Transportation And Path Distribution Of Preferential Flow In Citrus Soils Of Purple Sandstone Regions, Three Gorges Reservoir Area

Soil macropore characteristics under different citrus land in Jiangjin city of Chongqing was analyzed using brilliant blue dye method, water breakthrough curve and Poiseulle equation. The characteristic of preferential flow and preferential transport was analyzed with undisturbed and packed soil columns applied breakthrough curve (BTC). Brilliant blue dye method, water breakthrough curve, Poiseulle equation and fractal theory were applied to analyse the soil macropore quantitative characteristic and soil macropore flow hydraulic properties under different citrus land in Jiangjin city, Chongqing. The main results in this research were as follows:(1) The steady effluent rate of the dye-stained area was more than1.48times higher than the dye-unstained area and the ratio become higher with soil depth. Water breakthrough curves in the dye-stained area had a bigger fluctuation than that in the dye-unstained area. The radii of soil macropores were from0.3mm to1.7mm. Radii (0.3-0.7mm) had little effect on preferential flow despite the104magnitude. The macropores with radii larger than0.7mm was the main factor affecting the preferential flow. At the10-20cm soil layer, the number of soil macropores under20-year-old citrus land was larger than that under10-year-old citrus land. The macropores with radii larger than1.0mm was the main preferential flow path in the initial stage of water input. The macroporosity was positively (P<0.01) related to the steady effluent rate in the range from1.5%to19.5%which contributed71.9%to the variance of steady effluent rate. The macropores with radii larger than0.7mm was positively (P <0.01) related to the steady effluent rate which contributed90.9%to the variance of steady effluent rate.(2) Distribution of preferential flow path under different citrus land in Jiangjin city of Chongqing was analyzed. The relationship of the preferential flow paths to the properties of the soil, root length per soil volume was analyzed. The distribution of preferential flow path was analyzed using brilliant blue dye method and image analysis. The correlation of the preferential flow paths to the properties of the soil, root length per soil volume was analyzed with SPSS. The results showed that the percentage of both horizontal dye-stained area and vertical dye-stained area under different citrus land were below7%because of the infiltration of water and solute changed by preferential flow path. The saturated hydraulic conductivity was the only parameter of soil properties significantly (at the0.05level) related to horizontal dye-stained soil under different citrus land with similar soil texture. Preferential flow path is the important channel of water and solute despite the little dye coverage. The preferential flow path was significantly (at the0.01level) related to the root length per soil volume with root diameter in the range from1mm to3mm. The root in20-year-old citrus land was deeper and lager than the root in10-year-old citrus land. The preferential flow path was enlarged by the widely distributed roots in horizontal. The root length per soil volume with diameter in the range from1mm to3mm was the main affecting factor of preferential flow path under citrus land in Jiangjin city, Chongqing. The root length per soil volume with diameters both greater than3mm and less than1mm had no relationship with preferential flow path.(3) The effect of preferential flow and matrix flow was responsible for the turning point in the rising phase of BTC in undisturbed soil column. In the decreasing phase, compared with packed soil column with a relatively steady effluent rate, undisturbed soil column has a long trailing. Preferential flow was the contribution to the less stable of soil effluent rate and coefficient of variation. The average effluent rate of undisturbed soil column is3.5times higher than the average effluent rate of packed soil column. Preferential flow shortened the breakthrough time of37.7%while transported2.5times solute higher than matrix flow when the solute relative concentration reaching the peak. Preferential flow can lead a fast mass of soil solute migration.