Environmental impact from mountainous olive orchards under different soil-management systems (SE Spain)

Soil erosion, runoff and nutrient-loss patterns over a two-year period (1999-2000) were monitored in erosion plots on a mountainside with olive (Olea europaea cv. Picual) trees under three different types of soil management: (1) non-tillage with barley (Hordeum vulgare) strips of 4 m width (BS); (2) conventional tillage (CT); (3) non-tillage without plant strips (NT). The erosion plots, located in Lanjaron (Alpujarras) on the southern flank of the Sierra Nevada Mountains in south-eastern Spain, had 30% slope at an altitude of 565 m and 192 m(2) (24x8 m) in area. The highest erosion and runoff values, ranging from 10.5 to 40.7 t ha(-1) yr(-1) and from 26.5 to 51.5 mm yr(-1), respectively, over the entire study period, were measured under NT. In CT, erosion ranged from 1.0 to 10.4 t ha(-1) yr(-1) and runoff from 6.7 to 15.2 mm yr(-1), while under BS, erosion ranged from 1.7 to 2.4 t ha(-1) yr(-1) and runoff from 19.6 to 20.0 mm yr(-1). It is concluded that the BS and CT reduced the soil erosion by 92% and 78%, with respect to the NT, and the runoff by 49% and 72%, respectively. The total NPK losses (sediments and runoff) from BS averaged 0.87, 0.07 and 0.72 kg ha(-1), from CT 1.82, 0.11 and 0.97 kg ha(-1) and from NT 3.15, 0.29 and 2.45 kg ha(-1), respectively. In addition, nutrient concentrations in the surface runoff were higher than the recommended level for standard water quality for N-NO(3), N-NH(4) and soluble P, particularly from NT and CT. These results support the recommendation of non-tillage with barley strips for sloped agricultural land in order to reduce erosion and pollution.