Manuring and stable nitrogen isotope ratios in cereals and pulses: towards a new archaeobotanical approach to the inference of land use and dietary practices

This paper explores the impact of animal manure application on the delta N-15 values of a broad range of crops (cereals and pulses), under a range of manuring levels/regimes and at a series of locations extending from northwest Europe to the eastern Mediterranean. We included both agricultural field experiments and areas where 'traditional' farming is practised. Our aim is to ground-truth interpretation of delta N-15 values in archaeobotanical crop remains as evidence of past growing conditions and husbandry practices. The results confirm the potentially radical impact of manuring on delta N-15 values in cereals, depending on manuring level, but indicate only a slight effect on pulses, which can fix atmospheric nitrogen. The expected geographical trend towards greater delta N-15 with increasing climatic aridity is not apparent, probably because the growing conditions for crops are 'buffered' through crop management. Each of these observations has fundamental implications for archaeobotanical interpretation of delta N-15 values as evidence of land use practices and (together with analysis of bone collagen/tooth enamel in potential consumers) palaeodiet. (C) 2011 Elsevier Ltd. All rights reserved.