Phosphorus, physiological role, intake and movement through the plant. Mineral nutrition of plants, fertilizers in agricultural production - The role of phosphorus in plant nutrition

Phosphorus in plants

Phosphorus plays an extremely important role in plant life. Most metabolic processes are carried out only with his participation. It is almost always in the second minimum (after nitrogen).

The physiological role of phosphorus (C 3). It is included in the most important organic compounds, actively involved in the metabolism of plants: nucleic acids (DNA and RNA), nucleoproteins, phosphoproteins, phosphatides (phospholipids), macroergic compounds (ATP, etc.), sugar phosphates, phytin, vitamins, etc. Phosphorus content (P2O5) in plants and removal crop yields The average content is 0.5% dry matter, varying from 0.1 to 1.5%, and depends on biological features crops, age of plants and their organs, conditions of phosphorus nutrition, etc. So, the grain of leguminous crops contains 1-1.5% P2O5, cereals - 0.8-1%. The straw of those and other crops contains less phosphorus compared to seeds - 0.2-0.4%.

Phosphorus in plants is distributed similarly to nitrogen, is its companion. On average, the content of phosphorus in plant organs is 30% of the amount of nitrogen (C 17). More phosphorus is found in young and vital organs, leaves contain more phosphorus than stems.

The removal of phosphorus by crops averages 15-50 kg/ha, varying depending on the biological characteristics of crops and the level of productivity.

Sources of phosphorus for plants. The main sources are salts of orthophosphoric acid (C 19), which, being tribasic, is capable of forming three types of anions - H2PO4–, HPO42–, PO43– (C 20) and, therefore, three types of salts - one-, two- and three-substituted phosphates , whose solubility and availability for plants varies depending on the cations.

Salts of metaphosphoric and polyphosphoric (pyro-, tripolyphosphoric, etc.) acids, which are not directly absorbed by plants, but are hydrolyzed in the soil to orthophosphates (C 21-24), can also be sources of phosphorus.

In addition, the roots of some plants (peas, beans, corn, etc.) secrete the enzyme phosphatase, which splits off the phosphoric acid anion from simple organic compounds. As a result, the organic compounds of phosphorus can serve as a source of phosphorus for these plants.

Phosphorus transformations in plants. The phosphorus that enters the plants very quickly passes into the composition of organic compounds. However, phosphorus is in them directly in the form of a residue of phosphoric acid. Thus, 85-95% of phosphorus is in organic form (C 26). Mineral phosphates - calcium, potassium, magnesium and ammonium phosphates - are much less (5-15%), but they have great importance, being a reserve and transport form of phosphorus. For example, phosphorus from organic compounds in roots can move into above-ground part only after transformation into mineral phosphates.

Dynamics of phosphorus consumption during the growing season. The critical period in relation to phosphorus in all cultures is noted in the phase of seedlings. The lack of phosphorus during this period sharply reduces the yield, regardless of the further supply of plants. However, root system in the initial phases of growth, it is poorly developed and often cannot absorb soil phosphorus and fertilizers applied before sowing in sufficient quantities. Therefore, pre-sowing application of phosphorus is widely recommended.

The periods of maximum consumption of phosphorus by different cultures do not coincide. For example, spring wheat consumes all the phosphorus it needs by the end of the heading phase, while flax absorbs only 58% even by the full flowering period, and cotton absorbs only 10% of the maximum phosphorus content in plants in the full flowering phase. The absorption of phosphorus in wheat is observed in the phases of emergence into the tube and heading, in flax - in the phases of flowering and ripening, in cotton - during the period of fiber formation.

Signs of a lack of phosphorus for plants. The growth and development of plants slows down, the size of the leaves decreases, flowering and ripening of the crop are delayed (C 31-33). Phosphorus is recycled, so its deficiency first appears on the lower leaves, which turn dark green, dirty green, and then red-violet, purple or purple

Phosphorus in soils. Contents and reserves of phosphorus in soils. The total content varies from 0.01 to 0.3% and depends primarily on the mineralogical composition of the parent rocks. In addition, soils rich in humus contain more phosphorus (humus contains 1-2% P2O5). Thus, the minimum content of phosphorus in soddy-podzolic sandy soils, the maximum - in chernozem soils. The vital activity of plants causes the biological accumulation of phosphorus in the upper soil horizons

The total reserve of phosphorus in the arable layer per 1 ha varies from 0.3 tons in light soddy-podzolic soils to 9 tons in chernozems

Forms of phosphorus in soils and its transformation Phosphorus in soils is in organic and mineral forms Organic phosphorus is less, it is part of the non-specific part of humus, as well as undecomposed remains of plants and microorganisms.

Mineral phosphorus predominates, which in soddy-podzolic, chestnut soils and gray soils is 70-90% of the total content, and in soils with a high content of humus (hence, organic phosphorus) - gray forest soils and chernozems - 55-65% (C 44). Mineral phosphorus is mainly found in the form of primary minerals and, above all, fluorapatite [Ca3(PO4)2]3·CaF2 and hydroxyapatite [Ca3(PO4)2]3·Ca(OH)2.

