The scarifier is a manual or motorized, agricultural instrument, equipped with metal teeth or knives. It is primarily used to air the ground, i.e. to lacerate the layer of plants which appears with long on certain lawns and which becomes a barrier at the entry of water and elements nutritive in the ground. This layer comes from the foam proliferation (on the wet grounds, in the shade, too compacted) and of the accumulation of waste of shearings which occurs when grass is not collected. It is also used to remove the layer of foam which is unquestionably formed on any grass.