Calcium, magnesium and sulfur in plant organisms. What is calcium, the reaction of calcium with oxygen Calcium and sulfur heterogeneous reaction

Macronutrients are called elements that can be included in the composition of the plant in whole percents or in tenths of a percent. These include phosphorus, nitrogen, cations - potassium, sulfur, calcium, magnesium, while iron is an intermediate element between micro and macro elements.

The element is perfectly absorbed by the plant from ammonium and nitric acid salts. It is the main nutrient of the roots, because it is part of the proteins in living cells. The protein molecule has a complex structure, protoplasm is built from it, the nitrogen content ranges from 16% to 18%. Protoplasm is a living substance in which the main physiological process takes place, namely, respiratory metabolism. It is only thanks to protoplasm that a complex synthesis of organic substances takes place. Nitrogen is also a component of the nucleic acid, which is part of the nucleus and, in combination, the carrier of heredity. The great importance of the element is determined by the fact that this macroelement is part of chlorophyll-green, the process of photosynthesis depends on this pigment, and it is also part of some enzymes that regulate metabolic reactions and a number of different vitamins. A small amount of nitrogen can be found in an inorganic environment. With a lack of light or excess nitrogen nutrition, nitrates can accumulate in the cell sap.

Most forms of nitrogen are converted in the plant to ammonia compounds, which, when reacted with organic acids, form asparagine amides, amino acids and glutamine. Ammonia nitrogen most often does not accumulate in large quantities in the plant. This can be observed only with an insufficient amount of carbohydrates, in such conditions the plant is not able to process it into harmless substances - glutamine and asparagine. Excess ammonia in the tissues can lead to their direct damage. This circumstance should be taken into account when growing a plant in the winter in a greenhouse. A high proportion of ammonia nitrogen in the nutrient substrate and insufficient illumination, which can reduce the process of photosynthesis, can also lead to damage to the leaf parenchyma due to a high content of ammonia.

Vegetable plants need nitrogen throughout their growing season as they are always building new parts. With a lack of nitrogen, the plant begins to grow poorly. New shoots are not formed, the size of the leaves is reduced. If nitrogen is absent in old leaves, the chlorophyll in them is destroyed, because of this, the leaves become pale green, then turn yellow and die. In acute starvation, the middle tiers of the leaves become yellow, and the upper ones become pale green. This phenomenon can be dealt with easily. To do this, you only need to add nitrate salt to the nutrient, so that after 5 or 6 days the leaves become dark green in color and the plant continues to create new shoots.

This element can be absorbed by the plant only in the oxidized form - the SO4 anion. In this plant, a large mass of sulfate anion is reduced to -S-S- and -SH groups. In such groups, sulfur is part of proteins and amino acids. The element is part of some enzymes, also enzymes involved in the respiratory process. Consequently, sulfur compounds greatly affect metabolic processes and the formation of energy.

Sulfur is also present in cell sap as the sulfate ion. When sulfur-containing compounds decompose, with the participation of oxygen, sulfur is oxidized to sulfate. If the root dies due to lack of oxygen, then the compounds containing sulfur decompose to hydrogen sulfide, which is poisonous to living roots. This is one of the reasons for the death of the entire root system with a lack of oxygen and its flooding. If there is a lack of sulfur, then, as with nitrogen, chlorophyll is resolved, but the leaves of the upper layers are among the first to experience a lack of sulfur.

This element is absorbed only in the oxidized form with the help of salts of phosphoric acids. The element is also found in the composition of proteins (complex) - nucleoproteins, they are the most important substances of the plasma and nucleus. Also, phosphorus is part of fat-like substances and phosphatides, which play an important role in the formation of membrane surfaces in the cell, are part of some enzymes and other active compounds. The element plays an important role in aerobic respiration and glycolysis. The energy that is released during these processes is accumulated in the form of phosphate bonds, and is subsequently used to synthesize many substances.

