8 min
714 pplIn recent decades, soil salinization has become a major problem in land use, resulting in its compaction, loss of structure and disruption of the water regime. The consequence of these processes is a decrease and sometimes complete destruction of the crop areas productivity. The fight against alkali soils is currently the most important task for farmers, both in the reclamation of new arable lands and in maintaining the fertility of those already in use. We will discuss below how to overcome alkalinity and which methods have shown the greatest effectiveness.
Content:
- General information about alkali soils
- Physical and chemical properties of solonetzic soils
- Fighting methods
General information about alkali soils
Soils containing more than 20% of exchangeable sodium are classified as alkali soils. They have a prismatic, dense columnar or blocky horizon. An external sign is the presence of bald spots without sprouting. Due to the accumulation of groundwater, the soil surface swells and becomes viscous. As soon as the moisture evaporates, cracks appear followed by the formation of a crust. Solid conglomerates in the humus layer make it difficult for seedlings to germinate and prevent the formation of the root system.
Today, there is a lot of such land in Russia - over 40 million hectares. According to the V.V. Dokuchaev Institute, there are 9.4 million hectares of alkali soils in Russia, and alkalinity is typical for 15.5 million hectares. And unfortunately, the area of such plots is growing.
Unlike alkaline soils, which contain up to 2–3% of salt in the surface layer, solonetzic soils accumulate it at some depth. And this leads to the formation of an illuvial horizon with unfavorable physical and chemical properties.
- Alkali soils are classified into several types depending on the following parameters:
- amount of exchangeable sodium. Residual alkali soils contain less than 10% of the absorption capacity. Low-sodium - 10-15%, medium-sodium - 15-25% and multi-sodium - over 25%;
- thickness of the upper humus layer. Solonetzic soils can be crusty (up to 5 cm), shallow (5–10 cm), medium (10–18 cm) and deep (from 18 cm).
Thanks to such division, it is easier to choose effective agricultural measures and the right strategy to combat themю
Physical and chemical properties of solonetzic soils
Alkali soils contain 2–12% of humus, which depends, among other things, on the geographical location and particle size distribution. The pattern is that the further north the saline soils are located, the thicker the supra-solonetz horizon. And if there are many particles of different sizes in the soil, then the content of organic matter in it will be higher.
In addition to sodium, alkali soils may contain magnesium and soda. This leads to alkalization and increased acidity, which also negatively affects the soil - it becomes less permeable and stickier when wet, and after drying it becomes very hard. The life of microorganisms in such an environment is suppressed.
If we evaluate the density of alkali soils, then water can enter them only through cracks that appear due to the dryness of the surface. However, when it gets in, the illuvial horizon swells and stops allowing moisture to pass through. Therefore, the water regime in alkali soils is extremely unfavorable.
After the snow melts and heavy rains, there are puddles on such land for a long time, but it remains dry inside. Because of this, spring work is carried out much later. In addition, moisture reserves are low and are present only in the top layer at a depth of 2–30 cm, which is why plants form a superficial root system. And even under irrigation conditions, the yield from such sown areas is 2–3 times lower compared to non-solonetzic ones. At the same time, this measure has no effect on stopping the solonetzization process and threatens such fields to go out of production in just a few years.
What to know: despite all the negative properties of alkali soils, they also have positive qualities. These include the richness of soil compounds and their mobility, high microbiological activity. Grain grown on such soils is characterized by increased calorie content, glassiness and high protein content. Therefore, it is important to weaken the negative impact while maintaining all the benefits of alkali soils.
Fighting methods
The main reason for the poor agroclimatic properties of alkaline soils is considered to be high sodium content. Therefore, to increase fertility, the method of adding calcium to this element remains effective. To this end, a number of activities are being carried out.
Plastering
It is a chemical method of reclamation and involves the application of gypsum-containing fertilizers. Thanks to this, sodium compounds become easily washed out of the fertile horizon. In addition, gypsum is able to transform harmful soda, thereby reducing the alkaline reaction in the soil and improving its structure.
