Soil temperature and moisture jointly regulate agronomic processes; however, their coupled dynamics across the entire soil profile remain insufficiently resolved under contrasting tillage systems. This study investigated the annual hydrothermal dynamics of a Mollisol under a soybean–maize rotation managed with conventional (CT), reduced (RT), and no-till (NT) practices in Northeast China. High-resolution automated monitoring from 5 to 270 cm over multiple years revealed that tillage established two distinct pedophysical regimes. No-till functioned as a capacitively buffered system characterised by high structural inertia. NT exhibited a 33% slower autumn cooling rate, a 108% longer winter near-isothermal period indicative of prolonged latent heat release, and a 47% slower spring warming rate at the surface compared with CT. Concurrently, CT exhibited significantly lower volumetric water content (θᵥ) throughout most of the year. During peak summer deficit, surface θᵥ under NT was 49% higher than under CT. In contrast, CT operated as a conductive–advective regime, displaying rapid thermal responses, deeper frost penetration, and episodic winter warming pulses associated with advective heat transfer via upward water migration, which depleted deep soil moisture reserves. These findings reveal a critical agronomic trade-off: CT provided a warmer seedbed in spring (accumulating 55 additional growing degree days >5 °C by late May), whereas NT ensured superior moisture retention during climatically sensitive reproductive stages. Conservation management, therefore, engineers a more resilient soil environment that buffers hydrothermal extremes, enhances water-use efficiency, and supports sustainable crop production.