Is there water in the soil? Of course yes! It comes from precipitation, the amount of which depends on meteorological conditions and the climate of a particular area. The water regime of soils is the most important characteristic that determines the conditions for productivity and growth of tree stands.
Stocks
Moisture entering the soil surface forms a surface runoff. It is observed during snowmelt, after heavy rains and depends on the amount of precipitation, water permeability of the soil layer and the angle of inclination of the area. Lateral runoff is also distinguished, which occurs due to different density of soil horizons. The incoming moisture is first filtered through the upper horizons, and when it comes to a horizon heavier in terms of particle size distribution, it forms a soil high water. From it, part of the water seeps into the deepest layers, reaching groundwater runoff. If there is a slope of the terrain, part of the moisture from the aquifer drains into the lower relief areas.
Soil moisture and its evaporation
Is there water in the soil characterized by increased evaporation? It all depends on its speed, changing in accordance with a change in humidity. The amount of evaporation per day can reach ten to fifteen millimeters. Soils with close groundwater levels evaporate much more moisture than deep ones.
Water moves depending on the manifestation of different forces and the degree of hydration. A prerequisite for the movement of moisture is the gradient (the difference of forces). All forces act on soil water in the aggregate, but a certain one prevails. Depending on this, the main types of moisture in the soil are distinguished: free water, steam and ice. Also in the soil layers there is hydrated, hygroscopic, film, capillary and intracellular water.
Free and vaporous moisture
Gravity (free) water fills large pores, generates a downward current under the action of gravity and forms a water trap, partially falling into groundwater. Gravitational moisture undergoes illuvial and eluvial processes in the soil and forms all other forms of water. It itself is replenished mainly due to precipitation.
Vaporous water is present in the soil at any level of moisture. It can move actively, due to diffusion phenomena, or passively, together with the movement of air. Such moisture significantly affects the water cycle in the soil. Over time, the vapor disappears into the atmosphere, and vaporous moisture is replenished from other forms.
Ice as a form of water
Ice forms in the soil at lower temperatures. In non-saline areas, gravity water freezes at degrees close to zero. If an insufficiently moistened soil freezes, this leads to an improvement in its structure by compressing lumps and grains with frozen water. The freezing of a waterlogged layer leads to destructuring due to rupture of structural elements by ice. When moderately moistened soils freeze, some water permeability persists, while waterlogged soils remain water-resistant up to their thawing.
Water properties of the soil. Water permeability
The main properties that determine the behavior of moisture in the soil profile are water permeability, water capacity and water lifting capacity.
Water permeability is the ability of the soil to pass and absorb water. The intensity of this property depends on the number and size of pores. So, sandy and light sandy soils with a large number of large pores have high water permeability. Water on their surface, even after heavy rainfall, almost does not linger and quickly descends to the lower horizons. In layers with a heavy particle size distribution, the level of permeability depends on their structural state and density. Well-structured, loose soils always have a higher transmittance.
Moisture capacity and water lifting capacity
Moisture absorption is the ability to retain water. The soil, depending on the water holding forces, can have full, maximum field, maximum or capillary moisture capacity. As a rule, this indicator is expressed as a percentage of the mass of the dry layer.
Water-lifting capacity is expressed in the movement of moisture from the lower layers to the upper through the capillary pores. The larger the diameter of such pores, the greater the rate of water rise, but also the lower the height of its rise. This property in the water regime of soils is very significant. Due to the water-lifting ability, ground moisture can rise to the arable horizon and take part in the water nutrition of plants. This is especially important in dry periods when agricultural crops suffer from a lack of water.
Types of soil water regime in cold zones
For the allocation of types, they attach importance to such factors as the absence or presence of permafrost in the soil, the depth of soil wetting, the predominance of descending or ascending moisture currents. In accordance with this, the types of water regime are formed.
The permafrost type is characterized by the presence of permafrost in the soil, which thaws to a shallow depth in the warm period, but a significant part of the permafrost layer is preserved. It is inherent in tundra, arctic, permafrost meadow-forest soils.
Seasonal permafrost type is observed in the Khabarovsk Territory, Amur Region and other regions, where the greatest amount of precipitation falls in the summer, and moisture soils the soil to groundwater. Moreover, in winter, the soil layer freezes by more than three meters, and completely thaws only in July-August. Up to this point, the water regime of the soil has all the features of the permafrost type.
In wet and dry areas
The flushing type is observed in areas where precipitation evaporates less than it falls. Due to the predominance of downward currents of water, the soil is washed to groundwater, which under these conditions occur, as a rule, no deeper than two meters from the surface. Podzolic soils are characteristic.
Periodically, the flushing type is common in areas where precipitation is approximately as much as it evaporates. In humid years, a leaching regime is observed, and in dry years with high evaporation, an irrigation regime. This variant is characteristic of gray forest soils.
The non-flushing type is observed in areas where the water discharge is higher than the arrival, the groundwater has a deep laying, and the water circulation covers only the soil profile. The characteristic soils are chernozem soils.
The stagnant type is observed in wetlands, where all soil pores are filled with water due to the fact that specific vegetation prevents evaporation.
Alluvial type occurs during the annual flood of rivers and prolonged flooding of the territory. It is characteristic of alluvial (floodplain) soils.
Wet Management Methods
Regulation of the water regime of soils is mandatory in conditions of intensive agriculture. It consists in the implementation of a set of methods to eliminate adverse conditions for water supply to plants. Due to the artificial change in the flow rate and the arrival of moisture, it is possible to influence the water regime of soils and achieve a stable high yield of agricultural crops.
In specific soil and climatic zones, regulatory methods have their own characteristics. So, on soils with excessive temporary moisture, it is advisable to make ridges in the fall to remove excess water. High ridges increase physical evaporation, and a surface runoff of moisture outside the field is carried out along the furrows. Mineral wetlands and swamp soils require drainage reclamation in the form of closed drainage devices.
In humid areas where there is a lot of annual rainfall, regulation of the water regime is not limited to drainage measures. For example, in the summer, sod-podzolic soils are deficient in moisture and require additional moisture. In non-chernozem territories, the method of bilateral regulation is used to improve the moisture supply of plants, when excess water is diverted from the fields to special sources through drainage pipes and, if necessary, is fed back to the same pipes.
Soil moisture regulation in dry areas
In arid areas, regulation is aimed at the accumulation of moisture in the soil and its rational use. A common method of water accumulation is to delay meltwater and snow through the use of rocker plants, stubble, snow shafts. To reduce the surface runoff, deboning, autumn flash, slotting, intermittent furrowing, cellular soil cultivation, strip placement of crops and other techniques are used.
In the desert and desert-steppe zones, the main method for improving the water regime is irrigation. With this method, it is necessary to deal with unproductive water losses in order to prevent secondary salinization. It should be remembered that in different zones, in a set of actions aimed at improving the water supply of plants, it is important to provide for the improvement of the structural state and water properties of soils.