Phosphorus also takes part in the process of photosynthesis. Phosphoric acid cannot be reduced in a plant, it can only bind with other organic substances, forming phosphoric esters. Phosphorus is naturally found in in large numbers, and in the cell juice it accumulates with the help of mineral salts, which are a reserve fund of phosphorus. The buffering properties of phosphoric acid salts are able to regulate the acidity in the cell, maintaining a favorable level. The element is very necessary for the growth of the plant. If at first the plant lacks phosphorus, and then after feeding with phosphorus salts, the plant may suffer from an increased intake of this element and a violation due to this nitrogen metabolism. Therefore, it is very important to ensure good conditions phosphorus nutrition throughout life cycle plants.

Calcium, magnesium and potassium are absorbed by the plant from various salts (soluble), the anions of which do not have a toxic effect. They are available when they are in an absorbed form, namely, they are associated with some insoluble substance that has acidic properties. When released into the plant, calcium and potassium do not tolerate chemical transformations, but they are necessary for nutrition. And they cannot be replaced by other elements, just as sulfur, nitrogen or phosphorus cannot be replaced.

The main role of magnesium, calcium and potassium consists in the fact that when they are adsorbed on colloidal particles of protoplasm, they form special electrostatic forces around them. These forces play an important role in the formation of the structure of living matter, without which neither the synthesis of cellular substances nor Team work various enzymes. At the same time, the ions hold a certain number of water molecules around them, which is why the total volume of the ions is not the same. The forces that hold the ion directly on the surface of the colloidal particle are also not equal. It should be noted that the calcium ion has the smallest volume - it is able to stay on the colloidal surface with greater force. The potassium ion has the largest volume, which is why it is able to form less strong adsorption bonds, and the calcium ion can displace it. The intermediate position was occupied by the magnesium ion. Since, during adsorption, ions try to retain a water shell, it is they that determine the water-retaining power and water content of colloids. If there is potassium, then the water-retaining power of the tissue increases, and with calcium, it decreases. It follows from the above that in creating internal structures what matters is the ratio of the various cations, not their absolute content.

In plants, the element is contained in greater quantities than other cations, especially in the vegetative parts. Most often found in cell sap. There is also a lot of it in young cells, which are rich in protoplasm, a significant amount of potassium in the adsorbed state. The element is able to influence the plasma colloids, it liquefies the protoplasm (increases its hydrophilicity). Also, potassium is a catalyst for many synthetic processes: it usually catalyzes the synthesis of simple macromolecular substances, contributing to the formation of starch, proteins, sucrose and fats. If observed, a lack of potassium can disrupt the synthesizing processes, and amino acids, glucose and other decay products will begin to accumulate in the plant. If there is a lack of potassium, a marginal fuse forms on the leaves of the lower layer - this is when the edges of the plate near the leaf die off, after which the leaves become domed, and brown spots form on them. Necrosis or brown spots are associated with the formation of cadaveric poison in plant tissues and a violation of nitrogen metabolism.

The element must be supplied to the plant during the complete life cycle. A large part of this element is found in the cell sap. This calcium is not particularly involved in metabolic processes, it helps to neutralize excess acids of an organic nature. The other part of the calcium is in the plasma - here calcium works as a potassium antagonist, it works in the opposite direction compared to potassium, i.e. increases viscosity and reduces the hydrophilic properties of plasma colloids. In order for the processes to proceed in a normal way, the ratio of calcium and potassium directly in the plasma is important, since this ratio determines the colloidal characteristics of the plasma. Calcium is found in the nuclear substance, therefore it is very important in the process of cell division. It also plays an important role in the formation of various cell membranes, while the greatest role in the formation of the walls of the root hairs, where it enters as pectate. If calcium is not present in the nutrient substrate, the growth points of the root and aerial parts are affected at lightning speed, due to the fact that calcium is not transported from old to young parts. There is a sliming of the roots, while their growth is abnormal or stops altogether. When grown in artificial culture using tap water, the absence of calcium is rare.

