| Due to complex geological environment conditions caused conflicts in the water and soil resources with the incongruous form of double-layer spatial structure the agricultural drought frequently occurred in Guangxi region,combing with the extreme climate in rencent years.The study on soil moisture characteristic curve and soil shrinkage in dry and wet process,as well as the spatial structure characteristics of soil macropore is of great significance for making reasonable tillage system,improving the utilization efficiency of water and fertilizer and the capability of enduring drought in agricultural soil,as well as controlling soil and water loss and reducing groundwater pollution.In this paper,dry lands(sugar cane,pear tree,soybean areas)and paddy soil(paddy field),respectively located in experimental zone A(rotation area and non-rotation area in paddy,sugarcane area and pear tree area and soybean area in dryland)in Guilin institution of agricultural sciences in Guangxi Guilin Yanshan Town and in experimental zone B(tillage area of sugarcane in dryland,non-tillage area of sugarcane in dryland)in Lijian base of Nanning institution of Guangxi agricultural sciences in Guangxi Nanning Wuming,were set up to investigate soil moisture characteristic curve by using pressure membrane meter method fitting with RETC software,soil shrinkage curve through the depth vernier caliper measurement fitting by Soil Shrinkage Simulator(SSS)software,and the structure of soil macroporous scanned by CT(Computed Tomography)based on 3D reconstruction method.The soil water retention capability,the characteristics of soil shrinkage and the 3D structure of soil macropore were analysed.The main results were as follows:Within the effective suction range in determination of soil moisture characteristic curve by pressure membrane meter method,the corresponding soil moisture characteristic curve in no-rotation and no-tillage systems declined sharply more than rotation and tillage systems,respectively,which illustrated that the soil water retention capability was better in the former ones.The main reason was that the amount of water conserved and released by soil in the low suction depended on the distribution of soil macropores.However,human activities such as tillage and rotation could destroy soil construction,especially the structure of macropore with low water-holding ability,meanwhile increased the mesopore and micropore which can reduce water loss in the low suction and show better water-holding capability.Under the same crop types and cultivation measures,water-holding capability increased with the increase of soil depth,which was related to soil properties.It indicated that soil bulk density and soil texture were the main factors to affect the water-holding capability which behaved better with higher bulk density,while weaker with higher porosity.Because of soil increase in bulk density and decrease of soil porosity,the macropores declined but mesopore and micropore increased,which was beneficial to soil water conservation.In addition,soil with higher clay content,containing many water-stable aggregates,also promoted the soil water retention capability.In soil shrinkage experiment,the soil shrinkage was the largest in pear tree area of experimental zone A,while such phenomenon was not observed in sugarcane and soybean area.The soil shrinkage of non-rotation soil was less than that in rotation soil in paddy field in experimental zone A.The soil shrinkage in tillage soil was less than that in non-tillage soil in dry land of sugarcane in experimental zone B.Furthermore,the degree of soil shrinkage both decreased with the increase of soil depth,which caused by the crop types and soil types and cultivation measures as the main factors.Among them,water storage capacity of crops and tillage or not under different crops caused the changes,including soil moisture content,soil bulk density,soil porosity and soil organic content,and thus affectted the soil shrinkage.While the great difference in soil moisture condition induced by different soil types(dry land and paddy field)conducted the different soil structure which indirectly affected soil porosity.There was a positive relationship between soil porosity and soil shrinkage(P<0.01).While different cultivation measures could indirectly change soil properties,especially soil bulk density,which was negatively related with soil shrinkage(P<0.01).In addition,the development and extension of crop roots was also of benefit to soil shrinkage.In the results of soil column scanned by CT,the quantity and porosity mean value of macropore showed as follow: non-rotation(358,0.345%)<rotation(451,0.457%)in paddy soil of experimental zone A,and tillage(1194,1.069%)<non-tillage(1519,1.195%)in sugarcane soil of dry land in experimental zone B.The mean value of connectivity and tortuory showed as follow: rotation(1.332,0.474)>non-rotation(1.272,0.217)in paddy soil,tillage(1.374,0.512)> non-tillage(1.333,0.299)in sugarcane soil of dry land.The main reason was that crop types and cultivation measures resulted in the changes in the structure of macropore improved the quantity of mesopore and micropore,finally changed the porosity,which took positive influences on soil hydraulic conductivity.Reasonable paddy-dry land rotation system could reduce the time of soil submergence,promote the development and extension of crop roots,and contribute to cross and extension between pores.Meanwhile,soil swelling-shrinkage in dry and wet process also caused macropores.Both of them induced the water through the cracks and macropores,which increased soil hydraulic conductivity.The suitable cultivation measures could change the structure of soil pore,loosen the surface soil,increase soil aeration,finally benefit to the development and extension of crop roots.Furthermore,the roots also promoted the extension of soil pores and improved changes of the distribution of isolated macropores to creat interconnected paths,which was also of benefit to water flow and solute transport,as well as enhancing soil hydraulic conductivity.Therefore,the proposal of suitable rotation and tillage systems could promote water storage. |
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