Soil, fertilizer and plant density: Exploring the influence of environmental factors to stable nitrogen and carbon isotope composition in cereal grain

Stable isotope analysis (N and C) of fossil cereal grains is regularly explored as a means of obtaining insights to past crop growing conditions and agricultural practices. In this study, we assessed how several growth conditions can affect δ¹⁵N and δ¹³C values of modern cereal grain with the aim to help understand isotopic values from ancient cereal remains. We investigated the impact of fertilizer intensity, plant density, and soil type on cereal grain δ¹⁵N and δ¹³C values in a short-term field experiment using hulled and naked barley, bread wheat, emmer wheat, einkorn, spelt wheat, rye, and oat. We found the following key results: 1) while fertilizing had a significant effect on δ¹⁵N values in grain, the impact varied between species, and cereals grown in heavy clay had consistently higher δ¹⁵N values in grain compared to those grown in light sandy soil, and 2) the δ¹³C values were significantly different between cereal species, but the difference was very similar between the two experimental site-locations. These findings obtained from plants grown under known conditions contribute to better understand how natural conditions and anthropogenic activities effect crop isotopic data and is of relevance for isotopic research on archaeological crop remains.