Efficiency of four different seeded plants and native vegetation as cover crops in the control of soil and carbon losses by water erosion in olive orchards

Soil erosion is intense on steep slopes, where many olive orchards are located in Mediterranean areas. The adoption of cover crops is a promising soil and water conservation practice for these areas. Nevertheless, there has not been enough information to be able to advise farmers on the selection of plant species. The purpose of this report is to assess different plant species as cover crops to reduce erosion and soil organic carbon loss through sediments. Twenty-four tests were performed in 6 plots on a 20% slope in southern Spain. A gramineous plant (Brachypodium distachyon), 2 leguminous species (Vicia sativa and Vicia ervilia), and a cruciferous plant (Sinapis alba) were sown and compared with spontaneous vegetation and conventional tillage. Simulated rainfall with intensities of 18.1 (+/- 1.6) and 38.8 (+/- 2.3)mmhr(-1) was applied during 2years. All cover crop treatments, in comparison with tillage, significantly reduced soil and soil organic carbon losses by more than 92%, S.alba being the species with the lowest runoff values. The high rate of soil and water losses observed in the tillage treatment emphasizes the need to protect the soil and its fertility. A kinematic wave model considering variable soil infiltration rates was fitted to the runoff data to evaluate relevant soil and surface characteristics. The estimated saturated hydraulic conductivity and length of the capillary scale were not affected by the treatments, but the surface resistance to water flow indicated the efficiency of S.alba, B.distachyon, and V.ervilia in reducing the runoff velocity.