Soil erosion is a global issue, but particularly severe in Mediterranean hillside orchards due to the semi-arid climate, topography, climate change, and farming practices. Seasonal, annual cover crops successfully control soil erosion in orchards, this thesis used plant traits to determine effective cover species, as this not been previously considered.
Ten species, native to Spain and previously used as erosion-reducing cover crops, were assessed for above and below ground plant traits, infiltration and evapotranspiration. Brachypodium distachyon, Bromus rubens, Medicago sativa and Silene vulgaris showed the most promise for erosion control. In a field trial in Cordoba, Spain, these species revealed no nutrient competition between cover crops and tree crops but, the high carbon:nitrogen ratio and high nitrogen (N) content of the cover crops could increase soil N. A mesocosm trial was conducted using rainfall simulation to determine the runoff and soil loss from monocultures and a mix of Brachypodium distachyon, Medicago sativa and Silene vulgaris. All the vegetated plots significantly reduced soil loss compared to the bare plots, furthermore M. sativa had a dominant impact on the mix. Despite the knowledge that plants reduce soil loss, few tree crop farmers use vegetation cover. A survey and interviews were conducted to understand this practice, while most of the respondents used cover crops, they believed that lack of knowledge about sustainable soil management was a key barrier to the use of vegetation cover.
In conclusion, plant traits analysis provided vital information about the potential impact of species on soil erosion. However, the interactions of the species within mixes, and in the field, needs to be taken into consideration before widespread use. Any Mediterranean plant cover is better than none to prevent soil loss, which is a severe and urgent issue in Spain, therefore a clear transfer of information to farmers is vital.