Microfertilizers – chemical substances and their mixtures used in agriculture as a source of micronutrients for plant nutrition.
Micronutrients are chemical elements that are in plants in thousandths to hundredths of a percent and perform functions in the processes of life.
The theoretical basis of the use of trace elements in agriculture became possible after the establishment of the physiological role of trace elements in plant life. Y.V. Peyve, M.V. Katalymov, P.A. Vlasyuk, R.K. Kedrov-Zikhman, M.Y. Shkolnik made a significant contribution to solving theoretical and practical problems related to plant micronutrients.
Importance of microelements in plant life
The positive effect of trace elements is due to their participation in redox processes, carbohydrate and nitrogen metabolism. They increase plant resistance to diseases and adverse environmental conditions. Under the influence of trace elements in the leaves increases the content of chlorophyll, photosynthetic processes improve, assimilating activity of the whole plant increases. Many trace elements are part of the active centers of enzymes and vitamins.
Micronutrients can form complexes with nucleic acids, influence physical properties, structure and physiological functions of ribosomes. They influence the permeability of cell membranes and nutrient supply to plants.
Thus, when micronutrients are disrupted in corn, the intake of ammonium and nitrate nitrogen decreases. The greatest decrease in the absorption of ammonium nitrogen is noted with a deficit of zinc, molybdenum and an excess of cobalt, manganese. Nitrate nitrogen absorption rate decreases with copper and manganese deficiency. With an excess of zinc in the nutrient medium, the absorption of ammoniacal nitrogen decreases, with copper deficiency – increases. Molybdenum and zinc nutrition disorder results in increased difference in ammonium and nitrate nitrogen absorption.
In general, when micronutrient nutrition is disturbed, nitrate nitrogen intake decreases first of all. When cobalt and zinc nutrition is disturbed, the rate of ammonium nitrogen incorporation into proteins decreases.
In a number of soil and climate zones, crops are responsive to various microfertilizers. This is most often observed with prolonged application of high doses of mineral fertilizers, especially on drained peaty soils, irrigated lands and on light soils with a granulometric composition.
Table. Crop micronutrient requirements (according to scientific institutions, 1988)
|corn for silage and green mass|
Note. – low need for the element; + – medium need; ++ – high need.
Legumes have a higher molybdenum content and accumulate 2-10 times more iron than cereals. Legumes have a greater need for cobalt fertilizers.
Plants also accumulate trace elements differently, which becomes important in the use of crop products.
When the content of trace elements above or below the threshold concentrations, the body loses the ability to regulate metabolic processes, which is manifested by the development of endemic diseases. In modern conditions of intensification and chemicalization of agriculture, knowledge of the threshold concentrations of trace elements in plants and fodder is especially relevant.
Note. *Limits at normal regulation of functions in animals of different species in different biological states
Introduction of micronutrients provides a significant increase in crop yields.
On average, microfertilizers can increase crop yields by 10-12%. The greatest effect is achieved in regions where soils are depleted in certain micronutrients. There are many such soils. According to large-scale agrochemical survey of soils, low and medium provision with mobile boron 37,3%, molybdenum – 85,5%, copper – 64,9%, zinc – 94,0% cobalt – 86,9%, manganese – 52,5% of the total arable area.
Table. Influence of microelements on the yield of crops in the main areas of their applicationAgrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
|Sugar beets: roots|
|Vicia-oat mixture, hay|
|Sugar beets: roots|
|Winter wheat, grain|
Currently, the supply of micronutrients in agricultural production has decreased, while the need of agriculture in Russia in the near future is estimated at 12 thousand tons.
Table. Agricultural demand of the Russian Federation for microfertilizers (tons of nutrients) (according to VNIPTIHIM, 1999)
Content of microelements in soil
The criteria for plant microelements requirements are their content in plants and the level of their content in the soil. It does not matter the total (gross) amount in the soil, but the presence of mobile forms, which to some extent determine the availability of plants. Most often the content of trace elements in mobile form for copper, molybdenum, cobalt and zinc is 10-15% of the gross content in the soil, for boron – 2-4%.
Table. The content of trace elements in plants, mg/kg dry matter Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill..
|Winter wheat (grain)|
|Corn (green mass)|
The degree of mobility of trace elements in soil depends on: environmental reaction, composition of parent rock, vegetation, microbiological activity, carbonate, redox properties, granulometric and mineralogical composition, humus content, haloxides, application of a set of agrotechnical measures, especially water and chemical soil amelioration, application of organic and mineral fertilizers.
The influence of soil conditions is specific and may differ for different trace elements. For example, acidification increases the mobility of manganese, copper, boron, zinc, but reduces the availability of molybdenum.
The concept of “mobility” in modern science does not have a precise definition. In most cases, the mobility refers to all forms of trace elements that can move in water, salt extracts, solutions of strong and weak acids and alkalis. Often no distinction is made between mobile and plant-accessible forms.
The mobile forms of trace elements in the soil are divided into:
- weakly mobile – pass into solutions of strong acids;
- slightly mobile – pass into solutions of weak acids and alkalis; – acid-buffered solutions;
- readily soluble – pass into water and carbonic acid extracts.
