Going beyond Soil Conservation with the Use of Cover Crops in Mediterranean Sloping Olive Orchards

Among the agricultural practices promoted by the Common Agricultural Policy to increase soil functions, the use of cover crops is a recommended tool to improve the sustainability of Mediter-ranean woody crops such as olive orchards. However, there is a broad range of cover crop ty-pologies in relation to its implementation, control and species composition. In that sense, the in-fluence of different plant species on soil quality indicators in olive orchards remains unknown yet. This study describes the effects of four treatments based on the implementation of different ground covers (CC-NAT, CC-GRA and CC-MIX) and conventional tillage (TILL) on soil erosion, soil physicochemical and biological properties, and soil microbial communities after 8 years of cover crop establishment. Our results have demonstrated that the presence of a temporary cover crop (CC), compared to a soil under tillage (TILL), can reduce soil losses and maintain good soil physicochemical properties and modify greatly the structure and diversity of soil bacterial com-munities and its functioning. The presence of a homogeneous CC of gramineous (Lolium rigidum or Lolilum multiflorum) (CC-GR) for 8 years significantly increased the functional properties of the soil as compared to TILL; although the most significant change was a modification on the bacte-rial community composition that was clearly different from the rest of treatments. On the other hand, the use of a mixture of plant species (CC-MIX) as a CC for only two years although did not modify greatly the structure and diversity of soil bacterial communities compared to the TILL soil, induced significant changes on the functional properties of the soil, and reverted those properties to a level similar to that of an undisturbed soil that had maintained a natural cover of spontaneous vegetation for decades (CC-NAT).