Chemical reclamation of soils is a regulation of cation composition of soil absorbing complex by replacing hydrogen, aluminum, iron, manganese in acidic soils or sodium, sometimes magnesium in alkaline soils, with calcium. On acidic soils carry out liming, on soils with an alkaline reaction – gypsum or acidification.
Russian scientists I.A. Stebut, D.I. Mendeleev, A.N. Engelhardt, P.A. Kostychev, D.N. Pryanishnikov, P.S. Kossovich, K.K. Gedroyts, O.K. Kedrov-Zikhman and others studied liming and its effect on soil fertility and crop productivity.
In the scientific basis of the theory and practice of liming was the doctrine of the soil absorbing complex, developed by K.K. Giedroytz. According to the provisions of the doctrine, many agronomic properties of the soil depend on the degree of saturation of the soil absorbing complex calcium.
Liming as a method of improving soil properties has been known for a long time, but its use for increasing crop yields has been carried out only since the last century. There is no alternative to liming in terms of economic efficiency and resource availability.
Chemical reclamation of soils (Русская версия)
Importance of liming
Main article: Soil liming
Liming is a technique of chemical reclamation of soils consisting in the application of carbonate, oxide or hydroxide of calcium and/or magnesium to the soil to neutralize excessive acidity. Liming improves agrochemical, agrophysical and biological properties of soil, increases the provision of calcium and magnesium for plants, mobilizes or immobilizes macro- and microelements, reduces the arrival of radionuclides and heavy metals in plants, improves soil factors of plant life.
Soils with excessive acidity are characterized by:
- low content of mobile forms of nitrogen, phosphorus, potassium, trace elements;
- unfavorable agrochemical, agrophysical properties;
- increased content of mobile forms of aluminum and manganese;
- low biological activity;
- negative influence of high concentration of hydrogen ions H+ on physical and chemical state of protoplasm, growth of root system and plant metabolism
development of pathogenic microflora, such as fungi Penecillium, Fusarium, Trichoderma; - mobilization of heavy metals.
The systematic application of physiologically acidic fertilizers, such as ammonium nitrate, degrades the agrochemical properties of the soil, which reduces crop yields.
Table. Effect of soil agrochemical properties on barley yield (after 18 years of ammonium nitrate application)[1]Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/ Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
Liming allows:
- eliminate exchange acidity and reduce hydrolytic acidity;
- improve the cationic composition of the soil absorbing complex;
- activate microbiological processes;
- strengthen all types of nitrogen fixation;
- increase the content of nitrates, calcium, magnesium, mobile phosphorus;
- reduce the content of toxic forms of aluminum and manganese;
- reduce the availability of iron, copper, zinc, manganese, heavy metals to plants;
- increase the availability of nitrogen, phosphorus, calcium, sulfur, magnesium, molybdenum, potassium to plants;
Increase the quality of humus; - improve agrophysical properties of soils, water regime of soils;
- increase the efficiency of mineral fertilizers;
- improve the quality of products;
- due to calcium coagulation of soil colloids, improve soil structure, water permeability, permeability and aeration;
- reduce the possibility of crust formation;
- facilitate processing of heavy loam and clay soils.
Liming changes the ratio of calcium and potassium in the soil in the direction of the predominance of calcium, while worsening the potassium nutrition of plants, which negatively affects the development of potassium-loving crops such as flax, potatoes, lupine, grasses, and corn.
Liming reduces the solubility of phosphate meal and its effectiveness, so exclude direct contact of these fertilizers in the soil:
- lime and phosphoritic meal on the same plot are applied at different times for different crops (phosphoritic meal earlier and lime later);
- layer-by-layer application of these fertilizers – phosphorit flour under the plowing, lime under the cultivation;
- preliminary composting of phosphate meal with manure or peat to transfer phosphorus into available forms.
The use of phosphate meal is effective on the fields lime-fertilized with half doses of lime fertilizers. On soils where the reaction after liming does not exceed pH 5.1-5.2 in the salt extract, you can use phosphorit flour.
The total area of arable land in CIS countries with high acidity is about 45 million hectares (40 million hectares[2]Fundamentals of agricultural production technology. Farming and crop production. Edited by V.S. Niklyaev. – Moscow: “Bylina”, 2000. – 555 p.), needing lime – more than 60 million hectares (55 million hectares[3]Fundamentals of agricultural production technology. Farming and crop production. Ed. by V.S. Niklyaev. – Moscow: “Bylina”, 2000. – 555 p.). First of all, these include sod-podzolic, light gray and gray forest, swamp and red soil.