Phosphorus of organic compounds and primary minerals is not directly absorbed by plants. As a result of weathering of primary minerals, secondary minerals are formed, which are various salts of orthophosphoric acid. Phosphates are also formed during the mineralization of organic phosphorus under the influence of phosphorobacteria.

Salts of phosphoric acid are characterized by different solubility and, consequently, availability to plants.

Phosphates of monovalent cations [KH2PO4, (NH4)2HPO4, Na3PO4], as well as monosubstituted salts of divalent cations [Ca(H2PO4)2, Mg(H2PO4)2] are water-soluble. They are well available to plants.

Disubstituted calcium and magnesium phosphates (CaHPO4, MgHPO4) and freshly precipitated, amorphous three-substituted phosphates [Ca3(PO4)2, Mg3(PO4)2], which are insoluble in water, but dissolve in weak acids (organic, carbonic) are called acid-soluble. . These compounds, under the action of acidic root secretions, as well as organic and mineral acids produced by microbes, gradually dissolve and become available to plants.

They do not dissolve in water and weak acids, as a result, crystalline forms of trisubstituted calcium and magnesium phosphates are practically inaccessible to plants. But some plants - lupins, buckwheat, mustard, to a lesser extent peas, sweet clover, sainfoin and hemp - have the ability to absorb phosphorus from trisubstituted phosphates. The least available to plants are iron and aluminum phosphates (AlPO4, FePO4) Important role The chemical uptake of water-soluble phosphates (phosphorus retrogradation), which takes place in soils in any reaction of the environment, plays a role in the formation of conditions for phosphorus nutrition.

In neutral soils saturated with bases (chernozems, chestnut soils), two- and three-substituted calcium and magnesium phosphates are formed:

Ca(H2PO4)2 + Ca(HCO3)2 → 2CaHPO4↓ + 2H2CO3;

PPK)Ca2+ + Ca(H2PO4)2 → PPK)2H+ + Ca3(PO4)2↓.

AT acidic soils, characterized high content aluminum and iron (soddy-podzolic, red soils), phosphates of these elements precipitate:

Ca(H2PO4)2 + 2Fe3+ → 2FePO4↓ + Ca2+ + 4H+;

PPK)Al3+ + K3PO4 → PPK)3K+ + AlPO4↓.

As a result of retrogradation, water-soluble phosphates are found in soils in insignificant amounts (as a rule, no more than 1 mg/kg of soil).

Anions of phosphoric acid in the soil can be exchanged absorbed by fixing on the surface of positively charged colloidal particles of aluminum and iron hydroxides. The process of exchange absorption is reversible, that is, phosphate ions are capable of being displaced from the FPC into the solution by other anions. As a result, the exchange-absorbed anions of phosphoric acid are readily available to plants.

Soluble salts of phosphorus are consumed not only by plants, but also by microorganisms, turning into organic phosphorus-containing compounds. After the death of microbes, the main amount of biologically absorbed phosphorus again becomes available to plants, with the exception of a small part that has passed into the composition of humus.

For soddy-podzolic and gray forest soils, the Kirsanov method is standardized: the extract is 0.2 N. HCl, water-soluble and acid-soluble salts of phosphoric acid pass into the solution.

In non-carbonate chernozems, the content of mobile phosphorus is determined according to Chirikov: the soil is cultivated with 0.5 n. CH3COOH.

On carbonate soils, acids are not used, since weakly acidic extracts are spent on the decomposition of carbonates, while more concentrated ones can dissolve phosphates that are inaccessible to plants. Therefore, the content of mobile phosphorus in carbonate chernozems is determined according to Machigin using 1% (NH4)2CO3, which has an alkaline reaction.

Absolute results obtained by any method are not informative, since the constant impact of plant roots on the soil during the growing season is far from equivalent to the dissolving power of any reagent. For example, when the solution interacts with the soil, an equilibrium is established, and in the presence of plants that consume phosphorus, its concentration in the liquid phase of the soil constantly decreases, stimulating the transition of new amounts of phosphates into the solution.

However, comparing crop yields in field experiments conducted on soils with different contents of mobile phosphorus, one can conclude how well a particular soil is provided with phosphorus, and express the resulting pattern in the form of a grouping that has practical significance.

Phosphorus plays a special role among plant nutrients. It performs energetic and constitutional functions in plants and other organisms. Phosphorus is a constituent of many vital organophosphorus compounds, among which highest value have ATP and nucleic acids involved in almost all biochemical processes of energy metabolism in the cell, the transfer of hereditary information, the synthesis of enzymes, proteins, carbohydrates and other substances. The macroergic bonds of ATP are the main acceptor of energy generated during photosynthesis and during cell respiration, as well as the main supplier of energy necessary for the synthesis of proteins, fats, carbohydrates and the active supply of nutrients to plants. An important role of phosphorus in the composition of phosphatides is the formation of lipid cytoplasmic membranes that control the intake of nutrients into plants.

Since phosphorus "controls" almost all biochemical processes of plant life, the timely provision of their nutrition with phosphorus is of paramount importance for the formation high yields crops.

