Pedotransfer Functions of Soil Thermal Conductivity for the Textural Classes Sand, Silt, and Loam

Core Ideas The work describes the estimation of soil thermal conductivity (λ) from easily available soil data. Measured high‐resolution λ(θ) data were used to improve the accuracy of the model of Lu et al. (2014). Reliable pedotransfer functions estimated soil thermal conductivity of classes Sand, Silt and Loam. Good quality λ data need precise, quantitative measurements and accurate, model‐based estimations. Data of soil thermal conductivity (λ) covering the whole range of soil water content (θ) are needed in many environmental disciplines. However, laboratory measurements of λ(θ) are time consuming and costly. Therefore the use of pedotransfer functions is promising. In this study, we describe the procedure of deriving such λ(θ) pedotransfer functions for the FAO texture groups (TG) of Sand, Silt and Loam. First, high‐resolution λ(θ) measurements from saturation to dryness of 43 soils were conducted by two laboratory methods: the evaporation approach and single‐point measurements of λ at distinct water contents. Measurements were obtained for a set of sandy, silty, loamy, and clayey soils, and for two urban soils and two peat soils. The slope and magnitude of the λ(θ) curves show typical dependencies on bulk density (ρ b ) and soil texture. In a second step, the λ(θ) data were used to evaluate the λ(θ) model as suggested by Lu et al. (2014). Fitting this model to the complete data set yielded a poor agreement with RMSE = 0.53 W m ‐1 K ‐1 . However, satisfying results were obtained by dividing the data into TGs Sand, Silt and Loam resulting in RMSEs of 0.18, 0.11 and 0.24 W m ‐1 K ‐1 , respectively. Estimated λ values at low soil moisture (wilting point) were hardly different among texture classes, but λ differences become highly relevant when soil moisture increased to field capacity. The derived pedotransfer functions are an easy‐to‐use approach providing reliable λ(θ) curves for sandy, silty and loamy soils, when only basic soil information (texture and bulk density) are available.