| The seriously shortage of water resources is the first restrict factor for the sustainable development of agriculture in our country. The innovation of irrigation technology is foundation of the development of water-saving agriculture. Subsurface drip irrigation is one of micro-irrigation technology that has large potential of water-saving, and will become the new innovation in the future.The effective factors of uniformity of subsurface drip irrigation was analyzed in this paper, and the manufacturing variation of simple orifices, rules of soil water movement and emitter discharge under subsurface drip irrigation, hydraulic characteristics and calculation of lateral in air were studied through experiment. The main results are as follows:(1 )Exactly drilling techniques can ensure lower emitter manufacturing variation. Made simple orifices by electric drill obtained more uniform emitter discharge than by pricked, which is marginal. Pressure discharge relation of the simple orifice is exponential in air and soil. The flow regime of simple emitter is situated between laminar and turbulent.(2)The emitter discharge of simple subsurface drip irrigation is greater than the infiltration rate after formed saturate loop in the short time. Infiltration rate under subsurface drip irrigation is not only affected by soil texture, original soil moisture content and soil bulk density et al, but also by emitter discharge, which affect by water pressure. Under subsurface drip irrigation, soil wetted front movement when higher soil initial moisture content was quicker than that of when it is lower, so did the supplied water pressure and soil bulk density. The wetted front movement of clay loam was clearly slow than that of sandy soil, especially in the larger soil bulk density. Based on the approximate estimation of wetted front edge of one dimension soil column, the design parameters of SDI were determined primarily.(3) Based on the experiments data, it has been found that if the emitter discharge of SDI was little, the depth of pipe buried should be shallow, and the distance between two micro holes should be chosen to equal or close the distance between two lateral pipes, if the emitter discharge of SDI was great, the pipe may be buried deeper, and the distance between two micro holes could be greater than the distance between two lateral pipes. In above conditionsoil moisture distribution was uniform in tillage layer.(4)Through the hydraulic property experiment of micro-hole lateral pipes of simple SDI in air, it was found that the average pressure of 60 mitre length lateral pipes was at the position of per 40O/o~~~50% of the effectual pipe length from the fist micro-hole, major pressure-loss was occurred at the ahead part of half pipe. The pressure uniformity reduced with orifice aperture抯 increasing, and the relationship between pressure uniformity and initial water pressure was poor. Running under the initial water pressure of 1.5 meter, the discharge uniformity reduced with orifice aperture抯 increasing, and when the orifice aperture smaller than or equal 1.0mm, irrigation uniformity could achieve above 0.6. When orifice aperture larger than 1.2mm, irrigation uniformity was under 0.5. The effect of manufacturing variation on discharge uniformity was large than variation of water pressure in lateral.(5)It was more precise for using Darcy-Weisbach formula to calculate the hydraulic pressure slope curve in the lateral line, but too complexity. Although I-Pm Wu formula is simple, the estimated results were not agreement with the measured data. A coefficient including irrigation uniformity was presented to modify I-Pal Wu formula, and the results were agreement after using the coefficient.(6)According to the relation of pressure and discharge of different orifice aperture from the experiments. the largest available length of lateral pipes was calculated, and the combined method of varied orifice aperture and equal discharge in lateral line was discussed. |
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