Soil heat flux refers to the amount of heat passing through a soil profile per unit time. Its value depends on the temperature gradient between upper and lower soil layers and the soil's thermal conductivity. Soil temperature is a crucial factor in forest climate and is closely related to plant growth. Different slopes and aspects of forest stands, along with varying light conditions, cause corresponding changes in soil temperature and soil heat flux.
Different vegetation types and site conditions determine the variation pattern of soil temperature, which can affect plant transpiration, root respiration and absorption, and the dissolution rate of various inorganic salts in the soil solution, thereby affecting tree growth.
Studying the impacts of different cover and tillage practices on soil temperature and moisture can improve land productivity. Complete and accurate spatiotemporal distribution data of soil temperature are needed for research on global climate change, environmental process simulation, elemental geochemical cycling, and the evolution of soil physicochemical properties.
When the Earth's surface absorbs solar radiation, the heat is transferred to deeper layers through molecular conduction, warming the lower layers. Conversely, when the soil surface cools and the temperature drops below that of the deeper layers, heat is released from the deeper layers.
The thermal state of soil is expressed by temperature, but temperature is not a physical property of the soil itself. Soil thermal properties refer to the physical properties of soil that affect heat flow and temperature changes, mainly including thermal conductivity, heat capacity, and thermal diffusivity. Soil heat flux is an important component of the energy balance on the Earth's surface.
Soil thermal conductivity and heat capacity are commonly used to estimate soil heat flux. According to research, studies show that soil heat flux varies more significantly on sunny days than on cloudy days, and more significantly outside forests than inside them. As air temperature decreases, soil heat flux exchange shifts from downward conduction from the surface to upward conduction from the lower layers, causing soil heat flux values to gradually decrease into negative values, especially noticeable on cloudy days.
Soil heat flux sensors are primarily used to measure the energy balance of soil and the thermal conductivity of soil layers. ICBUY distributes several heat flux sensors, such as the Swiss greenTEG gSKIN-XI heat flux sensor, which uses 29 pairs of ultra-high sensitivity thermocouples to measure the heat flux through the sensor's surface. It has an area of 72 mm² and a thickness of 0.4 mm. It features a Class-0 package optimized polymer and a Class-1 packaged metal structure.
