Experimental Studies On The Characteristics Of Soil Moisture Movement Under Water Storage Pit Irrigation

According to two severe problems of drought and soil erosion in Northern China, water storage pit irrigation method was put forward. This method will be applied largely in fruit tree and forested area in hilly. It is significant to research on the characteristics of infiltration and soil moisture movement for applying this method. In this paper, using research methods of combining theoretical analyses with laboratory studies, and combining experiment with numerical simulation, the characteristics of infiltration and soil moisture movement were systematicly researched. The main consents and findings are as follows:(1) The experiment of simulating ID-lateral infiltration of water storage pit was designed, the effect of head on infiltration course was researched. The higher accurate testing equipment for horizontal infiltration was designed; In ranges of 0~60cm infiltration heads, horizontal infiltration experiments were conducted under the conditions of twelve different heads. New experiment phenomena were found that Kostiakov infiltration coefficient and index varied in the alternation of relative stability and steepness with increasing infiltration heads, it showed infiltration head was an important effect factor on infiltration; It was also found that Kostiakov infiltration coefficient and index not only varied in different extend with infiltration head increasing, but also their variances were opposite. The reasons of these new experimental phenomena were explained on some theories. The physical meaning of infiltration index was put forward while analyzing the causing reason. Based on this, the effect of infiltration head on cumulative infiltration and wetting front and the causing reason were analyzed.(2) Using the techniques of soil sections and digital images, the effects of different infiltration heads on topsoil pore and soil profile pore were analyzed. The results showed that topsoil porosities were decreased in different extend with infiltration head increasing, while topsoil bulk density were increased vice versa. Based on this, the mechanism of infiltration coefficients varying with heads was further explored.(3) Larger physics experimental device was developed, and the characteristics of infiltration and soil moisture movement of single water storage pit were studied in homogenous and layer homogenous soil respectively. The soil moisture was measured by using gamma ray instrument. The range, shape and advancing variance of wetting front and the distribution of soil moisture in soil mass were analyzed; Numerical model of 2-D infiltration and soil moisture movement of single water storage pit in layer homogenous soil was established, and complicated boundary conditions were determined, ADI and Gauss-Seidel iterative method were used to solve model, and verification test was conducted. Determining irrigation technical factors such as two-pit distances are based on these.(4) Numerical model of 3-D infiltration and soil moisture movement of complicated boundary conditions and multi water storage pit in layer homogenous soil was also established. The model was solved by using the methods of time-divided and Gauss-Seidel, and verification test was conducted. Both results showed that the calculated values were in accordance with the experimental results. This indicated the numerical model was correct, and the method of solution has better accuracy. Using this model, irrigation qulity of this method can be evaluated, and how to irrigate correctly is indicated.(5) The soil moisture distributions under the conditions of the interference infiltration in multi pits and the free infiltration in single pit were compared and analyzed. The results indicate that the distribution of soil moisture is more uniform and can improve irrigating quality under certain multi water storage pit irrigation condition. This provides theoretical foundation for determining irrigation technical factors reasonably.