Heat Flux Sensor_The Effect of Soil Temperature Changes on its Heat Flux

Soil heat flux sensors are instrumental devices mainly used to measure the energy balance of the soil and the thermal conductivity of the soil layer.

Heat flux is an important parameter describing the soil heat balance, which is one of the important components of the surface energy balance. Its change characteristics have an important impact on soil water-heat coupling process, climate change and agricultural production. When the soil surface absorbs solar radiant energy, the heat is transferred to the deeper layers by molecular conduction, which increases the temperature of the lower layers. Conversely, heat is exported outward from the deeper layers when the soil surface cools down and the temperature drops below the deeper layers.

The thermal state of the soil is expressed in terms of temperature, which in itself is not a physical property of the soil. Soil temperature is one of the most important factors affecting forest climate, and it is closely related to plant growth. Generally speaking, the optimum soil temperature required by plant roots is 20-25°C. Soil temperatures that are too high or too low will affect the growth of forest roots. Different vegetation types and terrain conditions determine the variation of soil temperature. Soil temperature directly affects plant transpiration, root respiration and absorption, soil infiltration and the rate of dissolution of various inorganic salts in the soil solution, thus affecting forest growth.

Soil thermal properties are soil physical properties that affect heat flow and temperature changes in the soil, mainly including thermal conductivity, heat capacity and heat diffusion coefficient. Under a certain soil temperature gradient, the intensity of heat exchange in the soil depends on the thermal conductivity of the soil. The magnitude of the coefficient of thermal conductivity depends on the morphological properties of the contact between particles in the soil and the water content of the soil.

Forest soil heat flux is mainly influenced by vegetation factors and soil temperature. The heat flux of forest soils is small due to the fact that the surface of forest soils is often covered by a thick layer of fallen leaves. At the same time, the absorption and reflection of solar radiation by vegetation also affects the distribution of heat flux on the surface of forest soils.

The heat flux of agricultural soils is affected by a variety of factors such as crop type, soil moisture status, and soil type. The variability of soil heat fluxes in agricultural fields is characterized differently for different crops. For example, there is a difference in soil heat flux distribution between wheat and corn fields. Soil heat flux in farmland increases with the increase of soil moisture content, but when the soil moisture content exceeds a certain range, the heat flux decreases instead.

The characteristics of heat flux changes in different soil types are different, and the changes in heat flux are influenced by a variety of factors. For example, the heat flux of wetland soils is higher than that of dryland soils, the heat flux of forest soils is smaller, the heat flux of agricultural soils is affected by moisture and crop type, and the heat flux of grassland soils is affected by the type of vegetation and cover.

Understanding the characteristics of heat flux changes in different soil types can better study the soil water-heat coupling process, climate change, agricultural production and other issues.