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23.10.2017
When growing most cultivated plants must take into account many various factors: weather and climatic conditions, soil fertility, humidity, soil composition, level ground water And so on.
High alkalinity, as well as increased soil acidity, can also create very unfavourable conditions for the growth and development of most crops, since they have a direct impact on the degree of penetration of heavy metals into the internal tissues of plants.
To determine the acidity of the soil, the "pH" indicator is used ( acid-base balance), the values of which usually range from three and a half to eight and a half units. If the “pH” of the soil is neutral (it is within six or seven units), then heavy metals remain bound in the soil and only a negligible amount of these harmful substances enters the plants.
How to determine the acidity of the soil and improve its "pH" can be read .
Alkaline soil has low fertility, since the soil is usually heavy, viscous, poorly permeable to moisture and poorly saturated with humus. Such land is characterized by a high content of calcium salts (lime) and high pH values.
According to their characteristics, alkaline soils can be divided into three main types:
Slightly alkaline soils (pH value of about seven, eight units)
Medium alkaline (pH value about eight, eight and a half units)
Strongly alkaline (pH value above eight and a half units)
Alkaline soils are very different - these are solonets and alkaline soils, lands that contain most of the stony loam, as well as heavy clay soils. In any case, they are all calcareous (that is, saturated with alkali).
To determine the presence of lime in the soil, it is enough to pour a little vinegar on a lump of earth. If lime is present in the soil, there will be an instantaneous chemical reaction, the earth will begin to hiss and foam.
The easiest way to determine exact value"pH" using litmus paper (a standard indicator specially provided for this purpose, showing the acidity of the soil). To do this, prepare a small amount aqueous solution in the form of a liquid suspension (based on one part of the earth to five parts of water), and then lower the litmus indicator into the solution and see what color the paper turns into.
Some plants can also indicate the presence of alkaline soil, for example, chicory, bluebell, thyme, euphorbia, mokrichnik.
Calcareous soils are most often located in the southern part of the steppe and forest-steppe zones of Ukraine and are alkaline chestnut and brown soils with poor vegetation. These soils are characterized by low humus content (no more than three percent) and low humidity, therefore, in order to successfully grow crops on these lands, it is necessary to oxidize the soil and provide additional irrigation.
As for solonetzes and solonchaks, these are extremely problematic, infertile lands, which also have a high salt content. These soils are typical for southern steppes, are present on the sea coasts and in the coastal areas of large and small rivers of our country.
Ways to Improve Alkaline Soil
Improve pH alkaline soils It is possible with the help of reclamation measures and the introduction of calcium sulfate into the soil, which is popularly called gypsum. When ordinary gypsum is added, calcium displaces absorbed sodium, as a result of which the structure of the solonetzic horizon improves, the earth begins to better pass moisture, as a result of which excess salts are gradually washed out of the soil.
The effect of applying gypsum is not limited to increasing the amount of sulfur in the soil, since it primarily improves the structure and quality of the soil, contributing to an increase in the content of bound sodium in it.
Granular sulfur is also used as an excellent soil oxidizer, which should be applied gradually (about twenty kilograms per hectare), with an interval of three or more months. But it should be remembered that the result of the introduction of sulfur can be expected only after a year or even after several years.
As an improvement of alkaline soil, deep plowing is also recommended, but without ameliorative additives, it is usually less effective.
To neutralize alkalinity due to the presence of sodium carbonates and bicarbonates in the soil, one should apply weak solutions various acids, most often sulfuric. Acid salts have a similar effect, which, as a result of the hydrolysis reaction, form acids (for example, iron sulfate is often used as a component for reclamation of alkaline soils).
In practice, to improve the alkalinity of the soil, farmers sometimes use waste from the phosphorus mining industry, that is, phosphogypsum, which, in addition to calcium sulfate, contains impurities of sulfuric acid and fluorine. But in recent times scientists sounded the alarm, because phosphogypsum, although it neutralizes the increased alkali, but at the same time pollutes the soil with fluorine. Plants may react differently to this substance (for example, it has been proven that the increased content of fluorine in plants intended for animal feed can be quite toxic).