The element enters the plant less than calcium or potassium. However, its role is very important, because the element is part of chlorophyll (1/10 of all magnesium in the cell is in chlorophyll). The element is vital - necessary for chlorophyll-free organisms, and its role does not end with photosynthetic processes. Magnesium is an essential element needed for respiratory metabolism and catalyzes and transports many different phosphate bonds. Since phosphate bonds, which are rich in energy, are involved in many synthesizing processes, they simply cannot go without this element. If there is a lack of magnesium, chlorophyll molecules are destroyed, but the veins of the leaves remain green, and the tissue areas located between the veins become paler. This is called patchy chlorosis, and is quite common when a plant is deficient in magnesium.

The element is absorbed by the plant with the help of complex, organic compounds, as well as in the form of salts (soluble). The total iron content of the plant is low (hundredths of a percent). In plant tissues, iron is represented by organic compounds. It is also worth knowing that the iron ion can freely change from the ferrous form to the oxide form, or vice versa. Consequently, being in various enzymes, iron is involved in redox processes. Also, the element is part of respiratory enzymes (cytochrome, etc.).

There is no iron in chlorophyll, but it takes part in its creation. If there is a lack of iron, chlorosis may develop - with this disease, chlorophyll is not formed, and the leaves turn yellow. Due to the low mobility of iron in old leaves, it cannot be transported to young leaves. Therefore, chlorosis usually begins with young leaves.

If there is a lack of iron, photosynthesis also undergoes a change - the growth of the plant slows down. To prevent chlorosis, you need to add iron to the nutrient substrate no later than 5 days after the onset of this disease, if you do this later, then the likelihood of recovery is very small.

In ancient times, people used calcium compounds for construction. Basically, it was calcium carbonate, which was in the rocks, or the product of its burning - lime. Marble and plaster were also used. Previously, scientists believed that lime, which is calcium oxide, is a simple substance. This misconception existed until the end of the 18th century, until Antoine Lavoisier expressed his assumptions about this substance.

Lime mining

At the beginning of the 19th century, the English scientist Humphrey Davy discovered pure calcium using electrolysis. Moreover, he received calcium amalgam from slaked lime and mercury oxide. Then, after distilling the mercury, he obtained metallic calcium.

The reaction of calcium with water is violent, but is not accompanied by ignition. Due to the abundant release of hydrogen, the plate with calcium will move through the water. A substance is also formed - calcium hydroxide. If phenolphthalein is added to the liquid, it will turn bright crimson - therefore, Ca(OH)₂ is a base.

Ca + 2H₂O → Ca(OH)₂↓ + H₂

The reaction of calcium with oxygen

The reaction of Ca and O₂ is very interesting, but the experiment cannot be performed at home, as it is very dangerous.

Consider the reaction of calcium with oxygen, namely, the combustion of this substance in air.

Attention! Do not try to repeat this experience yourself! you will find safe chemistry experiments you can do at home.

Let us take potassium nitrate KNO₃ as a source of oxygen. If calcium was stored in a kerosene liquid, then before the experiment it must be cleaned with a burner, holding it over a flame. Next, calcium is dipped into KNO₃ powder. Then calcium with potassium nitrate must be placed in the flame of the burner. Potassium nitrate decomposes into potassium nitrite and oxygen. The released oxygen ignites the calcium, and the flame turns red.

KNO₃ → KNO₂ + O₂

2Ca + O₂ → 2CaO

It is worth noting that calcium reacts with some elements only when heated, these include: sulfur, boron, nitrogen and others.

In relation to calcium, plants are divided into three groups: calciophiles, calciophobes and neutral species. The calcium content in plants is 0.5 - 1.5% of the dry matter mass, but in mature tissues of calciphilic plants it can reach 10%. The aerial parts accumulate more calcium per unit mass than the roots.

