Effect Of Water Head, Emitter And Water Quality On Soil Water Movements Under Negative Pressure Irrigation

The negative pressure irrigation is a new subsurface drip irrigation technology. The system can absorb water automatically from the elevation of water which is lower than the emitter depending soil matric potential (soil suction)in order to supply crop water loss caused by evaporation. In this way soil moisture can maintain constant. The entire process to irrigate is completed without outside pressure equipments. If we can combine brackish water and The negative pressure irrigation technology to irrigate, it not only can greatly reduce irrigation cost, but also can save freshwater resources, reduce groundwater level, thereby improve the quality of soil.This paper we did an indoor test about negative pressure irrigation on the basis of previous studies. The test used 30°fan-shaped cylinder organic glass soil box. Its height is 40cm and radial length is 35cm.The irrigation ware is porous argil board (5cm*3cm*2.5cm), which has the characteristics of waterproof airtight. Its aperture is 5-6μm and 3-4μm.We used the markov bottle to supply water under a constant level When we use salty water to improve irrigating, some factors may influence the soil moisture migration in the system of negative pressure irrigation. This paper mainly studied the following factors:water head (H=0.5m,0m,-0.5m,-1m,-1.5m,-2m), different diameter-water device (5-6μm,3-4μm) and different water quality (tap water and salty water). The results can provide test base for using salty water to irrigate under negative pressure.The test results showed that:(1)when we used the same water device aperture and water quality, he water head smaller, the wet body smaller.Under different water head, the cumulative infiltration Q, The maximum horizontal wet distance X, maximum vertical wet distance Z all increased with time. When H=-2m, the increase range of Q, X and Z with time is very small. The farther away from the irrigation device, the smaller the water content was.(2) when we used the same water head and water quality, but chosen different water device aperture, the wetting front under the first water device(5-6μm) was all larger than the second(3-4μm). In each contrast group test the cumulative infiltration Q under the first water device(5-6μm) is all bigger than the second(3-4μm).When the irrigation was finished we found that the influence of water device to the maximum horizontal wet distance X and the maximum vertical wet distance Z is different. The influence of water device for the water content in each sampling points had different rule.(3) when we used the same water head and water device aperture, but chosen different water quality, the wetting front under the first water quality (the tap water) was all larger than the second(the salty water). In each contrast group the cumulative infiltration Q and the maximum horizontal wet distance X, the Maximum vertical wet distance Z under the first water quality (the tap water) was all bigger than the second(the salty water).The influence of water quality for the water content in each sampling points had different rule.