The chemical composition of plants is the complex of chemical compounds that make up the organs of a plant, including proteins, fats, carbohydrates, ash (mineral) elements, and water. All these substances are synthesized and used by plants in the process of their life activity.
The content of chemical substances in the plant and its individual organs depends on genetic characteristics, specificity of their functions, biosynthesis processes, physiological state of organs and tissues.
The water content in most vegetative organs of plants is 70-95%, in seeds – from 5 to 15%.
Water availability in plant cells determines the speed and direction of plant life processes. In turn, the conditions of mineral nutrition, water supply and biological features of plants determine their water content.
Water in plant organism is the medium for biochemical reactions and directly participates in these processes. Proteins and some other organic compounds are hydrated in protoplasm into structural aggregates, giving them certain colloidal and physicochemical properties. Only under an optimal water regime can a plant make rational use of nutrients.
Lack of water in plants leads to disruption of all vital processes, reducing the intensity of photosynthesis, and its loss above a certain limit – to the death of the plant. A constant inflow of water is necessary to maintain a normal turgor state.
Plants have a mechanism of protection against temporary deficiency of moisture, but prolonged drought has a negative effect on their development. In this case not only free water but also colloid-bound water is lost, which leads to decrease of adsorption capacity of colloids, their watering degree, protoplasm viscosity; synthesis of proteins and chlorophyll stops; phosphorus exchange is disturbed; nucleic acids, phosphatides, nucleoproteins decay; transition of mineral phosphorus into organic one reduces; ratio of organic phosphorus to mineral phosphorus decreases.
The dry matter of plants consists of 90-95% organic compounds and 5-10% mineral salts.
The main organic matter includes proteins and other nitrogenous compounds (amino acids, peptides), fats (lipids, oils), carbohydrates (starch, sugars, glucose, fructose, cellulose, lignin, fiber, pectin substances).
Mineral salts are represented by inorganic compounds of calcium, phosphorus, potassium, magnesium, sulfur and others. Nitrogen and ash elements absorbed from soil account for 6-10% of dry matter.
Table. The content of nitrogen and ash in various plant organs (% of dry matter weight)Fundamentals of agronomy: textbook/Y.V. Evtefeev, G.M. Kazantsev. - M.: FORUM, 2013. - 368 p.: ill..
Table. Average chemical composition of agricultural plants, % (by Pleshkov)Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
|Rice (peeled grain)|
|Sugar beet (roots)|
|Fodder beets (roots)|
|Clover (green mass)|
|Dactylis glomerata (green mass)|
Table. Average chemical composition of oil-bearing crops seeds, % of dry weight Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
|Sunflower (whole seeds)|
Table. Average content of basic substances in vegetable, fruit and berry crops, % crude weight Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
The chemical composition of plants is represented by more than 70 chemical elements, with oxygen, carbon and hydrogen having the largest mass fraction.
Carbon dioxide and water are converted into nitrogen-free organic compounds in plants during photosynthesis. Carbon, oxygen, hydrogen and nitrogen account for 95% of the dry mass of plants (carbon 45%, oxygen 42, hydrogen 6.5, nitrogen 1.5%), these four chemical elements are called organogenic.
Table. Average content of chemical elements in plants (by Vinogradov), %Yagodin B.A., Zhukov Yu.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
The content of nitrogen and ash elements in plants can vary greatly and depends on the biological characteristics and growing conditions. For example, there are more ash elements in the roots, stems, and leaves than in the seeds.
Table. Content of basic nutrition elements in various agricultural plants, % on air-dry substance (by Petukhov et al.)Yagodin B.A., Zhukov Yu.P., Kobzarenko V.I. Agrochemistry/ Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
|Winter rye (grain)|
|Winter rye (straw)|
|Spring barley (grain)|
|Spring barley (straw)|
|Peas (green mass)|
|Lupine (green mass)|
|Sunflower (whole plant)|
|Sugar beet (roots)|
|Fodder beets (roots)|
|Fodder carrots (roots)|
|Grasses (meadow hay)|
|Alfalfa at the beginning of flowering|
|Meadow clover during flowering|
|Veatch in flowering period|
The composition of ash is also different for different plants, reflecting the varying needs of crops in the elements of mineral nutrition. The content of phosphorus, potassium, calcium and magnesium is usually expressed as their oxides.
