Stable isotope analyses (δ15N, δ34S, δ13C) locate early rye cultivation in northern Europe within diverse manuring practices

Stable isotopes provide insights into the early history of rye cultivation from the Migration period to the late Medieval period (fourth to fifteenth centuries CE). Manuring shows high intensity and diversity throughout. Rye as an undemanding crop resistant to drought was cultivated on nutrient-poor sandy soils to a limited extent only. It became a dominant crop owing to its integration into an existing labour-intensive manuring system mainly based on stable dung. Modern experiments demonstrate that the effect of manuring on cereal δ15N is strongly mediated by the soil substrate. Conspicuously low δ34S values can indicate additional manuring with peat. The Δ13C values suggest that the best harvests were achieved on dwelling mounds close to the sea and that relatively poor harvests resulted on fields on dry, sandy soils. Because the mounds were flooded with salt water during winter storm surges, the crop cultivated there might have been summer rye. Winter rye became the dominant crop in Germany around 1000 CE and continued to be until the mid-twentieth century. Intensive manuring allowed for high yields, which facilitated the emergence of village communities and towns and stable political and religious power systems.