Crop water status from plant stable carbon isotope values: A test case for monsoonal climates

Abstract

Stable carbon isotope analysis is increasingly used in archaeology as an indicator of crop water status and/or water management regime. While the technique shows promise, robust modern baseline studies are required to inform and validate archaeological interpretations. Here, we test stable carbon isotope values as a crop water status proxy in a monsoonal climatic context for the first time. Specifically, we test the relationship between grain stable carbon isotope values (δ13Cgrain), water availability, irrigation and soil type in barley ( Hordeum vulgare L. (Zohary and Hopf.)) in north-west India, with the aim of deriving a locally-appropriate model for isotopic interpretation. We test this relationship across a substantial rainfall gradient (200–1000 mm/year) and find a negative logarithmic relationship between climatic water availability and δ13C. However, there is significant noise in the relationship, and we report δ13Cgrain variation of over 3‰ amongst samples drawn from similar climatic contexts. Soil type, irrigation type and irrigation frequency have no clear modifying effects. We conclude that: (1) barley stable carbon isotope values can act as an archaeological water status proxy in monsoonal areas, but will be most sensitive in areas receiving <450 mm rainfall per year; and (2) it is not possible to precisely infer water management regimes. On the basis of our results, we propose guidelines for archaeological barley stable carbon isotope interpretation in north-west India and analogous monsoonal climates.

Water and soil management strategies and the introduction of wheat and barley to northern China: an isotopic analysis of cultivation on the Loess Plateau

“…The interpretation of δ 13 C and δ 15 N values from charred crops relies on principles established through measurements taken from controlled experiments and traditional non-mechanised farming settings in Europe and the Eastern Mediterranean, North Africa and South Asia (Bogaard et al 2007; Fraser et al 2011; Styring et al . 2016; Jones et al 2021). These studies provide comparative estimates of the degree of 13 C and 15 N enrichment produced by varying water and soil fertility regimes.…”

“…The dispersal of crops and farming techniques across prehistoric Eurasia led to profound social transformations and ecological impacts across the continent (Jones et al 2011;Liu et al 2019). Between the sixth and the second millennia BC, the cultivation of wheat and barley expanded from its centre of origin in South-west Asia into East Asia, while the cultivation of broomcorn millet (Panicum miliaceum) and foxtail millet (Setaria italica) dispersed in the opposite direction: from northern China into Central and South-west Asia and Europe (e.g.…”

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

“…vegetation type (C-3 versus C-4) and in turn dryness of soils (Agnihotri et Wang et al, 2008). This rationale is predominantly rely on the principle that C isotopic data is a good indicator of palaeo-hydrology and vegetation type (Ferrio et Different geological locations may have different sensitivities of these isotopic proxies (Jones et al, 2021 and reference therein), semi-arid conditions of the studied site 4MSR (Binjor) situated on the bank of dried Ghaggar river channel (~ 160 km away from major urban centre of Indus Civilization i.e. Harappa town) could be an ideal locale to investigate agricultural manifestations versus hydrological status of agri-elds in the past.…”