Tillage Effects on Thermal Conductivity of Two Soils in Northern British Columbia

Tillage management practices may affect crop growth, in part by altering soil thermal properties. Effects of long‐term conventional (CT), no tillage (NT), and modified no tillage (NTR: NT with surface residue pushed away from a 7.5‐cm zone over the seed rows) systems on soil thermal conductivity ( K ) and water content (θ) were evaluated on Donnelly silt loam and sandy loam (Typic Cryoboralfs). Measured K (M1) was compared with calculated K using the McInnes equation (M2) and a modified McInnes equation (M3, which included additional soil properties). The K in both soils increased with an increase in soil θ; the differences among the tillage systems decreased as the soil dried. Soil K for the silt loam was 0.81 (θ = 0.13 m 3 m −3 ), 0.83 (θ = 0.14 m 3 m −3 ), and 0.84 W m −1 K −1 (θ = 0.15 m 3 m −3 ) in CT, NTR, and NT, respectively, at 25 d after planting in 1992 (a dry year). It was 1.13 (θ = 0.42 m 3 m −3 ), 1.53 (θ = 0.50 m 3 m −3 ) and 1.55 W m −1 K −1 (θ = 0.57 m 3 m −3 ) in CT, NTR, and NT, respectively, at 47 d after planting in 1993 (a wet year). Soil K for sandy loam was significantly lower than for silt loam. Soil K measured by M1 and calculated by both the M2 and M3 methods were highly correlated. However, the calculated K values were somewhat improved, although not significantly, with the M3. Mean K was lower by 0.133 W m −1 K −1 in M2 and by 0.045 W m −1 K −1 in M3 than in M1 under CT on silt loam. Increased soil water storage under long‐term NT produced a greater thermal contact area and, consequently, a significantly greater K under NT and NTR than CT.