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.