土壤点源入渗自动测量系统监测滴头下土壤湿润过程

土壤水运动过程是滴灌系统设计和运行管理的重要内容。该研究采用点源土壤入渗自动测量系统,利用计算机可控数码相机和图像识别技术测量滴灌地表湿润面积和土壤湿润体随时间的变化过程。采用正三棱形有机玻璃土箱,设计一系列点源滴灌室内试验,获得点源滴灌入渗过程随时间的变化过程。试验采用3个流量:2、4及8 L/h处理,每个处理设置了3个重复。用数码相机每4 min拍摄一次地表湿润面积,用于计算地表湿润面积随时间的变化过程。同时,在1、2、3、4、6、8、10、12、20、30、40、50、60、70、80、90、100、120、140、160、180 min时刻,在贴在土箱侧面的透明胶片上,手工记录地表湿润面积和垂直湿润锋面随时间的变化过程。由测量系统根据记录的地表湿润面积随时间的变化过程自动计算得到土壤的入渗过程。通过入渗过程,计算得到滴头下地表土壤的湿润面积,由计算得到的土壤入渗率和计算得到土壤的湿润剖面,将计算结果与实测结果对比,检验测量的精度。结果表明,手工测量得到的地表湿润面积都略大于由土壤入渗自动测量系统计算得到的入渗率计算的地表湿润面积。由计算得到的入渗率预测的土壤入渗深度,略大于实测土壤入渗深度。计算得到前者的相对误差为2%~15%,后者的相对误差为1%~8%。说明土壤入渗自动测量系统,能够准确描述点源滴灌地表湿润过程及土壤入渗过程,并能预测不同流量下垂直入渗深度,测量方法可以为滴灌系统的设计提供相关参数。

Measurement of wetting process of soil under dripper with automatic system for point source infiltration

Abstract: Drip irrigation provides greater efficiency in terms of water usage. It requires adequate design and conscientious management. Soil water movement process is an important content of drip irrigation system design and operation management. Soil infiltration has important impacts on soil water movement and distribution process. Therefore, in this study, the automatic measurement system for point source infiltration of soil was used to measure the wetted areas at soil surface and the wetted depths of soil profile through image recognition technology and computer-controlled digital camera in real time. The digital camera was used to take images of the run-on water advancing in real time before they were processed and then by analysis the wetted areas were determined. According to the wetted soil surface areas, the system automatically computed the soil infiltration rate with the mathematic models outlined in the point source run-on method before the infiltration curve could be displayed on the real-time basis. The soil infiltration measurement system was based on the advancing process of the wetted radius at the soil surface under point source of water supply and based upon the assumption of the ellipsoid-shaped wetted soil body and the principle of water balance. An equilateral triangular-prism soil box of 50 cm long and 50 cm high, which was made of plexiglass, was used in this study for indoor drip irrigation experimental tests, to measure the processes of infiltration and water movement processes. Transparent plastic sheets were pasted on 2 side walls of the soil boxes. The soil materials, with the texture of silty loam consisting of 15% clay, 50.2% silt and 34.8% sand particles, were air-dried before passing through a 2 mm sieve, and then packed into the soil box in 5 cm depth layer at a bulk density of 1.3 g/cm3. The experiments involved 3 dripper discharge rates of 2, 4 and 8 L/h, with 3 replicates. Digital camera that was connected to and controlled by a computer was used to take picture of wetted areas at soil surface in 4 min time interval to get the changing process of the wetted surface areas. Meanwhile, at the time moments of 1, 2, 4, 6, 8, 10, 12, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 160 and 180 min, the surface wetting radius and vertical wetting front process were also manually recorded by using the transparent plastic sheets. AUTOCAD software was used to highlight the wetted surface areas and the wetting fronts before measuring the wetted radius at the surface and the vertical wetted areas by infiltration water. Based on the data, the soil infiltration process under point source was calculated by the automatic measuring system. The wetted surface areas and the vertical wetted areas by infiltration water were computed through the recorded images. The calculated infiltration results were compared with the measured data to verify the accuracy of the measurement. The results showed that the manually measured wetted surface areas were slightly larger than those measured by the automatic measurement system for soil infiltration under point source. The relative measurement errors in wetted soil surface areas were 2%-15%. The predicted vertical infiltration depths calculated by the computed infiltration rate were slightly higher than the manually measured soil infiltration depths. The errors in infiltration depth between the estimated and the manually measured were 1%-8%. Philip and Kostiakov infiltration models/equations were used to fit the measured infiltration processes. Kostiakov equation provided better predictions of the infiltration processes and Philip model produced dramatically different and irrational stable infiltration rates (negative values). The research results indicate that the automatic measurement system can accurately describe the point source surface wetting process of drip irrigation and soil water infiltration process, and can be used to predict the vertical infiltration depth under different dripper discharge. Soil infiltration automatic measurement system has realized the automation in the soil infiltration measurement under point source. The system and the method are verified by laboratory test data, which can provide basic tools to get the parameters of drip irrigation system, and the relevant reference for the design of drip irrigation system.