Reducing acidity contributes to an increase in grain yield by 0.25 t/ha, cabbage by 3-8 t/ha, and potatoes by 3 t/ha.
The table shows Shilnikov (2001) data on average crop yield gains from applying lime to soils of different acidity.
Table. Approximate yield increases of different crops depending on the dose of lime applied, 100 kg/ha (Shilnikov, 2001)
| Winter wheat | |||||
| Barley | |||||
| Winter rye | |||||
| Oats | |||||
| Corn (for silage) | |||||
| Spring wheat | |||||
| Perennial grasses (hay) | |||||
| Annual grasses (hay) | |||||
| Sugar beet | |||||
| Roots | |||||
| Potatoes | |||||
| Flax (straw) | |||||
| Cabbage | |||||
| Tomatoes | |||||
| Carrots | |||||
| Sown meadows and pastures and legume-grasses (hay) | |||||
| Natural meadows (hay) | |||||
| Soybeans (grain) | |||||
Of the cereal crops on acidic soils, winter wheat and barley respond well to lime treatment, of legumes – peas and fodder beans. Yield gains of these crops when lime is applied are higher than those of winter rye and oats. Clover as a cover crop also responds well to lime application.
According to calculations by specialists from Germany, an average annual increase in the pH of highly acidic soils by one unit can increase crop yields by 0.5-0.6 t/ha in terms of grain.
The cost of liming pays off as a rule within two years, and the effect of lime persists for a long time. The importance of liming of acidic soils increases with the transition to intensive farming systems.
Lime increases the protein content of legumes due to the activity of nodule bacteria. Plant products on calcareous soils contain 2-5% more protein than on acidic soils. Product quality increases due to immobilization of toxic elements and radionuclides.
Lime fertilizers
Main article: Lime fertilizers
Lime fertilizers – materials and mixtures of substances containing calcium compounds, sometimes magnesium, used for liming acidic soils and as a source of calcium and magnesium in plant nutrition.
Lime fertilizers are used as:
- lime flour and dolomite flour;
- industrial wastes (burnt and slaked lime, slate ash, defekat, slag, whitewash, etc.);
- local lime fertilizers (lime tuff, lake lime, peat tuff, marl, chalk).
Scientific rationale for liming
Influence on plant growth and development
Acidic reaction of the environment negatively affects the growth and development of plants. High concentration of hydrogen ions worsens physical and chemical state of protoplasm of cells of root system, prevents its growth, disturbs permeability of root membranes and metabolism in roots, thus worsening the nutritional conditions of plants.
The death of winter cereals and perennial grasses during overwintering under snow cover in the Non-Black Soil Zone is associated not with the effect of low temperatures, but with an acidic reaction of the environment and the increased content of mobile forms of aluminum. For example, during overwintering under the same temperature conditions of -12…-14°C (below which temperature under a snow cover of 15-20 cm rarely falls) plants of clover and winter wheat were completely lost on acidic, non-limey soils, while on limey soils they survived at 70-90% with yield of hay 5-8 t/ha and 2,5-3,5 t/ha of winter wheat grain.
The optimum soil reaction for most cultivated crops and soil biota is slightly acidic and close to neutral, i.e. with a pH of 6.0-7.5. For some crops, the optimum reaction can shift to a more acidic side or be in a wide pH range. All plants during the first 2-3 weeks from the moment of germination are sensitive to unfavorable reaction of the environment.
The reaction of the environment influences the nutrient regime of soils and plant nutrition conditions, mobility of macro- and microelements, microflora activity, and soil properties. Optimal pH values for growth and development of the same crop may differ depending on soil type. On soils with high organic matter content and light granulometric composition, the optimal pH interval shifts to the acid side.
In relation to soil acidity and responsiveness to lime application, crops are conventionally divided into five groups.
- The crops of the first group are the most sensitive to the reaction of the environment, the optimum is a slightly alkaline environment with рНH2O = 7,0-8,0; рНKСІ = 6,8-7,5. These include sugar, fodder and table beets, white cabbage, mustard, alfalfa, sainfoin, rape, onion, garlic, celery, spinach, pepper, parsnip, soybean, hemp, currant, cotton. These crops in very acidic soils reduce yields by 2-3 times and plants are severely affected by diseases. Soils intended for cultivation of crops of the first group are subject to liming in the first place.
