Long-term Tillage Effects On Pore Size Distribution Within Soil Aggregates

Soil is a loose porous body,not only has the inter-granular pores between grains,but also has the structural pores between aggregates.The sizes of pore,and its shape,amounts and distribute feature in different soil layers are highly complicated.Soil structure has important effects on soil fertility,culture, plant growth and microbial distribution.Soil aggregates is becoming one of the most hotspots in soil researches mainly concentrated on the pore distribution,geometry model,fractal dimension and water dynamic feature to probe the soil structural property.Applying with Arya- Paris model to simulate the water moisture characteristic curve,the result shows that comparing to conventional rotate tillage,it has smaller soil density,looser structure,larger gross porosity and higher water-holding capacity under ridge no-tillage.Soil water content and availability are both higher under the ridge no-tillage than the conventional rotate tillage under the same soil water potential that illuminates ridge no-tillage largely improve the plant root absorbency and soil water utilization.Flooded paddy fields widely exist in southern China,and have great potential in agricultural production.Paddy-upland rotation system is the main alternative way in "flooded paddy-field" utilization that has been practiced for more than 20 years.However,this kind of alternativeness results in some other problems.Ridging no-tillage in paddy fields is a kind of conservative tillage method that has been proved its benefits in improving of soil fertility.Soil pore distribution is a important characteristic of the soil structure.All of biological,physical and chemical processes are taken place here or at least related to.The objectives of this study were to study the characteristics of pore structure in different size of soil aggregates. The results show that pore volume between 0.053～0.200 mm size of soil aggregates are maximal in both tillage practices,it is 15.4～6.34 cm3 / 100g and 16.3～3.59 cm3 / 100g under ridging no-tillage and paddy-upland rotation system respectively.The pore volume of larger than 1.00 mm size of soil aggregates is minimal,that is 0.924 cm3 / 100g and 0.652 cm3 / 100g under ridging no-tillage and paddy-upland rotation system respectively.Present results indicated that pore size distribution under ridging no-tillage is more reasonable with both of soil water and air.Our experiments point to find out the pore distribute feature in different soil aggregates under the ridge no-tillage by comparing the soil aggregate two-dimensional pore distribution and CT faultage scan results under the long-term ridge no-tillage and conventional rotate tillage,the soil fractal dimension is greatly consistent with the result deduced by the water character curve.