At slightly alkaline soils, the structure of the fertile horizon is improved by plowing with the introduction of increased doses organic fertilizers that acidify the soil. The best of them is rotted manure, to which ordinary superphosphate (about twenty kilograms per ton of manure) or phosphorus flour (about fifty kilograms per ton of humus) should be added. To reduce the alkalinity of the soil, peat moss or marsh peat can also be added to the soil. The needles of pine trees, which are often used as the basis for soil mulching, acidify the soil well. A good result for normalizing alkalinity is compost from rotted oak leaves.
In arid areas with low monthly rainfall, additional irrigation of the land is required.
Significantly improve the alkaline soil crops of green manure plants, which are an excellent source of biological nitrogen. As green manure crops, crops such as lupine (contains a large amount of protein substances) and other plants of the legume family, as well as seradella, clover, sweet clover, white mustard, rye and buckwheat are used.
When using mineral fertilizers, one should choose those that acidify the soil, but do not contain chlorine (for example, ammonium sulfate).
Increased acidity has both direct (immediate) Negative influence on physiological processes in plant cells and tissues, and indirectly, due to the deterioration of the agrochemical and agrophysical properties of the soil and the decrease in its biological activity.
Acidification is characteristic of many soils and occurs constantly, since the process of soil formation is associated with significant losses of bases as a result of leaching and alienation by plants. The reaction of the soil is a reflection of the nature of the chemical and biological intrasoil processes occurring in it.
Increased acidity of sod-podzolic and gray forest soils is the main reason for the low productivity of agricultural land, high content in the soil of mobile aluminum, iron and manganese, as well as a decrease in the activity of soil microflora. At the same time, for many cultivated plants, the increased content of aluminum has a greater negative effect than the concentration of hydrogen ions, soil pH.
indirect action hyperacidity and mobile aluminum is manifested in a decrease in the availability of nitrogen, phosphorus, molybdenum to plants and a decrease in the activity of soil microflora. Mobile forms of aluminum, iron and manganese reduce the availability of phosphorus to plants by binding soluble phosphorus compounds to insoluble AlPO 4 and FePO 4 .
Increased soil acidity causes a change in the intensity and direction of biochemical metabolic processes in plants, as a result of which the synthesis of proteins, carbohydrates and fats is disrupted, and intermediate metabolic products accumulate - amino acids, mono- and disaccharides and nitrates.
Liming of acidic soils is the most cheap way improving the conditions of nitrogen, phosphorus and potassium nutrition of plants, which is especially important in connection with the high cost of mineral fertilizers in Russia. When lime is applied, the same increase in crop yield can be obtained with much lower doses of fertilizers.
The optimal reaction of the medium allows you to get good harvests(40-45 c/ha) of grain crops with an average content of available nutrients in the soil and average doses of fertilizers, while on acidic soils, to obtain such yields, the content of these elements should be 1.5-2 times higher.
In the agricultural use of land, soil acidification occurs more intensively than in natural grass stands due to the alienation of calcium and magnesium with the crop, their leaching beyond the root-inhabited soil layer and the introduction of physiologically acidic mineral fertilizers. As a result of long-term leaching of bases, acidic soils are widespread in areas with leaching. water regime soils.
The most significant influence on soil acidification is exerted by the removal of calcium and magnesium by crops and their leaching from the arable layer by precipitation. The removal of Ca and Mg by agricultural crops varies over a wide range and is primarily determined by biological features plants and yield. For example, from 1 ton of main products, taking into account side crops, 10-14 kg of CaO and MgO are taken out, legumes 40-45 kg. Depending on the yield, about 20-50 kg/ha of calcium and magnesium are annually alienated from the field with cereals, 100-200 kg/ha or more with legumes. Therefore, the higher the productivity of crops, the more bases are alienated, soil acidification occurs faster, and liming is required more often.
