Enhancing Soil Resilience to Climate Change: Long-Term Effects of Organic Amendments on Soil Thermal and Physical Properties in Tea-Cultivated Ultisols

This study examined the impact of the long-term application (25 years) of tea waste (TW), compost (COM), and neem oil cake (NOC) compared to conventional synthetic fertilizers (CONV) on soil thermal and physical properties of a tea-cultivated Ultisol. Soil samples were collected from 0–15 cm and 15–30 cm depths of an experimental site of the Tea Research Institute in Sri Lanka. These samples were analyzed for soil thermal conductivity (k), volumetric heat capacity (C), thermal diffusivity (D), bulk density (BD), aggregate stability, soil organic carbon (SOC), and volumetric water contents at 0 kPa (θ0) and 10 kPa (θ10). TW and COM significantly (p < 0.05) increased surface SOC, leading to better aggregation, lower BD, and, consequently, a substantial reduction in k and D compared to CONV plots. Further, TW and COM amendments slightly increased C compared to CONV plots due to elevated SOC and water content. However, NOC had no impact on soil thermal and physical properties compared to CONV. The reduced thermal conductivity and thermal diffusivity indicated an improved soil capacity to buffer extreme temperature fluctuations. Moreover, soils treated with TW and COM exhibited greater water retention and improved soil resistance to erosion. The findings suggest that the long-term application of tea waste and compost could be a sustainable soil management strategy for improving soil health and enhancing resilience to climate change in tea-cultivated Ultisols.