Stable water isotopes reveal modification of cereal water uptake strategies in agricultural co-cropping systems

Agricultural co-cropping is being evaluated in temperate environments as a potential nature-based solution to the
changing climate. However, the understanding of underlying physiological processes in co-cropping and its
potential to provide climate resilience in temperate agroecosystems remains limited. This study investigated
water sources for plants in five distinct cereal-legume co-cropping systems and four of their corresponding cereal
monocultures at four main growth stages, under contrasting temperate hydro-climatological conditions in
Scotland. Stable water isotope compositions (δ2H and δ18O) for soil water and xylem water were established.
Based on the isotope compositions, a Bayesian multi-source mixing model was used to explore proportional soil
water uptake patterns for cereal crop plants. Cereals grown in monocultures in this environment took more than
60 % of their water from the upper topsoil (soil depth <5 cm) during the main growth stages, under both wet and
dry conditions. However, cereals cultivated as co-crops with legumes modified their water uptake strategy
through increased water acquisition from the lower topsoil (5 – 30 cm) compared to monocultures, independent
of environmental conditions. These novel findings suggest that co-cropping systems could potentially provide
climate resilience for temperate agricultural systems. The findings provide an evidence-base for sustainable
water planning, drought preparation and environmental intervention policies.