Emitter clogging in subsurface drip irrigation (SDI) systems is affected by many physical, chemical, and biological factors, but field evaluation on emitter performance under varying clogging conditions is still lacking. Field evaluations were conducted on the SDI installations in a solar-heated greenhouse applied to tomato to investigate the effects of fertigation, dripline depth, andlayered-textural soil on emitter clogging. These installations, which had been operated for two years, included 33 experimental plots with dripline depths of 0, 15, and 30 cm, total number of fertigation events varied from 0 to 19, and total amount of urea fertigated varied from 0 to 1023 kg/hm~2. Field evaluation demonstrated that, averaged for all the plots, 2.7% ofthe emitters can be declared to be clogged with discharge reduced more than 25%, and 2.1% of the emitters were completely clogged. No significant influence of total number of fertigation events and fertilizer applied as well as layered textural soil structure on emitter clogging was observed, but a slightly greater discharge reduction resulting from clogging was found for surface drip irrigation plots than for subsurface drip irrigation plots. No emitter clogging caused by root intrusion was detected. An investigation on the distributions of clogged emitters in the systems revealed that most clogged emitters occurred at the terminals of the laterals. To quantitatively evaluate the effects of emitter clogging on the uniformity of water application, thecoefficient of variation for emitter discharge (CV) was related to discharge reduction percentage (Rq), showing that CV increased linearly with an increasing R_q resulting from clogging,
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