Characteristics Of Soil Macropores In Different Land Use Types In The Arid Valley Of The Red River

Soil macropores are the main channels for water movement in soil,which can cause soil nutrient loss and groundwater pollution.Studying the characteristics of soil macropores can provide a certain theoretical basis for proving the characteristics of soil infiltration and the law of soil and water loss,and provide scientific support for regional environment water resource management and soil and water conservation.This study takes the soil of agricultural land,wasteland,garden land and woodland in the arid valley of the Red River as the research object.Based on the water penetration curve method and classical statistical analysis,it quantitatively analyzes the characteristics of soil macropores,and studies the influence of environmental factors on the formation of soil macropores,the research results are as follows:(1)The soil physical and chemical factors and soil saturation hydraulic conductivity of the four land use types of forest land,garden land,waste land and agricultural land were significantly different(P<0.05).The soil content of the four types of land use was the highest,the soil clay content was the second,and the soil grit content was the least.In the vertical direction of the soil,the soil bulk density and soil powder content of the four land types increased with the depth of the soil.The soil bulk density is expressed as agricultural land>garden land>wasteland >forestland;soil clay content,total soil porosity,capillary porosity,aeration porosity,soil organic matter content,soil aggregates,soil saturated hydraulic conductivity and total soil nitrogen content of agricultural land as a whole deepen with soil depth In order to reduce,the total porosity is expressed as forest land(64.18%)> wasteland(51.59%)> garden land(48.15%)>agricultural land(47.72%),and organic matter content and soil saturation hydraulic conductivity are expressed as forest land >Ground> Agricultural land > Barren land;the overall content of Al,Fe,Na elements in deep soil is significantly larger than that in the table Soil(P<0.05),Ga element content greater than the overall showing deep soil topsoil(P<0.05),K,Mg elements in the soil distribution in the vertical direction no regularity.(2)The characteristic of soil water penetration curve of 4 types of land is that the stable outflow rate decreases with the increase of soil depth.It takes 40-100 s from the first water outflow to the water flow stability,in the range of 0-50 cm soil depth.The stable water flow rate ranges from 0.45-0.14 ml/s,0.56-0.12 ml/s,0.78-0.14 ml/s,and1.50-0.12 ml/s,respectively.Among the four types of land use,the number of macropores in the range of equivalent radius of 0.6-1.0mm is the largest,accounting for 96%-98% of the total macropores,and the density greater than 1.0mm is the smallest,accounting for less than 4% of the total number of macropores.The soil macropore density and soil macroporosity in different pore size ranges basically decrease with the deepening of soil depth.The overall trend is forestland >garden land >wasteland >agricultural land.The overall large pore density of garden and wasteland soils was not significantly different(P>0.05),and the large pore density of agricultural land,forest land,and the other three types of soils were significantly different(P<0.05).(3)The root density and biomass density of four typical types of plants decrease with increasing soil depth;fine root systems(root diameter d<1mm)have a high contribution to the formation of large pores in soil,while thick root systems(root diameter d>1mm)contribution is low.The volume content of gravel showed that forest land was significantly larger than agricultural land,wasteland and garden land.The total volume of gravel in farmland,wasteland and woodland,and the change in volume of gravel from 2 to 16 mm in diameter appear to increase as the depth of the soil increases.The distribution of gravel in the garden soil is irregular.Regression analysis shows that the soil macroporosity has a negative correlation with the gravel volume content,soil bulk density,Al and Na element content in the four land types,and the biomass in the range of d≤5mm root diameter in the four land use types.Density,soil silt content,total soil porosity,soil organic matter content,soil saturated hydraulic conductivity,and Ga and Fe element content showed a positive correlation with the biomass density of>5mm root diameter,K and There was no correlation between Mg element content and total nitrogen content.Significantly correlated with the content of water-stable aggregates in agricultural land and woodland(P<0.05),and was not related to the content of water-stable aggregates in wasteland and garden land(P>0.05).(4)Principal component analysis was used to study the relationship between different environmental factors and the characteristics of soil macropores.It was found that there are three main factors for soil macropore formation,which reflect the soil pore structure,plant root system,gravel content,and soil type.The contribution rate of variance to the formation of soil macropores was 40.736%,26.195%,and 19.233%,and the cumulative contribution rate of variance reached 86.166%.Among them,the structure of soil pores had the greatest influence on the formation of macropores.