Impact of erosion in the taluses of subtropical orchard terraces

The coast of the provinces of Granada and Malaga (SE Spain) are economically important areas for the subtropical fruit cultivation. The climate is characterized by heavy periodic rainfall, which is one of the main factors responsible for soil erosion in this agroecosystem. However, the erosion depends on a host of factors, including soil, topography, cropping and soil-conservation techniques. The most widely taken soil-conservation measure taken on steeply sloped coastal mountains in the zone is terracing. We hypothesise that despite these soil-conservation measures erosion remains a major problem in these steep uplands. Soil loss and runoff were evaluated over a 2-year period (2001-2002) on the taluses of terraces, in this zone of intense subtropical orchard cultivation. The experimental erosion plots (4 m x 4 in in area) were located on a terrace of 214% (65 degrees) slope at 180 in in altitude. The results indicated that soil loss occurs from rainfall runoff depositing topsoil at the foot of the terrace. The average annual soil loss by erosion from the tal uses of the orchard terraces was 9.1 Mg ha(-1) year(-1), with a runoff of 100 mm year(-1) and a rain erosivity index (EI30) of 219.7 MJ mm ha(-1) h(-1). Therefore, under these conditions the terraces had a high risk of rockslide and slump, causing environmental and agricultural damages. The runoff coefficients ranged from 6 to 31%, depending on the intensity and energy of the rainfall events. The present study highlights the severity of erosion in taluses of orchard terraces of southeast Spain and reflects the urgency of planning strategies to protect these structures against chronic destruction