First Direct Evidence of Agrarian Practices in the Alava Plateau (Northern Iberia) During the Middle Ages Through Carbon and Nitrogen Stable Isotope Analyses of Charred Seeds

This paper presents the results of carbon and nitrogen stable isotope analyses on 50 charred seed samples from the medieval villages of Zornoztegi and Aistra, dated to between fourth and fourteenth centuries CE. The assemblage was mainly formed by Triticum aestivum/durum, although some Hordeum vulgare, Avena and Vicia ervilia samples were also included. Despite the social and political differences between the sites, no big contrasts were found between them. According to Delta C-13 values, watering was predominantly low to moderate. There were statistically significant differences in the distribution of carbon stable isotope ratios of wheats between Zornoztegi and Aistra, as moderately and well watered grains were more common in the former. Barley samples were consistently in the range of poorly watered grains, while bitter vetch were extremely variable. Nitrogen isotope ratios were very homogeneous across taxa and between sites, and they pointed at the predominance of low manuring regimes, with only a few samples within the range of medium manured crops. No significant chronological changes in any of the indicators were found throughout the Middle Ages.