Application and Measurement of Soil Moisture Analyzer

First, the concept of soil water is the main source of plant water absorption (except hydroponic plants), in addition to plants can also directly absorb a small amount of water falling on the leaves. The main source of soil water is precipitation and irrigation water, and it participates in the water cycle of the lithosphere-biosphere-atmosphere circle-circle-water circle.

Second, the existence of morphological soil water exists in the soil pores, especially in the small and medium pores, the large pores are often occupied by air. Plant roots interspersed in soil pores draw water from the pores of the aqueous soil for transpiration. There is a gradient of moisture in the water-air interface in the soil. The temperature rises and the gradient increases. Therefore, the water will become water vapor and evaporate out of the soil surface. The transpiration and evaporation of water, together with the addition of evapotranspiration, are two ways that water enters the atmosphere.

The soil water in the surface layer will seep downwards due to gravity. Under the condition that there is enough water on the surface, the soil water can infiltrate into the groundwater level, and then it may enter surface waters such as rivers, rivers, lakes and seas.

3. Representation Method There are two ways to express the amount of water in the soil: one is based on the soil moisture content, and the other is the weight-based moisture content and the volumetric moisture content. The relationship between the two is converted by the soil bulk density. The other is the soil water potential. The negative value of the soil water potential is the soil water suction.

Fourth, important indicators Soil moisture content has three important indicators. One is the saturated soil moisture content, indicating how much water the soil can contain, at which point the soil water potential is zero.

The second is the amount of water held in the soil, which is the amount of water that can be held by the soil after the saturated soil moisture content minus the gravity water. Gravity water is basically not absorbed by plants, and the soil water potential is -0.3 bar.

The third is the wilting coefficient, which is the moisture that the soil can still hold when the plant is wilting. This part of the water can not be absorbed and utilized by plants. At this time, the soil water potential is -15 bar.

The water between the field water holding capacity and the wilting coefficient is called soil effective water, which is the part that plants can absorb and use. Of course, measures are generally taken to provide irrigation at 60% of the field's water holding capacity, ie about 1 bar of soil water potential.

Soil water potential can be subdivided into gravitational potential, base mode potential, and solute potential.

The gravitational potential of soil moisture is 0 when the surface of soil water is normal to the soil surface. The water surface is positive when it is above the surface of the soil (this is also called pressure potential). The water surface is negative when it is below the soil surface (soil water suction is positive).

Soil base mode potential refers to the tension of water on the surfaces of mineral particles and organic particles on the soil. Its value is always a negative value, which means that the water on the soil surface is always drawn into the soil.

Soil moisture solute potential is related to the amount of solute contained in the soil solution. The more solute, the smaller the solute potential (ie, the more negative). When the water source infiltrates, the water flows along the gradient of moisture from the high water potential to the low water potential, and gradually forms a ellipsoidal shape with a distinct wet and dry junction, which is called a wet ball. The water potentials of the soils on the spheres are equal. The spherical surface is called the infiltration front. When the water head is fixed, the forward speed of the infiltration front will slow down as time goes by.

Most plant nutrients are dissolved in water and transported along with water to be transported to the plant roots. Regardless of whether the root system absorbs plant nutrients in the form of mass flow, diffusion, or interception, it is carried out in the soil solution.