Effects of marine biofertilisation on Celtic bean carbon, nitrogen and sulphur isotopes: Implications for reconstructing past diet and farming practices.

Darren R Gröcke,Jonathan J Lester,Kurt J Gron,Edward R Treasure,Mike J Church

doi:10.1002/rcm.8985

Darren R Gröcke, Jonathan J Lester + Show 3 more

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https://doi.org/10.1002/rcm.8985

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Abstract

RationaleThe application of fertilisers to crops can be monitored and assessed using stable isotope ratios. However, the application of marine biofertilisers (e.g., fish, macroalgae/seaweed) on crop stable isotope ratios has been rarely studied, despite widespread archaeological and historical evidence for the use of marine resources as a soil amendment.MethodsA heritage variety of Celtic bean, similar in size and shape to archaeobotanical macrofossils of Vicia faba L., was grown in three 1 × 0.5 m outdoor plots under three soil conditions: natural soil (control); natural soil mixed with macroalgae (seaweed); and 15 cm of natural soil placed on a layer of fish carcasses (Atlantic cod). These experiments were performed over two growing seasons in the same plots. At the end of each growing season, the plants were sampled, measured and analysed for carbon, nitrogen and sulphur stable isotope ratios (δ13C, δ15N, δ34S).ResultsThe bean plants freely uptake the newly bioavailable nutrients (nitrogen and sulphur) and incorporate a marine isotopic ratio into all tissues. The bean δ15N values ranged between 0.8‰ and 1.0‰ in the control experiment compared with 2‰ to 3‰ in the macroalgae crop and 8‰ to 17‰ in the cod fish experiment. Their δ34S values ranged between 5‰ and 7‰ in the control compared with 15‰ to 16‰ in the macroalgae crop and 9‰ to 12‰ in the cod fish crop. The beans became more 13C‐depleted (δ13C values: 1–1.5‰ lower) due to crop management practices.ConclusionsHumans and animals consuming plants grown with marine biofertilisers will incorporate a marine signature. Isotopic enrichment in nitrogen and sulphur using marine resources has significant implications when reconstructing diets and farming practices in archaeological populations.

Highlights

Evidence for deliberate soil amendment strategies, or the use of crop fertilisers, has been identified amongst the earliest farming communities in many areas of the world.[1,2] the continued use of synthetic and chemical fertilisers in modern environments is under increasing scrutiny due to climate and human-induced changes in the Earth System.[3]
Different fertilisers can be traced in archaeobotanical remains of crops using stable isotope ratios, current research has predominantly focused on the impact of animal manure,[5] despite evidence for the use of other biofertilisers.[6]
The overall research aim of experimental archaeology is to aid interpretation of the material remains from the human past.[64]

Summary

| INTRODUCTION

Evidence for deliberate soil amendment strategies, or the use of crop fertilisers, has been identified amongst the earliest farming communities in many areas of the world.[1,2] the continued use of synthetic and chemical fertilisers in modern environments is under increasing scrutiny due to climate and human-induced changes in the Earth System.[3]. Szpak et al[62] showed that the use of marine bird guano with very elevated δ15N values (e.g., > +20‰) had a significant effect on the δ15N values of maize (Zea mays), common bean (Phaseolus vulgaris) and summer squash (Cucurbita pepo) in a growth chamber experiment; a similar shift was reported in δ34S values They reported no change in δ34S values in a northern Peru field experiment due to previous, long-term application of ammonium sulphate. The plants were harvested 16 weeks after sowing, measured and dried for subsequent whole tissue carbon, nitrogen and sulphur isotope analysis

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