| Due to the emitter buried in the soil,subsurface drip irrigation effectively inhibits the evaporation of surface soil,reduces the loss of water evaporation,and has obvious water saving and yield increasing effect.However,subsurface drip irrigation has the problems of high energy consumption of system operation,and emitter clogging caused by negative pressure suction and root invasion.To this end,inspired by the ancient pot irrigation,the research group developed a porous ceramic emitter by replacing the labyrinth channel of the traditional emitter with ceramic micropores,and realized continuous and adaptive irrigation under micro-pressure（working pressure of the emitter<0.5 m）.Because the flow rate of ceramic emitter is affected by soil water content,outflow is a dynamic process.The existing hydraulic design method of micro-irrigation engineering is no longer suitable for irrigation system with porous ceramic emitters.Therefore,this paper analyzed the working pressure,flow rate of ceramic emitter and the variation law of soil water content along the lateral through experiments,established the flow calculation model of ceramic emitter,and proposed the lateral hydraulic design method of irrigation system with porous ceramic emitters with soil water uniformity as the evaluation index of system irrigation quality.In order to ensure the long-term effective operation of the irrigation system,the clogging status of ceramic emitters used in the field for two years was analyzed,and the influence of different flushing time on the flow recovery rate of emitters was studied,and then the corresponding flushing measure was recommended.The main conclusions are as follows:（1）The working pressure,flow rate and soil water content distribution of ceramic emitter along the lateral under different irrigation times were studied,and the flow calculation model of ceramic emitter was established.At the beginning of irrigation,the water flow quickly reaches the middle of the lateral,the pressure along the lateral decreases gradually,and the flow rate of the emitter decreases in turn.With the increase of irrigation time,the water in the lateral gradually flows to the end,and the working pressure of the ceramic emitter gradually increases.However,the flow rate of the emitter close to the lateral inlet gradually decreases.The flow rate of the emitter far from the lateral inlet increases first and then decreases,and the soil mois ture content gradually increases.When the pressure along the lateral is no longer changed,the flow is filled with the whole lateral,and the irrigation reaches a stable state.At this time,the flow of the emitter is basically consistent with the soil evaporation,and the soil water content remains unchanged.Based on the experimental data,the mathematical relationship between emitter flow rate and lateral pressure and soil moisture content was established.（2）The allowable value of lateral pressure deviation was established,the limit laying length of lateral was calculated,and the hydraulic design method of micro-porous ceramic root-irrigation lateral was proposed.Based on the soil water infiltration test of the ceramic emitter on a single lateral in the laboratory,combined with the practical application of the ceramic emitter in the field,the allowable deviation of the flow rate of the ceramic emitter was determined,and the allowable deviation of the pressure was calculated.With the allowable pressure deviation as the limitation,the calculation formula of the limit laying length of the lateral was established by combining the head loss and the ceramic emitter flow calculation model.According to the maximum water consumption intensity and irrigation upper limit of crops,combined with the actual size of the field,the formula for calculating the limit laying length of the lateral was applied.The inlet pressure of the lateral was determined by knowing the diameter and length of the lateral,or the inlet pressure of the lateral and the diameter calculated by the length of the lateral were known,and then the hydraulic design method of the lateral for the root irrigation of microporous ceramics was proposed.（3）The clogging status of ceramic emitters used in field for two years was analyzed.The flow recovery rate under different irrigation time was studied,and the irrigation method suitable for microporous ceramic root irrigation was proposed.The main reason for the decrease of the flow rate of the ceramic emitter used in the field for two years is that a layer of sediment is formed on the inner wall of the emitter and a small amount of material enters the micropore.Although the external wall of the emitter was covered with soil particles,it did not enter the micropore,which effectively avoided the occurrence of negative pressure suction.Sediments contain inorganic compounds and organic matter,and the main components are Si O2,Ca CO3,Mg Al2O4 and PLFAs secreted by bacteria and fungi.When the emitter was flushed for 15 min,the flow rate could be restored to 75.56%of the designed flow rate.Further increasing the flushing time had no significant effect on the flow recovery of the emitter.Therefore,it is recommended to flush the irrigation system for 15min under 100 k Pa flushing pressure after a period of operation to ensure the long-term effective operation of the system. |
