Terracing is a method of farming consisting of building platforms along a slope. Often stone walls are built at the hedges of the terraces to support their weight and to ensure them to stay in place. There are two types of terracing techniques: graded terracing and level terracing. In the first ones, the slope can vary along its length, whereas, in the second ones, the terraces follow a contour line. The main goal of terraces is to reduce slope gradient and the length by interrupting the slope at periodic intervals. As a consequence, water speed will be reduced to a non-erosive velocity leading to reduce soil erosion and surface runoff. By slowing down water velocity, this intervention avoids washing away of nutrients and promotes a better water infiltration and, hence, soil moisture is improved.
Terracing has already been used by Inca populations living in South American mountains who took advantages of this technique to make hilly and mountainous terrains arable. Terracing is mostly used in arable lands, vineyards and orchards. It adapts to a large range of slope gradients (in the Mediterranean area from moderate, >15%, to steep, 25%, slopes). This technique has been intensively developed in the Mediterranean area to deal with the risk of soil erosion after heavy rainfall events, that are typical in this region. Indeed, the increasing demand for agricultural products often leads to deforestation in Mediterranean region and to conversion of the land use in the hillsides, exposing soil to atmospheric agents.
Building terraces can involve the use of heavy machineries for cutting and levelling the steps, as well as for building the walls and digging a drainage dyke. Optionally, every step can also have a drainage ditch just above the ridge that collects water and channels it to the next step. Usually, steps have a slight grade so that the water collected by the ditch can move toward the outlet.
Terracing is widely spread and applied in many different regions. Moreover, to improve its efficiency, terracing can be combined with other intervention that aim to reduce soil erosion, like zero tillage or cover crop.
Food and Agriculture Organization of the United Nations, 1991, Chritchley & Siegert, Water harvesting, http://www.fao.org/3/u3160e/u3160e00.htm. Reproduced with permission
WOCAT, 2012, Schwilch, Hessel & Verzandvoort, Desire for Greener Land, https://edepot.wur.nl/212528. Reproduced with permission.