Speakers - 2027

Title: Shallow subsurface thermal response and crop-root zone interactions

Abstract

Shallow borehole heat exchangers and horizontal collector fields are being installed at depths that overlap the rooting zone of arable crops, yet the thermal signature they leave in the upper two metres is rarely measured against what the roots there actually experience. We report monitoring from instrumented shallow-geothermal test sites in Franconia, Germany, combining distributed temperature profiles with soil moisture and crop development records across two growing seasons. Seasonal cooling during the heating period propagates further laterally in loamy substrates than the standard design assumption allows, while the summer recovery phase is the limiting factor for co-use rather than the winter extraction itself. We discuss what this means for dual-use siting of shallow geothermal arrays on agricultural land, and where the current German design guidance would need a correction factor.