For example, potassium accounts for 30 to 50% of leaf ash in most plants; in alfalfa, vetch, and clover, calcium content is much higher than potassium. In old leaves, the content of potassium, phosphorus and sulfur decreases, and calcium increases from 20-40 to 50-60% of ash mass.
Table. Approximate content of individual elements in the ash of plants, % of its mass (Smirnov, Muravin) Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
|Sugar beet (roots)|
|Sugar beet (haulm)|
Chemical elements necessary for plants
According to modern data, plants need 20 elements and 12 of them are conditionally necessary:
- Essential (biogenic, or biophilic): hydrogen, sodium, potassium, copper, magnesium, calcium, zinc, boron, carbon, nitrogen, phosphorus, vanadium, oxygen, sulfur, molybdenum, chlorine, iodine, manganese, iron, cobalt.
- Conditionally necessary: lithium, silver, strontium, cadmium, aluminum, silicon, titanium, lead, chromium, selenium, fluorine, nickel.
Table. Content of the main elements of mineral nutrition in the dry matter of a typical plant (Smirnov, Muravin)Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/ Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
Necessary elements are those that are involved in the life processes of plants and cannot be replaced by others. The conditionally necessary elements are those that, according to research data, can have a positive effect on the development of some plants.
Macronutrients (macroelements) – elements which content in plant organism ranges from hundredths to even percent.
Micronutrients (microelements) – elements, the content of which is expressed in thousandths and hundred-thousandths of a percent. The effectiveness of some trace elements depends on natural and climatic conditions. For example, a positive effect of zinc, manganese and iron is observed on neutral soils of the steppe zone, especially on carbonate black soils, whereas plants often suffer from their excess on sod-podzolic soils. In the forest-steppe and steppe zones there is rarely an increase in yield from the use of copper microfertilizers, except for corn in some cases. On the contrary, on drained boggy peat soils copper as a microfertilizer is a prerequisite for high yields of grain crops.
Molybdenum almost universally has a positive effect on the yield of legume crops, which is associated with its participation in the physiological and biochemical processes of atmospheric nitrogen fixation by nodule bacteria. However, the effectiveness of molybdenum in different soil and climatic conditions is different, which is explained by the different content of its mobile forms in the soil.
Ultra-micronutrients are elements with a content of less than one hundred thousandth of a percent.
Ultra-micronutrients include gold, silver, chromium, nickel, tungsten, bromine, uranium, rubidium, cesium, and others. The physiological significance of these elements in plant life is poorly understood.
The division into macro-, micro- and ultra-microelements is conditional. For example, iron, according to its content in plants, belongs to macronutrients, but according to the functions it performs, to micro-nutrients.
The content of trace elements in various plant organs follows certain patterns. Thus, manganese and molybdenum, more often, in large amounts are contained in leaves, while zinc, boron, cobalt, copper with sufficient supply are accumulated in both vegetative and generative organs. Grain crops are characterized by higher content of boron in grain and legumes – in vegetative organs.
Different biological groups of plants differ in their requirements for optimal concentrations of trace elements. For example, corn and tobacco have a greater need for zinc, and grain crops – for manganese and molybdenum.
Forms of compounds in which plants absorb nutrients
Plants absorb most of their nutrients in ionic form through the root system. Amino acids, sugars, and sugar-phosphates can be used in small amounts for plant nutrition.
Once in the plant, amino acids are deaminated and the ammonia released is used in synthetic processes.
