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Little attention has been given to the utilization of permanent cover crops in vineyard agroecosystems in semi-arid Mediterranean climatic conditions to increase soil organic carbon or its effects on N availability. We evaluated the effect of permanent cover crops with resident vegetation on labile organic matter fractions and inorganic N availability with respect to conventional tillage in a semi-arid vineyard. The field experiment was conducted on Typic Haploxerept soil, located in La Rioja area (Central River Ebro Valley). Soil samples were collected during June 2009, 5 years after covers crops were established. Soil organic carbon (SOC), water-soluble carbon (WSC), potentially mineralizable nitrogen (PMN), nitrate (N-NO3-) and ammonium (N-NH4+) were measured. At soil depths of 0-2.5 and 2.5-5 cm the cover crops increased SOC, WSC and PMN. So the results indicated a soil quality improvement. The cover crop treatment reduced soil N-NO3- and increased the WSC to inorganic N ratio at 0-45 cm depth. PMN and WSC increments suggest a more active microbial biomass that could promote the immobilization and recycling of N-NO3-, and therefore might partially explain the reduction in N-NO3- pools under cover crops.