Experiment And Simulation Of Soil Water Movement Characteristics Of Bubbled Root Irrigation

Bubbled root irrigation is a new type water-saving irrigation technique, and it belongs tounderground localized irrigation. Its emitters buried under the soil surface. and the irrigationwater and the liquid fertilizer will be transmitted to the zones of crop’s root using irrigationemitters and auxiliary facilities. It haas many advantages of no effecting on the soil surface,improving soil physical and chemical properties, resucing the soil evaporation and cropdiseases and insect pests. Due to the large discharge rate and high terrain adaptability，bubbledroot irrigation has been applied in jujube and afforestation irrigation，the water use efficiencyhad been improved greatly. The emitter of bubbled root irrigation can prevent blockingeffectively because it has broad passageway and the external casing which can store water canprevent the soil to enter the emitter’s outlet When the water flow out from the emitteroutlet,it will store in the casing, then move into the soil from the holes on the casing, so, theboundary of water connetts with the siol is columnar. This is different with traditional dripirrigation and infiltrating irrigation in the rules of the soil infiltration characteristics, themoisture soil wetting-body form and the soil moisture distribution compared. The studies onthe soil water movement characteristics and influencing factors of bubbled root irrigationwere short as present. It’s necessary to study the soil water movement characteristics ofbubbled root irrigation in the different boundary conditions and determine the influencingfactors and related laws, for which were the design basis of the irrigation system and providetheoretical basic for the effective management of crop moisture of bubbled root irrigation.Because the bubbled root irrigation has the external casing for storing water，the flowboundary contacting with the soil is columnar. This is different with drip irrigation andinfiltrating irrigation. Based on four discharge rates, three opening rates and two openinglength of the external casing, the infiltration experiments of the bubbled root irrigation weredid for studing the changing of soil moisture body shape, the distribution condition of soilmoisture in the wetting body, the process of soil moisture distribution and fading again afterthe water. The results showed that under the bubbled root irrigation, soil moisture is affectedby not only Gravitational potential and Capillary potential but also the water head in thecasing. The range of high water content area in wetting body significantly enlarged with the flow rate increases, but the uniformity decreased with the gradient of the moisture distributionincreasing. The contour level of wetting body shrink to infiltration surface and upwardelongation at vertical with the casing length having holes increasing. The high water contentarea changes significantly, the contour has an offset upward trend as a whole. The choice ofthe casing length having holes should let the wetting circle formatting after irrigation cancontain the plant root as far as possible. And through the vertical social distance of moisturecircle had increased，the zone of high water content in the wetting body had been included inthe distribution range of the main root system as far as possible. The recommendation openinglength should not more than15cm in this study. The wetting body water distribution was moreuniform and infiltration rate increased with the increases of casing holing rate. According tothe experimental results，it is reasonable to choose opening rate of21.94%.This paper was based on the theory of unsaturated soil water dynamics and combined thecharacteristics of soil water movement under bubbled root irrigation，established a infiltrationmodel with columnar flow boundary and solved the model numerically by using theHYDRUS-3D software. The model is validated through the contrast of measured values andsimulated values of the soil moisture changing with times. The results showed that thesimulation results agreed well with measured values. The relative error between simulatedand measured values is less10%，both of them have better consistency. The simulation resultscan provide some theoretical basis for the rational design and operation of the bubbled rootirrigation system. The influences on soil moisture content by emitter’s discharge and casingholing length were studied through numerical simulation. The results showed that the rate ofmoisture migration increased with the increasing of emitter’s discharge The differencescaused by emitter’s discharge decreased over time. The range of soil wetting body slightlyreduced with the dripper discharge increased when the test adopted same water capacity；Theincreases of the opening hole areas had no significant effect on the wetting body shape andsize；But it caused larger influence on soil moisture distribution. The moisture circle whichformed by Infiltration became bigger with the increasing of initial moisture content in thecondition of the same irrigation water and flux. After the initial moisture near the infiltrationsurface had increased for10%and20%，the soil moisture content had increased for0.67%、1.12%after infiltration，and the soil moisture content of wetting position had increased for5.13%、9.52%，the farther from the infiltration surface，the difference caused by the initialmoisture content will be bigger.