Nitrogen is absorbed in the form of nitrate NO3– and ammonium NH4+. These ions are formed in the soil from organic matter by microbial ammonification and nitrification. The nitrate form is reduced to ammonia by enzymes.
The ammonia form of nitrogen is used in the reaction of substitution of the oxygen atom of the carbonyl group of keto acids to form the corresponding amino acid:
The process of nitrogen fixation of molecular nitrogen under the action of soil microorganisms plays an important role in the nitrogen nutrition of plants. Important functions in this process are performed by the enzymes nitrogenase, light hemoglobin, compounds of vitamin B12 group, iron, molybdenum, cobalt, copper, etc.
Sulfur is assimilated by plants in the form of sulfate SO42-. In plants, sulfate is reduced to sulfite SO32- and sulfide S2-, which form sulfhydryl groups (S-H) or disulfide (-S-S-) groups by adding hydrogen. Sulfur is a part of acetylcoenzyme A, the amino acids cysteine, cystine, and methionine.
Phosphorus is absorbed by plants in the form of phosphates H2PO4–, HPO42- or PO43-. In plants, phosphorus is part of nucleic acids, phospholipids – compounds responsible for the properties of cell membranes, coenzymes, including pyridine nucleotides and nucleoside phosphates. Adenosine phosphates are important in energy metabolism.
Primary metabolism of phosphorus involves its involvement in nucleotide synthesis within milliseconds. At exposures of up to 10 minutes, phosphorus is detected as part of nucleic acids. Exposures over 3 h, when the metabolic pool of phosphorus acceptors is saturated, show phosphorus entering the vacuole in inorganic form. In the absence of air, the accumulation of phosphorus acceptors not used in respiratory metabolism occurs, which explains the intense accumulation of phosphorus in the roots in the absence of oxygen.
Chlorine enters plants in the form of Cl– chloride. In many plants, chlorine can be present in high concentrations without having a negative effect. First of all, this applies to halophytes, salt-tolerant plants.
Boron and molybdenum enter plants as borates and molybdates.
Calcium, potassium, magnesium, copper, iron, zinc come to plants in the form of cations, manganese – in the form of cations and anions.
High concentration of potassium ions up to 50-100 mM is a characteristic feature of all plant and animal cells. Only at a certain concentration of potassium ions can protein biosynthesis, photosynthesis, respiration, and synthesis of high-molecular-weight compounds (starch, fats, carbohydrates) proceed normally in the cell.
Biological needs of crops in nutrients
Differences in the nutrient requirements of species and varieties of crops under the same soil and climatic conditions are due to the different material composition of plants. All environmental factors have a significant impact on the chemical composition of plants, and therefore the plant nutrient requirements of any crop.
The differences in crop requirements for nutrients are clearly presented in the values of biological and, more often, economic removal of elements with harvests or in the form of their costs per unit of the main with the corresponding amount of by-products.
Practical significance for determining the optimum doses and ratios of fertilizers for crops in crop rotations is the economic removal and expenditure of nutrients per unit of the main product with the corresponding amount of by-products.
Table. Approximate costs of nutrients (kg) per unit (t) of the main with the corresponding amount of by-products in some cropsYagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/ Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
|Clover with timothy|
Root and stubble residues are part of the biological export. But remaining in the field, they are also after mineralization an additional source of nutrients for the following crops after harvesting. Taking this into account, in practice determine the economic export, and on it – the cost of nutrients per unit of production.
Intensification of farming, accompanied by an increase in productivity of cultivated crops, leads to an increase in the economic removal of nutrients with crops.
The average long-term data on the consumption of nutrients per unit production of each variety for specific soil and climate conditions as a genotypic trait are relatively constant and serve as the basis for calculations of economic removals, balances of nutrients and optimal doses of fertilizers at any productivity of the variety.
Each crop in its development undergoes a typical only for it cycle of nutrient consumption, so with the help of fertilizers you can regulate the processes at different stages of growth and development of plants.
