| The application of water-saving irrigation technology in the West Liao River Plain,such as drip irrigation under mulch,reduced the ineffective evaporation of water and improved the water using efficiency;but to a certain extent,the farmland underlying surface is changed by the ridging and film due to the implementation of drip irrigation under film,which further affected the evaporation and infiltration process farm land water circulation system.Agricultural irrigation area as one of the main recharge area of groundwater,from the long-term perspective,the change of the underlying surface also affects the groundwater level.In this paper,the characteristics of rainfall infiltration under different subsurface conditions such as drip irrigation under film,drip irrigation without film,surface irrigation and flat bare land were analyzed and compared by field in situ observation test;in addition,two dimensional field infiltration models of drip irrigation under film and surface irrigation was established by using Hydrus-2D,after examination,by changing the initial soil water content condition of the model,the initial water content influence on the characteristics of rainfall infiltration under drip irrigation under film was analyzed.The main study results include the following aspects:(1)The uneven surface water content changes are caused by ridging and mulching,under different rainfall progress,the soil water content and it's change value were all different between film middle?film edge and furrow middle of drip irrigation under film;compared with surface irrigation,the water content added value and increase rate of drip irrigation under film are less than surface irrigation but with the passage of time,the differences of the soil water content increased value would gradually decreased.(2)Ridging can increase rainfall infiltration,while film mulching can decrease the rainfall infiltration,the effect of latter is more effective than the former.The increase of rainfall quantity and rainfall intensity can reduce the blocking effect of plastic film mulching on rainfall infiltration to a certain extent,so as to reduce the difference of the percentage of rainfall infiltration between under-film drip irrigation and surface irrigation.At the same time,the plastic film mulching can reduce the evaporation amount,and the amount of accumulated infiltration under mulch drip irrigation will be larger than that of surface irrigation after a certain amount of rainfall.(3)The maximum vertical infiltration depth of rainfall is mainly affected by rainfall quantity and rainfall intensity,and has little relation with the underlying surface forms.Under the same rainfall condition,the maximum infiltration depth under the four types of underlying surface is approximately the same.The wetting front migration rate,was double affected by rainfall and surface conditions,ridging and film catchment effect,can improve the vertical migration rate of rainfall infiltration of drip irrigation under film,the shorter the duration of rainfall,and the bigger the rainfall,the effect is more obvious.(4)The fitting effect of rainfall infiltration models of drip irrigation under film and surface irrigation is good,which are established by Hydrus-2D.The simulation results of rainfall infiltration process under three different initial soil water content show that,about drip irrigation under film and surface irrigation,increasing the soil initial water content can shorten the surface infiltration time,promote the wetting front vertical migration,and also can reduce the accumulated amount of rainfall infiltration.At the same time,under the influence of lateral migration of drip irrigation under film,the increase of initial water content would reduce the cumulative infiltration gap between drip irrigation and subsurface irrigation. |
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