[en] The majority of the world's olive production is concentrated in the Mediterranean basin. Problems of erosion and loss of soil fertility pose a particular threat to the sustainability of this crop. In comparison to tillage systems, cover crops have proven to be an effective way of protecting the soil and producing improvements in its organic matter content. The aim of this thesis is to gain a better understanding of cover crops, in particular in terms of which species most reduce runoff and erosion losses, and which have the most positive effect on soil fertility. The study was carried out with plant species typically used as covers: graminoids, crucifers and legumes. Dead mulches, which to date have been the focus of limited study, were also analysed. Such covers include pruning residues and their benefits were examined in relation to different amounts and residue size. The existence of a vegetation cover, whether sown or spontaneous, reduces runoff and erosion losses. The study carried out using a sprinkler rainfall simulator on 50 m2 plots with a 20% slope showed that the cover crop system significantly reduces soil loss and loss of soil organic carbon (SOC) associated with sediment wash-off. The experiment was carried out over two years with two rainfall intensities (40 mm h-1 and 15 mm h-1) and at two different times of the year (when the cover crop is growing and after it has been mechanically mowed). The results showed that with a cover crops system runoff was reduced by more than 60% compared to a tillage system, and that there were reductions of soil and SOC loss of more than 90%. In addition to protecting the soil against erosion and the associated loss of organic matter, cover crops offer other advantages such as improved physical and chemical properties of the soil as well as contributing to the capture and fixation of atmospheric carbon in the soil. A study was carried out over three seasons on a farm in southern Spain in order to assess the degree of protection during the period of decomposition of the cover after mechanical mowing, and the release of C to the soil. Three species, a gramineous plant (Brachypodium distachyon) and two cruciferous (Eruca vesicaria and Sinapis alba), were compared with the spontaneous vegetation in the area, which is the cover most widely used by farmers. The decomposition of the cover crops released between 2.4 y 4.7 t ha-1 of C, depending on the species, with B. distachyon being the species that generated most biomass and best protected the soil throughout the decomposition period. The climate of the area exerts a significant influence on the growth of the cover crops and thus on the benefits they provide. In fact, meteorological conditions in the third season meant that the gramineous species did not develop as it had in previous seasons, leaving S. alba as the species that fixed the most C as SOC in the soil profile studied. A dead mulch of pruning residues protects the soil for a longer period of time, as it decomposes more slowly. Our study confirms that coverage did not drop below 60% in any of the different treatments tested in an experiment carried out over two seasons (704 days). The treatments involved the use of fine chopped residue (leaves and twigs of up to 8 cm) from spur pruning, as well as both fine and thick residue from a renewal pruning...

[es] En la cuenca mediterránea se concentra la mayor parte de la superficie mundial de olivar. La sostenibilidad de este cultivo está amenazada especialmente por problemas de erosión y pérdida de fertilidad de sus suelos. Las cubiertas han demostrado ser un sistema de cultivo eficaz para proteger el suelo del olivar y favorecer la mejora de su contenido en materia orgánica en comparación con el sistema de laboreo. El objetivo que se pretende con esta tesis doctoral es tener un mayor conocimiento sobre las cubiertas vegetales, en concreto qué especies reducen más la escorrentía y las pérdidas por erosión, y cuáles son más favorables para mejorar la fertilidad del suelo. El estudio se ha desarrollado con especies vegetales típicamente empleadas como cubierta: gramíneas, crucíferas y leguminosas. Se ha trabajado también con cubiertas inertes, poco estudiadas hasta la fecha, como son los de restos de poda, valorándose los beneficios del uso de distintas dosis y tamaño de restos. La existencia de una cobertura vegetal, ya sea sembrada o espontánea, reduce las pérdidas por escorrentía y erosión. El estudio desarrollado mediante un simulador de lluvia por aspersión en parcelas de 50 m2 y una pendiente del 20% demostró que el sistema de cubiertas reduce de forma significativa las pérdidas de suelo y las pérdidas de soil organic carbon (SOC) asociadas al sedimento arrastrado. En el experimento, desarrollado durante dos años con dos intensidades de lluvia (40 mm h-1 y 15 mm h-1) y en dos momentos del año (con la cubierta en su desarrollo y tras su desbroce mecánico), la escorrentía se redujo más de un 60% con el sistema de cubierta y las pérdidas de suelo y SOC en más de 90% respecto al sistema de laboreo. Además de la protección del suelo contra la erosión y la pérdida de materia orgánica que ésta supone, las cubiertas vegetales tienen otras ventajas como la mejora de las propiedades físicoquímicas del suelo y contribuir a la captura de carbono atmosférico y su fijación en el suelo. Para evaluar el grado de protección en el periodo de descomposición de la cubierta tras su desbroce mecánico y la liberación de C al suelo, se realizó un estudio desarrollado durante tres campañas en una finca del sur de España. Se emplearon tres especies, una gramínea (Brachypodium distachyon) y dos crucíferas (Eruca vesicaria y Sinapis alba), que fueron comparadas con la hierba espontánea de la zona, la cual es la cubierta más ampliamente utilizada por los agricultores...