Quantitative Description Of Soil Structure Under Long-term No-tillage Farming

Conservation tillage,as represented by no-tillage,is seen as an effective measure to promote soil structure,soil pore distribution and water holding properties.However,the quantitative soil structure as influenced by this alternative farming needs to be well understood.This study is based on the long-term tillage field experiment in the arid area of the Loess Plateau of North China.Three tillage farming were selected,namely conventional tillage without residue?CK?,shallow tillage with residue?ST?and no-tillage with residue?NT?.Soil structural characteristics were quantified by analyzing the basic soil physicochemical traits,aggregate size distribution and stability,and CT scanning methods in the 0-20 cm layer.The key measured properties and methods are listed as following.?1?The saturate hydraulic conductivity?K_s?was measured by the constant head method.The sandbox method was used to determine soil air-filled porosity.The soil bulk density was determined by oven heading method and thus the total soil porosity was calculated.?2?The soil aggregate distribution and stability were determined by wet-sieving method.The mean weight diameter?MWD?and the percentage of soil large aggregates(>0.25 mm,R_0.25)were used to indicate the aggregates stability.The related soil pore parameters?pore anisotropy,fractal dimension,connectivity,mean pore diameter,maximum pore diameter,etc.?were identified using the Bone J Plug.The soil pore structure was processed using Image J software.The main results are listed as following.Firstly,NT and ST treatments significantly increased the K_s in the 0-10 cm soil layers.The ST treatment significantly increased the total porosity and the NT increased the air-filled porosity in the 10-20 cm soil layer.This study suggested that NT treatment improved the physical properties in the tilled layer.Secondly,NT could significantly increase the macroaggregate percent and stability(as measured by MWD and R_0.25)in the 0-10 cm soil depth.These data suggested that tillage practice is a key factor influencing the soil aggregate distribution and stability in 0-10 cm soil layers.Thirdly,long-term no-till significantly improved the pore connectivity,reduced pore fractal dimensions and improved pore morphology in 0-10 cm soil.In addition,the NT treatment significantly increased the soil macro-porosity in 10-20 cm soil layer.Finally,interrelationship existed among the soil bulk density,macro-porosity,pore connectivity,macroaggregate percent and mean weight diameter.Thus,the combined parameters are needed to evaluate the soil structural conditions.Taken together,we concluded that no-tillage farming could improve the basic physical properties,such as soil aggregation,saturate hydraulic conductivity,soil pore characteristics and thus soil physical quality in tilled layer?especially 0-10 cm?.