The chemical properties of calcium are such that it easily forms sufficiently strong and at the same time labile complexes with oxygen compounds of macromolecules. Calcium can bind intramolecular sites of proteins, leading to a change in conformation, and form bridges between complex compounds of lipids and proteins in the membrane or pectin compounds in the cell wall, ensuring the stability of these structures. Therefore, accordingly, with calcium deficiency, the fluidity of membranes sharply increases, the processes of membrane transport and bioelectrogenesis are also disrupted, cell division and elongation are inhibited, and root formation processes stop. Lack of calcium leads to swelling of pectin substances and disruption of the structure of cell walls. Necrosis appears on the fruits. At the same time, the leaf blades are bent and twisted, the tips and edges of the leaves turn white at the beginning, and then turn black. Roots, leaves and parts of the stem rot and die. First of all, young meristematic tissues and the root system suffer from a lack of calcium.

Ca 2+ ions play an important role in regulating the uptake of ions by plant cells. The excess content of many cations toxic to plants (aluminum, manganese, iron, etc.) can be neutralized by binding to the cell wall and displacing Ca 2+ ions from it into the solution.

Calcium plays an important role in cell signaling processes as a second messenger. Ca 2+ ions have a universal ability to conduct a variety of signals that have a primary effect on the cell - hormones, pathogens, light, gravitational and stress effects. A feature of the transmission of information in the cell with the help of Ca 2+ ions is the wave method of signal transmission. Ca-waves and Ca-oscillations initiated in certain areas of cells are the basis of calcium signaling in plant organisms.

The cytoskeleton is very sensitive to changes in the content of cytosolic calcium. Local changes in the concentration of Ca 2+ ions in the cytoplasm play an extremely important role in the assembly (and disassembly) of actin and intermediate filaments and in the organization of cortical microtubules. Calcium-dependent functioning of the cytoskeleton takes place in processes such as cyclosis, flagellar movement, cell division, and polar cell growth.

Sulfur is one of the main nutrients needed for plant life. Its content in plant tissues is relatively low and amounts to 0.2 - 1.0% based on dry weight. Sulfur enters plants only in an oxidized form - in the form of a sulfate ion. Sulfur is found in plants in two forms - oxidized and reduced. The main part of the sulfate absorbed by the roots moves to the aerial part of the plant through the xylem vessels to young tissues, where it is intensively included in the metabolism. Once in the cytoplasm, sulfate is reduced with the formation of sulfhydryl groups of organic compounds (R-SH). From the leaves, sulfate and reduced forms of sulfur can move both acropetally and basipetally to the growing parts of the plant and storage organs. In the seeds, sulfur is found mainly in organic form. The share of sulfate is minimal in young leaves and sharply increases with their aging due to the degradation of proteins. Sulfur, like calcium, is not capable of reutilization and therefore accumulates in old plant tissues.

Sulfhydryl groups are part of amino acids, lipids, coenzyme A and some other compounds. The need for sulfur is especially high in protein-rich plants, such as legumes and cruciferous plants, which synthesize sulfur-containing mustard oils in large quantities. It is part of the amino acids cysteine ​​and methionine, which can be found both in free form and as part of proteins.

One of the main functions of sulfur is associated with the formation of the tertiary structure of proteins due to the covalent bonds of disulfide bridges formed between cysteine ​​residues. It is part of a number of vitamins (lipoic acid, biotin, thiamine). Another one important function sulfur is to maintain a certain value of the redox potential of the cell with the help of reversible transformations:

Insufficient supply of sulfur to plants inhibits the synthesis of proteins, reduces the intensity of photosynthesis, the rate of growth processes. External symptoms of sulfur deficiency are pale and yellowed leaves, which manifests itself first in the youngest shoots.

Magnesium in terms of content in plants ranks fourth after potassium, nitrogen and calcium. In higher plants, its average content in terms of dry weight is 0.02 - 3.1%, in algae 3.0 - 3.5%. Especially a lot of it in young cells, generative organs and storage tissues. The accumulation of magnesium in growing tissues is facilitated by its relatively high mobility in the plant, which makes it possible to reutilize this cation from aging organs. However, the degree of reutilization of magnesium is much lower than that of nitrogen, phosphorus and potassium, since part of it forms oxalates and pectates that are insoluble and incapable of moving through the plant.

