Characteristics Of The Soil Water Movement Channel Covered By Sugarcane Under Different Straw Mulching Conditions

Guangxi is located in the karst area,and its complex and fragile karst geological environment,coupled with extreme weather in recent years,has led to frequent agricultural droughts.The following elements including soil basic physical and chemical properties,geometry structure of soil water movement channel and undisturbed soil column ion infiltration under the conditions of straw mulching and no-straw mulching are comprehensively analyzed in Guangxi karst area.It is of great significance to understand the characteristics of soil water movement channel and Water-Fertilizer Use Efficiency in typical agricultural field of Guangxi.In this study,the soils of six plots covered by sugarcane under the conditions of straw mulching and no-straw mulching in the research base of Nanning Lijian,Guangxi,which includes soil physical and chemical properties,CT scan of soil column with ion infiltration test using a PVC pipe to obtain the undisturbed soil column,were studied to understand the characteristics of soil water movement channel under the conditions of straw mulching and no-straw mulching.The main results of this study are as follows:(1)The soil physical properties of the whole soil profile of the sugarcane experimental plot after straw mulching showed that the bulk density increased and the soil water content increased,Meanwhile in soil chemistry,soil organic matter and total nitrogen content decreased.The decrease of soil organic matter and total nitrogen content may be related to the increase of crop roots which resulted into the more absorbed soil nutrients.For crop roots,as soil depth increased,soil root length density and root weight density decreased gradually in both plots.Furthermore the plant root length density in the soil under straw mulching was greater than that under the no-straw mulching condition,but the soil root density was slightly different except for the surface layer 0-10 cm.(2)Based on CT scan and three-dimensional reconstruction,there were significant differences in the geometric structure characteristics of soil water movement channels between the straw mulching and the no-strawing mulch.Under the straw mulching condition,the number of pores and the soil porosity increased,which led to the increase of soil pore surface density.The averaged specific surface area and connectivity under the straw mulching condition(1.647 mm,0.713)were larger than that under no-straw mulching condition(1.439 mm,0.611)However the averaged soil hydraulic radius under straw mulching(0.663 mm)was less than that under no-straw mulching(0.703 mm)..three-dimensional visualization can more intuitively reflected the differences in geometric characteristics and connectivity of soil water movement channels.(3)Based on soil column ion infiltration test,it is known from the solute transport characteristic curve that under the straw mulching condition,the maximum and stable concentration of outflow and averaged concentration during the test time for chloride ion,electroconductibility,electrical resistivity and Total dissolved solids(TDS)were greater than the no-straw mulching condition.In addition the former one took the less time for the infiltration process.During the deionization infiltration process,the absolute slope of the trend line in the process of decreasing for above 4 index were greater than that under the no-straw mulching condition.It indicated that straw mulching could improve the soil water movement channels which resulted into the changes in solute transport.In a conclusion combined with the geometry structure of the soil water movement channel and the solute transport characteristic curve,it can be known that straw mulching could increase the connectivity of soil pores and improve soil structure which led to accelerate solute transport and promote nutrient absorption in the cultivation of sugarcane in Guangxi.