Experiment And Numerical Simulation On Water And Nitrogen Distributions Under Multi Water Storage Pit

Water storage Pit irrigation is a new orchard irrigation in order to resolve the two severe problems of drought and soil erosion in Northern China. This method will be applied largely in fruit tree and forested area in hilly. The study with respect to the irrigation process has reached a leap from indoor to the farm and the research on water evaporation and movement has become mature. However, the investigation on nutrient migration characteristics in the case of single pit irrigation has just started and not be involved in the situation of multi pit irrigation.In the recent years, leaching loss of nitrogen and environmental contaminate pollute strain caused by blind fertilization have become more and more critical. For this reason, carrying through experimental simulation and research on water and nitrogen transformation in the event of this method can bring significant theoretical and practical sense for further development of water storage pit irrigation.Linking with the national physical science fund (50979065), laboratory experiments on the multi-pit irrigation is carried out. And on the basis of soil water dynamics and the solute transport theory, the 3-D mathematical model of water and nitrogen transportation was established, which is settled by making use of time splitting-Finite Volume Method united with Gauss-Seidel iterative means. The primary peroration are as shows:(1)This infiltration of multi water storage pit includes two phases that are free seepage and interfered infiltration. The infiltration law in the stage of free seepage is similar to the single water storage pit. This means that water infiltration tends to horizontal diffusion and the radial promoting distance is farer than the vertical. Meanwhile, the shapes of the wetting pattern is ellipsoidal dome with the storage pit axle at the center. Interfered infiltration begins with the moment that water is going to the dam-board. Vertical wetting front is becoming bigger by the side of dam-board. Moreover, Vertical moisture content greatens firstly then decreased. The higher moisture locates in the depth of 30cm-70cm and vertical vanguard is downgrade by the time following the diminution of moisture content. Water content in radial section has declined, but as time goes by, amplitude of variation is gradually reducing. Water content in the center of the dam-board is also the same tend but as time goes by that inside the whole wetting pattern is tending to homogenization.(2)In the case of multi water storage pit irrigation, soil moisture is similar to the single water storage pit irrigation, that largely accumulated nearby the wetting front and the distribution of soil nitrate features with low in the middle and high around it. The area of high concentration in vertical orientation distributes at moist boundary and come up Leaching phenomenon inside the wetting pattern. However, in radial direction that mainly centralizes nearby the dam-board where the distribution of soil nitrate is homogeneous. Hence, the transportation of nitrate nitrogen tread on the heels of moisture and convection is the first and foremost motion machining.(3)Because of the influence that the ionic of ammonium nitrogen is adsorbed by the soil colloid, the soil ammonium nitrogen distribution is different from nitrate.It mainly distributes around the storage pit and gradually decreases with the increase of radial distance. The vertical concentration distribution is relatively uniform and is able to decrease below 80cm. Thus, the distributional feature of ammonium nitrogen is high in the middle and low around it. Ammonium nitrogen transportation is lags behind the movement of moisture and the uppermost movement mechanism is dispersion.In accordance with the distribution feature of water and nitrogen in the soil, as everyone knows that water storage pit irrigation has the strong point of keeping moisture and fertilizer.(4)Through contrasting and analyzing between experiment and simulation, the consequence indicated that they basically conformed to each other. And the simulation accuracy of moisture movement is higher than that of nitrogen. Ultimately, it is regard as the mathematical model can be used for simulating movement of nitrogen and water in the soil.