- Crops of the second group are characterized by optimal soil reaction close to neutral, with an optimal value of рНКCІ = 6,0-6,5. Decrease in acidity to pH 4,5 leads to a decrease in the yield of crops of this group in 1,5-2 times and increases morbidity. Cultures of the second group include: wheat, barley, corn, clover, peas, vetch, beans, chickpeas, lentils, cauliflower and fodder cabbage, kohlrabi, turnips, rutabaga, lettuce, leeks, cucumber, chickpeas, foxtail. They respond well to liming.
- Crops of the third group tolerate moderately acidic and alkaline soils, do not have a pronounced optimum value of environmental reaction. Their growth is influenced by associated growth factors. With a favorable nutrient regime, they can give good yields in the range of рНКCІ from 5 to 7,5. A slightly acidic environment with a pH of 5.5-6.0 is considered optimal. Plants of the third group respond positively to liming of strongly and moderately acidic soils. Cultures of the third group include winter rye, oats, buckwheat, tomato, sunflower, carrot, pumpkin, zucchini, parsley, radish, turnip, rhubarb, topinambur, timothy.
- Cultures of the fourth group belong to cultures well tolerating moderately acidic soil reaction, the optimal value of рНKСІ = 5,1-5,6. For flax, the optimal values are in the range of pH 5,5-6,0, for potatoes and berry crops – pH 4,5-6,5. These crops respond positively to liming while maintaining an optimal ratio of calcium, potassium, magnesium, boron, and other nutrients. An excess of calcium causes a decrease in yield and quality of products, potatoes have an increased incidence of scab, flax has an increased incidence of bacteriosis. Neutralization of excessive acidity reduces the availability of boron, copper, zinc for these crops, and excessive calcium impedes the arrival of potassium and magnesium. Liming for crops of the fourth group is effective with a strongly acidic reaction of the environment. Crops of this group include potatoes, fiber flax, millet, sorghum, raspberries, strawberries, and gooseberries.
- Cultivars of the fifth group are characterized by optimal values of soil reaction at рНKСІ = 4,5-4,8. Cultivars of the fifth group are slightly sensitive to excessive acidity; liming is conducted only in very acidic soils with рНKСІ < 4,0 as calcium may negatively influence growth of these cultures, especially during germination and initial phases of growth. Crops of the fifth group include: sorrel, tea, coffee, cocoa, yellow and blue lupine, goatweed, seradella.
Most crops during germination and in the initial phases of growth require a medium close to neutral – pHKCl 5.8-6.2 or pHH2O – 6.4-7.0.
Physiological (biological) optimum of medium reaction for plants may differ from ecological (technological), which is associated with the mobility of nutrients and conditions of disease development. For example, for potato and flax plants, if the soil is not infected with diseases, the biological optimum is рНKСІ 6,0-6,2, but under disease-infested conditions (potato in neutral and weakly alkaline reaction is affected by scab caused by actinomycetes, flax by fusariosis), in field conditions the yield and quality of these crops are higher at рНKСІ 5,2-5,6, that is, at ecological optimum. The mismatch of biological and ecological optimum of environmental reaction for many crops is due to the change in the availability of nutrients when the soil pH changes.
In this regard, changes in the availability of macro- and micronutrients during liming should be considered. Liming the soil with a pH above 6.6 is ineffective, as the removal and leaching of calcium from the soil increases and the mobility of trace elements with the exception of molybdenum decreases.
Lime fertilizers have a long-lasting effect, so take into account the attitude of all (or leading) crops of the crop rotation, that is, the specialization of the crop rotation and the granulometric composition of the soil.
The table provides indicative optimum pHKCl levels of soils for crop rotations with different specialization.Optimal on sod-podzolic and gray forest soils are lime application rates close to full hydrolytic acidity, providing a pHsalt reaction of 5.4-5.8.
Table. Approximate optimal levels of soil reaction (pHKCl) for crop rotations of different types[4]Yagodin B.A., Zhukov Yu.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. — М.: Колос, 2002. - 584 p.: ill.
| Sandy and sandy loam | |||||||
| Light and medium loamy | |||||||
| Heavy loam and clay | |||||||
| Peat | |||||||
Influence on soil properties
The colloidal part of soils is depleted of calcium, magnesium, but contains a large amount of hydrogen and mobile cations of aluminum, manganese and iron. This explains the low content of the colloidal fraction of acidic soils, the low absorption capacity and buffer, lack of structure.
