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Nitrogen (N) is the main nutrient affecting the yield of the grapevine and its must and wine quality. However, little information exists about the optimum nitrate (NO3-)-N levels for vineyard soils in semiarid climatic conditions. We selected 14 vineyards of the cultivar Tempranillo (Vitis vinifera L.), with ages ranging from 10 to 25 years and located in the lower Najerilla River area (Rioja AOC). There were no climatic variations within the study area. Soil was sampled at depths of 0-15 and 15-45 cm at vineyard bloom (29 June 2010) when the grapevines peaked in their N demand, and the extractable NO3--N in soil was determined. Nitrogen contents in both blade and petiole tissues were determined at veraison (23 August 2010). Anthocyanins and polyphenols content in the must were determined just before harvest. Finally, yield parameters such as grape weight per vine and shoot weight per vine were determined. The soil NO3--N was significantly correlated with the N content in blade and petiole tissues. Also the soil NO3--N contents had a significant correlation with yield parameters. Regarding must, the soil NO3--N was negatively correlated with anthocyanins and polyphenols concentrations, so it seems that a soil with high NO3--N availability decreases must quality. Therefore in these conditions, the determination of the available soil NO3--N at vine flowering could be an indicator of vine N nutritional status, potential yield, and must quality. These preliminary results indicate that more studies are needed to establish an adequate soil NO3--N content to obtain must of the highest quality.