Organic manure and lime change water vapour sorption of a red soil by altering water repellency and specific surface area

Manure and lime as fertiliser and conditioner are widely used on red soils to improve soil fertility and to alleviate soil acidity. Investigating the effects of these compounds on soil interfacial properties is very important for understanding some physical, chemical, and biological processes that are often overlooked. Using a long-term field experiment (2002–2018) on a red loamy clay soil, we explored how the soil water vapour sorption isotherm, soil organic carbon (SOC), pH, cation exchange capacity (CEC), specific surface area (SSA), and water repellency (WR) interacted and were affected by low-rate pig manure (LM, 150 kg N ha⁻¹ year⁻¹), high-rate pig manure (HM, 600 kg N ha⁻¹ year⁻¹), and high-rate pig manure with lime (HML). The HML only increased soil pH relative to the HM. The SSA determined with N₂ (SSA_N2) showed a significant negative correlation with SOC. Both SSA determined with H₂O (SSA_H2O) and contact angle (CA) were significantly positively correlated with SOC. Manure amendments increased soil water content change (WCC) in the water activity (a_w) range of 0.05–0.2 (WCC_0.05–0.2) by 6.3–30.2%, but decreased WCC_0.2–0.6 and WCC_0.6–0.93 by 5.1–12.5% and 2.8–7.0%, respectively. Local hysteresis became more pronounced with high manure or high manure with lime amendment in the intermediate a_w range (0.45–0.75). The observed changes of water vapour sorption were attributed to the alteration of SOC affecting SSA and WR. HIGHLIGHTS: Manure effects on soil water vapour sorption depended on sorption stage and direction. Manure with lime treatment did not affect soil interfacial properties relative to manure treatment. Increasing manure application increased local hysteresis at the intermediate a_w range (0.45–0.75). Soil water vapour sorption behaviour was linked to SOC, SSA, and WR.