| To reveal the mechanism of soil water conservation and provide the basis for mountain ecological management, chose Dalaoling and Baishutou of Three Gorges of the Yangtze River as the study area,chose the broad-leaved forest brown soil,mixed needle leaf and brown soil, Secondary mixed yellow brown soil and soil covered by tea garden,then taken the centrifuge tests to study the soil aggregate?bulk density?porosity and other soil structure parameters, analyzed mountain soil water characteristic curve and its model Analysis. The results showed:(1)The soil mechanical composition of different experimental areas were various. It was found that proportion of sand and silt content were biger, the clay content was smaller. sand content of tea garden was largest than others. The proportion of sand content increased with soil depth going down. But the proportion of silt and clay content decreased with soil depth going down. Mixed brown soil relative to the other types of soil had a minimum (2.33%) of sand content,silt and clay of mixed brown soil was bigger than others. Sand?silt and clay content was stable in the different layers of the mixed yellow brown soil. Compared with woodland soil,the variations of sand?silt and clay was small in different layers of soil covered by tea garden.(2)The porosity and capillary porosity decreased with the increase of the depth of soil profile. Besides economic forest yellow soil, the maximum of porosity occurred in the surface soil,the maximum was 1.05?1.76 times that of other soil layers,the minimum value was in the bottom of each sample point. The average (12.4%) of soil capillary porosity in mixed mountain brown was the biggest in the all samples, and it was 1.38?2.14 times that of others. With the increase of soil depth, the distribution of macropore also decreased. In the context of surface soil, macropore in the mixed needle leaf and brown soil was the biggest, followed by secondary mixed forest brown soil,yellow brown soil and broad-leaved forest economic forest yellow soil was minimal.Compared with woodland soil, the difference of distribution of macropore was small in the soil covered by tea garden, the distribution was more uniform.(3)Using the dry and wet sieve method to study the soil aggregate structure under different vegetation. R0.25 was in the range between 94.54 % and 99.05 %, the content was high. R0.25 under the dry sieve was gradually increasing with the deepening of the soil profile.Water stability of aggregate R0.25 ranged in 60?93.31%, the change was bigger, soil water erosion resistance was different in different layers. The soil mechanical stability MWD and GMD in mixed needle leaf and brown soil, yellow brown soil secondary mixed forests and soil covered by tea garden mechanical all iecreased with the increase of soil depth. Water stability MWD and GMD in lower layer was bigger than the upper layer. It showed that soil water stability was poorer in upper layer, it was impacted to water erosion. R0.25 (dry) were negatively related to the organic matter content?total porosity?0.03 ?0.06 mm macropore and > 0.06 mm macropore. MWD (dry ) and GMD(dry ) were positively related to the quality of volume, it had obvious negative correlation with organic matter?total porosity and > 0.06 mm macropore. MWD (wet)and GMD (wet) were positively related to the organic matter, and it had obvious negative correlation with silt?clay and porosity.(4)soil release rate quickly reduced first, then gradually flatten out with the increase of soil water suction rate. The change of moisture content was bigger on the surface (0?15 cm) of forest soil,value was between 14.2%?66.53%. Curve was relatively steep at the low suction stage (S < 20 KPa) , water content changed quickly. And the curve were parallel at 20 < S < 200 KPa. Characteristic curve of mixed needle leaf and brown soil in the figure was higher than other samples, showed that the moisture content in all period of the suction was not less than other samples, the water-holding ability was better.Mixed needle leaf and brown soil had stronger water-holding ability than the other two types of woodland soil. Compared with forest land, the change of water characteristic curve between different layers of tea garden were small, almost overlap. Soil water content of tea garden was smaller than needle mixed brown soil, was similar to secondary mixed forests soil and broad-leaved forest soil. By van Genuchten ( VG ) model to simulate soil water characteristic curve in the mountain area, the correlation coefficient R2 between fitting data and measured data were greater than 0.95 , the model had high reliability, parameter n was different in different samples.(5)According to correlation analysis on soil physical and chemical properties affected water characteristic. volume mass were negatively related to saturated water content, field capacity and negatively related to the effective water content, namely soil water characteristic parameter values decreased with the increase of test quality volume.Sand had obvious negative correlation (P < 0.05 ) , silt content was positively related to the field capacity,the positive correlation of clay?saturated water content and field capacity also reached significant level (P < 0.01 ) . Meant less content of sand, more content of silt and clay, the soil moisture content was higher. R0.25 (dry) were negatively related to saturated water content, field capacity and effective water content. MWD(dry ) and GMD ( dry ) were negatively related to the saturation water content significantly (P < 0.05 ) , so the mechanical stability of aggregate geometric mean diameter was smaller, the greater the saturation water content of soil. GMD (wet) was negatively related to the field capacity significantly (P < 0.05 ) , It was shown that when the geometric mean diameter of the water-stable macromolecule was larger, the better the water holding capacity was. Capillary porosity and total porosity were positively correlated with saturated water content, field water holding capacity and effective water content. There was a high significant positive correlation between 0.03 ? 0.06 mm large pore and saturated water content, field water holding capacity and effective water content(P < 0.01) , > 0.06 mm large pore and water content were very significantly correlated(P < 0.01) .It indicated that whitch affected water characteristic mainly was clay and soil pore structure. |
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