| Aerated drip irrigation directly transports oxygen or oxygen-containing medium to the crop root zone through the pipe network,optimises the growth environment of the crop root system,and improves the crop yield and quality.However,aeration will interfere with the movement of the original medium in the pipe network,which is easy to cause uneven distribution of water,fertilization and aeration in the drip tape,thus affecting the performance of the drip irrigation system.At the same time,aeration will unbalance the original micro-ecological environment of the drip system,and affect the clogging process of the emitters.The critical aspects to ensuring the quality and effect of aerated drip irrigation are to master the gas production characteristics of the aerated device,clarify the water and gas transmission characteristics of the pipe network under different aeration modes,study the spatial distribution characteristics of water,fertilization and aeration in the pipe network,explore the clogging law and reveal the clogging mechanism of emitters.The venturi injector and micro/nano bubble generator,which are commonly used as aerators in the aerated drip irrigation system,were adopted in this study.Focused on the aero genesis characteristics of the aerating device,distribution law of water,fertilization and aeration in the pipe network,and the clogging mechanism of emitters,numerical simulation and experimental research were integrated designed for systematic study on aerated drip irrigation.The main research results and conclusions are as follows.1.Studying the gas production characteristics of venturi injector and micro/nano bubble generator and their effects on water and gas transportation in drip tape.The gas production characteristics of venturi injector and micro/nano bubble generator under different working conditions was studied,and the movement and distribution of water and gas in the drip pipe network under two aerated conditions were also studied through numerical simulations and high-speed photography experiments.The research found that different aerated devices had their unique gas-producing characteristics.Moreover,the bubbles generated by venturi injector were large and unevenly distributed,while the micro/nano bubbles were evenly distributed.The pressure difference between the inlet and outlet of venturi injector had a significant impact on its gas production characteristics.The internal flow of venturi injector was stable when the pressure difference was small,and the bubbles were distributed evenly with a relatively ideal working condition.When using the venturi injector in the aerated drip irrigation system,the bubbles were easily escaped from the emitters if the drip tape was laid upwards.In contrast,it was easy to form large air plugs if the drip tape was applied downwards,which would form layered flow at the end of drip tape and increase the risk of water hammers.When using the micro/nano bubble generator in the drip system,the mixed flow and transmission of gas and water in the drip tape were almost unaffected by other factors.Therefore,the micro/nano aeration method was more suitable for drip tape to be laid over long distances.2.Studying the spatial distribution and uniformity of water,fertilization and aeration in the drip network under different irrigation modes.A performance test on the aerated drip irrigation system was carried out,to analyse and evaluate the effects of various technical parameters on the spatial distribution and uniformity of water,fertilization and aeration in the pipe network in a comparison between the venturi and micro/nano aerated methods.The results showed that the spatial distribution of water,fertilization and aeration was gradually reduced along with the drip tape.Aeration had no significant effect on emitter discharge but had a substantial impact on the spatial distribution of the total fertiliser and dissolved oxygen content.The impact of the system working pressure on the uniformity of water,fertilization and aeration was extremely significant.However,the impact of aeration mode and the pressure difference between inlet and outlet of fertiliser tank on the uniformity of water,fertilization and aeration were not significant.At the same time,the effect of emitter orientation on fertilisation uniformity only reached a very considerable level.A comprehensive evaluation of the irrigation,fertilisation and aerating quality of the drip irrigation system was conducted with two aerating conditions.It revealed that the micro/nano aerated drip irrigation reached the optimal level in all aspects when the working pressure was 0.1 MPa,and the emitters were set downward.3.Studying the law of emitters clogging and its influence on irrigation uniformity in the aerated drip irrigation.Five types of emitters were analysed to find the law of emitters clogging and the impact on irrigation uniformity in the aerated drip irrigation system.The emitters were flat and cylindrical with different flow rate and pressure compensation functions,and the average discharge ratio variation(Dra)of the irrigation system was adopted as the evaluation index.The dynamic development process of emitters clogging in the experiment was observed.The results showed that the clogging process of different types of emitters was the same as that of the contrast test,but the clogging process of micro/nanoaerated emitters was slow.Micro/nano aerator increased the average working time of each emitter by 20% ? 130%,but with varied aeration effects in different irrigation systems.The multiple linear regression analysis showed that the impact of micro/nano aerating mode on emitter clogging was extremely significant.In the same working time,the irrigation uniformity of micro/nano aerator was higher than that of the contrast test.The clogging process of the emitter intensified when Dra<95%,but the decline rate of irrigation uniformity of micro/nano aerated mode was significantly less than that of contrast test.The micro/nano aeration could make the clogged irrigation devices more uniformly distributed in the pipe network,which is helpful to maintain the irrigation uniformity and further increase the service life of the drip irrigation system.4.Studying the mechanism of emitter clogging in the aerated drip irrigation system.The clogging mechanism of emitters based on the clogging law of micro/nanoaerated drip irrigation emitters was studied.The physical morphology and chemical components of the attachments blocking the emitter channel were observed and analysed by scanning electron microscope and energy spectrum analyser.The microbial community diversity within the emitter clogging was investigated by 16 S r RNA high-throughput sequencing technology,and the core bacterial community affecting the clogging of the emitter was obtained by statistical method.The results showed that the adherence of clogs in the emitter runner was effectively reduced with micro/nano aeration,but had no substantial effect on the composition of the irrigation clogs.Micro/nano aeration significantly reduced the diversity and abundance of microbial communities in the clogs attached to the drip irrigation emitters,considerably reducing the number of core flora which influenced the clogging of emitters.In engineering applications,the number of harmful microbial communities in drip irrigation emitters could be regulated through micro/nano aeration to alleviate the irrigation clogging process and prolong the service life of the drip irrigation system. |
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