It has been established that insufficient provision of plants with phosphorus in the first 12-15 days after germination negatively affects the growth and development of plants during the entire growing season, and consequently, the yield, even if the plants were well supplied with phosphorus in the future. The first two weeks after germination are the critical period for plants in terms of phosphorus nutrition. Phosphorus starvation during this period leads to metabolic disorders in plants and a decrease in their productivity.

The results of long-term experiments show that on soddy-podzolic soils with a low content of mobile phosphates (40-70 mg P 2 0 5 per 1 kg of soil), the productivity of crop rotations is less than 2.0 t ze/ha. With a content of P 2 0 5 of 120-140 mg/kg, it increases to 3.5-4.0 t.e./ha, and with a high content of P 2 0 5 (250-300 mg/kg), productivity increases to 5 -6 t z.e./ha and above. As the content of mobile phosphates in the soil increases, the dependence of crop yields on adverse weather conditions is significantly reduced.

Phosphorus (from the Greek. phosphorus- luminiferous) has one stable nuclide 31 P ( atomic mass 30.974). In agrochemical research, artificial radioactive isotopes 32 P and 33 P, which have high and soft energy, respectively (3-radiation with a half-life of 14.3 and 25.3 days. Phosphorus was discovered by N. Brandt in 1669, were also widely used. Initially, it was obtained from the urine of animals.In 1771, K. Scheele proposed a method for obtaining phosphorus from bone ash.

Among chemical elements the earth's crust (lithosphere) phosphorus occupies the 13th place. The average content of phosphorus in earth's crust- 0.12%. Thanks to the high reactivity Phosphorus is not found in the free state in nature. All phosphorus-containing minerals are salts of phosphoric acid. They are common among igneous and sedimentary rocks. Phosphorus has also been found in meteorites in the form of iron, nickel, and cobalt phosphides; therefore, it can be assumed that before the appearance of oxygen on Earth, phosphorus was a part of metal phosphides.

In accordance with the electronic structure of the phosphorus atom lS 2 2s 2 2p 6 3s 2 3p 3, its oxidation state can vary from 3 _ to 5 +, however, in its most stable compounds, it exhibits valence 5 +, 3 + and 3 ".

Known a large number of minerals containing phosphorus. Among them, apatites are the most common. Vivianite Fe 3 (P0 4) 2 - 8H 2 0 is quite often found locally in peat bogs and swampy places. Much less often, soil-forming rocks contain phosphorus-containing minerals - torbernite Cu (U0 2) 2 (P0 4) 2 12H 2 0, triphylite Li (Fe ,Mn)P0 4 , amblygonite LaAl(P0 4)F.

“Phosphorus, an “element of life and thought,” will always be needed by mankind, and this must be kept in mind both today and in the future” (Fersman, 1983).

The desire of organic farming advocates to provide plants with phosphorus without the use of phosphate fertilizers does not have real basis. Phosphorus is not accidentally called the "key of life", since in nature there are no such vital biochemical processes in which it would not take a direct part. In terms of its importance in plant nutrition, increasing crop yields and the quality of crop production, phosphorus follows nitrogen, and on peaty soils and chernozems, phosphorus occupies a leading place.

An important indicator of the growing importance of phosphorus for humanity can be its industrial consumption.

From 1985 to 2005, 29 billion tons of phosphates were produced and used, while in the previous 80 years, about 24 billion tons.

It should be noted that, unlike nitrogen, the content of which in the soil in vivo is constantly replenished due to atmospheric precipitation and nitrogen-fixing microorganisms, the only source of phosphorus in soils are soil-forming rocks. The leading factor determining the reserves of phosphorus in the soil is its content in the parent rock.

Phosphorus is part of the mineral, organic and organomineral compounds of the soil. Conventionally, soil phosphorus can be divided into four groups: 1) phosphorus contained in the soil solution - phosphate ions and soluble organic phosphorus-containing compounds; 2) phosphates adsorbed on the surface of soil colloids; 3) phosphorus-containing amorphous and crystalline minerals; 4) phosphorus, which is part of the organic matter of the soil.

With polyvalent metals, phosphate ions form a wide range of poorly soluble and insoluble phosphates, which are firmly retained in the soil at the place of their formation and become poorly available to plants. The forms of these compounds can be exchange absorbed phosphate ions, phosphates chemically firmly bound on the surface of mineral and organic colloids, amorphous and crystalline phosphates (minerals) Ca, Al, Fe, Mg, Ti, Pb, etc. Phosphates are a direct reserve for plants in the adsorbed state.

Exchange adsorption of phosphate ions occurs on the surface of secondary clay minerals, iron and aluminum oxides:

The replenishment of the equilibrium concentration of phosphorus in the soil solution (phosphate buffering capacity of the soil) occurs constantly due to both the mineralization of organic matter and the transfer of exchange adsorbed phosphate ions and phosphorus compounds of amorphous and crystalline minerals into the solution.

