Soil Erosion Mitigation by Perennial Species Under Mediterranean Environment

Soils of the Mediterranean area are subjected to erosion due to the cropping systems and crop managements adopted. This causes a loss of crop productivity that could be initially replaced with an increase of fertilizers, but in the end leads to land abandonment. The areas subjected to soil erosion in the Mediterranean area cover 1,309,000 km(2), equal to 15 % of the land of Mediterranean countries. In dry farming condition, the farmer's choices are often constrained by the prevailing climatic conditions. Rainfall amount and distribution represent the main constraints that lead farmers to choose annual autumn-winter crops. In this environment, the growing cycle of autumn-winter crops, such as durum wheat, determines a lack of soil covering during the first rains that occur in early autumn and winter. Soil losses by erosion also determine nutrient losses and affect soil organic matter content. All these aspects are evaluated by ongoing research started in 1996 in an area of the internal hills of Sicily (Italy) in the center of the Mediterranean basin. In this experimental site, on a 27 % slope, the effect of different cropping systems to determine surface runoff and soil losses was evaluated. In each plot, (40 x 8) m, a series of devices were installed in order to determine the amount of runoff and sediment: four covered trap channels were installed at the bottom of each plot, each channel drained into pipes which emptied into a tank to collect surface runoff and soil losses. After each erosive rainfall, the amount of water, of sediments, and the nitrate-nitrogen were measured. Soil organic matter was determined every fall at 0-30 and 31-60 cm depth. The highest annual values of soil losses were observed in the annual tilled crops, such as the typical Mediterranean crop rotation "durum wheat-durum wheat-fallow" (11.2 t ha(-1) year(-1)). Very low soil losses were observed in the plots managed with perennial crops, alfalfa (0.34 t ha(-1) year(-1)), Italian ryegrass in pure stand and in mixtures with subterranean clover (3.2 t ha(-1) year(-1)), and subterranean clover (1.7 t ha(-1) year(-1)). The perennial giant miscanthus and moon trefoil reduced soil losses to 0.1 t ha(-1) year(-1). The benefit of the cultivation of perennial crops instead of tilled crops was also highlighted in relation to organic matter content. The rotation "giant miscanthus (from 1997 to 2001)-moon trefoil (from 2002 to 2015)" made it possible to increase soil organic matter from 1.03 to 2.51 % in the average of the first 60 cm soil depth.