What is a soil moisture sensor?
Introduction of Soil Moisture Sensor
Soil moisture is a physical quantity that expresses the degree of soil dryness and humidity in a certain depth of soil layer, also known as soil moisture content. The level of soil moisture is restricted by the various components of the farmland water balance. Soil moisture sensor is also known as soil moisture detector, soil moisture transmitter. The soil moisture sensor is composed of a stainless steel probe and a waterproof probe, which can be buried in the soil and dams for a long time, and can be used for fixed-point monitoring and online measurement of the surface and deep soil moisture. Used in conjunction with a data collector, it can be used as a fixed-point moisture monitoring or mobile measurement tool to measure soil volumetric water content, mainly used for soil moisture detection, agricultural irrigation and forestry protection.
what is soil moisture
Soil moisture, that is, the actual water content of the soil, can be expressed as a percentage of the soil water content in the dried soil weight: soil water content = water weight/dried soil weight × 100%. It can also be expressed as relative water content, such as the percentage of soil water content and field water capacity, or the percentage of saturated water.
According to the relative humidity of the soil, we can know the degree of water content in the soil and how much water can be retained, which has reference value for irrigation. Soil moisture affects field climate, soil aeration and nutrient decomposition, and is one of the important conditions for soil microbial activities and crop growth and development.
How to measure soil moisture
Soil is a heterogeneous, heterogeneous, dispersed, granular porous system. It is also a multi-component composite system composed of inert solid, active solid, solute, gas and water. Its physical properties are very complex and highly spatially variable. This makes soil moisture measurement difficult. The in-depth study of soil moisture measurement methods requires a series of basic theoretical support related to it. In particular, the study of soil as a heterogeneous porous water-absorbing medium and its water content measurement method involves the parallel crossing of various disciplines such as applied mathematics, soil physics, medium physics, electromagnetic field theory and microwave technology. However, the real-time requirement must be taken into account in order to realize the rapid measurement of soil moisture, which further increases its technical difficulty.
The characteristics of soil determine that when measuring soil water content, the basic physical and chemical characteristics and changing laws of soil bulk density, soil texture, soil structure, soil chemical composition, and soil salinity must be fully considered.
① Weight method. The soil samples were taken and dried, and their dry soil weight and moisture content were weighed for calculation.
②Resistance method. Measured using a resistive soil moisture meter. Soil moisture is determined from the relationship between the electrical conductivity of the soil solution and the soil moisture content.
③ Negative pressure meter method. Measured using a negative pressure gauge. When the water absorption of the unsaturated soil is balanced with the negative pressure in the device, the negative pressure shown on the pressure gauge is the water absorption of the soil, and then the soil water content is calculated accordingly.
④ neutron method. Measured using a neutron detector. The moderation ability of fast neutrons emitted by the neutron source in the soil is related to the soil water content, and the soil water content can be obtained by calibration in advance.
⑤ remote sensing method. Through the interpretation of low-altitude or satellite infrared remote sensing images, the soil moisture of the surface in a large range can be determined.
Soil moisture sensor classification
After more than half a century of development, soil moisture sensors have come in a wide variety and in various forms. The measurement of humidity has a certain complexity, and the well-known hair hygrometer and psychrometer can no longer meet the actual needs of modern requirements. Therefore, various soil moisture sensors have been developed. Humidity sensors can generally be divided into capacitive, resistive, ion-sensitive, light intensity, and surface acoustic wave types according to their measurement principles.