It is known that H 2 PO" and H PO ^ - ions move to the roots of plants mainly as a result of diffusion with a mass flow of water consumed for transpiration. At low soil moisture, the movement of phosphorus to the roots is especially slow and can limit its consumption by plants. Therefore, poorly soluble phosphorus fertilizers should be evenly distributed in the moist soil layer to increase their availability to plants.

Phosphorus contained in soil organic matter can be available to plants only after enzymatic hydrolysis by its microorganisms, and since a significant part of phosphorus is included in organic compounds, its mineralization requires complete decomposition of phosphorus-containing organic matter. This process is not specific and can be carried out by many types of microorganisms.

Soil organic matter also has a great indirect effect on the availability of phosphorus to plants due to the ability of humic and fulvic acids to form non-dissociable complexes (chelates) with cations of di- and trivalent metals: Al 3+, Fe 2> 3+, Ca 2+, Mg 2+, Mn 2+ , Ti 23+ , Pb 2+ , etc. As a result of chelation of polyvalent metal cations, their concentration in the soil solution decreases and, in parallel, the formation of insoluble phosphorus compounds with metals decreases. In addition, acids released during the decomposition of soil organic matter and plant residues, markedly increase the solubility of calcium phosphates. In all soils, without exception, with an increase in the content of organic matter, the availability of phosphorus to plants increases significantly. Therefore, in order to make the phosphorus of insoluble fertilizers more accessible, they are applied to the soil along with organic fertilizers.

Phosphorus is one of necessary elements nutrition. In the words of Academician Fersman, "Phosphorus is an element of life and thought." Without it, life is impossible not only higher plants but also the simplest organisms. Phosphorus is a constituent of many substances that play an important role in life phenomena. It is found in nucleic acids (RNA and DNA), i.e. phosphorus takes part in the synthesis of proteins and in the transfer of hereditary properties and biological information. High-energy compounds containing phosphorus, such as ATP, play a very important role. It is the main energy accumulator and its carrier for many synthetic processes. In particular, without ATP, the processes of photosynthesis and respiration will not go on. adenosine diphosphate plant photosynthesis

Phosphorus is a companion of nitrogen; Where there is nitrogen, there is also phosphorus. In plants, it is represented by mineral and organic compounds. Mineral phosphates are present in plant tissues most often in the form of calcium, potassium, and magnesium salts of orthophosphoric acid. Although they are usually found in small quantities, they play an important role in creating a buffer system of cell sap and serve as a reserve for the formation of organic phosphorus-containing compounds. Organic compounds predominate and play the most important role in plants. These include nucleic acids, nucleoproteins, phosphoproteins, phosphatides, phytin, sugar phosphates, macroergic compounds, etc. Among them, nucleic acids should be put in the first place. These are complex macromolecular substances that are involved in the most important processes life activity: RNA (ribonucleic) - in the synthesis of proteins specific to a given organism, DNA (deoxyribonucleic) - in the transfer of hereditary properties and the transfer of biological information. Nucleic acids with proteins form complex proteins, nucleoproteins, which are found in embryonic tissues and cell nuclei. An important group are phosphoproteins - compounds of protein substances with phosphoric acid. These include proteins - enzymes that serve as catalysts for many biochemical processes.

Phosphatides (or phospholipids) play a very important biological role. They form protein-lipid molecules that contribute to the permeability of various substances into the cell. There are phosphatides in any plant cell, but seeds, especially oilseeds and legumes, differ in their highest content.

An important compound is phytin. There is a lot of phytin in young organs and tissues, and especially in seeds, in the form of a reserve substance. When seeds germinate, phosphoric acid is released, which is used by the young plant. In the seeds of legumes and oilseeds, phytin is 1--2% of the weight of the dry mass, in the seeds of cereals - 0.5--1.0%. Sugar phosphates play an important role in the processes of photosynthesis, respiration and in the mutual transformations of carbohydrates (sucrose, starch). The content of sugar phosphates in plants varies depending on the age of the plants, their nutritional conditions and other factors and ranges from 0.1 to 1.0% of the dry mass weight. The total content of phosphorus in plants is much lower than that of nitrogen and ranges from 0.3 to 2% (nitrogen - 1 - 5%). Young growing tissues are rich in phosphorus; a lot of it accumulates in the marketable part of the crop (in the generative organs). Phosphorus accelerates the maturation of plants. Under its influence, the processes of protein breakdown and the transition of decay products into reproductive organs in particular in grain. Since phosphorus plays an important role in carbohydrate metabolism, phosphate fertilizers contribute to the accumulation of sugars in beets, and in potato tubers - starch. Good phosphorus nutrition contributes to better overwintering of winter crops, fruit and berry crops.

Thus, phosphorus takes the most direct involvement in many life processes of plants, and ensuring high level phosphorus nutrition is one of essential conditions obtaining large crop yields. Phosphorus is found in plants in much smaller quantities than nitrogen. It occurs in soil in both mineral and organic forms. Phosphorus found in organic compounds becomes available to plants only after mineralization (decomposition) of organic matter. Salts of orthophosphoric acid H 3 PO 4 are the main source of phosphorus nutrition, although it has been proven that plants can also use salts of other phosphoric acids: metaphosphoric, pyrophosphoric, and others.