More calcium and magnesium are lost from the soil as a result of precipitation leaching. The leaching of these elements from the soil depends on its granulometric composition, the amount and nature of precipitation, the state of the vegetation cover and the doses of mineral fertilizers. The results of lysimetric experiments of VIUA, VNII fodder, Ramenskaya agrochemical station NIUIF showed that the losses of Ca 2+ and Mg 2+ from the soil due to leaching largely depend on precipitation and doses of mineral fertilizers. Their least losses were in a dry summer without fertilization. The leaching of calcium and magnesium increases significantly with increasing doses of ammonium nitrogen and potash fertilizers. When these fertilizers are applied, for example, NH 4 Cl or (NH4) 2 SO 4, plants mainly use ammonium nitrogen (NH4 +) for nutrition in exchange for a hydrogen ion (H +), which, with the chloride anions Cl - or SO 4 remaining in the solution - forms the corresponding acids. These fertilizers are physiologically acidic. Thus, in the case when plants mainly consume cations from fertilizers compared to anions, they will be physiologically acidic (NH 4 Cl, (NH 4) 2 SO 4 , KCl, K 2 SO 4), and, on the contrary, if plants use more intensively anions, alkalization of the solution occurs and such fertilizers are physiologically alkaline.
According to the data of lysimetric experiments (I. A. Shilnikov et al., 2001), in the conditions of the Moscow region, the loss of calcium and magnesium from the soil increased with increasing doses of mineral fertilizers and rainfall. The leaching of calcium from the loamy soddy-podzolic soil averaged over 15 years in the variants without fertilizers 35 kg/ha, with the introduction of increasing doses of mineral fertilizers - 80-140 kg/ha. Losses from sandy loamy soil were 1.5-2 times higher than their loamy soil. Average content of Ca 2+ in lysimetric waters loamy soils was about 5 times higher than Mg 2+ , and sandy soils ah - 6-7 times.
AT last years Much attention is paid to acid atmospheric precipitation, which is associated with emissions of sulfur dioxide and nitrogen oxides by motor vehicles and industry. However, studies have shown that "acidic" atmospheric precipitation does not play a significant role in soil acidification, as was supposed, since the emission of bases into the atmosphere also increased in parallel.
It is important to note that the loss of calcium and magnesium in lysimetric experiments should not be completely identified with real field conditions, since lysimeters can only take into account the downward migration of nutrients. AT field conditions As a result of water consumption by plants for transpiration, the upward migration of nutrients, including calcium and magnesium, is essential.
If we take into account that in sandy loamy soils the total content of Ca is 0.10.3%, then with an annual calcium leaching of 200 kg/ha for 30-50 years, its losses would exceed the content in the soil. It follows that the results of short-term lysimetric experiments reflect the general patterns of water migration of nutrients, but cannot give an objective quantitative assessment of calcium losses from the soil.
The study of the balance of nutrients in field experiments showed quite significant losses of calcium and magnesium, however, in general, they are 1.5-2 times lower than in lysimetric experiments and occur mainly in early spring and autumn on soils not covered with plants. Under plants, during the period of intensive consumption of water and nutrients, calcium losses are minimal or absent.
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Questions: 1. Liming of acidic soils
2. Gypsum treatment of solonetzic soils
In our country, significant areas are occupied by acidic and alkaline solonetzic soils. Presence in an absorbed state in acidic soils a large number hydrogen and aluminum ions, and in solonetz soils - sodium cations sharply worsen the physical, physico-chemical and biological properties of these soils, their fertility. For the radical improvement of acidic and solonetzic soils, their chemical reclamation is necessary in combination with other agrotechnical measures.
Methods for the chemical amelioration of acidic and solonetze soils are based on changing the composition of absorbed cations, mainly by introducing calcium into the PPC. To neutralize acidity and increase the fertility of acidic soils, liming is the main measure, and gypsum is used to eliminate increased alkalinity and improve the properties of solonetzic soils.
The use of chemical reclamation methods on acidic and alkaline soils is the most important condition for the intensification of agricultural production. production on these soils, increasing their fertility and the efficiency of applied organic and mineral fertilizers.
The relation of various page - x. crops to soil reaction and liming
For each plant species, there is a certain most favorable environmental reaction for its growth and development. Most of the page - x. cultures and useful soil microorganisms develops better when the reaction of the environment is close to neutral (pH 6-7).
In relation to the reaction of the environment and responsiveness to liming with. - x. cultures are divided into the following groups:
1. Cannot tolerate acid reaction alfalfa, sainfoin, root crops, hemp, cabbage: for them, the optimum pH lies in a narrow range from 7 to 7.5. they respond very strongly to liming even on slightly acidic soils.
