Sustained Bronze Age Agricultural Practice at the North Sea Coast: Insights from Weed Ecology and Charred Cereal Grain Stable Isotopes at Bjerre, Denmark

The Nordic Bronze Age (1700–500 BCE) was a period of profound socio-cultural transformation, evidenced by the interment of elites in mortuary monuments and by novel participation in wider European exchange networks. Emmer, spelt and naked barley were staple crops cultivated throughout the Bronze Age, with other cultivars added to the agricultural repetoire and permanent fielding systems installed by the mid-first millennium BCE. However, little is known about how these crops were managed through manuring and watering. Here, we investigate agricultural development at the multi-period Bronze Age site of Bjerre through stable carbon and nitrogen isotope analysis of charred emmer/spelt, naked barley and free-threshing wheat grains combined with functional weed ecology analysis. Cultivation strategies at Bjerre minimally disturbed soils and involved limited manuring, suggesting low labour inputs and an extensive agricultural regime. By the Late Bronze Age, agricultural investment at Bjerre intensified somewhat, a development that was accompanied by a shift to more permanent fields. Notably, manuring intensity did not change over the course of the Bronze Age for any crop species. Furthermore, low carbon and nitrogen isotopic variation visible in free-threshing wheat compared to emmer/spelt and naked barley may indicate that cultivation of free-threshing wheat took place on a more limited scale. Overall, these agricultural practices were largely sustained over the Bronze Age, suggesting strong transmission of agricultural knowledge passed along generations.