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The straw composite pipe is a permeable pipe made of straw and soil as the main raw materials, which can replace the field capillary for underground irrigation. In order to provide reference for the design and application of straw underground irrigation system, the working pressure and drying time were used as experimental factors to study the effects of working pressure, pressure increasing process, depressurization process and drying time on the water permeability of straw composite pipe under the condition of free outflow. Influence. The results show that: under the condition of free outflow, the cumulative water seepage amount of the straw composite pipe increases with the increase of the working pressure, and the cumulative water seepage amount has a power function relationship with the water seepage time. The water seepage process of the straw composite pipe can be fitted by the Philip infiltration formula; When the working pressure head is 10-50 cm, the water seepage of the straw composite pipe is 0.6-3.6 L/(m h); the steady water seepage rate has a linear relationship with the working pressure. The uniform coefficient of water seepage after the composite pipe reaches stable water seepage is all above 0.85; the pressure rise and fall process affects the seepage flow rate of the free outflow of the straw composite pipe, and the change range of the seepage rate in the depressurization process is greater than that in the pressure increase process; drying time and working pressure The water seepage of the straw composite pipe is affected interactively. Increasing the drying time can increase the water seepage of the straw composite pipe, but its water seepage stability decreases. [ABSTRACT FROM AUTHOR]

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Subsurface irrigation is a type of water-saving technology. However, poor anti-clogging abilities and large energy consuming of the existing subsurface irrigation emitters present a significant obstacle to the development of subsurface irrigation. Aimed to this problem, a new type of subsurface irrigation emitter, vertical tube emitter, was proposed. This study investigated the effects of pressure head, vertical tube diameter, initial moisture content, and soil bulk density and infiltration time on infiltration characteristics of soil moisture under irrigation system with vertical tube emitter. Laboratory experiments were carried out in State Key Laboratory Base of Eco-hydraulic Engineering in Arid Area in silt loam. The experiment was conducted using an orthogonal design method including 9 treatments and one control test. In the experiment, the pressure head was designed with different levels of 0.6, 1.3 and 2.0 m, the vertical tube diameter was 4, 8 and 12 mm, initial moisture content was 7%, 10% and 13% and soil bulk density was 1.32, 1.37 and 1.42 g/cm3. During the experiment, the cumulative infiltration was measured by difference of water levels in Markov bottle. The water level was recorded every 1, 2, 5, and 10 min in the first 100 min, every 20 min from 100 to 180 min, and every 30 min from 180 to 300 min, and every 60 min from 300 to 420 min. The empirical equation was established between cumulative infiltration and influence factors. The first derivative of the equation with respect to time was considered as the infiltration rate empirical equation. Then the partial deviation of the equation with respect to each factor could reflect sensitivity of infiltration rate to each factor. Based on the curves of influence factors and cumulative infiltration, an empirical model was established to estimate cumulative infiltration. The model had the determination coefficient of 0.96 and the measured and estimated values were correlated with correlation coefficient 0.98 (P<0.01). The model was validated with measured values of control test. The validation revealed R2 higher than 0.99 and the root mean square error from 0.1125 to 0.1353 L, indicating that the established model was good at cumulative infiltration estimation under irrigation system with vertical tube emitter. The effect of pressure head, vertical tube diameter and infiltration time on cumulative infiltration was the largest among all the factors. The infiltration rate decreased greatly during the first 2 h of experiment then stabilized after 5-6 h. The stable infiltration rate was 0.08-0.25 L/h when the pressure head was 0.6-2.0 m, vertical tube diameter was 4-12 mm, initial moisture content was 7%-13 % and soil bulk density was 1.32-1.42 g/cm3 during 7 h. The sensitivity analysis results showed that pressure head was the main factor affecting the infiltration rate, followed by vertical tube diameter, soil bulk density and initial soil moisture content. The infiltration rate had a positive correlation with pressure head and vertical tube diameter, however, had a negative correlation with initial moisture content and soil bulk density. And the rate of change of infiltration rate reduced gradually for all the influence factors. In the future, depth of vertical tube emitter and muddy water infiltration should be considered in studying the infiltration characteristics of soil moisture in the irrigation system with vertical tube emitter, and filed experiments should be combined with pipe network system to study the practical application effects of vertical tube emitter. [ABSTRACT FROM AUTHOR]