Phosphoric acid - tribasic; it can dissociate three anions:

N 3 RO 4 N 2 RO 4 - NRO 4 2- RO 4 3-

pH=5-6 pH=6-7 digestible in an alkaline environment

The most favorable pH for phosphorus availability is close to neutral to slightly acidic. Soils with a slightly alkaline reaction are usually characterized by an abundance of calcium. Under such conditions, phosphorus is converted into sparingly soluble calcium phosphates and phosphorus deficiency usually occurs. Plant availability various salts phosphoric acid depends on their solubility. The most soluble in water are salts of phosphoric acid with monovalent cations of potassium, sodium, ammonium. They are well absorbed by plants:

H 2 RO 4 - + K + \u003d KN 2 RO 4 HRO 4 2- + 2K + \u003d K 2 HRO 4 RO 4 3- + 3K + \u003d K 3 RO 4

Salts of various solubility are formed with divalent cations:

H 2 RO 4 - + Ca 2+ Ca (H 2 RO 4) 2 - monosubstituted calcium phosphate (Ca monophosphate); water-soluble compound (forms the basis of superphosphate)

HPO 4 2- + Ca 2+ CaHRO 4 - disubstituted calcium phosphate (Ca diphosphate); a water-insoluble compound, but soluble in weak acids, including organic ones. Due to the acidity of the soil and root secretions, it is also an important source of phosphorus nutrition (it forms the basis of the precipitate)

RO 4 3- + Ca 2+ Ca 3 (RO 4) 2 - trisubstituted calcium phosphate. A compound insoluble in water and weak acids (forms the basis of phosphorite flour). This compound can be partially dissolved and absorbed only in acidic (not saturated with bases) soil.

With trivalent cations (Al, Fe), phosphates form sparingly soluble compounds (AlPO 4, FePO 4), available to plants only in freshly precipitated form

The amount of dissolved phosphates increases with increasing humidity and, consequently, the provision of plants with phosphorus increases. So, for example, soils of heavy granulometric composition retain large quantity water than light, and therefore contain more phosphorus in solution. A. V. Sokolov notes that in wet years, plants show a lower need for phosphorus and respond less well to the application of phosphorus fertilizers than in dry years. Most plants absorb H 2 RO 4 - more easily than HPO 4 2- .

Although phosphorus is not part of fats, carbohydrates, and many of the simplest protein molecules in plant cells, the formation of these organic compounds without its participation becomes impossible. During photosynthesis, plants take in carbon dioxide and water, which are the basic elements for the synthesis of complex organic molecules. It is with the participation of phosphates found in chloroplasts that carbon dioxide is converted into carbonic acid anions - the fundamental "building block" of all organic compounds. Phosphorus stimulates the formation of the root system: the roots branch more actively and penetrate deeper into the soil. This helps plants better provide themselves with food.

Plants experience the greatest need for phosphorus at the earliest stages of their development, during the formation of the root system, as well as in the phase of flowering and fruit formation. Critical in terms of phosphorus nutrition for all crops is the germination phase, when a relatively weak root system is able to absorb phosphorus compounds only in a limited area.The lack of an element during this period causes further pathological changes in the growth and reproductive processes of plants.

M maximum need for phosphorus different cultures observed in different periods, but this occurs mainly during flowering, fruit formation and ripening. An insufficient amount of available phosphorus negatively affects the development of crops and the formation of yields. Due to a decrease in plant productivity, a significant deterioration in the organoleptic qualities of fruits, agricultural producers suffer heavy losses. So get good harvests with high quality indicators is possible only if the plants are provided with complete phosphorus nutrition.

The content of phosphorus in the arable layer is variable and ranges from 0.05 to 0.25%, and about 75 - 90% of its total amount is represented by inorganic sparingly soluble compounds (iron, calcium, aluminum phosphates). The low mobility of phosphates makes it difficult for them to migrate in soil horizons, wash out, weathering, so they remain in fertile soil balls, but such forms of phosphorus cannot be assimilated by crops. Only phosphorus, which is in the soil solution, remains available to plants. With a total element content of 1 t/1 ha of soil, its mobile compounds are no more than 1 kg/1 ha. Therefore, from the total reserves of phosphorus located in the root layer, crops are able to assimilate only 3-5% of the total available to them.

The absorption of phosphorus in the soil solution by plants depends entirely on the acid reaction of the soil. In both acidic and alkaline soils, phosphorus forms insoluble compounds: with calcium (at pH > 7.5), with aluminum (pH< 4,8 – 5,0), железом (рН < 3,8 – 4,5). Поэтому наиболее эффективны фосфорные соединения в грунтах с нейтральной реакцией кислотно-щелочной среды. Для повышения доступности элемента нередко прибегают к раскислению почв известкованием.

