Introduction of Measuring Methods for Soil Moisture and Soil Moisture Constants

Introduction of Measuring Methods for Soil Moisture and Soil Moisture Constants

Soil moisture has an extremely important position in the process of plant growth. He is mainly reflected in these aspects: 1) for crop growth needs; 2) to affect the dissolution and movement of nutrients; 3) the redox potential of soil; 4) organic matter Decomposition and accumulation; 5) Soil thermal conditions; 6) Soil ploughability, and then additional points to measure the soil moisture at the same time we must first understand the changes in soil water content, you can use the rapid soil moisture analyzer, regular positioning soil moisture test The instrument and soil moisture temperature measuring instrument are used to measure, and at the same time, the soil moisture constant value is also known. It is the conversion point of soil water properties, and is an important basis for engineering planning, design and management.

Maximum amount of hygroscopic water: The maximum amount of soil that absorbs gaseous water from saturated air. This part of the water can not be used for plants at all. The determination method is to place the dried soil sample in a closed dryer containing 10% potassium sulfate solution so that the soil absorbs water vapor and the soil moisture content is measured after reaching a stable equilibrium.

Withered water content: The soil moisture content of a plant with permanent wilting characteristics due to water shortage. It includes all hygroscopic water and part of the filmy water, and is the lowest moisture limit for crop growth and development. The method of determination is as follows: pot seedling method, or approximate value obtained by dividing the maximum amount of moisture absorbed by 0.68.

Field water holding capacity: The maximum amount of water that can be held in a certain depth of soil in the field under irrigation or precipitation is the upper limit of the available water for plants, and is also an important parameter for calculating irrigation water volume. If the amount of irrigation water exceeds the amount of water in the field, the excess will be used as gravity infiltration or supplementary groundwater. When measuring, in a certain area of ​​the plot, the water volume calculated according to the planned wetting layer depth is 1.5 times of the irrigation volume. When the gravity water infiltration moves to a stop, the retained moisture content in the soil is measured layer by layer, that is, the field water holding capacity. .

Saturated water holding capacity: Soil moisture content when all pores in the soil are filled with water. The method of determination is generally determined by calculation based on pores. The results of other indoor or field measurement methods are often too small.

Capillary water holding capacity: The maximum amount of capillary rise water that can be held in the soil. The amount of water generally varies between the amount of water held in the field and the amount of saturated water, which is the effective moisture for the crop. The method of determination is to measure the moisture distribution curve of the entire capillary water activity layer in the field, and then obtain the capillary water holding capacity of any layer in the capillary water activity layer according to this curve; it is also possible to use the ring knife to take the undisturbed soil and set the lower end thereof. In the water tray, the pores of the soil capillary are filled with water, and then the water content is measured as the capillary water holding capacity.

By understanding these variables in the use of instruments that measure soil moisture, this reduces the problem of under irrigation or multi-irrigation due to an unstandard measurement of soil moisture content.