2. Sensitive to increased soil acidity - wheat, barley, corn, sunflower, all legumes (with the exception of lupins and seradella), cucumbers, onions, lettuce. They grow better in slightly acidic and neutral reactions (pH 6-7) and respond well to liming not only strongly but also moderately acidic soils.
3. Less sensitive to hyperacidity rye, oats, millet, buckwheat, timothy grass, radishes, carrots, tomatoes. They can grow satisfactorily in a wide range of pH (from 4.5 to 7.5), but the most favorable for their growth is a weakly acidic reaction (pH 5.5 - 6.0). These crops react positively to liming of strongly and moderately acidic soils.
4. Need liming only on moderately and strongly acidic soils flax and potatoes. Potatoes are not very sensitive to acidity, and flax grows better on slightly acidic soils (pH 5.5 - 6.5). high standards lime has a negative effect on the quality of the harvest of these crops: potatoes are severely affected by scab, the starch content in tubers decreases, and flax becomes ill with bacteriosis, deteriorating fiber quality.
5. Tolerates acid soil well and negatively react to liming lupine, seradella and tea bush, therefore, when liming with increased rates, they reduce the yield.
Thus, the increased acidity of the soil has a negative effect on most agricultural crops, so they respond positively to liming.
The acidic reaction of the soil has a multifaceted negative effect on plants, but they can be combined into two groups: a direct negative effect and an indirect negative effect.
direct negative action is that the permeability of cell membranes is deteriorating, therefore, the use of water and nutrients soil and applied fertilizers, metabolism is disturbed, protein synthesis is weakened, the processes of converting simple carbohydrates into more complex organic compounds are suppressed, growth and branching of roots deteriorate. Plants are especially sensitive to acid reaction in the first period of growth, immediately after germination.
Indirect negative effect acidity is just as versatile. Acidic soils have unfavorable biological, physical and Chemical properties. Their colloidal part is poor in calcium and other bases. Due to the displacement of calcium by hydrogen ions from soil humus, its dispersion and mobility increase, and the saturation of mineral colloidal particles with hydrogen leads to their gradual destruction. This explains the low content of the colloidal fraction in acidic soils; therefore, they have unfavorable physical, biological physicochemical characteristics, poor structure, low absorption capacity and poor buffering.
The negative effect of increased acidity is largely associated with an increase in the mobility of aluminum and manganese and a decrease in the availability of phosphorus and molybdenum. In addition, in acidic soils, the entry of calcium and magnesium into plants is difficult, therefore, their nutrition with these elements also deteriorates.
The influence of lime on the properties and nutritional regime of the soil
The introduction of lime neutralizes free organic mineral acids in the soil solution, as well as hydrogen ions in the soil absorbing complex, that is, the actual and exchangeable acidity is eliminated, hydrolytic acidity is significantly reduced, and soil saturation with bases is increased.
The replacement of hydrogen absorbed by PPC with calcium is accompanied by coagulation of soil colloids, as a result of which their destruction and leaching are reduced, and the physical properties of the soil are improved - structure, water permeability, aeration.
When lime is introduced, the content of mobile forms of aluminum and manganese in the soil decreases, therefore their harmful effect on plants is eliminated.
As a result of a decrease in acidity and an improvement in the physical properties of the soil, under the influence of liming, the vital activity of beneficial soil microorganisms and the mobilization of nitrogen, phosphorus, sulfur and other macro and microelements from the soil are enhanced. Only the mobility of boron and manganese may decrease, but this can be corrected by the application of appropriate microfertilizers.
The improvement of plant nutrition with nitrogen and ash elements is also due to the fact that plants develop more power on calcareous soils. root system capable of assimilating large quantity nutrient elements.
A quick way to radically improve solonetz soils by earthing is that the surface of solonetzic spots is covered with a scraper with a layer of 15-20 cm next to it rich in calcium and humus. chernozem soil in one go. With this amount of soil per 1 ha, getting into the solonets horizon improves it.
Materials used for gypsuming soils:
1. Raw ground gypsum (CaSO 4 2H 2 O) - contains gypsum 71-73%. It is a finely ground natural gypsum of white or gray color. Its humidity should not exceed 8%, otherwise it cakes and turns into lumps.