The first stage – seed germination and emergence – is characterized for all crops by a relatively low need for nutrients. However, it is during this period that crops are most sensitive to shortage, excess and increased concentration of salts in the soil solution. Crops at this stage do not have a developed root system and significant root excretions, so they need small amounts of elements, about 5-20 kg/ha a.d., in an available water-soluble form.
Water-soluble salts of nitrogen and potassium, as a rule, even in poor soils are contained in small amounts at the depth of seed embedment, while water-soluble salts of phosphorus even in fertile soils are almost absent. Therefore, small doses of superphosphate (10 kg/ha of P2O5) are often effective as a pre-sowing (pre-sowing) fertilizer for all crops and on all soils.
Under such crops as legumes, vegetables, row crops, especially on very nitrogen-poor soils, nitrogen is used together with phosphorus. Certain crops, such as all types of beets, respond favorably to a complex fertilizer, including phosphorus, nitrogen and potassium.
Micronutrients are added to the pre-sowing complex fertilizer when the seed (planting) material is not treated with trace elements. Doses of pre-sowing (starter) fertilizer are usually 3-10% of the total need, although sometimes with a lack of fertilizer and this is limited. The lack of a nutrient element during this period can not be fully compensated in subsequent periods of plant development.
The second stage is a period of intensive growth and development of vegetative mass. For most crops it is characterized by intensive absorption of nitrogen and, to a lesser extent, phosphorus and potassium. For potassium-loving crops, such as sunflowers, beets, potatoes, corn, potassium exceeds phosphorus. In this and subsequent stages of development, fertilizers can be in the form of salts, but they should be located in the area of the actively absorbing root system.
Depending on the characteristics of crops, agrotechnical and soil and climate conditions, fertilizers can be applied before sowing or after sprouting. Micro fertilizers are applied as foliar, nitrogen – as a root and foliar, potassium – only as a root fertilizer.
The third stage is fruiting or formation of reproductive organs. For most crops it is characterized by a decrease in the consumption of nutrients with a simultaneous change of minimums: the need for phosphorus and potassium increases, for potassium-loving crops, primarily in potassium, and decreases in nitrogen. At this stage in plants there is an intensive redistribution of previously absorbed elements: the outflow from leaves to seeds, fruits and root crops. Consumed substances should be in the zone of active absorption by the root system, i.e. they should be applied earlier in the form of pre-sowing or post-sowing fertilizer.
Hemp, flax, rice, and spring cereals have the shortest period of nutrient consumption, ending by the end of the second stage of growth. For example, hemp consumes about 2/3 of all nutrients from budding to flowering, rice and spring cereals up to 3/4 – from tillering to flowering, and at the stage of fruiting these crops can even lose some of the consumed elements with dead lower leaves.
For this reason, for crops, fertilizer must be applied before or at sowing. Fertilization is possible only for a portion of the nitrogen fertilizer to reduce nitrogen losses in areas of adequate and excessive moisture or to increase grain protein content.
The vast majority of other crops have an extended period of nutrient uptake that peaks in the second stage.
In some crops, such as cotton, tomato, nutrient consumption is extended to the end of the growing season with maximum consumption in the third stage of growth and development. For such crops in addition to pre-sowing (phosphorus-potassium and part of the nitrogen) and pre-sowing (phosphorus and / or phosphorus-nitrogen) fertilizer nitrogen, trace elements and nitrogen-potassium fertilizers are used.
The ratio in the elements of nutrients in crops is different. Thus, the ratio of N:P2O5:K2O in economic yields on average in grain crops is 3:1:2,5, in root crops – 3:1:4, in grain legumes – 4:1:2. Even in one crop and variety, the ratio of elements may change over time, because as the plant grows and develops, the mass and composition of the forming organs change.
