The Relationship Between The Soil Aggregates Water Stability And Soil Erodibility

Soil aggregate is an important soil composition to be evaluated because it mediates many biological and physical processes in soils. Soil aggregate structure determines porosity, infiltration and soil erosion susceptibility. Soil aggregate stability has a close relation with soil erodibility, so it has been selected as a good indicator for credibility ?(Chan and Mead, 1988; Cooteetal., 1988; Wang youmin, 1994 ; et al.). Combined with soil aggregate breakdown experiment, simulated rainfall erosion experiment and the analysis of some soil physical and chemical data, factors that affected soil aggregate water stability, the mechanism of aggregate's breakdown and the relationship between soil aggregate water stability and soil erodibility is studied in this paper. With the equation of Williams, the soil erosion erodibilty K was calculated in use of the field data. Following conclusions can be reached:(1) There are several factors affecting water stability of soil aggregate (WSA) such as soil OM (organic matter), soil nitrogen and phosphorus content, vegetation, and no-tillage years, et al. The results show that soil OM content has obviously closer relationship with >0.25mm soil water stable aggregate content (%) than that of soil nitrogen and phosphorus content. The relationship is linear. Soil nitrogen and phosphorus content (%) have exponential relationship with >0.25mm water stable aggregate content (%). No-tillage years and vegetation can also affect >0.25mm water stable aggregate content (%) accordingly. In general, Soil OM (%) and the mean weight diameter (MWD) can be used to assess the water stability of soil aggregate.(2) There are several factors which can Jesuit the breakdown of soil aggregate, but the main reasons are due to rainfall density (including single raindrop) and different prewetting rate. So they are selected to study the process and the mechanism of the breakdown of soil aggregate. The results show that energy needing in the breakdown of soil aggregate (>5mm) by single raindrop is much more than that of soil aggregate (5-2mm and 2-1mm), prewetting can increase the water stable aggregate content in given range and the rainfall is able to accelerate the breakdown of soil aggregate through affecting the soil cementing agents (OM). Furthermore, the mechanism of breakdown of soil aggregate is discussed.(3) Three methods are to be used to quantitatively assess WSA on the basis of wet -sieve methods. The first is the energy-consumption method. The energy discharged in the breakdown of soil aggregate has a close relation with soil structure and water stability ofsoil aggregate. The better the water stability is, the more the energy need. According to these relations and experimental data, one equation is put forward to assessing WSA with different aggregate size. Secondly, the nutrients in aggregates are used to quantitative assess WSA. The results show that soil OM (%) and nitrogen content (%) have a good exponential relation with the WSA, but soil phosphorous has little relation WSA. So the phosphorous content can't be used to assess the WSA. Thirdly, air encapsulation in aggregate and the lasting time of breakdown of soil aggregate also has close relation with water stable aggregation. The longer the time, the better the water stability is. A model is founded to quantitatively assess WSA. The result shows that the time has a direct relation with soil erodibility K: ziwuling < yangling < ansai.(4) The relation between WSA and soil erodibility is studied in this paper. The result indicates that the relation is very close and >0.25mm water stable aggregate content (%) even can be used to assess the soil erodibility. In the first time Williams equation is used to calculate soil erodibility K of the main type of soils in Loess Plateau and the soil cultivated different years in ziwuling forest area on basis of data available. K huangmiamu >K heiiutu >K loutu >K heigaitu>K senlinhetu >K ligaitu. Result indicates that the forest soil has smaller soil erodibility K than that of other type of...