Direct evidence for agricultural intensification during the first two millennia AD in northeast Burkina Faso

Archaeobotanical evidence from archaeological sites in northeast Burkina Faso dating to the first and second millennia AD has provided a useful insight into crop cultivation and the development of the West African savanna landscape. Nitrogen isotopic analysis of charred pearl millet grains from the same sites now provides the first opportunity to investigate how increased crop production and permanence of cultivated fields related to the intensity of household waste/manure application. Nitrogen isotope values of pearl millet grains increased during the first two millennia AD, indicating an intensification of manuring that would have enabled soil to stay fertile for longer, reducing the agricultural footprint of shifting cultivation. This may have been advantageous as population and settlement density increased, thereby increasing competition over land. The intensity of manure application in the second millennium AD at sites close to the Mare d’Oursi suggests that manure was likely sourced from outside the farming settlements, from livestock herded by nomadic pastoralists who would have been drawn to the mare for water. This is rare evidence for specialisation of sedentary farmers and pastoralists, demonstrating how the novel combination of fruit/seed, charcoal, faunal and isotopic evidence used in this study can enrich our knowledge of past lifeways in West Africa.