Is there water in the soil? Of course yes! It comes from atmospheric 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 the productivity and growth of tree plantations.
Stocks
Moisture entering the soil surface forms surface runoff. It is observed during snowmelt, after heavy rains, and depends on the amount of precipitation, the water permeability of the soil layer and the angle of the terrain. Lateral runoff is also distinguished, which occurs due to the different density of soil horizons. The incoming moisture is first filtered through the upper horizons, and when it reaches a horizon with a heavier granulometric composition, it forms a soil top water. From it, part of the water seeps into the deepest layers, reaching the ground runoff. If there is a slope of the terrain, part of the moisture from the aquifer flows into lower relief areas.
Soil moisture and evaporation
Is there water in the soil, which is characterized by increased evaporation? Everything depends on himspeed, which changes in accordance with the change in humidity. In a day, the amount of evaporation can reach ten to fifteen millimeters. Soils with shallow groundwater evaporate much more moisture than deep ones.
Water moves depending on the manifestation of different forces and the degree of moisture. A prerequisite for the movement of moisture is a gradient (force difference). All forces act in aggregate on soil water, but some definite 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
Gravitational (free) water fills large pores, forms a downward current under the action of gravity and forms a perched water, partially falling into groundwater. Gravitational moisture goes through illuvial and eluvial processes in the soil and forms all other forms of water. It itself is replenished mainly due to precipitation.
Steamy water is present in the soil at any level of moisture. It can move actively, due to diffusion phenomena, or passively, along with the movement of air. This moisture significantly affects the water cycle in the soil. Over time, the vapor escapes into the atmosphere, and vaporous moisture is replenished from other forms.
Ice as a form of water
Ice forms in the soil when temperatures drop. ATnon-saline areas, gravity water freezes at degrees close to zero. If insufficiently moistened soil freezes through, this leads to an improvement in its structure by compressing lumps and grains with frozen water. Freezing of the waterlogged layer leads to destructuring due to the rupture of structural elements by ice. When moderately moist soils freeze, some water permeability is retained, while waterlogged soils remain impermeable until they thaw.
Water properties of the soil. Water permeability
The main properties that determine the behavior of moisture in the soil profile are water permeability, water holding 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 the 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 precipitation, almost does not linger and quickly descends to the lower horizons. In layers with a heavy granulometric composition, the level of water permeability depends on their structural state and density. Well structured, loose soils always have a higher carrying capacity.
Moisture capacity and water-lifting capacity
Moisture capacity is the ability to hold water. The soil, depending on the water-retaining forces, can have a total, field-limited, maximum, or capillary moisture capacity. As a rule, this indicator is expressedas a percentage of dry weight.
Water-lifting capacity is expressed in the movement of moisture from the lower layers to the upper ones through the capillary pores. The larger the diameter of such pores, the greater the rate of rise of water, but also the lower the height of its rise. This property in the water regime of soils is very important. Due to the water-lifting capacity, soil moisture can rise to the arable horizon and take part in the water nutrition of plants. This is especially important during dry periods when crops suffer from lack of water.
Types of soil water regime in cold zones
To distinguish types, factors such as the absence or presence of permafrost in the soil, the depth of soil wetting, the predominance of descending or ascending currents of moisture are given importance. Accordingly, 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 during the warm period, but a significant part of the permafrost layer remains. It is inherent in tundra, arctic, frozen meadow-forest soils.
Seasonal-frozen type is observed in the Khabarovsk Territory, the Amur Region and other regions where the greatest amount of precipitation falls in summer, and moisture soaks the soil to groundwater. At the same time, 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 noted in areas whereless precipitation evaporates than falls. Due to the predominance of downward currents of water, the soil is washed down to groundwater, which, under these conditions, usually occurs no deeper than two meters from the surface. Podzolic soils are characteristic.
Periodic flushing type is common in areas where precipitation is about as much as it evaporates. In wet years, a leaching regime is observed, and in dry years with high evaporation, a non-leaching regime is observed. This option is typical for gray forest soils.
The non-flushing type is noted in areas where the water discharge is higher than the inflow, groundwater is deep, and the moisture cycle covers only the soil profile. Typical soils are chernozem.
The stagnant type is observed in wetlands, where all soil pores are filled with water due to the fact that specific vegetation prevents evaporation.
The alluvial type occurs during the annual flooding of rivers and prolonged flooding of the territory. It is typical for alluvial (floodplain) soils.
Regulation methods in wet areas
Regulation of the water regime of soils is mandatory in conditions of intensive agriculture. It consists in the implementation of a set of techniques to eliminate unfavorable conditions for the water supply of plants. Due to the artificial change in the consumption and inflow of moisture, it is possible to influence the water regime of soils and achieve a sustainable high yield of agricultural crops.
In specific soil and climatic zonesregulation 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 the surface runoff of moisture is carried out along the furrows outside the field. Mineral waterlogged and swampy soils require drainage reclamation in the form of closed drainage devices.
In humid areas where there is a lot of annual precipitation, the regulation of the water regime is not limited to drainage measures. For example, soddy-podzolic soils experience a moisture deficit in summer and require additional moisture. In non-chernozem territories, to improve the moisture supply of plants, the method of bilateral regulation is used, when excess water is diverted from the fields to special sources through drainage pipes and, if necessary, is fed back through the same pipes.
Soil moisture management in dry areas
In arid regions, regulation is aimed at the accumulation of moisture in the soil and its rational use. A common method of water accumulation is the retention of melt water and snow through the use of rock plants, stubble, snow banks. To reduce surface runoff, bunding, autumn flash, slotting, intermittent furrowing, cellular tillage, strip placement of crops and other methods are used.
In the desert and desert-steppe zones, the main method of improving the water regime is irrigation. With this method, it is necessary to deal with unproductive waterlosses to prevent secondary salinization. It should be remembered that in different zones in the complex 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.
