Cereal production in the Late Bronze Age to Mamluk periods in the Zerqa Triangle, Jordan, based on irrigation, rainfed farming or a combination of the two?

Abstract

The Zerqa Triangle in Jordan is a steppe zone with low annual precipitation and high potential evaporation. The region is not suited to dry farming, at least not on a reliable scale. This applies not only to the present, but also to a long stretch of the past. From c. 2300 BCE onwards, the climate was comparable, with the exception of a number of short wetter intervals. The prevailing assumption is that from the Late Bronze Age onwards the inhabitants of the Zerqa Triangle subsisted on products from irrigated land.A means to test the validity of this assumption is to measure the Δ13C value of their crops. This figure offers insight into the water availability during the growth of the plants. Barley crops from three sites in the Zerqa Triangle with dates from 1100 BCE to CE 1225 were analysed. The grain was grown during periods with dry climatic conditions. The outcome is that the barley fields were not well-watered, but were not as dry as the present-day rainfed fields in dry south-west Morocco (Styring et al., 2016) or the runoff fed fields in tributary wadis in the Negev Desert (Van Bommel et al., 2021). It might be that truly rainfed fields were cultivated in addition to irrigated fields and gardens during the successive periods. That irrigation systems existed is known (Kaptijn, 2009). An alternative is the combination of crop raising based on precipitation with some boosts from irrigation. Anyhow, the assumption that crops could only be obtained through a well-functioning irrigation system should be questioned.