The invention concerns a system for the artificial underground irrigation or watering of soil, with flexible tubing of porous material. 
It is known to irrigate or water soil with the said of pipes or tubes laid underground. 
In German Auslegeschrift No.  1,759,909, tubes of plastic resin for the irrigation or watering of soil are described, which is composed of swellable plastic foam, and the outer surface of which is a substantially non-permeable membrane, in which at appropriate intervals from each other, openings are disposed.  In order to obtain these openings, the membrane must be provided with cuts or punctures. 
It is disadvantageous that it is extremely difficult to provide the cuts or punctures with an exactly accurate size and depth as desired.  It thus becomes unavoidable, that from the openings which turn out too deep or too large, undesirably much water escapes from the irigation pipe, so that flooding can occur at such places in the ground, whereas other places are provided with too little water.  In addition, such openings tend to become easily obstructed as a result of the infiltration of earth or plant roots. 
Moreover foam materials, which are produced according to customary methods working with swelling agents, are less suitable for the provision of a controlled addition of water, since on the one hand the structure of the cavities is very irrigular, and, on the other hand, such structures react very strongly to pressure changes. 
Also, as mentioned in U.S. Pat.  No.  2,807,505, pipes having a foam structure possess the risk of collapse when they are not filled with water, so that one is forced either to keep the pipes permanently under pressure or to increase the wall thickness, which measures lead to difficulties of their own while providing the water.  It is also a disadvantage of these pipes that they have a wrinkled surface. 
A flexible continuous porous tube is described in German Offenlegungsschrift D.E.-O.S. No.  1,954,748, which is supposed to serve for the distribution on the suface.  This pipe, which is produced from twists, mats, or webs of fibers, should display a porosity which is the least in the vacinity of water supply and is the greatest at the end of the tube.  The production of such tubing is extremely complicated.  Beyond that, with webs, twists or the like of fibers or filaments, a constant or a continuously decreasing porosity is obtained only with great difficulty; with the slightest defect in the web construction there arises larger openings, through which the water can penetrate unhindered into the ground, so that also with this type of tubing there are problems similar to those which have already been mentioned above. 
German Offenlegungsschrift D.E.-O.S. No.  2,642,623 describes a tubing for the purpose of irrigation, in particular for droplet or below ground watering, the cross-section of which has an approximately spiral form.  The ends of the spiral are connected by an elastic longitudinal cross-piece, which is closed during pressure-less state of the tubing, and proceeds approximately radially and with increasing interior pressure becomes bent in the direction of a peripheral position.  At lengthwise intervals, there are disposed in the cross-piece from time to time outflow canals, through which with suitable pressure, the water should be admitted into the ground.  Apart from the fact that such constructions are complicated, the matter of operation of such irrigation tubes is strongly endangered when the tubing becomes pinched, e.g. through stones or compressed masses of earth, to such an extent that with increasing interior pressure they cannot expand. 
Such a system only a watering concentrated at points, and no uniform continuous irrigation at all places along the pipe; in other respect, there is also present here the risk of clogging. 
Although already a great number of arrangements are known for the underground irrigation of soil, there persists yet a need for improved systems for the underground irrigation and watering of soil, which do not display the above-mentioned disadvantages.