The dynamics of nutrient consumption also depends on the ripeness of varieties. Early varieties, which have a short growing season, consume nutrients more intensively, and therefore have higher nutritional requirements. In contrast, mid- and late-ripening varieties consume nutrients over a longer period, usually in large quantities, so for them fertilizer is applied in several steps.
To determine the optimal rates and techniques of fertilizer for crops use the reference data and recommendations of zonal research institutions, as well as agronomic characteristics of zoned varieties. In the absence of data are determined by experiment with field experiments.
For this purpose determine the economic removal and the cost of nutrients per unit of the main with the corresponding amount of by-products. In this case, the results obtained are as close to the local soil and climatic conditions.
Economic and biological removal
Biological removal is the removal of nutrients from the soil by all parts of the plant: the main and by-products, stubble residues, roots, fallen leaves left in the field.
Economic removal is the removal of nutrients with the crop harvested from the field of the main and by-products.
Table. Economic removal of main nutrients by crop yield, % of biologicalYagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
|Perennial grasses (clover and timothy)|
|Clover first year of use|
|Clover second year of use|
|Annual grasses (vetch, peas and oats)|
|Corn for silage|
|Forage beans for silage|
|Onions for a bulb|
The plant’s nutrient requirements are determined by the economic removal per unit mass of the main product, taking into account the amount of by-products. The economic removal is used to calculate fertilizer application rates for the planned yield of crops.
Table. Average economic removal and the ratio of major nutrients per 1 ton of crop yield, kgFundamentals of agronomy: textbook / Yu.V. Evtefeev, G.M. Kazantsev. - MOSCOW: FORUM, 2013. - 368 p.: ill. Plant breeding/P.P. Vavilov, V.V. Gritsenko, V.S. Kuznetsov et al; Edited by P.P. Vavilov. - M.: Agropromizdat, 1986. - 512 p.: ill. - (Textbook and textbooks for higher education institutions).
|Peas with oats|
*Nitrogen excluding fixation by nodule bacteria
Maximum intake is the greatest amount of nutrients needed to create a unit yield. Always greater than biological removal.
The ratio of nutrients consumed to create products may vary depending on the crop and crop structure. Thus, an increase in the share of straw in the biological yield of crops for the creation of 1 ton of grain consumes more elements of nutrition. Potatoes, sunflowers, cabbage, sugar beets consume significantly more potassium compared to other crops. Clover and hemp are characterized by high calcium intake.
Grain generally contains about 4 times more nitrogen and phosphorus than straw, while potassium and calcium in straw are 2-3 times higher than in grain.
Table. Average ratio of nutrients in the yield of various crops Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
Cultivation conditions influence the removal of nutrients with commercial products. For example, for the formation of 10 tons of roots and the corresponding amount of haulm in the forest-steppe zone sugar beet consumes 50 kg of nitrogen, 15 kg P2O5 and 60 kg K2O, whereas when growing in the Non-Black Earth zone sugar beet leaves are more developed, and for every 10 tons of roots consumes 80-100 kg of nitrogen, 35 kg P2O5 and 145 kg K2O.
With a wheat yield of 3 t/ha, 110 kg N, 40 kg P2O5, and 70 kg K2O are needed. With a yield of 30 t/ha of potatoes, 150 kg/ha of N, 60 kg/ha of P2O5, 270 kg/ha of K2O are taken out.
Quality of agricultural products
The quality of agricultural products is determined by the content of organic and mineral compounds. Crops are grown to obtain products with a certain content of proteins, sugars, fiber, vitamins and minerals. Thus, high fiber content in hay leads to deterioration of its fodder quality, while, cotton, flax, hemp are grown to produce fiber, the quality of which increases with increasing fiber content. The quality of sugar beets is evaluated by their sucrose content, while legumes are evaluated by their protein content.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.
Fundamentals of Agronomy: Tutorial/Y.V. Evtefeev, G.M. Kazantsev. – M.: FORUM, 2013. – 368 p.: ill.