Thermal Properties of Soil Irrigated with Treated Municipal and Industrial Wastewater

Abstract Soil thermal properties are essential for quantifying the coupled heat and moisture flow in the vadose zone and important for developing soil and crop models. This study evaluated the thermal properties of soils at the West Mesa land application site near Las Cruces, NM, which has been irrigated with treated industrial and municipal wastewater (TIMW) for 0 (control), 8, and 14 years. Core and bulk soil samples were collected from 0 to 20‐cm depth and analyzed for bulk density, volumetric water content ( θ ), thermal conductivity ( λ ), thermal diffusivity ( D ), and volumetric specific heat capacity ( C ). The λ and D were significantly lower in soils irrigated with TIMW for 8 and 14 years compared with the control. Long‐term irrigation also increased θ across all soil water pressures, reflecting structural alterations and salt accumulation in pore spaces. Strong negative correlations between sodium (Na + ) concentration and λ ( r = −0.93, −0.92, and −0.94 for 0, 8, and 14 years, respectively) indicate that increasing Na + reduces soil heat conductivity. In contrast , C exhibited a strong positive relationship with θ ( R = 0.94, 0.98, and 0.97), confirming that higher moisture content enhances soil heat storage capacity. Elevated Na + likely promoted salt‐layer formation on soil particles and altered pore geometry, reducing particle contact and thermal pathways. Overall, the findings highlight the importance of monitoring Na + concentrations in wastewater and adopting management strategies to minimize salt buildup, while supporting the improved modeling of soil temperature and moisture dynamics in semi‐arid environments.