Effect Of Water Quality On Soil Water-salt Distribution Under Negative Pressure Irrigation

As a new type of water-saving irrigation technology, the negative pressure irrigation system can draw water automatically from water source below emitter by soil matric potential (soil suction). This irrigation system can save energy and reduce the cost. Saline water irrigation can not only use salt water resources, re-duce the underground water level, but also can improve the quality of soil.The further tests are carried out on the basis of predecessors’ research.The30°wedge-shaped organic glass containers were remaining used. Its height is40cm and radial length is35cm.we use porous argil board as diameter-water de-vice (aperture is3-4μm and the size is5cm*3cm*2.5cm). Graduated cylinders were used to keep constant water head. A series laboratory experiments were arranged to study the effects of different water head (H=0m、-0.5m、-1m、-1.5m)and different water quality (C=80meq/L、20meq/L、2meq/L, SAR=20、10).The experimental results indicated that:(1)Under the same water quality, the lower water head, the smaller wetted soil volume. The cumulative infiltration rate, maximum horizontal and vertical wetted distance all increases with time. The greater the distance from emitters, the lower the water content under all treatments. At the same level, ratio of width to depth increases with the increase of water head, and the increase range decreases with the decrease of the water head. Water moisture decreased with the decreasing of water head. On the contrary, the greater the distance from emitters, the higher salt concentration under all treatments. Salt concentration increased with the decreasing of water head.(2) Under different water quality, the cumulative infiltration rate, wetting front maximum horizontal and vertical wetting front increase with the decrease of the water head when salt concentration and sodium adsorption ratio are high. Lower water head is advantage to the high salt concentration and sodium ad-sorption ratio of irrigation. On the low water head, the ratio of the width and depth is large when salt concentration and sodium adsorption are small. On the whole, the influence of water quality on the ratio of the width and depth is not big, the range is between0.6to0.8.The distribution of water content and electric conductivity in wetted soil volume may be described as a series of concentric ellipsoid, the maximum moisture content distribution in the center of the ellip-soid and the maximum electric conductivity distribution in the margin. With the increasing of SAR, average soil water content decrease and average electric conductivity increase.