Root zone temperature effects of underground HVDC cables on crop yield, root growth and nutrient composition in agricultural cropping systems

Abstract

Underground high-voltage direct current (HVDC) cables cause persistent soil warming and increase root zone temperature (RZT). However, their effects on crop yield, root growth, and soil–plant interactions remain insufficiently quantified. To address this gap, we developed a low-cost, large HeAted soiL Monolith (HAL-M) system for use under controlled greenhouse conditions. This system simulates cable-induced soil heating at a depth of 1.4 m, enabling an integrated assessment across multiple crops. Using this system, we investigated effects on plant growth, root development, yield, nutrient concentrations, and quality parameters within a sequential crop sequence comprising spring barley, sugar beet, spring wheat, and lucerne grown on two contrasting soils and under three water regimes. To enable a crop-independent analysis across the crop sequence, a group-specific ratio normalization was applied to isolate heat-induced responses, using the final, fully integrated dataset of the entire experimental period. Across all investigated crops, elevated RZT reduced root intensity and aboveground biomass and were generally associated with reduced crop yields, while quality parameters, namely protein concentration and adjusted sugar content, increased. However, responses were highly crop-specific. The strongest negative effects occurred during the first growth phase following soil reconstruction, whereas later phases showed reduced or no yield responses. In contrast, sugar beet exhibited increased yields under elevated RZT. Excluding the initial growth phase eliminated significant yield differences at the crop-sequence scale, although reduced root growth persisted. This approach provides a framework for assessing the agricultural risks of underground energy infrastructure and supports evidence-based decision-making in land-use planning, cable routing, and mitigation strategies to minimize the impact on crop productivity.