Stable isotope analysis (δ¹³C,δ¹⁵N,δ³⁴S) reveal divers manuring practices of rye (Secale cereale) in northern Europe since 1500 years

First analysis of stable isotopes in rye from northern and eastern Germany provides insights into the early history of rye cultivation from the migration to the late medieval period. A comparison of the δ 15 N with modern experiments reveals that already the early cultivation involved the practice of intensive manuring. The intensity of manuring does not demonstrate a discernible trend over time but high variability. In some instances, it is likely that rye was cultivated as part of a rotation cultivation system including manuring. Through its δ 34 S values some rye turned out to be manured with marine peats. Rye, reputed to be a frugal crop, was cultivated on poor sandy soils to a limited extent only. Statistically significant correlation between the 13 C content and yields demonstrates that the highest yield success on dwelling mounds was achieved, while the majority of fields on dry sandy soils yielded in relation only 40 to 70 %. Manured rye facilitated the emergence of multi-headed village communities and towns and stabilized the political power systems. The cultivation on mounds flooded by winter storm surges emphasises that summer rye was initially cultivated, before winter-rye became the dominating crop in Germany until the mid-20th century.