Research On Reasonable Value Of Micro-Irrigation Uniformity

Uniformity is an important criterion to measure the irrigation quality of micro-irrigationsystem. Also it's a key parameter in the procedure of micro-irrigation system design. In orderto get the reasonable micro-irrigation uniformity for different plants, this paper firstlyproposed the equation for emitter local head loss calculation, on the basis of which,established the uniformity calculation model considering hydraulic, manufacturer andmicro-topography deviation through hydraulics analytical theory of forward step method,analyzed the relationship between irrigation water amount and yield. On the same time, theuniformity and output-input ratio(the ratio of output and irrigation annual investment) fordifferent submain unit was simulated, moreover, regarding uniformity as decision variable,the maximum output-input ratio as objective function, micro-irrigation uniformityoptimization model for different plants was established. Through the above research, theconclusion are listed as follows:(1) The effecting factors of lateral local head loss were emitter flow rate, emitter plugsection area, emitter number and lateral diameter. Lateral local head loss was withproportional relation to emitter number, emitter plug section area and emitter flow rate andwith inverse relation to lateral diameter.(2) The proportion of lateral local head loss to frictional loss changed from0.02to1.10,which was determined by emitter plug section area, number, flow rate, spacing and diameter.In some extreme cases, the local head loss was larger than the frictional head loss. Therefore,in micro-irrigation design, using Eq.(2-4) to calculate local head loss was recommended.(3) The output-input ratio increased and then decreased when uniformity increased.There was a maximum value for output-input ratio. Taking watermelon as example, thereasonable uniformity is0.78, a tiny increase in uniformity would cause a sharp decline ofoutput-input ratio when it was beyond reasonable value range. When uniformity increasedfrom0.83to0.93, the output-input ratio would decreased by58.57%. Therefore, blindlypursuit high irrigation uniformity was not acceptable in micro-irrigation otherwise wouldcause the economic loss.(4) Emitter manufacture variation, micro-topography deviation and manifold inletpressure effected the uniformity and output-input ratio dramatically. Through the analysis ofrelationship between uniformity and effecting factors, the emitter manufacture variation coefficient should be controlled in the range of0.00-0.10. The micro-topography deviationcoefficient should not be larger than0.10for micro-pressure drip irrigation or when themanifold inlet pressure is small. Manifold inlet pressure could be lower than6m when fieldslope is smaller than0.09cm. The exact optimized value of manifold inlet pressure should beexplored further.(5) The software for micro-irrigation aid design was developed, which can select theoptimized value of uniformity for different plant, calculate the pressure and flow rate of eachemitter, calculate the crop yield and system investment, generate the pipe line layout diagram.