Experimental Study Of The Effect Of Soil Aggregate Water Stability On The Water Movement Processes

Good soil structure and higher aggregate water stability is very important to improve soilfertility and soil porosity, increase crop productivity and reduce the corrosion resistance. Theimprovements of soil aggregate water stability benefit to adjust measures to local conditions,to improve the limited land resources utilization, also it is necessary to provide a scientificbasis for a better understanding of the relationship between the soil structure improvement,soil properties and land use. In this paper, through a lot of laboratory experiments with soilcolumns, the effects of soil aggregate water stability on water infiltration processes andsaturated hydraulic conductivity were further studied, and the main conclusions were givernas follows:1. Under different land use types, soil saturated hydraulic conductivity values in field andorganic matter content were all various. The wet sieving>0.25mm water-stable aggregatessize fractions and wet sieving MWD under four land use types, followed the same sequence:cropland> farmland> grassland> orchard, while the PAD values were just opposite. For thefour land use types, soil organic matter contents increased with the reduction of the drysieving aggregate sizes in turn, and decreased with the reduction of the water-stable aggregatesizes. The organic carbon contents of the various fractions of water-stable aggregates wereless than dry sieving aggregates. There were significant positive correlation between drysieving mean weight diameter values and5~2mm,2~1mm water-stable aggregates C/N ratios;meanwhile the significant positive correlation between the wet sieving mean weight diametervalues and5~2mm,2~1mm,0.5~0.25mm water-stable aggregates C/N ratios. PAD valuesonly performed a significant negative correlation with2~1mm,0.5~0.25mm water-stableaggregate C/N ratios.2. For the top water supply method, the infiltration rate were all increasing with theincreases of>0.25mm water-stable aggregate content. And for the bottom water supplymethod, the infiltration rate were all decreasing with the reduction of>0.25mm water-stableaggregate content. When the>0.25mm water-stable aggregate content was different, the finalstable infiltration rates of grassland and orchard were higher, and the final stable infiltrationrates of farmland and cropland were lower. For the top water supply method, there was asignificant positive correlation between the final stable infiltration rate and>0.25mmwater-stable aggregate content; while for the bottom water supply method there was a significant negative correlation. Moreover, when the>0.25mm water-stable aggregate contentwas constant, the cumulative infiltration and wetting front changes were under the influenceof land use type but had nothing to do with water supply method, at the same time followed asequence of grassland>orchard>farmland>cropland. The cumulative infiltration of thegrassland at the same time were the largest, and the infiltration duration were the shortest;while the cumulative infiltration of the cropland at the same time were the lowest, and theinfiltration duration were the longest. When the>0.25mm water-stable aggregate content wasdifferent, for the top water supply method, the cumulative infiltration and wetting frontchanges were all increasing with the increases of>0.25mm water-stable aggregate content,but it was just opposite for the bottom water supply method. Using the power functionequation to fit the changes of the infiltration rate with time, the fitting results were very good.The cumulative infiltration data could be fitted by the Kostiakov and Philip infiltrationequation. The results showed that both the Kostiakov and Philip infiltration equation could beused to better describe the processes of cumulative infiltration changes over time. Meanwhilethe changes of wetting front with time could also be fitted by the power function and thefitting results showed that it was much better for the top water supply method than the bottomwater supply method, the parameter B values from the power function y=AtBwere greaterthan those values for the bottom water supply method.3. Both for the the top and bottom water supply method, the Ksvalues were all increasingwith the increases of>0.25mm water-stable aggregate. Under different land use types, the Ksvalues of the top water supply method had a larger magnitude than those of the bottom watersupply method. For the grassland, Ksvalues had an order of magnitude higher than those inthe other three land use types. The relationship of mean weight diameter and saturatedhydraulic conductivity could be fitted by linear variance and nonlinear variance. For the topwater supply method, the linear fitting results of farmland were the best, and the nonlinearfitting results of orchard were the best. For the bottom water supply method, the fitting linearand nonlinear relationships between mean weight diameter and saturated hydraulicconductivity of grassland were all the best. Through the correlation analysis, under differentland use types and water supply method, there was a positive correlation between meanweight diameter and saturated hydraulic conductivity (P <0.01) and were all corresponding toa linear relationship or non-linear relationship; the linear relationship was better than thenon-linear relationship.