Study And Simulation On Soil Moisture Movement Of Rainwater Collection And Infiltration System

Drought and water shortage are the main bottlenecks restricting the sustainable development of the apple industry in the Loess Plateau.Severe water deficits not only affect the yield and quality of fruit trees,but also lead to the drying of deep soils and exacerbate ecological degradation in the area.Therefore,the effective use of limited rainfall has important scientific and practical significance for improving the quality and efficiency of dry farming orchards.The Rainwater collection and infiltration systems?RWCI?is an in situ filtration technology that can not only preserve but save water for dry farming orchards.This technology has been applied in mountainous orchards in the Loess Plateau,but the mechanism of water regulation of this system is still unclear,and the research on the optimal design depth is weak.This study utilized this technology as the research object,with the method of indoor soil box simulation test and HYDRUS-2D numerical model,studied the soil moisture migration process of typical RWCI system,and proposed the optimal design depth for different ages of the orchards system;together with long-term monitoring explored the relationship between the spatial and temporal distribution of soil moisture and rainfall infiltration in the RWCI system.This paper provided a reference for the rational design and promotion of the RWCI system in the dryland orchard of the Loess Plateau.The study drawed the following main conclusions:?1?The numerical model of RWCI system was established to determin the influence of the designed pit depth and irrigation amount of RWCI system on soil water transport.To established the soil moisture movement model of RWCI system by HYDRUS-2D model,and the numerical model was verified by laboratory soil box test.The simulated and measured values of moisture front in vertical and horizontal direction and soil moisture content were RMSE,MAE,and NE of 1.900 cm,1.410 cm,0.984,and 1.632 cm,1.260 cm,0.944 and 0.047 cm³cm^-3,0.016 cm³cm^-3,0.916,respectively.Of the same irrigation amount,the design depth had little effect on the horizontal wetting front migration,but as the design depth increasing,the wetting front had a significant difference in the vertical migration and horizontal direction;as the irrigation amount increasing,the speed of wetting front vertical movement was greater than the horizontal moving speed,and the difference between the vertical and horizontal moving distances increased gradually.?2?The optimal design depth of the RWCI system under different apple tree age conditions was determined.The optimal design depth of fruit trees of different ages was obtained by the ratio of root length to root length and the coincidence degree of simulated soil moisture.When the design rain intensity was 60 mm/h,the optimal RWCI system design depths for 6a,14a and 22a age fruit trees were 50 cm,40 cm and 85 cm respectively;when neglected the surface coincidence degree,the optimal design depths for the three different ages of apple trees were 60 cm,70 cm and 85 cm,respectively.When the design rain intensity was 80 mm/h,the optimal RWCI systems corresponded to 6a,14a and 22a age fruit trees were designed to be 50 cm,65 cm and 75 cm respectively.When neglected the surface overlap,the optimal design depths for the three different ages of apple trees were 65 cm,65cm,and 80 cm,respectively.Therefore,the optimal design depth range of 6-year-old fruit trees was 50-65 cm,the optimal design depth of 14-year-old fruit trees was 40-70 cm,and the optimal design depth of 22-year-old fruit trees was 75-85 cm.?3?It revealed the law of water storage and water retention in RWCI system.There was significant differences in the water storage and water retention effects of the fish scale pit?CK?and the RWCI system in different stages of the apple tree growth period from 2016 to2018.The water content of CK soil in the three growth periods was lower than that in RWCI treatment,and the soil moisture change in RWCI treatment fluctuated with rainfall.In 2016,2017 and 2018,the soil moisture content of RWCI40,RWCI60 and RWCI80 was higher in soil water content than the CK in the 0-120 cm soil layer by 4.99%,5.31%,4.60%,5.85%,6.10%,7.12%and 4.46%,4.58%,5.24%.Before rainfall,the soil moisture content of the CK treatment profile was lower than that of each RWCI;on the third day after rain,the migration velocity of each treatment in the vertical direction tended to be stable,and the water content of the RWCI60 profile soil layer increased most significantly;In each treatment,the water content of the soil layer gradually decreased with the evapotranspiration of the soil in 0-40cm.The vertical distribution of soil moisture indicated that the vertical soil moisture content of each treatment during the growth period of 2016-2018 fluctuated greatly in the 0-120 cm soil layer,and the soil moisture content of each RWCI treatment in the 120-280 cm soil layer increased year by year.