In natural conditions the process of depletion of absorbing complex of soil by bases proceeds constantly. Under the influence of atmospheric precipitation and intensive application of fertilizers the share of calcium and magnesium in PPK is replaced by hydrogen. Soil absorbing complex is gradually destroyed.
Annual losses of calcium from soil according to lysimetric experiments amount to 187 kg/ha. Depending on the amount of precipitation the losses vary from 89 to 287 kg/ha.
Calcium contributes to the coagulation of soil colloids and delays their leaching. On sandy humus soils calcium provision contributes to water absorption capacity, on heavy clay soils – the formation of soil aggregates and clodding, their water permeability is improved.
Liming creates a positive balance of calcium, and with the addition of dolomite flour additionally magnesium.
Without the use of lime, the positive effect of physiologically acidic fertilizers fades over time and may have a negative effect, when areas with the use of mineral fertilizers yields are lower than unfertilized areas. The combination of liming with the use of fertilizers increases the effectiveness of the latter by 25-50%.
Toxic effects of mobile forms of aluminum and manganese
Acidic soils have increased content of mobile forms of aluminum, which has a negative effect on most plants.
Many crops begin to experience the toxic effects of mobile forms of aluminum at concentrations of more than 2 mg/100g of soil, the greatest sensitivity is noted in the first periods of growth and during overwintering.
According to plant sensitivity to mobile aluminum N.S. Avdonin divided all crops into four groups:
- most sensitive – oppression occurs at relatively small concentrations of aluminum. For example, the toxic effect on clover notes the content of aluminum ions more than 2 mg/100 g of soil, at a content of 6-8 mg/100 g of soil clover falls off strongly. The most sensitive include sugar beet and table beet, alfalfa, clover, winter wheat and winter rye (in overwintering);
- sensitive – flax, barley, spring wheat, peas, beans, buckwheat;
- resistant – lupine, potato, corn, millet;
- highly resistant – oats, timothy.
For some crops, no direct correlation between sensitivity to acidity and mobile aluminum was revealed. For example, maize does not tolerate high acidity, but shows resistance to high aluminum content. Flax, on the other hand, is sensitive to aluminum, but is tolerant of an acidic environment.
According to the sensitivity to the content of mobile forms of manganese in the soil, three groups of crops are distinguished according to the data of VIUA (1992):
- very sensitive – winter rye and wheat, sugar, table and fodder beets, flax, lucerne;
- spring wheat, barley, vetch, peas, white cabbage, cauliflower and fodder cabbage, rape, potato, clover meadow and hybrid, corn, turnip, carrot, rutabaga, cucumber, tomato, onion;
- relatively resistant – oats, creeping clover, timothy, meadow fescue.
There is also no direct correlation between the sensitivity of crops to environmental acidity and the concentration of mobile manganese. Thus, flax is resistant to acid medium, but sensitive to the concentration of mobile manganese. On the contrary, white cabbage has medium sensitivity to manganese, but cannot tolerate elevated acidity.
Suppression of biological activity of soils
On soils with excessive acidity the activity of useful microorganisms is suppressed, ammonifying, nitrifying, nitrogen-fixing and destroying organophosphorus bacteria do not develop, for which a neutral environmental reaction of pH 6.5-7.5 is more favorable.
On the contrary, favorable conditions are created for the development of pathogenic microflora and fungi such as Penicillium, Fusarium and Trichoderma.
Table. Optimal reaction of the medium for various soil microorganisms[5]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. - 854 p.
| Nitrogen fixers that bind molecular nitrogen in the air | Symbiotic (nodule): | ||
| Free-living: | |||
| Microorganisms that decompose plant residues | |||
| Microorganisms that mineralize humus substances | |||
Mobilization of heavy metals, radionuclides and toxic substances
Liming leads to the immobilization of heavy metals, radionuclides and toxic substances, reducing their entry into plants and products.
Soil gypsum
Main article: Soil gypsum
Soil gypsum is a method of chemical reclamation of saline soils with a large proportion of sodium in the soil absorbing complex (SAC) and alkaline reaction using gypsum (CaSO4⋅2H2O). Saline soils are characterized by unfavorable physical, chemical, physical-chemical and biological properties and low fertility. Gypsum treatment allows to improve soil properties and contributes to the normalization of plant growth conditions.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Fundamentals of agricultural production technology. Farming and crop production. Ed. by V.S. Niklyaev. – Moscow: Bylina, 2000. – 555 с.