However, sodium can only be washed out with sufficient moisture. For this reason, plastering is carried out under conditions of at least 350 mm of annual precipitation. The application of gypsum is carried out under deep fall plowing for its more uniform distribution.
Nuances:
- If these are crusty and small alkali soils, then the substance is applied during cultivation. In case of medium ones - in 2 stages: during plowing, and then during bursting without inversion. In case of deep ones - before plowing with burying with plows and skim colters.
- The application rate depends on the volume of exchangeable sodium: the more sodium there is, the higher the amount of gypsum. This parameter can be accurately determined only after analyzing soil samples.
- Uniform field plastering is possible only if the field is covered with alkali soil by more than 70%. Otherwise, each salinized area is dealt with separately.
Raw-ground gypsum, phospho or clay-gypsum, and soda production waste can be used as a gypsum additive. For maximum effectiveness, the measure requires simultaneous implementation of a number of other actions. These include crop rotation of salt-resistant crops, moisture saturation by snow retention, row spacing, and deep cultivation with a chisel plow.
Acidification
This chemical treatment is suitable for soils containing solonetzic compounds in the form of bicarbonates and carbonates. Due to the high level of alkaline environment, practically nothing grows in them. Plastering will be useless, since the gypsum itself practically does not dissolve under such conditions.
For acidification, sulfuric acid is taken and added using irrigation systems in a ratio of 0.8–1% to the total supplied volume of water. The method also allows using iron sulfate.
Earth mulching
With this method, a fertile layer of soil removed from another, healthy part of the field is artificially applied to the surface of the alkalized plot. The thickness is at least 10–20 cm. At the same time, organic fertilizers are applied to the donor sectors, followed by sowing green manure and cover crops.
Self-plastering
It can only be used if calcium carbonate or gypsum lies beneath the alkali claypan. First, plantation plowing is carried out to a depth of 55 cm, which allows mixing the lime or gypsum layer with alkali soil.
If this is an area with deep or medium alcalination, three-tier plowing is required, due to which the humus layer remains intact, and the gypsum and alkali soil layers change places. If this is a shallow alkali soil, then partial plantation plowing and processing with a heavy disc harrow are suitable, as a result of which all horizons are evenly mixed.
Phytomelioration
It involves crop rotation of salt-tolerant crops. They increase the water permeability of the soil and help launch biological processes in alkaline soil. With this method, salinity decreases at a slow pace, but it itself is cheaper and more accessible and does not require the use of special equipment.
Most often, mixtures of crops with taproot and fibrous root system structures are sown. The latter are designed to improve the structure of the soil and ensure its division into small lumps, which has a positive effect on saturation with air and moisture. And tap roots are responsible for moisture exchange between horizons and stimulate the leaching of harmful compounds into the lower layers.
The most suitable are chickpeas, sweet clover, rapeseed, barley, alfalfa, sorghum and Sudan grass. However, specific plants are selected experimentally. First, the mixture includes from 2 to 4 crops, based on the results of germination and growth of which the most resistant ones for a particular area are selected. The next time, seeding is carried out with the dominance of the crop that demonstrated itself better than others. And at the same time, changes in the chemical composition of the soil are monitored. This is how a crop rotation strategy is gradually built in the problem field.
What to expect?
Chemical and phytomelioration can significantly increase the fertility of alkaline soils. But since the first method requires high costs for delivery and application of ameliorant, more and more farms give preference to planting salt-resistant plants. And this approach allows restoring productivity in problem areas in at least 4–5 years. At the same time, a relapse cannot be ruled out in the future - the land freed from alkali soil must be constantly monitored in order, if necessary, to stop promptly the salinization process that has begun again. Only under such conditions can one count on obtaining a decent harvest in the future.
State support to subsidize the costs of transporting gypsum from the plant to the saline field would also be useful. This would help most farmers in the fight against low yields and high financial costs for the implementation of this measure.
