PROBLEM TO BE SOLVED: To provide an irrigation system with negative pressure difference which can stably function for a long period of time. ;SOLUTION: A plurality of perforated tubes 2 are buried in the soil and the tubes are saturated with water from the storage tank and the water in the tube is oozed into the soil or the soil water is taken in the tube 2 according to the difference between the negative pressure in the soil contacting with the perforated tube 2 and the negative pressure within the perforated tube. This irrigation system is equipped with a free air remover which can remove the free air in the water-flowing path by forcibly flowing the water through the path connecting the perforated tubes to the water tank intermittently.;COPYRIGHT: (C)1997,JPO
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