| Groundwater is the key to economic development and ecological security in the semi-arid agro-pastoral zone.Rainfall infiltration is the main mode of recharge under natural conditions.In recent decades,irrigated agriculture has developed rapidly,and the semi-arid agro-pastoral ecotone has become an important agricultural development zone in China.Under the irrigation conditions,groundwater recharge mainly comes from rainfall and irrigation return water.With the development of irrigation districts and the promotion of irrigation technology,drip irrigation under the membrane has been implemented in large scale in the West Liao River Plain.For this region,which is generally dominated by ground irrigation,it will promote rainfall infiltration and regression after drip irrigation under film.Both have a major impact and are bound to change the critical depth of infiltration recharge.On the one hand,there is basically no irrigation return water,which leads to an increase in the equilibrium water level of groundwater.On the other hand,it affects the key hydrological process of rainfall infiltration and recharge of groundwater,further affecting the equilibrium water level of groundwater and forming a new critical depth.This change will bring new problems to the rational development and utilization of regional water resources,and have a fundamental impact on regional water resources management.Therefore,revealing the impact of irrigation mode change on rainfall infiltration and recharge of groundwater has become a key issue in the scientific management of groundwater in the semi-arid agro-pastoral ecotone,and it also has an important practical significance of groundwater safety and water resources for the protection of semi-arid agro-pastoral ecotone.Based on the above problems,the effects of mulched drip irrigation on water infiltration compared with traditional ground irrigation were analyzed by in-situ observation,analysis of deep soil samples and observation of groundwater depth in Xiliao River Plain,and artificial control rainfall observation test in Beijing Daxing.And then,the differences of rainfall infiltration under mulched drip irrigation and ground irr:igation under different rainfall scenarios were analyzed by Soil hydrodynamic model based on the above experiments.Furthermore,in the context of a combination of rainfall,irrigation and evapotranspiration in the study area,the differences of rainfall infiltration under mulched drip irrigation and ground irrigation both in the crop(corn)growth period and the complete simulation year were also analyzed.Based on the above experiments and simulations,combined with soil hydrodynamics theory and the actual effect of mulched drip irrigation on rainfall infiltration.We analyzed the mechanism of the influence of mulched drip irrigation on rainfall infiltration,and established the simulation model of the critical depth of groundwater based on the infiltration principle under mulched drip irrigation in semi-arid area.We then quantitatively calculate the change of critical depth of groundwater after the change of the irrigation method,and propose the critical groundwater depth of the safety control of groundwater under the condition of mulched drip irrigation,and apply it to the study of the suitable area for the promotion of mulched drip irrigation.The main conclusions are as follows:(1)According to the in-situ observations in the field,the effects of mulched drip irrigation on soil water content can be divided into the following two stages according to the growth of corn.One is the initial growth stage:the initial water content unde mulched drip irrigation is 5.8%higher than that of the ground irrigation,which is mainly because that the film preservation can significantly increase the soil water content.The other is the main growth stage:mulched drip irrigation can provide a relatively better growth environment.The soil moisture loss caused by corn growth is greater than that of ground irrigation.The initial water content of drip irrigation under the membrane is 8.8%smaller than that of ground irrigation.Under natural rainfall conditions,with the combination of the in-situ observation data of two fields in the Horqin left flag and Kailu counties,and the effective infiltration of secondary rainfall under mulched drip irrigation was less than that of flood irrigation.The difference between the two was 5.9%.That is,Compared with flood irrigation,the implementation of drip irrigation under mulched drip irrigation will reduce the effective infiltration of rainfall.In terms of rainfall infiltration depth,the two fields in situ observation points showed the same trend:the depth of flood infiltration was greater than that mulched drip irrigation.(2)Through the analysis of deep soil sampling(4-5m),it is found that the infiltration depth under ground irrigation can reach 5 meters or deeper,and the infiltration depth under mulched drip irrigation can reach 4 meters rarely.According to the changes of the well water level,it can be seen that during the growth period of maize(July and August),under the combined effect of rainfall and irrigation,at the depth of about 5 meters,the rainfall infiltration recharge and irrigation return water supply groundwater in the ground irrigation area is obvious.The well water level is uplifted,while the well water level in the mulched drip irrigation area is in a downward trend.After the corn is harvested,the rainfall is reduced and the irrigation is stopped,this means that the groundwater is in a recovery phase.It can be seen from the fluctuation of the well water level that the well water level under ground irrigation is larger than mulched drip irrigation.(3)Under artificial rainfall conditions,the result of water volume change is that the soil moisture in the middle position of bare furrow is the largest,and the ground irrigation is the second,and the position in the middle position of ridge tillage is the smallest.After the end of the rainfall,the water in the middle position of bare furrow disappeared obviously,and the water in the ground irrigation was changed gently.As for the changes on infiltration time,the moisture in the middle position of bare furrow increased at the earliest,and the migration time of water was the shortest between the depths,followed by the ground irrigation,and there was a significant delay in the the middle position of ridge tillage.The infiltration form shows the two-dimensional infiltration change process under the drip irrigation mode under the membrane,that is,the infiltration of the wavy curved surface gradually becomes tangent to the process of planar infiltration.(4)With the simulation of water infiltration under mulched drip irrigation and ground irrigation under different rainfall levels and a whole year,we obtained the difference in infiltration depth between the two irrigation methods under different soil water contents.Combined with the distribution of rainfall during the year and the status of corn planting in the Xiliao river Plain,the change trend of infiltration depth after the change of irrigation method is mostly the category of simulation results of the main growth stages of crops,and the corresponding sub-rainfall infiltration depth is less than the ground.Irrigation.The simulation results of the complete year show that the infiltration process can be divided into infiltration fluctuation stage,infiltration significant stage and infiltration stability stage.The final infiltration depth result is that the ground infiltration depth is 1.3 meters larger than mulched drip irrigation.(5)According to the difference of infiltration process,the effective infiltration amount and soil water content under the two irrigation methods,We calculated of critical depth of rainfall infiltration and recharge to groundwater under mulched drip irrigation.The calculation results show that the critical depth of rainfall infiltration to groundwater under mulched drip irrigation conditions is between 5.1 m and 8.0 m,therefore,the objective of groundwater management under mulched drip irrigation should be tightened.Taking this critical depth range as the control condition,we introduce the mining strength method to generalize the mulched drip irrigation area into the mining area.And then push out the suitable area for the implementation of mulched drip irrigation based on the mining intensity and the maximum allowable depth reduction.The calculation results show that the area promoted by the single-film mulched drip irrigation in the semi-arid area should be controlled within 150,000 mu,which helps to ensure the infiltration of rainfall into the groundwater and maintain the groundwater safety in the area. |
PDF Full Text Request