Water And Salt Transport And Regulation Technology Driven By Farmland Tile Drainage In Arid Area

Water scarcity and soil salinization are two key factors affecting the ecological environment and sustainable agricultural development.High soil salinity in farmland will significantly reduce food yield,and unreasonable irrigation and salt washing will cause serious waste of water resources.Subsurface pipe drainage can effectively regulate soil moisture and salinity to improve soil salinity elution efficiency.In order to study the effects of field-scale subsurface pipe burial depth,subsurface pipe outlet regulation height and irrigation volume on soil water and salt transport characteristics under the surface irrigation mode of northwest arid irrigation area,this study verified the HYDRUS-2D model rate based on the field data monitored by Yichang Experimental Station in Hetao Irrigation District in2019 and 2020,and set up different scenario schemes to simulate the spatiotemporal distribution characteristics of drainage salt discharge and soil profile water and salt distribution under the synergistic influence of free drainage of subsurface pipe,controlled drainage and drainage and irrigation.The results of the study showed that:(1)Under the condition of free drainage,the cumulative drainage and salt discharge are inversely proportional to the spacing of the subsurface pipe and proportional to the buried depth of the subsurface pipe.The moisture content of soil profile decreases with the decrease of spacing and burial depth during the drainage period,and the decrease decreases with the increase of time,and the upper layer decreases greatly in the early stage of drainage and the lower layer decreases greatly at the end of drainage.The difference in soil profile moisture content between 5 m and 100 m at a burial depth of 1.5 m was 9.16% at the beginning of the growth period and 0 at the end of the growth period.The difference in soil profile moisture content between 0.6 m and 2.5 m at a distance of 25 m was 7.69% at the beginning of the growth period and 0.12% at the end of the growth period.The soil moisture content showed a "sickle" shape change with the increase of depth,and the initial amplitude change of drainage decreased with the decrease of subsurface pipe spacing and the increase of burial depth,and then the amplitude decreased and the maximum value decreased.The salt content of soil profile decreased with the decrease of subsurface pipe spacing and burial depth during the non-drainage period,and the decrease increased with time,and the decrease was greater than that in the upper layer.The salt content of soil profiles between 5 m and 100 m at a burial depth of 1.5 m reached a maximum difference of 55.16% with the increase of growth time.The average salt content of soil profiles buried at a depth of 0.6 m and 2.5 m at a distance of 25 m reached a maximum of 50.39% with the increase of crop growth time.(2)Under the condition of subsurface pipe control drainage,the cumulative discharge amount and salt discharge amount are inversely proportional to the control height of the subsurface pipe outlet.Under the condition that the buried depth of 25 m was 25 m,the cumulative displacement was reduced by 27.28%,61.67%,76.98% and 92.03% when the outlet was raised by 0.2,0.5,0.7 and 1.0 m compared with the outlet elevation of 0 m.The cumulative salt discharge decreased by 26.86%,61.30%,76.72% and 91.93%,respectively.The regulation of subsurface pipe outlet highly affected the temporal and spatial changes of soil profile moisture content and salt content.The moisture content of soil profile increased with the increase of the elevation height of the outlet of the subsurface pipe during the drainage period,and the increase decreased with the increase with time,and the upper layer increased greatly in the early stage of drainage and the lower layer at the end of drainage.Contrary to the temporal variation of soil water content,the salt content of different treated soil profiles increased with the increase of the elevation height of the subsurface pipe outlet during the non-drainage period,and the increase increased with the increase with time.Compared to free drainage,controlled drainage can increase soil profile moisture content and salinity.(3)The level and vertical distribution uniformity of soil water content and salt content under the conditions of free drainage and controlled drainage of subsurface pipe after irrigation were improved.The coefficient of variation of the water content level of free drainage soil was within 3.50%,and the controlled drainage was within 3.57%.The vertical coefficient of variation of free drainage soil water content was within 5.35%,and the controlled drainage was within 5.85%,both of which were weak variability.The coefficient of variation of salinity content in freely drained soil after irrigation was within 2.42%,and the controlled drainage was within 4.04%,both of which were weak variability.The vertical coefficient of variation of the salinity content of free-drained soil was about 14.82%,and the controlled drainage was about 13.71%,both of which were moderate variations.Under the condition of subsurface pipe spacing of 25 m,the uniformity of water and salt distribution in controlled drainage soil was higher than that of free drainage.Subsurface pipe control drainage has better water and salt control effect than free drainage.(4)Irrigation and rinsing supporting subsurface pipe drainage facilities have a significant impact on soil water and salt transport and improvement of salinized soil.Reducing the amount of irrigation water can increase the accumulated drainage and salt discharge of the subsurface pipe.For soil water and salt,with the decrease of irrigation water,the average water content and soil storage of soil profile decreased,the average salt content of soil profile increased,and the soil desalination rate also decreased,but the overall level remained at a high level of more than 60%.There was no significant difference in the average water content and salinity of soil profile treated with 10% reduction in irrigation on the basis of conventional irrigation and subsurface pipe drainage treatment.On the other hand,the drainage salt discharge and soil profile water content under the drainage control treatment of the subsurface pipe were greater than the free drainage of the subsurface pipe.Therefore,from the comprehensive analysis of soil water and salt transport,water saving and moisture preservation and salt control,the drainage and irrigation coordination technology that reduces 10% on the basis of conventional irrigation and combines the drainage and drainage control of subsurface pipe is an irrigation and drainage mode suitable for Hetao irrigation area.