Durum wheat and barley yields in antiquity estimated from C-13 discrimination of archaeological grains: a case study from the Western Mediterranean Basin

This study develops a novel approach by which to estimate cereal yields in ancient times based on the C-13 discrimination (Delta) of ancient grains. F irst, a yield model based on Delta in grains from modern durum wheat (Triti cum durum Desf.) and barley (Hordeum vulgare L.) crops was developed using a wide range of genotypes and Mediterranean environments. For both crops, a strong positive linear regression between yield on a logarithmic basis and the Delta of grains (r(2) = 0.72, 506 d.f. for durum wheat and r(2) = 0.50 , 316 d.f. for barley) was observed; the slope of the relationship was sign ificantly higher for durum wheat than for barley. Initial estimates of yiel d were subsequently corrected from bibliographical data to take into consid eration the two major differences between ancient and modern crops unaccoun ted for by the Delta of ancient samples: atmospheric CO2 levels and the har vest index ratio. As a case study, this method was used to obtain estimates of ancient yields of durum wheat and barley in two areas of the Western Me diterranean Basin (NE and SE Iberian Peninsula) using Delta data of grain s amples from a number of archaeological sites. These sites dated from the be ginning of agriculture in these areas (Neolithic Age, ca 7500 years before present (BP)) to the Middle Ages (ca 800 years BP). Our results show the ab sence of a marked trend in the yields of both durum wheat and barley, which seem to have remained relatively high from the Neolithic to the Middle Age s. The average values for the whole period (mean +/- SD) were 1.61 +/- 0.49 and 1.08 +/- 0.25 Mg ha(-1) for durum wheat and barley, respectively in th e NE Iberian Peninsula, and 1.18 +/- 0.48 and 0.97 +/- 0.30 Mg ha(-1), resp ectively, in SE Iberian Peninsula. These yield estimates are within the ran ge indicated by the limited data (mostly from contemporary written sources) available for the Mediterranean Basin, and suggest relatively good growing conditions throughout the period studied, particularly in the NE Iberian P eninsula.