What is soil moisture?

 Moisture refers to the humidity of the soil suitable for the growth and development of plants. Moisture refers to the condition of soil moisture. Soil moisture is the degree of soil dryness and wetness, that is, the actual soil moisture content, which can be expressed as the percentage of soil moisture content in the dry soil weight: soil moisture content = moisture weight / dry soil weight x 100%. It can also be expressed in terms of relative water content such as the percentage of soil water content equivalent to field water holding capacity, or the percentage relative to saturated water content.

The existence form of soil moisture actually refers to the existence form of soil water. Soil water exists in soil pores, especially small and medium pores, and large pores are often occupied by air. Plant roots interspersed in the pores of the soil absorb water from the pores of the water-bearing soil. There is a humidity gradient at the water-air interface in the soil, and the temperature rises and the gradient increases. Therefore, the water will become water vapor and evaporate out of the soil surface. The combination of transpiration and evaporation of water is called evapotranspiration, which is the two pathways for soil water to enter the atmosphere.

There are three important indicators of soil moisture content. One is the saturated water content of the soil, which indicates how much water the soil can hold at most. At this time, the soil water potential is zero. The second is the field water holding capacity, which is the water that the soil can hold after subtracting the gravity water from the saturated water content of the soil. Gravity water is basically unable to be absorbed and utilized by plants, and the soil water potential is -0.3 bar at this time. The third is the wilting coefficient, which is the water that the soil can retain when the plant wilts. This part of water cannot be absorbed and used by plants, and the soil water potential is -15 bar at this time. The water between field water holding capacity and wilting coefficient is called soil effective water, which is the part that plants can absorb and use. Of course, measures are generally taken for irrigation when the field water holding capacity is 60%, that is, the soil water potential is about -1 bar.

In the past, the measurement of soil moisture was mostly concentrated in the laboratory. Therefore, to determine the soil moisture often requires cumbersome processes such as sampling, drying, and measurement. Now, with the development of science and technology, the use of advanced soil moisture sensors and other advanced Equipment, combined with geographically suitable mathematical models, relying on the computer network environment, established a decision support system integrating moisture information management, query services, and predictive analysis.