| Water storage Pit irrigation is a new irrigation method which was proposed to solve the problem of orchard drought and erosion in hilly region of north China. Its most prominent feature is the combination of water saving-irrigation and soil conservation. The research on this irrigation method has achieved a leap from indoor to the field, the studies on water movement have tended to mature, however, the investigation about nutrient transport characteristics had not been covered. Nowadays, the wasting of manure and environmental pollution caused by blindly fertilizing have become more and more serious.Therefore, conducting experimental research and simulation on water and nitrogen distribution on this method could bring important theoretical and practical significance for further development of water storage pit irrigation.The indoor experiment of single water storage pit fertigation on homogeneous soil was conducted based on the combination of experimental investigation and simulation. The water and nitrogen distributions on different irrigation volume(6,8,10L)with different fertilizer solution of 800,1700,2600mg/L were studied. And the 2-D mathematical model of water and nitrogen transportation on single water storage pit irrigation was established, which was solved by using time splitting–Finite Volume Method. The main conclusions are as follows:(1) In the condition of single water storage pit irrigation, the shape of final wet soil is a irregular ellipsoid whose axis is the pit centre. The relationship between the advancing distance of horizontal and vertical wetting front and the time is logarithmic, the advancing distance enlarges with the increase of irrigation volume, and the horizontal advancing distance always greater than that in vertical, so water spread mainly by horizontal infiltration. Moreover, the higher water content region locates in the 30cm-70cm depth, and the vertical wetting front is deep by the time. Fertilizer concentration has no effect on water content distribution, but the increment of irrigation volume can increase the water content peak.(2) In the condition of single water storage pit irrigation,soil nitrate content increases in the radial direction, and largely accumulating nearby the wetting front where moisture content is low but large in matrix suction. The region of higher concentration in vertical direction distributes in deep soil (z = 40cm-70cm) and around moist boundary. However, soil nitrate could leach if the irrigation volume was excessive. When fertilizer concentration increases, nitrate concentration in vertical profile and the peak value also enlarge. Thus, the transportation of nitrate keeps pace with soil water and that the convection is the uppermost movement dynamics. (3) The soil ammonium distribution in radial, which is contrary to nitrate, decreases with the increment of radial distance while it is still higher than the background value. The concentration distributes uniformly in vertical with the depth increase, but gets a rapid decline below the water pit bottom. The concentration of ammonium is high in the range which near the pit wall about 20cm, but it is uniform in contrast of the nitrate distribution. Besides this, the irrigation amount has no effect on its distribution, but it can increase with the enlargement of fertilizer level. Therefore, the ammonium transportation lags behind the movement of soil water, and that the dispersion is the uppermost movement dynamics.According to the distribution characteristics of soil water and nitrogen, it is known that water storage pit irrigation has the advantages of retaining water and fertilizer.(4) Comparison of simulation and experimental results showed that they are basic coincidence with each other. And the simulation precision of soil water movement is higher than that of nitrogen. Finally it is considered that the mathematical model can be used to simulate the transportation of soil water and nitrogen on water storage pit irrigation. |
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