2. Phosphogypsum is a waste from the production of double superphosphate and precipitate. Very fine white or gray powder containing 70-75% CaSO 4 and a small amount of P 2 O 5 2-3%.
3. Clay gypsum is extracted from natural deposits. In its natural state, loose does not require grinding. Contains 60 to 90% CaSO 4 and 1 to 11% clay.
Lecture 9
1. Attendance check
2. Questions on the previous lecture
1. How do crops relate to soil acidity?
2. What is the importance of soil liming?
3. What kind of lime fertilizers are there?
4. What soils are gypsumed?
5. What processes take place in the soil during gypsum?
Chemical melioration (melioration is a radical improvement of soils) has to be resorted to in cases where it is necessary to quickly change their properties unfavorable for plants, to increase fertility. To do this, chemicals are introduced into the soil that improve the properties that change it. AT agriculture liming of acidic soils and gypsum is most often used, and sometimes acidification of alkaline soils.
Liming of acidic soils
In the post-Soviet space, about half of all lands suitable for cultivation are located in the non-chernozem zone. Atmospheric precipitation enough falls here, and sometimes too much. But the yields on the podzolic and soddy-podzolic soils prevailing in this zone are small. The reason for their low fertility is a lack of nutrients, a bad and acidic reaction of many of them. cause organic and partly mineral and hydrogen ion, located on the surface of the smallest, colloidal soil particles.
Most agricultural crops do not grow well in highly acidic soils and produce low yields. Especially sensitive to soil acidity are beets,,. Somewhat less, but also sensitive to high acidity, wheat, cauliflower, cucumbers; from fruit -,; from herbs - a fire,. Oats and rye are weakly sensitive to acid reaction, but they also react positively to liming.
There are crops that easily tolerate increased acidity and usually do not need liming of the soil. Some of them increase yields with incomplete liming, when strong acidity is replaced by weak acidity. This is turnip, radish.
In increasing the fertility of acidic soils, liming belongs to one of the first places. It eliminates acidity, converts some toxic compounds, such as aluminum, into an insoluble, and therefore harmless form for plants, and, conversely, promotes the solubility of some other substances, including phosphates (by binding mobile aluminum and), and thereby increases their availability for plants. At the same time, the living conditions of beneficial microorganisms are improving, their growth is increasing. Humic substances accumulate in the soil, improving its structure. becomes more water - breathable, it is easier to process.
Depending on the degree of acidity of the soil, the amount of humus and clay particles in it, it is necessary to add different types of lime to the soil. For example, on clay soils it is necessary to add about one and a half times more lime than on light loamy and sandy loamy soils. Slightly acidic soils do not need liming.
Mineral and must be added to limed soils. Only under this condition can you get the most from the elimination of soil acidity. The best results are obtained by applying lime along with organic and mineral fertilizers. Lime increases the efficiency of mineral and organic fertilizers by 25-50%. For example, the harvest of barley and perennial herbs when applying 20 tons of manure and 6 tons of lime per hectare, it is equal to the yield that occurs when 40 tons of manure is applied. Even the introduction of half doses of lime significantly increases the yield. On limed soils, winter wheat increases by an average of 3-6 centners per hectare, spring wheat, barley and rye - by 2-5 centners, clover for hay - by 10-15 centners, fodder root crops - by 60 centners.
The more acidic the soil, the greater the increase in yield gives the introduction of lime. But one liming is very
poor soils may not give positive result, since lime reduces the solubility of some other substances, such as potassium and trace elements. Therefore, on poor soils, it is often necessary to introduce microelements during liming:, on some soils, sulfur,. increase not only plants, but also them against various diseases.
Remove waste from the salt lick during the production of soda. Calcium chloride is chemically more active than gypsum, but it is bad because the chloride ion associated with it is poisonous to plants. After reclamation with calcium chloride, soils need more rapid flushing, which is possible only with artificial irrigation. After washing, they become good, fertile soils.
Salt licks, which contain calcium carbonate from the very top layer, can be improved by adding acidic minerals to the soil. industrial waste, best waste from the production of technical sulfuric acid. This technique is called acidification of salt licks.
scattered on the surface of the soil, and then plowed.
Acidification is also used on soils saline with soda. This most toxic salt found in soils cannot be removed by leaching. You have to first destroy the soda - combine the sodium ion with the sulfate ion - and then rinse the soil.