Every year, more than 10 million tons of phosphoric acid are removed from the soil along with crops around the world. The situation is further complicated by the fact that in nature there is no natural sources replenishment of phosphorus reserves in the soil. The main phosphorus-containing minerals - apatites and phosphorites, the volumes of which are limited in the world, serve as raw materials for obtaining the necessary phosphorus compounds. To solve the problem of providing plants with a sufficient amount of phosphorus, farmers usephosphate fertilizers . According to the degree of solubility in water, and therefore availability, they are classified into three groups: easily soluble (superphosphates), slightly soluble (precipitate) and sparingly soluble (phosphorite, bone, fish meal). Fertilizers included in the last two groups can easily dissolve in a slightly acidic and acidic environment.

An indicator of the effectiveness of each fertilizer is expressed in percentage quantity in itactive substance (d.v.) , i.e. quantitythe main element (phosphorus) that can be absorbed by plants. For superphosphate, this value is 20%, enriched superphosphate contains up to 24% of available phosphorus, the maximum amount of active substance (40 - 50%) is present in double granular superphosphate. The amount of available phosphorus (a.i.) in phosphate rock can range from 20% to 30%, in bone meal– from 15% to 33%. For the precipitate, the indicator of the active substance is 38%. In ammophos and diammophos, the content of available phosphorus reaches 45- 52%, and in thermophosphates - from 20% up to 30%.

Perhaps the most common mineral phosphate fertilizer is superphosphate. Easily digestible by plants, phosphorus oxide (P 2 O 5) makes up to 20% in it (in more concentrated double superphosphate - more than 45%). Superphosphate also contains calcium, zinc, sulfur, boron and others. useful elements. The fertilizer is produced in the form of fine powder and granules. Suitable for all types of crops. It is brought in in the fall, before plowing or in the spring, during pre-sowing work. It goes well with other fertilizers, therefore it can be used in combination with them. Requires thorough mixing with the soil. It is most effective in a dissolved state, on neutral soils. Its systematic application does not cause any changes in the acid-base reaction of soils.

Ammophos and diammophos(ammonium hydrogen phosphate) are complex nitrogen-phosphorus mineral fertilizers containing more than 60% nitrogen and phosphorus. The phosphates included in their composition are mostly soluble in water. Preparations are intended for use in any soil-climatic zone. Phosphorus in ammophos is more mobile and better absorbed by crops compared to that contained in superphosphate. The use of ammophos and diammophos on soils with a neutral and slightly alkaline reaction is more preferable, as they create plants Better conditions for phosphorus nutrition than superphosphate.

Natural sources of phosphorus organic origin serve bone and fish flour, which are universal natural top dressings used for almost all types of garden, garden and field crops. These fertilizers are absolutely harmless, so they can be applied during any growing season of plants. But it is impossible to carry out the prompt elimination of phosphorus deficiency by introducing bone or fish meal. They are characterized by a long period of action, since the decomposition of their components under the influence of soil microorganisms and the transition of the mobile form of phosphorus into the soil solution occurs gradually. At the same time, a single application of flour is enough to provide plants necessary quantity phosphorus for a period of 5 - 8 months.

Bone meal is rich not only in phosphorus, but also in other valuable compounds and elements, including nitrogen, calcium and potassium, iron, magnesium, zinc, etc. acid reaction. Fish meal surpasses bone meal in the amount of nitrogen it contains (up to 10%), and it leaches the soil less than bone meal. Recommended for application on calcareous and loamy soils. Good result achieved by mixing bone and fish meal. Fertilizer can be used throughout the season. The introduction of bone and fish meal into the soil simultaneously with other organic fertilizers (manure, humus, mullein, compost) during autumn or spring plowing helps to increase land fertility and ensure an increase in future yields.

is a mineral phosphorus-containing fertilizer obtained from apatites and other sedimentary rocks. Differs in low cost, ecological safety and duration of action. The amount of phosphorus contained in it reaches 17 - 30%, but it is represented by inorganic tricalcium phosphate (Ca 3(PO 4 ) 2 ), which in an acidic environment gradually turns into a dihydrophosphate compound available to plants (Ca (H 2 PO 4 ) 2 H 2 O). That is why the use of phosphate rock is most appropriate on acidic soils (peat bogs, podzolic soils), as well as in combination with organic (manure, humus, compost) or acidic fertilizers (ammonium sulfate, ammonium nitrate, ammonium chloride). Fertilizer is applied before sowing, average rate consumption of phosphate rock: 1.5 - 2 t / ha.

Precipitate refers to sparingly soluble phosphorus-containing fertilizers: very slightly soluble in water, but has good solubility in organic and mineral acids. This is a non-hygroscopic powdered preparation, the concentration of phosphorus in which reaches 30%. It can be used on any type of soil and, in fact, for all crops. In terms of effectiveness, it is not inferior to superphosphate. Possesses side effect- reduces the level of acidity during soil acidification.

Thermophosphates include fertilizers obtained by calcining natural minerals (apatites and other phosphates) with soda, carbonates, silicates, etc. They also include some waste from the metallurgical industry (thomas slag, fluorine-free phosphate, open-hearth slag). The content of phosphorus in thermophosphates can vary from 15% to 30%. Most of thermophosphates are poorly soluble fertilizers, so they should be applied to the soil in advance so that the phosphorus contained in them has time to dissolve in the soil solution.

