Study On The Influence Of Temporal And Spatial Variations Of Soil Temperatures In Different Pithead Structures In Winter And Farmland Works Plan And Design Under Water Storage Pit Irrigation

Shanxi Province,in the middle reaches of the Yellow River,located in the east of Loess Plateau,which has complex topography,drought,little rainfall,and serious soil erosion.The main commercial crop,apples,of which the cultivated area is more than 5 million mu,have an effect on the development of rural Shanxi.Popularizing high-efficiency water-saving irrigation technology in mountain areas becomes an urgent issue.Water storage pit irrigation,which was put forward by Professor Sun Xihuan in 1998,is a middle-deep three-dimensional irrigation method,having the characteristics of runoff interception and conservation of water and soil.The pithead structure of water storage pit irrigation is important for maintaining a steady temperature of root-zone soil and supporting normal growth and development of fruit trees.In order to determine the pithead structure in farmland works plan and design on sloping land under water storage pit irrigation reasonably,in this study,the diameter and coverage of pitheads are used as control factors of the research on the influence of diurnal variations,inter-monthly variations,and two-dimensional distributions of root-zone soil temperature in winter with different pithead structures under water storage pit irrigation.Accordingly,the type of the pithead structure is selected.The study results are also compared with surface irrigation.Five treatments are set up: DF30(covered,30 cm in diameter),DB30(uncovered,30 cm in diameter),DF5(covered,5 cm in diameter),DB5(uncovered,5 cm in diameter),DM(surface irrigation).Combined with the study results,theoretical basis,and the field condition,the farmland works on sloping land under water storage pit irrigation is planned and designed.The main conclusions are as follows:(1)The diurnal temperature variations of pit soil under water storage pit irrigation varies with the change of atmospheric temperature.Soil temperature increases gradually with the increase of soil depth in vertical direction;the vertical amplitude of diurnal temperature difference: DF30<DB30,DF5<DB5,DF30<DF5;the vertical soil temperature: DF30>DB30,DF5>DB5,DF30>DF5.In radial direction,with the distance from the pit wall increasing,the soil temperature difference near the pit wall between covered treatments and uncovered treatments is larger,and decreases with the increasing distance from the pit wall;the radial soil temperature: DF30>DB30,DF5>DB5,DF30>DF5;the soil temperature difference between DF30 and DF5 decreases with the increasing distance from the pit wall.(2)The inter-monthly temperature variations of pit soil under water storage pit irrigation varies obviously with the change of atmospheric temperature.From November to February,the soil temperature decreases gradually with the decrease of atmospheric temperature.The soil temperature increases gradually with the increase of soil depth in vertical direction;the monthly decline of soil temperature of each treatment: DF30<DB30,DF5<DB5,DF30<DF5.The soil temperature variation becomes less obvious with the increasing distance from the pit wall.From February to March,the soil temperature increases gradually with the increase of atmospheric temperature;the range of rising temperature: DF30<DB30,DF5<DB5,DF30<DF5.The soil temperature after rising: DF30<DB30,DF5<DB5.(3)Every treatment under water storage pit irrigation has the similar spatial distribution of soil temperature.The soil temperature difference between covered treatments and uncovered treatments is larger at the bottom of the pit.Covered treatments have lower soil temperature amplitude and higher soil temperature.(4)The diurnal variation and inter-monthly variation of soil temperature under water storage pit irrigation at different positions in vertical direction and radial direction are obviously different.Near the surface,covered treatments under water storage pit irrigation and surface irrigation treatment almostly have the same soil temperature,and the soil temperatures of uncovered treatments under water storage pit irrigation are lower than any other treatments obviously.In the middle-deep soil layers,the rising ranges of soil temperature with the increasing depth in covered treatments under water storage pit irrigation are obviously larger than the surface irrigation treatment.The soil temperature in the deep soil layers of uncovered treatments under water storage pit irrigation is larger than uncovered treatments or the surface irrigation treatment.(5)Compared with other treatments,the soil temperatures in DF30 are more stable.The pithead structure in DF30 is selected in the farmland works plan and design.The pithead structure is a circular plate made of polyethylene plastic,which is 30 cm in diameter,5 cm thick.(6)The plan and design of farmland works on sloping land under water storage pit irrigation: parallel ditches are adopted in land leveling;each tree is allocated 4 pits,the water storage pits are 40 cm deep,under the retention capacity of rainfall runoff standard of 24 h maximum rainstorm volume occurred 5 years,according to the principle of simultaneous runoff producing and confluence in the control area of single tree,the pit diameter is calculated to be 30 cm;every pit is decorated with a baseplate,a solid wall and a head cover as a whole;the annular grooves are 20 cm deep,30 cm wide,with a radius of 50 cm;the pipe network is T-type,including main pipes,branch pipes and laterals;the laterals which each has 4 exit holes are 3 m long,25 mm in inner diameter;the branch pipes are 92 m long,50 mm in inner diameter;the main pipes are 195 m long,81.4 mm in inner diameter;a type 200QJ40-104/8 well pump is adopted,with a rated power of 18.5 kW.