Chemical reclamation- an important part of the huge work on the radical improvement of land, which has unfolded throughout the vast territory of our country.
In the south, salinization and alkalinity of soils are being carried out and eliminated, in the north, waterlogged lands are being drained and the harmful acidity of soils is being carried out.
>> Chemistry: Chemical soil reclamation
Land reclamation (from Latin melioration - improvement) are methods by which soil properties are improved for a long time. These include hydrotechnical, forestry and chemical methods.
For plants at each stage of their development, the most favorable conditions are created with a certain composition of the soil solution. Special meaning has a solution reaction, depending on the concentration of hydrogen ions in it, i.e. soil acidity.
Soil acidity is one of key indicators characterizing its fertility.
The acidity of the soil solution is due to the presence of H+ cations in it, and the alkalinity is determined by the presence of OH- anions. AT clean water contained the same number H+ and OH- ions. With an increase in the concentration of H +, the solution becomes acidic, with an increase in the concentration of OH - - alkaline. The concentration of H + is expressed as negative powers of 10, for example 10-3, 10-4 mol of ions per 1 liter. To characterize acidity, one exponent is used, taking it with the opposite sign. It is called pH indicator or pH. The number at the pH sign indicates the degree of acidity. For example, pH = 5 means that the solution contains 0.00001 mol of H + ions, i.e., the medium of the soil solution is medium acid; at pH \u003d 7 - the medium is neutral, i.e. the concentrations of H + and OH- ions are equal; at pH > 7 the reaction of the medium is alkaline.
Many soils in Russia are acidic. Hydrogen ions, when they are in significant excess, are harmful to plants not only by themselves. In excessively acidic soils, the vital activity of beneficial microorganisms is sharply reduced. Physical properties such soils are unsatisfactory, they are poorly permeable to air and water.
Improving the properties of acidic soils is achieved by chemical reclamation by liming, that is, by introducing lime materials into the soil - slaked lime Ca (OH) 2 or limestone CaCO3. The most commonly used is crushed limestone, a very common natural mineral. In acidic soil, these compounds react with hydrogen ions:
CaCO3 + 2H + = Ca 2+ + H20 + CO2
Liming improves the activity of nodule and nitrogen-fixing bacteria, increases the ion-exchange capacity of soil particles, and therefore increases the efficiency of mineral fertilizers by 30-40%, improves soil structure, their water and air mode, contributes to the development of the root system of plants.
Cultivated plants react differently to soil acidity and liming. Alfalfa, cabbage, clover, beets are very sensitive to soil acidity, they need a soil reaction close to neutral (pH 6.2-7.2), so they respond well to liming. Wheat, barley, corn, peas, beans, vetch, turnip, rutabaga grow well with a weakly acid reaction (pH 5.1-6) and liming. Rye, oats, timothy, buckwheat tolerate moderate acidity (pH 4.5-5.0) and respond positively to high doses of lime. Potatoes, flax, sunflower easily tolerate moderate acidity and require liming only on strongly and medium acid soils. Lupine, seradella, tea bush are insensitive to high soil acidity and do not need liming.
In addition to limestone as lime fertilizers calcareous tufa, marl, dolomite, chalk, etc. are used.
1. Reclamation.
2. Chemical melioration.
3. Soil acidity.
4. Liming and its significance.
Write molecular equation reaction corresponding to the abbreviated ionic equation given in the section. Why does insoluble calcium carbonate dissolve?
What is the pH value of saliva and gastric juice? Remember from biology lessons that saliva is alkaline. The fact that the environment of gastric juice is acidic is also known to you from the course of chemistry. Why do dentists recommend brushing your teeth or chewing certain types of chewing gum after eating?
For sandy loamy soils with a pH of less than 4.5 (what does this mean?), the lime application rate is 4 t/ha. Calculate the dose of lime required to apply on 6 acres suburban area with this type of soil. Write the equations for the reactions that occur in the soil solution during liming.
The formula of dolomite is CaCO 3 MgCO 3. Write the equations for the reactions that occur when soils are limed with dolomite.
What methods of hydrotechnical and forestry melioration do you know? Is it possible to confine ourselves to only one group of reclamation methods?
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