In the seeds, most of the magnesium is in the composition of phytin. About 10-15% Mg is part of chlorophyll. This function of magnesium is unique and no other element can replace it in the chlorophyll molecule. The participation of magnesium in the metabolism of a plant cell is associated with its ability to regulate the work of a number of enzymes. Magnesium is a cofactor for almost everyone. enzymes that catalyze the transfer of phosphate groups are necessary for the operation of many of the enzymes of glycolysis and the Krebs cycle, as well as alcoholic and lactic acid fermentation. Magnesium at a concentration of at least 0.5 mM is required for the formation of ribosomes and polysomes, activation of amino acids, and protein synthesis. With an increase in the concentration of magnesium in plant cells, enzymes involved in the metabolism of phosphate are activated, which leads to an increase in the content of organic and inorganic forms of phosphorus compounds in tissues.

Plants experience magnesium starvation mainly on sandy and podzolic soils. Its deficiency primarily affects phosphorus metabolism and, accordingly, the energy of the plant, even if phosphates are present in sufficient quantities in the nutrient substrate. Magnesium deficiency also inhibits the conversion of monosaccharides to polysaccharides and causes serious disturbances in protein synthesis. Magnesium starvation leads to a disruption in the structure of plastids - the grana stick together, the stroma lamellae break and do not form a single structure, instead of them many vesicles appear.

An external symptom of magnesium deficiency is interveinal chlorosis, associated with the appearance of spots and stripes of light green, and then yellow, between the green leaf veins. The edges of the leaf blades will turn yellow, orange, red or dark red. Signs of magnesium starvation first appear on old leaves, and then spread to young leaves and plant organs, and the leaf areas adjacent to the vessels remain green longer.

DEFINITION

calcium sulfide- an average salt formed by a strong base - calcium hydroxide (Ca (OH) 2) and a weak acid - hydrogen sulfide (H 2 S). The formula is CaS.

Molar mass - 72g / mol. It is a white powder that absorbs moisture well.

Hydrolysis of calcium sulfide

Hydrolyzed at the anion. The nature of the medium is alkaline. Theoretically, a second step is possible. The hydrolysis equation looks like this:

First stage:

CaS ↔ Ca 2+ + S 2- (salt dissociation);

S 2- + HOH ↔ HS - + OH - (anion hydrolysis);

Ca 2+ + S 2- + HOH ↔ HS - + Ca 2+ + OH - (equation in ionic form);

2CaS + 2H 2 O ↔ Ca(HS) 2 + Ca(OH) 2 ↓ (molecular equation).

Second step:

Ca (HS) 2 ↔ Ca 2+ + 2HS - (salt dissociation);

HS - + HOH ↔H 2 S + OH - (anion hydrolysis);

Ca 2+ + 2HS - + HOH ↔ H 2 S + Ca 2+ + OH - (equation in ionic form);

Ca(HS) 2 + 2H 2 O ↔ 2H 2 S + Ca(OH) 2 ↓ (molecular equation).

Examples of problem solving

EXAMPLE 1

Exercise	When calcium sulfide is heated, it decomposes, resulting in the formation of calcium and sulfur. Calculate the masses of the reaction products if 70 g of calcium sulfide containing 20% ​​impurities were subjected to calcination.
Solution	We write the equation for the reaction of calcium sulfide calcination: Find the mass fraction of pure (without impurities) calcium sulfide: ω(CaS) = 100% - ω impurity = 100-20 = 80% = 0.8. Find the mass of calcium sulfide that does not contain impurities: m(CaS) = m impurity (CaS)× ω(CaS) = 70×0.8 = 56g. Let's determine the number of moles of calcium sulfide not containing impurities (molar mass - 72 g / mol): υ (CaS) \u003d m (CaS) / M (CaS) \u003d 56/72 \u003d 0.8 mol. According to the equation υ (CaS) = υ (Ca) = υ (S) = 0.8 mol. Find the mass of reaction products. The molar mass of calcium is - 40 g / mol, sulfur - 32 g / mol. m(Ca)= υ(Ca)×M(Ca)= 0.8×40 = 32g; m(S)= υ(S)×M(S)= 0.8×32 = 25.6g.
Answer	The mass of calcium is 32 g, sulfur - 25.6 g.

