The effect of mole drainage on soil temperatures under pasture

Abstract

SUMMARYDrainage is often claimed to increase soil temperatures in early spring by decreasing the soil's heat capacity. Measurements of water table depth, soil water content and soil temperature were made during winter and spring on mole‐pipe drained and undrained plots of a silt loam soil under pasture. Despite differences in water table depth and soil water content, drainage had no observable effect on soil temperature.Laboratory measurements of the thermal properties of soil cores at a matric potential of −4kPa and then at saturation showed the volumetric heat capacity increased from 3.1 to 3.3 MJ m−3 K−1, with a proportional increase in the thermal conductivity from 1.1 to 1.2 W m−1 K−1. The thermal diffusivity remained unchanged. These values were used in a numerical simulation of the effects of drainage on the seasonal and diurnal oscillations in soil temperature. It is argued that the soil heat flux under pasture in spring is unaffected by drainage. The predicted temperature differences due to drainage are of the order of 0.2°C. As differences of this magnitude were observed between replicate thermometers in the field, it follows from the calculations above that any differences in soil temperature due to drainage would be too small to detect.