Soil moisture is the main source of water for plants (except for hydroponics), and plants can also absorb small amounts of water that fall directly on their leaves. The main sources of soil water are precipitation and irrigation water, which participate in the larger lithosphere-biosphere-atmosphere-hydrosphere water cycle.

Soil water is found in soil pores, especially small and medium-sized pores, and large pores are often occupied by air. Plant roots dispersed in the soil pores draw water from the water-bearing soil pores for transpiration.

There is a moisture gradient at the water-air interface in the soil, and as the temperature increases, the gradient increases, so water evaporates and escapes from the soil surface in the form of water vapor. Transpiration and evaporation of water together are called evapotranspiration and are the two ways in which soil water enters the atmosphere.

Soil water at the surface leaches downward under the influence of gravity. When there is sufficient water replenishment at the surface, soil water can seep all the way down to the water table and then may enter surface waters such as rivers, lakes and oceans.

Most plant nutrients are dissolved in the water and then transported to the plant roots for uptake. Whether the roots absorb plant nutrients by mass flow, diffusion or sequestration, it is in the soil solution.

Soil conditions have a significant impact on crop growth. Soil moisture monitor, also known as non-contact soil moisture monitor and soil moisture meter, is a sensor based on the principle of dielectric constant. It can dynamically observe the soil moisture content of different soil layers for fast, accurate and comprehensive observation, allowing people to achieve a high degree of soil perception.

https://www.renkeer.com/soil-moisture-monitoring-system/