The effect of seaweed fertilisation on sulfur isotope ratios (δ³⁴S) and grain size in barley: Implications for agronomy and archaeological research.

Blanz, M., Gröcke, D.R., Martin, P., Church, M., 2024. The effect of seaweed fertilisation on sulfur isotope ratios (δ³⁴S) and grain size in barley: Implications for agronomy and archaeological research. Frontiers in Environmental Archaeology 3, 1465082.

Introduction: Stable sulfur isotope ratios (δ³⁴S) in bone collagen are often employed to study the consumption of marine and freshwater fish, wetland grazing, marine foraging patterns, and the possible geographic origins of food sources. However, a recent small-scale crop experiment showed that biofertilisation with seaweed can elevate δ³⁴S in Celtic beans by ca. 10 ‰. Consumption of this food could erroneously suggest a marine diet and therefore has important implications for the reconstruction of past diets and dietary origins. However, limited research has so far been undertaken on cereals.

Methods: To address this issue, a large-scale field trial was undertaken on the Orkney Islands, whereby bere barley (a Scottish landrace, Hordeum vulgare L.) was biofertilised with seaweed at different dosages (25 t/ha, 50 t/ha), with a mineral NPK fertiliser, and left unfertilised as a control.

Results: The total barley biomass yield was higher and barley grains were enlarged following all fertilisation treatments compared to the control barley. Barley grain and straw from seaweed-fertilised crops had more elevated δ³⁴S values by around 2–3 ‰ compared to unfertilised plants, while the NPK-fertilised grains and plants had δ³⁴S values 1 ‰ lower.

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