Were prehistoric cereal fields in western Norway manured? Evidence from stable isotope values (δ 15 N) of charred modern and fossil cereals

Charred cereal grains from archaeological contexts in western Norway were selected for stable carbon and nitrogen isotope analysis. Single grain analysis was used on 76 grains from 16 sites covering the Late Neolithic (2300–1800 bce ) to the Middle Ages (1030–1537 ce ). The cereals from archaeological contexts (postholes and agricultural layers in soil profiles) indicate increasing δ 15 N values with time. In the Late Neolithic–Early Bronze Age δ 15 N values for Hordeum vulgare var. nudum range from 1.2 to 8.9‰, and in the Early Iron Age the values range from 0.7 to 13.6‰. The values of Hordeum vulgare var. vulgare range from 4.3 to 6.1‰ in the Pre-Roman Iron Age to 3.3–8.7‰ in the Middle Ages. The δ 15 N values of fossil cereals were compared to modern cereals grown in test-plots in western and north-western Norway. The results from the modern cereals show a clear difference between cereals grown in low level and high-level manured fields. Hordeum vulgare var. nudum dated to the Late Neolithic, show δ 15 N values mostly falling within the range of modern day ecologically grown cereals with a low-level manuring regime. Cereals from later time-periods show higher δ 15 N values equivalent to modern day moderate- to high-level manuring regimes. Our results indicate manuring and possible use of marine resources and the existence of permanent fields from the Late Bronze Age (1200 bce ) onwards.