Drawn or self-propelled agricultural machine intended to form in situ an underground waterproof film. The invention relates to equipment intended to form an obstacle to the losses of rain water in sandy soil by forming in situ an underground waterproof film. This result is obtained by sending out under pressure a liquid or pasty product capable of hardening after extrusion into the sand by means of a die 10 of elongate shape. In order to reach this die 10, the product is firstly injected by the screw press 7 into the pipe 8 which directs it through a space 5 made in the coulter 3 to the back of the plough-share 4 where the extrusion die 10 is located. This method allows the cost-effective formation of buried waterproof pockets which can be used in soil-less cultivation, as well as artificial oases in those places where rainfall is sufficient. <IMAGE>
