Underground irrigation or watering of soil

System for the artificial underground irrigation or watering of soil, with flexible tubing of a porous material, characterized by tubes with a non-expanded porous inside structure. The tubes are obtained through extrusion of a homogeneous mixture of at least two components, one component a meltable polymer and the other component a liquid inert in relation to the polymer. Both components forming a binary system displaying in liquid aggregate state a range of complete miscibility and a range with a miscibility gap. Preferred parameters include an inside tubing wall surface with open pores and an outer wall surface, the degree of openings of which, calculated as fraction of open area, is reduced at least 20% in relation to the inside wall surface; open pores in the outer wall surface for the most part of a pore diameter of less than 4 mu m; tubes with a pore cavity volume of from 50-90%; tubes made of polypropylene; tubes made of glass fiber-reinforced polypropylene; tubing wall thickness of about 0.5 to 2.5 mm and outer diameter of about 2.5 to 25 mm. The tubing may be disposed within tubular-shaped sheaths of a matted web, composed of a plurality of fibers melt-spun from synthetic polymer, crossing over in places and fused together at the places of crossing. The sheaths may have a longitudinal grooved contour, and the matted web may be composed of polycaprolactam fibers with a diameter of about 0.2 to 1.5 mm. Couplings composed of the same material as the sheaths may be disposed at intersections thereof. The system is useful for the irrigation of grass, for irrigation in several layers, for permanent irrigation in arid zones, for the distribution of fertilizer, herbicides and/or pest control agents.