EXAMPLE 2

Exercise	A mixture consisting of 15 g of calcium sulfate and 12 g of coal was calcined at a temperature of 900 o C. As a result, calcium sulfide was formed and carbon monoxide and carbon dioxide were released. Calculate the mass of calcium sulfide.
Solution	We write the reaction equation for the interaction of calcium sulfate and coal: CaSO 4 + 4C \u003d CaS + 2CO + CO 2. Find the number of moles of the starting substances. The molar mass of calcium sulfate is 136 g/mol, coal is 12 g/mol. υ (CaSO 4) \u003d m (CaSO 4) / M (CaSO 4) \u003d 15/136 \u003d 0.11 mol; υ (C) \u003d m (C) / M (C) \u003d 12/12 \u003d 1 mol. Calcium sulfate in short supply (υ (CaSO 4)<υ(C)). Согласно уравнению реакции υ(CaSO 4)=υ(CaS) =0,11 моль. Найдем массу сульфида кальция (молярная масса – 72 г/моль): m(CaS)= υ(CaS)×M(CaS)= 0.11×72 = 7.92 g.
Answer	The mass of calcium sulfide is 7.92 g.

As yields increase, the importance of providing fields with sufficient amounts of each of the 17 essential nutrients increases. In particular, due to a number of factors, the need for calcium, magnesium and sulfur has increased. In this regard, we place the recommendations of American consultants on the introduction of mesoelements.

Application of fertilizers that do not contain mesoelements. Fertilization is usually carried out with fertilizers that do not contain magnesium or sulfur: diammonium phosphate, urea, ammonium nitrate, nitrogen, phosphorus or potassium chloride. Because of this, there is a deficiency of sulfur or magnesium. These fertilizers, as well as monoammonium phosphate and anhydrous ammonia, do not contain any calcium, magnesium or sulfur at all. Among all common fertilizers, only triple superphosphate contains 14% calcium and does not contain any magnesium or sulfur.

Yield growth. Yields have increased significantly over the past decade. Corn, which yields 12.5 t/ha, uses 70 kg/ha of magnesium and 37 kg/ha of sulfur. For comparison: with a yield of 7.5 t/ha, magnesium is taken out 33 kg/ha, and sulfur - 22 kg/ha.

Reducing the use of sulfur-containing pesticides. Previously, farmers could rely on a source of sulfur such as insecticides and fungicides. Many of these pesticides have now been replaced with products that do not contain sulfur.

Limitation of emissions into the atmosphere. In the USA, emissions from metallurgical furnaces and power plants are limited. In many other countries, emissions of sulfur into the atmosphere from gas combustion in domestic and industrial boilers have decreased. In addition, in modern cars, catalytic converters absorb sulfur, which previously entered the atmosphere along with exhaust gases. All these factors have reduced the return of sulfur to the soil along with rainfall.

Removal of mesoelements with yield, kg/ha

culture	productivity, centner/ha
corn
tomatoes
sugar beet

Calcium

Calcium is given insufficient attention in the preparation of fertilization schemes for many high-yielding and fruit crops. The exceptions are tomatoes and peanuts, which require good calcium nutrition when grown.

In soil, calcium replaces hydrogen ions on the surface of soil particles when lime is added to reduce acidity. It is essential for micro-organisms that convert crop residues into organic matter, release nutrients and improve soil structure and water-holding capacity. Calcium helps to earn nitrogen-fixing nodule bacteria.

