设计流量和土壤质地对微孔陶瓷灌水器入渗特性的影响

为探明微孔陶瓷灌水器土壤中入渗流量变化的原因,明确微孔陶瓷灌水器的出流原理,该研究基于土桶模拟试验,研究3种设计流量(0.72、1.87和4.40 L/h)的微孔陶瓷灌水器下2种土壤(黄绵土、塿土)的渗流特性。结果表明,使用不同灌水器灌溉后,短时间内入渗流量均迅速减小,而后缓慢减小趋于稳定。设计流量与土壤质地均影响灌水器的出流。灌水器周围土壤水势的变化是造成入渗流量变化的直接原因,土壤含水率的变化是入渗流量变化的根本原因。在没有淹没出流的情况下,土壤含水率越高,入渗流量越小。设计流量为1.87 L/h灌水器应用于塿土中,当土壤含水率由13%增大至40%时,入渗流量由1.4 L/h下降至0.3 L/h左右。灌水器周围土壤含水率对入渗流量具有反馈调节作用。采用微孔陶瓷灌水器作为灌溉系统的核心部件,在内部水头适宜(微压或零压)的情况下,通过灌水器入渗流量与土壤含水率的耦合作用,可实现土壤水分的自动调控,达到主动灌溉的目的。该文可为微孔陶瓷灌水器的推广应用提供参考。

Effects of designed flow rate and soil texture on infiltration characteristics of porous ceramic irrigation emitters

Abstract: Subsurface irrigation has been achieved by using pitchers, pots and ceramic tubes, which has gained a certain degree of interest in arid regions due to its high-water use efficiency. Porous ceramic irrigation emitter is an improved version of the traditional method of subsurface irrigation, and it has good performance and low cost. In order to minimize evaporation losses and deep percolation, a proper design for an irrigation system with ceramic emitters as the core component is required. In this study, we investigated the effects of designed flow rate and soil type on seepage characteristics of soil water content under the irrigation system with ceramic emitter. Soil tank laboratory experiments were conducted with 2 different soil types and 3 designed flow rates. The designed flow rates were 0.72, 1.87 and 4.40 L/h for the 2 soil types (Lou soil and Loessial soil). The Marriote bottle with 15 cm in diameter and 66 cm in height was used to supply water for the ceramic emitter during the experiment, the designed working pressure was 20 cm. The cumulative infiltration was measured by different water levels in Markov bottle. Porous ceramic emitter was prepared by a sintering and compression molding technology using silica, talc and silica sol as raw materials. The discharge coefficient of ceramic emitter was 4.23, 11.71, and 22.85, respectively. When the soil tank was filled with soil, the soil moisture sensors were installed around the ceramic emitter to record the changes of soil water content. The variations of cumulative infiltration, infiltration rate, soil water content, and soil water potential around emitters in the 6 different treatments were analyzed. The results showed that: 1) Infiltration rate of ceramic emitter in the soil decreased gradually with time and finally stabilized. On the contrary, the soil water content around the emitter increased rapidly, tending to approach saturation; 2) Soil texture had a great influence on the infiltration rate. The infiltration rate in lou soil was smaller than that in the loessial soil under the same designed flow rate. Designed flow rate had a great effect on the emitter flow rate in the soil. The average emitter flow rate increased at first then decreased with increase of the designed flow rate; 3) The change of soil water potential was the direct cause for changing of infiltration rate. When the designed flow rate higher than soil saturated hydraulic conductivity, a saturated zone formed around the emitter and a certain positive pressure was generated. Therefore, the infiltration rate was less than the designed flow rate. On the contrary, when the designed flow rate was smaller than soil saturated hydraulic conductivity, the soil water potential around the emitter would be negative pressure and promoted the outflow of emitter, and the infiltration rate would be bigger than designed flow rate; 4) When experiment started, soil water content around the emitter increased rapidly and reached closely to the saturated water content. For the emitter with designed flow rate of 1.87 L/h, the infiltration rate in lou soil decreased from 1.4 to 0.3 L/h when the soil water content increased from 13% to 40%. The higher the soil water content was, the smaller the infiltration rate was. Soil water content around emitters had an appreciable negative effect on emitter infiltration rate in the soil. There was a feedback regulation relationship between the water content and emitter flow rate. If a porous ceramic emitter with an appropriate designed flow rate, which working pressure head was extremely low or zero, the soil water content can be automatically controlled and the emitter would take the initiative to irrigate. Irrigation system is an interrelated subsurface system of irrigation water, ceramic emitter and soil, therefore, in the future, more factors such as working pressure, designed flow rate and soil saturated hydraulic conductivity should be comprehensive/y considered in studying the seepage characteristics of ceramic emitter.