The Research On The Characteristics Of Soil Water Movement Under Negatively Pressurized Irrigation System

The Negatively Pressurized Irrigation (NPI) is a new efficient irrigation method which the water elevations lower than the emitter elevation during the irrigation. By using this method, the irrigation water can be automatically supplied without pumping system. The research of new efficient irrigation technology have great significance in improving water use efficiency, relieving the pressure of water resource and realizing the precision irrigation of crops.Based on the principle of soil water dynamics, the principle and feasibility of the NPI system were analyzed. A series of laboratory experiments which composed by mariotte bottle,plexiglass box,emitter and rubber pipes were designed and conducted to study the effects of different water head(H=0.5m 0m,-0.5m,-1.0m,-1.5m,-2.0m),different soil texture (loamy soil and sandy soil)and different emitter specification (5cm×3cm×2.5cm and 15cm×10cm×2.5cm)on the water moving of NPI system and to give a metric on a particular scale in using NPI.The conclusions are as follows: It can be known from soil water energy state that when negative pressure is maintained at a certain scope, the NPI system is feasible. Its working principle as follows:when water is short in soil, soil matrix suction could actively absorb water from a water source at a lower place into the emitter and then the soil by the water potential difference between soil matrix suction and water source without pumping system.It can be known from the experiments on different water head that the shape of wetting front are all nearly ellipsoid, the wetting front advances quickly at first, the timeline at the same time is sparse, but will be slowing down as time going on, the timeline at the same time become intensive. The cumulative infiltration, maximum horizontal and vertical wetted distance increases with the advance of time, and the infiltration rate decreases with the advance of time. The higher the pressure of negative water head, the faster the penetration of irrigation when other conditions are the same. The results also indicate that the suitable negative water head of NPI is no less than-2.0m in practical application.It can be known from the experiments on different soil texture that The numeric of cumulative infiltration, maximum horizontal and vertical wetted distance of sandy soil is more than loamy soil under the conditions of pressure and no pressure(H≥0m), and on the contrary under the negative pressure(H<0m). For the sandy soil, small amount of water penetrate into soil in the beginning, but then the flow in water pipe is discontinuous, the numeric of cumulative infiltration is almost zero when the negative water head between -1.0m and -2.0m. So the loamy soil has the better irrigation effects than the sandy soil.It can be known from the experiments on different emitter specification that no matter the water head is positive pressure, zero pressure and negative pressure, the contact area between emitter and soil is in direct ratio with the numeric of cumulative infiltration, maximum horizontal and vertical wetted distance. In practical application, we need to select the appropriate emitter specification to have a better effect on irrigation.