Functions of calcium in the plant:

calcium, along with magnesium and potassium, helps to neutralize organic acids formed as a result of cellular metabolism in plants;

improves the absorption of other nutrients by the roots and their transport by the plant;

activates a number of enzyme systems that regulate plant growth;

helps the conversion of nitrate nitrogen into the forms necessary for the formation of proteins;

necessary for the formation of cell walls and normal cell division;

improves disease resistance.

calcium deficiency

Calcium deficiency most often occurs in acidic, sandy soils due to leaching from rain or irrigation water. It is not typical for soils where enough lime has been added to optimize the pH level. As the acidity of the soil increases, plant growth becomes more difficult due to an increase in the concentration of toxic elements - aluminum and / or manganese, but not due to a lack of calcium. Soil analysis and adequate liming is the best way to avoid these problems.

Calcium deficiency can be avoided by regularly analyzing the soil and adjusting the acidity by applying optimal doses of lime. It is necessary to adhere to a balanced application of calcium, magnesium and potassium. There is an antagonism between these elements: an overdose of one leads to a deficiency or neutralization of the other. In addition, calcium must be applied for a reason, but in certain phases in order to ensure certain functions of the plant.

Sources of calcium

Good liming effectively provides calcium to most crops. High quality calcite lime is effective when pH adjustment is required. When magnesium is also deficient, dolomitic limestones or calcite limestones can be applied along with a magnesium source such as potassium magnesium sulfate. Gypsum (calcium sulfate) is a source of calcium at an appropriate pH level.

Main sources of calcium

Magnesium

Plants need energy to grow. Wheat and other crops need magnesium for photosynthesis. Magnesium is an essential component of chlorophyll molecules: each molecule contains 6.7% magnesium.

Magnesium also acts as a transporter of phosphorus in the plant. It is necessary for cell division and protein formation. Absorption of phosphorus is impossible without magnesium, and vice versa. Thus, magnesium is essential for phosphate metabolism, plant respiration, and the activation of a number of enzyme systems.

Magnesium in the soil

The earth's crust contains 1.9% magnesium, predominantly in the form of magnesium-containing minerals. With the gradual weathering of these minerals, part of the magnesium becomes available to plants. The reserves of available magnesium in the soil are sometimes exhausted or exhausted due to leaching, absorption by plants and chemical reactions of exchange.

The availability of magnesium to plants often depends on the pH of the soil. Studies have shown that the availability of magnesium to plants decreases at low pH values. On acidic soils with a pH less than 5.8, excess hydrogen and aluminum affect the availability of magnesium and its uptake by plants. At high pH (greater than 7.4), excess calcium can interfere with the uptake of magnesium by plants.

Sandy soils with a low cation exchange capacity have a low capacity to supply plants with magnesium. High calcium lime applications can exacerbate magnesium deficiencies by promoting plant growth and increasing magnesium requirements. High application rates of ammonium and potassium can upset the nutritional balance due to the effect of ion competition. The limit below which the content of exchangeable magnesium is considered low, and the application of magnesium is justified, is 25-50 ppm or 55-110 kg/ha.

For soils with a cation exchange capacity greater than 5 mEq per 100 g, the calcium to magnesium ratio in the soil should be maintained at approximately 10:1. For sandy soils with a cation exchange capacity of 5 mEq or less, the calcium to magnesium ratio should be maintained at approximately level 5:1.

How to compensate for magnesium deficiency

If foliar analysis reveals a deficiency of magnesium in a vegetative plant, it can be compensated by the supply of magnesium in soluble form along with rain or irrigation water. This makes magnesium available to the root system and uptake by plants. Small doses of magnesium can also be applied through the leaf in order to correct the content of this element or prevent its deficiency. But it is better to add magnesium to the soil before sowing or before the crop begins to actively grow.

