Effect Of Managements On Transport Properties Of Soil Gas And Water

In order to study the effect of different managements on the transport properties of soil gas and water,two regions were selected as the experimental areas: tableland region of the Loess Plateau in Changwu county and water-wind crisscross region of the Loess Plateau in Shenmu county.In tableland region,the paper studied the effects of physical,chemical properties of dark loessial soil(especially transport properties of soil gas and water)and maize agronomic characters under different tillage and mulching.Some indexes were measured such as soil moisture,soil temperature,bulk density(?b),soil compaction,saturated hydraulic conductivity(ks),air permeability(ka),relative gas diffusion(Dp/D0)at a soil matric suction of 100 cm H2O,total N,total P,available P,canopy height,leaf area index,yield and so on.Meanwhile,in water-wind crisscross region,the transport properties of soil gas and water were investigated under different vegetation types(abandoned land,Caragana land,Alfalfa land,bare land and farmland)and under different ages of abandoned lands and Alfalfa lands.Some indexes were measured such as bulk density,total porosity,air content at a soil matric suction of 100 cm H2O,saturated hydraulic conductivity(ks),air permeability(ka),relative gas diffusion(Dp/D0)and so on.Here are the main results.(1)In the tableland region of the Loess Plateau,no-tillage reduced the soil bulk density(?b)and temperature of emergence stage and reduced total P and available P of soil in mature stage,improved the soil compaction and surface soil moisture from Apr.28 to Oct.15,which caused the reduction of canopy height,leaf area index and yield.On the contrary,film mulching which can reduce diurnal temperature because of the ability of maintaining and adjusting the temperature had effects of increasing soil bulk density significantly(P<0.01),decreasing saturated hydraulic conductivity significantly(P<0.05)and decreasing organic matter and total N of soil in mature stage,moreover all kinds of film mulching was capable of gaining high yield by improving height and leaf area index of the maize significantly(P<0.01).Under different tillage methods,straw mulching had different effects on ?b and soil moisture.Straw mulching increased soil bulk density under conventional tillage and decreased it under no-tillage but both of them were statistically not significant.Straw mulching under conventional tillage which had the highest soil moisture played an effective role in drought resistance by postponing moisture peak and reducing decreasing rate of moisture.While straw mulching under no-tillage which had the lowest soil moisture was most sensitive to the rainfall for the moisture changed fastest,reached the peak at the earliest and declined fastest after rainfall.Compared with the no-straw-mulching treatments,straw mulching can lead very significant improvement of agronomic characters including canopy plant height,leaf area index and yield(P<0.01);furthermore straw mulching can reduce the surface temperature of soil and increase organic matter and total N of soil significantly(P<0.05).Both straw mulching and film mulching can decrease soil compaction of no-tillage,but had no significant effects on conventional tillage.Air permeability of conventional tillage was greater than that of no-tillage under the same covering condition.All kinds of coverage under conventional tillage can increase air permeability and relative gas diffusion,while those can decrease air permeability and relative gas diffusion under no-tillage.(2)In water-wind crisscross region of the Loess Plateau,the order of soil bulk density was Alfalfa land> farmland> abandoned land,the order of total porosity was Alfalfa land <farmland <abandoned land,the order of macropore(pore diameter ??30?m)porosity was abandoned farmland> farmland> Alfalfa land,and the order of small pore(pore diameter ??30?m)porosity was farmland> Alfalfa land> abandoned land in slope lands.In terraced plots,the order of soil bulk density was Alfalfa land > bare land> abandoned land> Caragana land> farmland,the order of total porosity was Alfalfa land <bare land <abandoned land <Caragana land <farmland,the order of macropore(pore diameter ??30?m)porosity was farmland> abandoned land> Caragana land> bare land> Alfalfa land,and the order of small pore(pore diameter ??30?m)porosity was bare land> Alfalfa land> Caragana land> farmland> abandoned land.The soil pore continuity index,air permeability and relative gas diffusion of Alfalfa lands both in slope lands and terraced lands were significantly higher than those of other vegetation types.And pore tortuosity of Alfalfa lands was significantly lower than those of other vegetation types.While the soil pore continuity index,large pore continuity of farmlands were the least and pore tortuosity was the highest in all vegetation types.The results demonstrated that the Alfalfa land could improve soil structure and transport properties of soil gas and water,compared with the farmland.(3)In water-wind crisscross region of the Loess Plateau,with the increase of the ages of the abandoned land,the soil bulk density(?b),macropore(pore diameter ??30?m)porosity,saturated hydraulic conductivity(ks),air permeability(ka)and relative gas diffusion(Dp/D0)increased,while the total porosity and small pore(pore diameter ??30?m)porosity decreased.In Alfalfa lands,the saturated hydraulic conductivity(ks),air permeability(ka)and relative gas diffusion(Dp/D0)decreased with the increase of the ages.In addition,with the increase of the ages of the abandoned land,soil pore tortuosity,large pore continuity increased.And the pore continuity index decreased and the connectivity of large pores increased.With the increase of the ages of the Alfalfa land,the pore continuity index and large pore continuity had a decreasing trend.(4)The relationships of saturated hydraulic conductivity,air permeability and relative gas diffusion of dark loessial soil and sand loess respectively illustrated that ka vs.ks,(Dp/D0)vs.ks,ka vs.(Dp/D0)were correlated significantly(P<0.05).