The practice of using phosphate fertilizers shows that more favorable conditions for nutrition of crops, and therefore for obtaining high yields, are created with regular dosed replenishment of phosphorus reserves in soils than in the case of a single application of a significant amount of phosphorus-containing preparations.

Phosphorus in plants

Phosphorus plays an extremely important role in plant life. Most metabolic processes are carried out only with his participation. It is almost always in the second minimum (after nitrogen).

The physiological role of phosphorus (C 3). It is part of the most important organic compounds actively involved in plant metabolism: nucleic acids (DNA and RNA), nucleoproteins, phosphoproteins, phosphatides (phospholipids), macroergic compounds (ATP, etc.), sugar phosphates, phytin, vitamins, etc. Phosphorus content (Р2О5) in plants and removal by agricultural crops The average content is 0.5% of dry matter, varying from 0.1 to 1.5%, and depends on the biological characteristics of crops, the age of plants and their organs, the conditions of phosphorus nutrition, etc. .d. So, the grain of leguminous crops contains 1-1.5% P2O5, cereals - 0.8-1%. The straw of those and other crops contains less phosphorus compared to seeds - 0.2-0.4%.

Phosphorus in plants is distributed similarly to nitrogen, is its companion. On average, the content of phosphorus in plant organs is 30% of the amount of nitrogen (C 17). More phosphorus is found in young and vital organs, leaves contain more phosphorus than stems.

The removal of phosphorus by crops averages 15-50 kg/ha, varying depending on the biological characteristics of crops and the level of productivity.

Sources of phosphorus for plants. The main sources are salts of orthophosphoric acid (C 19), which, being tribasic, is capable of forming three types of anions - H2PO4–, HPO42–, PO43– (C 20) and, therefore, three types of salts - one-, two- and three-substituted phosphates , whose solubility and availability for plants varies depending on the cations.

Salts of metaphosphoric and polyphosphoric (pyro-, tripolyphosphoric, etc.) acids, which are not directly absorbed by plants, but are hydrolyzed in the soil to orthophosphates (C 21-24), can also be sources of phosphorus.

In addition, the roots of some plants (peas, beans, corn, etc.) secrete the enzyme phosphatase, which splits off the phosphoric acid anion from simple organic compounds. As a result, the organic compounds of phosphorus can serve as a source of phosphorus for these plants.

Phosphorus transformations in plants. The phosphorus that enters the plants very quickly passes into the composition of organic compounds. However, phosphorus is in them directly in the form of a residue of phosphoric acid. Thus, 85-95% of phosphorus is in organic form (C 26). Mineral phosphates - calcium, potassium, magnesium and ammonium phosphates - are much less (5-15%), but they are of great importance, being a reserve and transport form of phosphorus. For example, the phosphorus of the organic compounds of the roots can move to the aerial part only after transformation into mineral phosphates.

Dynamics of phosphorus consumption during the growing season. The critical period in relation to phosphorus in all cultures is noted in the phase of seedlings. The lack of phosphorus during this period sharply reduces the yield, regardless of the further supply of plants. At the same time, the root system in the initial phases of growth is poorly developed and often cannot absorb soil phosphorus and fertilizers applied before sowing in sufficient quantities. Therefore, pre-sowing application of phosphorus is widely recommended.

The periods of maximum consumption of phosphorus by different cultures do not coincide. For example, spring wheat consumes all the phosphorus it needs by the end of the heading phase, while flax absorbs only 58% even by the full flowering period, and cotton absorbs only 10% of the maximum phosphorus content in plants in the full flowering phase. The absorption of phosphorus in wheat is observed in the phases of emergence into the tube and heading, in flax - in the phases of flowering and ripening, in cotton - during the period of fiber formation.

Signs of a lack of phosphorus for plants. The growth and development of plants slows down, the size of the leaves decreases, flowering and ripening of the crop are delayed (C 31-33). Phosphorus is recycled, so its deficiency first appears on the lower leaves, which turn dark green, dirty green, and then red-violet, purple or purple

Phosphorus in soils.Content and reserves of phosphorus in soils. The total content varies from 0.01 to 0.3% and depends primarily on the mineralogical composition of the parent rocks. In addition, soils rich in humus contain more phosphorus (humus contains 1-2% P2O5). Thus, the minimum content of phosphorus in soddy-podzolic sandy soils, the maximum - in chernozem soils. The vital activity of plants causes the biological accumulation of phosphorus in the upper soil horizons

The total reserve of phosphorus in the arable layer per 1 ha varies from 0.3 tons in light soddy-podzolic soils to 9 tons in chernozems

Forms of phosphorus in soils and its transformation Phosphorus in soils is in organic and mineral forms Organic phosphorus is less, it is part of the non-specific part of humus, as well as undecomposed remains of plants and microorganisms.

Mineral phosphorus predominates, which in soddy-podzolic, chestnut soils and gray soils is 70-90% of the total content, and in soils with a high content of humus (hence, organic phosphorus) - gray forest soils and chernozems - 55-65% (C 44). Mineral phosphorus is mainly found in the form of primary minerals and, above all, fluorapatite [Ca3(PO4)2]3·CaF2 and hydroxyapatite [Ca3(PO4)2]3·Ca(OH)2.

