the interference of external human factors,there is no significant difference in the content of amorphous iron oxide between the surface layer and the bottom layer of dry land and woodland;and because of the high organic matter of paddy field utilization mode,the content of amorphous iron oxide in the surface layer and the bottom layer of soil is higher.The content of amorphous iron oxide in paddy field surface soil is abnormally high due to the frequent alternation of wetting and drying.The content of organic matter in the surface layer was higher than that in the bottom layer.Then,through correlation analysis,it is concluded that the main controlling factor affecting aggregates is soil organic matter.(3)The distribution of organic carbon components in Typical Soils in eastern Hunan is mineral-bound organic carbon > Free coarse-grained organic carbon > fine-grained organic carbon in micro-aggregates > Free fine-grained organic carbon.The inert carbon pool is 9.10g/kg,the active carbon pool is 3.75 g/kg,and the inert carbon pool is significantly higher than the active carbon pool.The distribution and proportion of soil organic carbon components in different parent materials,utilization modes and soil layers have different characteristics,but the regularity is not obvious.The correlation analysis showed that the content of organic carbon components was positively correlated with the stability of aggregates,especially mineral-bound organic carbon,and the proportion of organic carbon components had no significant correlation with the stability of aggregates.In general,inert organic carbon is the main factor controlling the stability of aggregates.