Water balance and soil properties, types of regime and ways to regulate it

Anyone involved in farming is advised to pay attention to the water properties of the soil. Soil scientists note the importance of issues of moisture supply, movement and accumulation. They are associated with the features of accumulation, movement and leaching of organic substances, which are products of soil-forming processes. The water regime is understood as the totality of all processes of moisture entering the soil structure, its state in the soil and the process of consumption.

Soil water categories, characteristics, availability to plants

Water in the structure of the earth has a heterogeneous structure, and therefore differs significantly in physical characteristics.

Solid

This form of water is ice. It is considered a potential source of liquid and vapor moisture. Ice formation is seasonal or perennial. At temperatures above 0 degrees it becomes liquid or vapor.

Chemically bound

This type of water is present in minerals in the form of a hydroxyl group or whole molecules. In the first case, moisture is called constitutional. It is removed from the soil by calcination to 400-800 degrees. Water presented in the form of molecules is called crystallization water. It can be removed by heating the earth to 100-200 degrees.

Chemically bound water is considered the most important parameter by which the composition of the soil can be understood. This substance is present in the solid phase of the earth and does not belong to independent physical bodies. The composition does not move, does not have solvent characteristics and is not available to plants.

Vaporous

This substance is present in the soil air and in the pores in the form of water vapor. Vaporous moisture can move with the current of soil air and depends on the moisture capacity of the soil.

Although the volume of vaporous moisture is no more than 0.001% of the soil mass, it is very important for the proper redistribution of soil moisture and helps protect crop root hairs from drying out. During condensation, steam transforms into liquid.

Sorbed

This substance is formed as a result of the sorption of vapor and liquid water on the surface of solid soil elements. It is also called physically bound. Such water is divided into tightly bound and loosely bound. This gradation is based on the strength of the bond with the solid phase of the earth.

Strongly bound or hygroscopic water is formed due to the adsorption of molecules from a vapor state on the soil surface. The ability of the earth to pass and absorb vaporous moisture is called hygroscopicity. Strongly bound water is fixed on the surface by increased pressure. In this case, a thin film is formed on the soil particles.

When soil particles come into contact with water, additional absorption is observed, and loosely bound water is formed. It is not so firmly fixed and moves slowly from fragments with a larger film to particles with a smaller one.

Free

This water is located in the active soil layer on top of loosely bound water. It is not connected with soil fragments by forces of attraction. Free water in the soil can be capillary or gravitational.

Capillary

This type of moisture is located in the thin capillaries of the earth. It moves under the influence of capillary forces that appear at the interface of all phases - solid, liquid and gaseous. This type of moisture is considered the most accessible to plants.

Water properties of soils

Soils differ in certain properties and characteristics. Gardeners should definitely take this into account.

Water holding capacity

This term refers to the ability of soil to retain moisture, associated with the influence of sorption and capillary forces. The maximum volume of water that can be retained by soil by certain forces is called moisture capacity.

Depending on the form in which the moisture retained by the soil is located, total, capillary, minimum and maximum molecular moisture capacity are distinguished.

Soil water permeability

This concept includes the ability of the earth to absorb and pass water through itself. There are 2 stages of water permeability:

1. Absorption – represents the absorption of water by the soil and its passage through the soil unsaturated with moisture.
2. Filtration - this term refers to the movement of moisture in the soil under the influence of gravity and pressure gradient when the soil is fully saturated with moisture.

Water permeability is measured by the volume of water that flows through a certain unit of soil area per unit of time at a water pressure of 5 centimeters. The indicator is constantly changing. The balance of water permeability is determined by the granulometric composition and chemical characteristics of the soil. It is also affected by their structure, density, and humidity.

Soils of heavy granulometric composition have lower water permeability compared to light soils. The presence of sodium or magnesium in the earth, which causes its rapid swelling, makes the structure almost waterproof.

Water lifting capacity

This term refers to the ability of soil to provoke upward movement of the moisture it contains due to the action of capillary forces. The height of the rise of moisture in the soil and the rate of its movement are influenced by the granulometric and structural composition of the soil.

Also, the rate of moisture rise is determined by the degree of mineralization of groundwater. Highly mineralized waters are characterized by a lower height and rate of rise. But the high location of mineralized water increases the risk of rapid soil salinization. This danger arises when they are located at a level of 1-1.5 meters.

Types of soil water regime

Water regimes have a variety of types, each of which has certain characteristics.

Permafrost

This water regime is common in permafrost conditions. At the same time, the frozen part of the soil is waterproof. It is an aquifer, above which there is a supra-permafrost perch. It leads to saturation of the upper part of the thawed soil with water. This regulatory regime is observed throughout the growing season.

Flushing

According to the theory, this regime is observed in regions in which the total amount of annual precipitation exceeds its evaporation rate. Every year the entire soil profile is subjected to through wetting to groundwater and rapid leaching of soil-forming products. Under the influence of the leaching type, red soils, yellow soils, and podzolic soils are formed.

If there is a close location of groundwater, and the soils are characterized by weak water permeability, a swamp subtype of water regime is formed. This leads to the formation of bog and podzolic-marsh types of soil.

Periodically flushing

This variety is characterized by an average balance of precipitation and evaporation. In this case, limited soil wetting in dry years alternates with through wetting in wet periods.

Land washing by excess precipitation occurs 1-2 times over several years. This type of water regime is typical for gray forest soils, leached and podzolized chernozems. Soils are characterized by unstable moisture supply.

Non-flushing

This regime is characterized by the distribution of precipitation, mainly in the upper layers of the soil. However, it does not reach groundwater.Moisture is exchanged by moving it in the form of steam. This type of water regime is typical for steppe soil types. These include chestnut, gray-brown desert, brown semi-desert soils and chernozems.

In such soils, a decrease in precipitation and an increase in evaporation are observed. To assess the water regime, a moisture coefficient has been developed. In this case, it decreases from 0.6 to 0.1.

The water reserves that were accumulated in the steppe soil during the spring are actively spent on transpiration and physical evaporation. By the time autumn arrives they become very low. In desert and semi-desert areas, farming without irrigation is impossible.

Vypotnoy

This regime of saline soils is typical for steppe, desert and semi-desert zones. It is characterized by high groundwater levels. Soils with good water permeability are characterized by upward flows of moisture. With increased mineralization of groundwater, easily soluble salts penetrate into the ground, which provokes its salinization.

Irrigation

This water regime is formed by additional moistening of the soil with irrigation waters. With proper rationing of water for irrigation, it is possible to obtain a non-flush type with the highest moisture coefficient, close to unity.

How to regulate water regime

Proper regulation of water regime is of great importance in conditions of intensive farming. It is important to use special techniques that are aimed at eliminating unfavorable factors.

To achieve the desired results, it is important to try to balance the amount of moisture that enters the soil with its consumption through physical evaporation. As a consequence, the humidification coefficient should be as close as possible to 1.

Regulation of the water regime is carried out on the basis of taking into account climatic and soil conditions. The moisture requirement of crops is also of great importance.

To improve the water regime of poorly drained soil in areas of excess moisture, it is necessary to plan the surface and level out various types of depressions. It is in these places that moisture stagnation occurs.

In soil with temporary excess moisture, it is necessary to remove excess moisture. To do this, it is recommended to make combs in the fall. Swampy soils require drainage reclamation.

The water properties of soil are of great importance for successful farming. That’s why it’s so important to familiarize yourself with them before planting certain plants.