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) mm hr−1 was applied during 2 years. 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.
Establishment of groundcovers (GC) is an efficient practice to reduce soil and nutrient losses in olive orchards, so they can act as a sink of atmospheric carbon and improve soil fertility. The aim of this study was to assess the carbon sequestration potential of several species used as groundcovers in two olive orchards. The experiment was conducted during three growing seasons in two olive orchards in Andalusia (Spain). In an experimental field, a grass (Brachypodium distachyon) and two crucifers (Eruca vesicaria and Sinapis alba) were used; in the other experimental field, three legumes were sown: common vetch (Vicia sativa), bitter vetch (Vicia ervilia) and hairy vetch (Vicia villosa).In both fields the species were sown and compared with the spontaneous vegetation of the area. The carbon release from groundcovers was studied and soil organic carbon (SOC) analysed during the decomposition period to assess the atmospheric carbon fixation. The increments of SOC in the first 20 cm of soil reached higher values with crucifers and grass than legumes. Sinapis alba obtained the best result with 2.56 Mg SOC ha À1 yr À1 . Establishment of groundcovers are an efficient tool for atmospheric carbon sequestration and to protect the soil from erosion.
The organic olive orchard represents about 0.5 Mio ha in EU and 36% are locatedin Spain. This production system implies an economic opportunity for rural areas.The use of cover crops between the rows of olive trees is an agricultural practicethat farmers are progressively adopting since they reduce soil erosion whileimprove soil quality. Due to an usual fertilisation strategy in organic farming is theuse of leguminous plants, three legumes (Vicia sativa, Vicia ervilia and Viciavillosa) used as cover crops were compared to study their capacity to protect thesoil and improve soil fertility during 4 years. Two soil managements wereconsidered after mowing cover crops: plant residues left on surface or incorporatedinto the soil. Soil nitrate and coverage were monitored monthly and soil organiccarbon (SOC) was analysed at the end of every growing season. Despite not beingthe best species to protect the soil, the coverage at the end of decomposition periodincreased by 32% in 4 years in the management without incorporation, providingvalues over 30% of cover. The soil nitrate recorded in May, when the demand forN by the olive tree is greater, increased in the study period by 70% with theresidues left on surface and by 50% when the residues were buried. A carbonsequestration rate of 1.08 Mg C ha-1 y-1 was reached by V. villosa withoutincorporation. Where residues were incorporated, V. sativa obtained the highestcarbon fixation with 1.21 Mg C ha-1 y-1.
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