Agricultural resilience and land-use from an Indus settlement in north-western India: Inferences from stable Carbon and Nitrogen isotopes of archaeobotanical remains

Stable isotopic compositions of carbon and nitrogen (δ13C, δ15N) of archaeological grains/seeds recovered from different cultural layers of an Indus (Harappan) archaeological site 4MSR (29°12'87.2"N; 73°9'421"E; Binjor, western Rajasthan, India) provide insights into the Harappan agriculture between 2900 to 1800 BCE. The δ13C values were used to retrieve hydrological status, while δ15N values were used to gauge agricultural intensification. Isotopic data of grains/seeds were generated representing three Indus phases (i) Early phase ( 2900−2600 BCE), (ii) Transitional phase ( 2600−2500 BCE), and (iii) Mature phase ( 2500−1800 BCE). We find δ13C values of barley grains (winter crop) varied in overlapping ranges for all the three phases −21.34‰ ± 1.9; −22.55‰ ± 1.6 and −22.75‰ ± 1.7 respectively (n=10 for each phase) indicating insignificant changes in hydrology for winter crops. For summer crops like cotton, average δ13C values for Transitional phase −23.44‰ ± 1.8 were not significantly different from those of Mature phase −22.55‰ ± 2.5. The δ15Nbarley values varied in wider range, however, intra-phase variability appears to have overlapping values but showing overall increase from Early (7.72‰ ± 1.8) to Mature phase (11.17‰±7.2) indicating a plausible agricultural intensification. We also measured δ13C of host soil organic matter (SOM) and sediment δ15N to assess regional environmental conditions. In contrast to the trends observed for archaeological grains/seeds, δ13CSOM values showed a statistically significant enriching trend from Early (−23.54‰ ± 1.4) to Mature phase (−20.40‰ ± 1.9) hinting a growing aridity in the region. We surmise that Harappan farmers of western Rajasthan region might be managing arable hydrological conditions in their fields through agricultural interventions to continue agriculture practices despite growing aridity in the vicinity. The high proportion of water-demanding crop cotton during the Mature phase despite of changing environmental conditions, also corroborate our interpretation, possibly grown for the trade purposes.