A COMPARISON OF UNIFORMITY MEASURES FOR DRIP IRRIGATION SYSTEMS

Abstract

Three drip irrigation systems were installed in 1984, two with laterals on the soil surface and one withlaterals about 0.30 m below the soil surface. These systems were used to apply irrigation water and nutrients to severalexperiments from 1985 to 1992. Emitter plugging, system uniformity, and overall performance were evaluated for bothsurface and subsurface systems using several methods, and the results were compared to those obtained for unused tubingthat had been saved from the original lot. Emitter uniformity values calculated for the unused laterals by the traditionaland ASAE EP458 methods were similar, but differences between parameter values calculated by the two methods weregreater for the used laterals, especially in the subsurface system. All uniformity values were lower for the subsurfacesystem, primarily because of plugged emitters. Uniformity values calculated by the EP458 method (randomly selectedemitters) indicate lower emitter uniformity for the used laterals in the subsurface system, but these values were not as lowas those calculated using all emitters on three laterals for that system. These values indicate that the EP458 method maynot always reflect true system uniformity, probably because of the small sample size and existence of completely pluggedemitters. Correction of emitter flow rates for temporal pressure variation among test times improved uniformityparameter values slightly. Uniformity values predicted by design/evaluation models were similar for both surface andsubsurface systems, and generally indicate better system uniformity than values calculated from emitter flowmeasurements. The models were unable to predict reliable uniformity values for systems because of their inability tohandle emitter plugging. Based on these results, it appears that both traditional and ASAE EP458 methods can be used toevaluate drip irrigation systems, but the EP458 method generally indicates lower uniformity and should be used carefullyfor systems where completely plugged emitters may exist. When emitter plugging occurs, the accuracy of predictions byeither method will depend primarily upon the number of emitters measured and the extent of plugging. Entry of soilparticles into this eight-year-old subsurface system during construction and/or repair operations probably caused theobserved emitter plugging, which emphasizes the need for exercising great care in installation and maintenance ofsubsurface systems if a long system life (10-15 years) is expected.