Phosphorus of organic compounds and primary minerals is not directly absorbed by plants. As a result of weathering of primary minerals, secondary minerals are formed, which are various salts of orthophosphoric acid. Phosphates are also formed during the mineralization of organic phosphorus under the influence of phosphorobacteria.

Salts of phosphoric acid are characterized by different solubility and, consequently, availability to plants.

Phosphates of monovalent cations [KH2PO4, (NH4)2HPO4, Na3PO4], as well as monosubstituted salts of divalent cations [Ca(H2PO4)2, Mg(H2PO4)2] are water-soluble. They are well available to plants.

Disubstituted calcium and magnesium phosphates (CaHPO4, MgHPO4) and freshly precipitated, amorphous three-substituted phosphates [Ca3(PO4)2, Mg3(PO4)2], which are insoluble in water, but dissolve in weak acids (organic, carbonic) are called acid-soluble. . These compounds, under the action of acidic root secretions, as well as organic and mineral acids produced by microbes, gradually dissolve and become available to plants.

They do not dissolve in water and weak acids, as a result, crystalline forms of trisubstituted calcium and magnesium phosphates are practically inaccessible to plants. But some plants - lupins, buckwheat, mustard, to a lesser extent peas, sweet clover, sainfoin and hemp - have the ability to absorb phosphorus from trisubstituted phosphates. Iron and aluminum phosphates (AlPO4, FePO4) are the least available to plants. An important role in the formation of phosphorus nutrition conditions is played by the chemical absorption of water-soluble phosphates (phosphorus retrogradation), which occurs in soils with any reaction of the environment.

In neutral soils saturated with bases (chernozems, chestnut soils), two- and three-substituted calcium and magnesium phosphates are formed:

Ca(H2PO4)2 + Ca(HCO3)2 → 2CaHPO4↓ + 2H2CO3;

PPK)Ca2+ + Ca(H2PO4)2 → PPK)2H+ + Ca3(PO4)2↓.

In acidic soils characterized by a high content of aluminum and iron (soddy-podzolic, red soils), phosphates of these elements precipitate:

Ca(H2PO4)2 + 2Fe3+ → 2FePO4↓ + Ca2+ + 4H+;

PPK)Al3+ + K3PO4 → PPK)3K+ + AlPO4↓.

As a result of retrogradation, water-soluble phosphates are found in soils in insignificant amounts (as a rule, no more than 1 mg/kg of soil).

Anions of phosphoric acid in the soil can be exchanged absorbed by fixing on the surface of positively charged colloidal particles of aluminum and iron hydroxides. The process of exchange absorption is reversible, that is, phosphate ions are capable of being displaced from the FPC into the solution by other anions. As a result, the exchange-absorbed anions of phosphoric acid are readily available to plants.

Soluble salts of phosphorus are consumed not only by plants, but also by microorganisms, turning into organic phosphorus-containing compounds. After the death of microbes, the main amount of biologically absorbed phosphorus again becomes available to plants, with the exception of a small part that has passed into the composition of humus.

For soddy-podzolic and gray forest soils, the Kirsanov method is standardized: the extract is 0.2 N. HCl, water-soluble and acid-soluble salts of phosphoric acid pass into the solution.

In non-carbonate chernozems, the content of mobile phosphorus is determined according to Chirikov: the soil is cultivated with 0.5 n. CH3COOH.

On carbonate soils, acids are not used, since weakly acidic extracts are spent on the decomposition of carbonates, while more concentrated ones can dissolve phosphates that are inaccessible to plants. Therefore, the content of mobile phosphorus in carbonate chernozems is determined according to Machigin using 1% (NH4)2CO3, which has an alkaline reaction.

Absolute results obtained by any method are not informative, since the constant impact of plant roots on the soil during the growing season is far from equivalent to the dissolving power of any reagent. For example, when the solution interacts with the soil, an equilibrium is established, and in the presence of plants that consume phosphorus, its concentration in the liquid phase of the soil constantly decreases, stimulating the transition of new amounts of phosphates into the solution.

However, comparing crop yields in field experiments conducted on soils with different contents of mobile phosphorus, one can conclude how well a particular soil is provided with phosphorus, and express the resulting pattern in the form of a grouping that has practical significance.

Phosphorus balance in soils

Incoming articles:

1) mineral and organic fertilizers- main;

2) plant seeds - 2-3 kg/ha year.

Expenditure items:

1) removal of agricultural crops - the main one;

2) losses as a result of water erosion - 5-10 kg/ha·year;

3) leaching into groundwater - observed only on light and peaty soils, where it can reach 3-5 kg/ha·year.

An analysis of income items shows the absence of any significant sources of compensation for phosphorus losses from the soil, except for fertilizers. An exceptional role in ensuring a deficit-free balance of phosphorus is played by mineral fertilizers, because much less phosphorus returns to the soil as part of organic fertilizers than is alienated by crops.