First, the definition of soil moisture
Soil moisture refers to the moisture held in the soil pores, also known as soil moisture. The soil moisture measurement is a measurement when the soil sample is placed in a volume of water released from the soil void at 105 to 110°C.
Second, the source of soil moisture
The main source of soil moisture is atmospheric precipitation and irrigation water, in addition there is condensation of water vapor near the ground, rise of groundwater level, and moisture in soil minerals.
Third, soil moisture classification
Soil moisture can be divided into physical, water, and liquid soils according to their physical properties.
Among them: solid soil moisture exists only when frozen at low temperature; gaseous water often exists in the pores of the soil; liquid water exists in the surface area of ​​the soil particles and intergranular pores. Solid, vapor, and liquid phases can be converted to each other under certain conditions.
IV. Soil Moisture and Atmospheric Precipitation
The atmospheric precipitation, which is one of the sources of soil moisture, directly determines the amount of soil moisture content by its magnitude, intensity, and nature. Under normal circumstances, the precipitation in the atmosphere is large, and the moisture content in the soil is large; the precipitation in the atmosphere is small, and the moisture content in the soil is small. However, if it is a strong rainfall or trembling precipitation, because the ability of the soil to absorb water at a time is limited, and the soil will be lost, the moisture content actually infiltrated into the soil is not large; but the intensity of small precipitation or continuous precipitation, On the contrary, the soil moisture content will be greater.
V. Soil Moisture and Soil Texture
Soils with different textures and structures have different seepage and storage properties. The sand is coarse and loose, and it has strong water permeability, but it has poor water storage. The clay is compact and has strong water storage, but it has poor water permeability. The loamy soil with suitable sand and stickiness not only seeps water, but also stores water. In places where the slope is large and where the vegetation coverage is relatively thin, the absorption of precipitation by the soil is relatively small; where the soil is flat and vegetation is densely covered, the soil absorbs more precipitation.
Sixth, soil moisture and weather conditions
The effect of meteorological conditions on soil moisture is mainly due to the large loss of soil moisture due to evaporation. The amount of soil moisture evaporation is related to the air humidity near the ground floor. The smaller the air humidity, the faster and more the soil moisture evaporates. In the days of continuous hot sunny days, the air near the ground floor is relatively dry, and the intensity of solar radiation is large, the temperature and the soil temperature are significantly increased, the evaporation of soil moisture is large, the soil water loss is serious, and drought conditions will develop rapidly. If the southwesterly wind is again encountered, the loss of soil moisture is even more intensified.
Seven, soil moisture method
1, soil water weight percentage
The weight of water actually contained in soil accounts for the weight of dry soil. which is
W(%)=(W1-W2)/W2*100
In the formula, W (%) is the soil moisture content (percentage); W1 is the wet weight of the sample soil; W2 is the dry weight of the sample soil.
2. Soil water volume percentage
Refers to the percentage of soil water volume in unit soil volume. which is
In the formula, W capacity (%) is soil volume water content (percentage); P is soil bulk density, ie dry soil weight per unit volume of undisturbed soil.
The relationship between soil volume percentage and soil weight percentage is usually expressed by the following formula: W volume (%) = W (%) × P
Eight, soil moisture measurement method
At present, soil moisture determination methods mainly include the following: titration, Karl Fischer method, weighing method, gamma ray method, microwave method, neutron method, nuclear magnetic resonance method, time domain reflectometry (TDR), soil moisture sensor method, Infrared remote sensing method. Among these various soil moisture determination methods, there are several methods that actually use high frequencies: the weighing method, the γ-ray method, the neutron method, and the soil moisture sensor method. In addition, these soil moisture determination methods have their own strengths and are used in different situations. The weighing method is simple and intuitive but inaccurate; the neutron method can be measured repeatedly, and so on.
For a description of the specific soil moisture measurement method, see the Soil Moisture Measurement Method.
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