Trench is understood to be a deep loosening of the soil to three digs of the spade.
Rigoling is necessary, when deep-rooted vegetables are to be grown on land with a weak layer of topsoil and firm subsoil. In addition, you can transform moorland with a sandy subsoil into fertile vegetable land by trenching. In the first case, care must be taken, that the topsoil, so the top layer, does not get into the subsoil when digging. After digging, all layers must be back in their original place. The lower ones are then only loosened. In the second case, the layers must be mixed when trenching, i.e. the sand lying in deeper layers with the peat soil previously lying on top. Since the peat soil is usually acidic, lime must also be worked into the upper layer, in order to achieve the required degree of reaction. Trenching should generally be carried out in autumn and when the ground is open.