Sources of magnesium

substance		water solubility
dolomitic limestone
magnesium chloride
magnesium hydroxide
magnesium nitrate		+
magnesium oxide		-
magnesium sulfate

Sulfur

Sulfur in the soil

The source of sulfur for plants in the soil is organic matter and minerals, but often they are not enough or they are in a form inaccessible to high-yielding crops. Most soil sulfur is bound in organic matter and is not available to plants until it is converted to the sulfate form by soil bacteria. This process is called mineralization.

Sulphates are as mobile in the soil as nitrogen in the nitrate form, and in some soil types can be washed out of the root zone by heavy rainfall or irrigation. Sulphates can move back to the soil surface with water evaporation, except in sandy or coarse soils where the capillary pores are broken. The mobility of sulphate sulfur makes it difficult to measure its content in soil analysis and use such analyzes to predict the need for sulfur application.

Sulfur is contained to a greater extent by clay soil particles than nitrate nitrogen. Intense rains in early spring can wash sulfur out of the topsoil and bind it in the bottom if the topsoil is sandy and the bottom is clayey. Therefore, crops that grow in such soils may show symptoms of sulfur deficiency in the early stages of the growing season, but as the roots penetrate the lower soil layers, this deficiency may disappear. On soils that are sandy throughout the profile, with little or no clay layer, crops will respond well to sulfur application.

Sulfur in plants

Sulfur is a part of every living cell and is necessary for the synthesis of certain amino acids (cysteine ​​and methionine) and proteins. Sulfur is also important for photosynthesis and crop hardiness. In addition, sulfur is important for the process of converting nitrate nitrogen into amino acids.

Sulfur deficiency

In visual analysis, sulfur deficiency is often confused with nitrogen deficiency. In both cases, there is a lag in growth, accompanied by a general yellowing of the leaves. Sulfur in the plant is immobile and does not move from old to young leaves. With sulfur deficiency, young leaves often turn yellow first, while with nitrogen deficiency, older ones. If the deficiency is not very acute, its symptoms may not be visually manifest.

The most reliable way to diagnose sulfur deficiency is to analyze plant samples for both sulfur and nitrogen. The normal sulfur content in plant tissues of most crops ranges from 0.2 to 0.5%. The optimal level of the ratio between nitrogen and sulfur is from 7: 1 to 15: 1. If the ratio goes beyond the above limits, this may signal a sulfur deficiency, but for an accurate diagnosis, this indicator should be considered in combination with absolute indicators of nitrogen and sulfur.

In conditions of sulfur deficiency, nitrogen in the nitrate form can accumulate. Accumulation of nitrates in the plant can prevent seed formation in some crops such as rapeseed. Therefore, balancing the sulfur content with the nitrogen content is important for plant health.

Crops such as alfalfa or corn, which produce high dry matter yields, require the highest doses of sulfur. Also, potatoes and many vegetable crops need sulfur in large quantities and produce better fruit when fertilizers containing sulfur are applied. Without a balanced sulfur diet, crops that receive high doses of nitrogen fertilizers may suffer from sulfur deficiency.

Sources of sulfur

Irrigation water can sometimes contain significant amounts of sulfur. For example, when the sulfate sulfur content in irrigation water exceeds 5 parts per million, there is no prerequisite for the occurrence of sulfur deficiency. Most sulfur-containing fertilizers are sulfates, which have medium to high water solubility. The most important source of water-insoluble sulfur is elemental sulfur, which can be oxidized to sulfates by microorganisms before being used by plants. Oxidation occurs when the soil is warm, has adequate moisture, aeration, and sulfur particle size. Elemental sulfur is well absorbed by the soil, and then by crops.

Sources of sulfur

type of fertilizer		water solubility	increased soil acidity
ammonium sulfate
ammonium thiosulfate
ammonium polysulfide
elemental sulfur	at least 85
magnesium sulfate
normal superphosphate
potassium sulfate
potassium thiosulfate
sulfur coated urea