Soil moisture capacity

Moisture capacity (water capacity , water holding force, capillarity of the soil ) - the property of the soil to accept and retain in its hair wells a known amount of drip- liquid water , not allowing the latter to drain.

The percentage of its weight to the weight of the soil or, accordingly, its volume to the volume of soil, expressed as a percentage , as well as millimeters of water ^[1] , is called the indicator of soil moisture capacity.

Moisture content of the soil - a quantity quantitatively characterizing the water holding capacity of the soil ; the ability of the soil to absorb and retain a certain amount of moisture from dripping by capillary and sorption forces. Depending on the conditions that hold moisture in the soil, there are several types of soil moisture capacity: maximum adsorption , capillary, smallest and most complete. The maximum adsorption moisture capacity of the soil, bound moisture, absorbed moisture, estimated moisture - the largest amount of firmly bound water held by sorption forces. The heavier the granulometric composition of the soil and the higher the content of humus in it, the greater the proportion of bound, almost inaccessible soil moisture. Capillary moisture capacity of the soil - the maximum amount of moisture held in the soil above the groundwater level by capillary ( meniscus ) forces. Depends on the thickness of the layer in which it is determined, and its remoteness from the groundwater mirror. The greater the thickness of the layer and the less its distance from the groundwater mirror, the higher the capillary moisture capacity of the soil. At an equal distance from the mirror, its value is determined by the total and capillary porosity , as well as by the density of the soil. A capillary rim is associated with the capillary moisture capacity of the soil (a layer of supported moisture between the groundwater level and the upper boundary of the soil wetting front). The capillary moisture capacity of the soil characterizes the cultural condition of the soil. The less structured the soil, the more there is a capillary rise in moisture, its physical evaporation and, often, accumulation in the upper part of readily soluble, including and salts harmful to plants. The smallest is the field moisture capacity of the soil — the amount of water actually held by the soil under natural conditions in equilibrium, when evaporation and additional water inflow are eliminated. This value depends on the granulometric, mineralogical and chemical composition of the soil, its density and porosity. It is used when calculating irrigation rates. The full moisture capacity of the soil, the water capacity of the soil is the moisture content in the soil, provided that all pores are completely filled with water. At full soil moisture capacity, moisture located in large gaps between soil particles is directly held by a water mirror or water-resistant layer. The water capacity of the soil is calculated by its total porosity. The value of the total moisture capacity of the soil is necessary when calculating the ability of water absorption without the formation of surface runoff, to determine the ability of soil water loss, the height of the rise of groundwater during heavy rains or irrigation.