FOCUS: Estimated wheat yields during the emergence of agriculture based onthe carbon isotope discrimination of grains: Evidence from a 10th millennium BP site on the Euphrates

The analysis of carbon isotope discrimination (Delta) in crop seeds from ar chaeological sites may help to assess yield during early agriculture. Wheat was among the first crops to be domesticated in the Near East. Here, a yie ld model based on Delta in grains from present-day crops of durum wheat (Tr iticum durum Def.) is developed using a wide range of genotypes, most of wh ich were cultivated in the Eastern Mediterranean basin (Syria). A strong po sitive linear regression (r(2)=0 (.)72) between yield on a logarithmic basi s and grain A was observed. Initial estimates of ancient wheat yield were t hen obtained by fitting the Delta values of archaeological grains to the ab ove relationship. The yield estimates were subsequently corrected to take i nto consideration the two main differences between ancient and modern crops not accounted for by the Delta of ancient sample: atmospheric CO2 levels a nd grain/total above-ground biomass ratio. The model was then used to estim ated yields of naked wheat (Triticum durum/aestivum) attained at Tell Halul a, and early agricultural site, ranging from Middle Pre-Pottery Neolithic B (PPNB, c.9550 BP calibrated) to Late Neolithic (Pre-Halaf, c8630 BP calibr ated). This is the earliest archaeological settlement in the Middle Euphrat es region (Rakka Governorate, Syria) at which the cultivation of domesticat ed, naked wheat has been reported. Productivity, calculated from Delta of w heat grains found at this site, was relatively high, with an average (mean +/- S.D.) of 1(.)56 +/-0(.)28 Mg ha(-2). Although these yields are well bel ow those attained in this region by present-day wheat crops under irrigatio n (e.g. 3(.)83 Mg ha(-2), mean value for 1987-1996 period at Rakka Governor ate), they are higher than those achieved for wheat under the current rainf ed conditions of this semi-arid region (1(.)95 Ng ha(-1)) and suggest natur al growing conditions were wetter than those that are prevalent today. In a ddition, our estimates for Tell Halula suggest that Neolithic agricultural practices may have produced greater yields than those to be expected from s trands of wild cereals, which would have favoured the transition from gathe ring to cultivation.