It is important that the selected extract when determining the mobile form is the most appropriate for the assimilating ability of a particular plant. Assessment of the suitability of extracts to determine the provision of soils with microelements carry out field experiments with microfertilizers, which establish a correspondence between the content of mobile forms of trace elements and efficiency of microfertilizers.
In our country a differentiated approach to the choice of methods for determining mobile forms of trace elements in the soil depending on soil type, properties and agrochemical characteristics is applied.
The system of extracts proposed by J.V. Peyve and G.J. Rinkis is used for sod-podzolic soils. The scale of soil provision with microelements is developed.
When analyzing forest, chernozem, chestnut, carbonate and saline soils for determination of mobile forms of manganese, zinc, copper, cobalt acetate-ammonium buffer solution pH 4.8 (by Krupsky-Alexandrov) is used; boron is determined in a water extract after boiling, molybdenum in oxalate extract (by Grigg).
When analyzing carbonate and saline, brown, swampy-meadow soils and gray soils, zinc, copper, and cobalt are extracted using 1 n acetate-sodium buffer solution with pH 3.5 (according to Kruglov); molybdenum is extracted by oxalate buffer solution with pH 3.3 (according to Grigg); boron is determined in an aqueous extract.
Extensive agrochemical studies of soils have shown that soils of certain biogeochemical provinces are often poor in mobile forms of some trace elements. For example, in the Moscow region up to 80% of the studied lands need boric fertilizers; molybdenum deficiency is found in 60% of areas, copper – in 50-60%.
B.A. Yagodin and I.V. Vernichenko summarized the data on the provision of soils of the main biogeochemical zones with mobile forms of trace elements obtained from soil and plant analysis, field and vegetation experiments.
Table. Gradations of soil sufficiency of Russian soils with mobile forms of trace elements
The range of extracts used is wide, from strong acids to aqueous solutions. Much of it is aggressive and is unlikely to extract only the trace elements available to plants. When comparing the values of consumption of trace elements by plants with their content in the soil, extracted by aggressive extracts, it was found that plants assimilate less than 1% of trace elements extracted from them.
When assessing the provision of soils with available forms of trace elements and developing practical recommendations, changes in the content of mobile forms depending on the time of sampling should be taken into account. These fluctuations can be so significant that in different periods of vegetation the soil is both well and poorly supplied with trace elements.
Fertilization changes the mobility of trace elements by changing the reaction of the environment, synergism and antagonism. Thus, phosphorus reduces the intake of zinc and copper, sometimes increasing the intake of manganese. The introduction of magnesium increases the intake of phosphorus to plants. Organic matter changes the adsorption of all mineral elements. Therefore, along with soil analysis of the content of mobile trace elements, it is possible to more accurately assess the availability of plants with the help of the plants themselves.
Depending on the amount of trace elements in the soils of the Non-Black Earth zone, the following levels of their provision with trace elements have been established (table).
Table. Grouping of soils of the Non-Black Soil Zone by the provision of plants with microelements  Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill. Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
Note. The first group – crops of low micronutrient removal and with comparatively high assimilative capacity: cereals, corn, legumes, potatoes. The second group – crops with high and medium microelement removal, with high and medium assimilating ability: root crops, vegetables, grasses (legumes, cereals, grasses), orchards. The third group – crops of high micronutrient removal – all above mentioned crops in conditions of good agrotechnical background: irrigation, high doses of fertilizers, use of the best varieties, good soil treatment and plant care.
The grouping of soils according to the availability of manganese, copper, zinc, and cobalt extracted from soils by acetate-ammonium buffer solution with pH 4.8 (according to Krupsky-Alexandrova) is shown in the table below.
Table. Grouping of soils according to the provision of plants with trace elements (extractant: acetate-ammonium buffer with pH 4.8 according to Krupsky-Alexandrova)Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. - 854 p.
The content of mobile manganese in soils extracted by acetate-ammonium buffer solution with pH 4.8 is about 3-4 times lower than in the 0.1 n H2SO4 extract (according to Peiwe-Rinkis). In contrast, the zinc content in the acetate-ammonium extract is 2-4 times higher than in 1 n KCl. The extraction of copper and cobalt in the buffer solution is, on average, 6-8 times less (with the variation from 3 to 15 times) than in 1 n HCl and 1 n HNO3.
The Don State Agrarian University has developed a scale of zinc availability for carbonate chernozem and chestnut soils (table).
Table. Scale of zinc availability in carbonate black soils and chestnut soils (E.V. Agafonov, 2012)
For carbonate soils of Uzbekistan (sulfur soils), “limit values” of normal provision of cotton with mobile forms of microelements in sodium acetate extract with pH 3.5 were developed.
Table. Limits of normal provision of cotton with mobile forms of trace elements for carbonate soils of Uzbekistan (sulfur soils) (sodium acetate (sodium acetate) extract with pH 3.5).
Classification of microfertilizers
Microfertilizers are usually classified according to the main microelement:
- boron fertilizers;
- copper fertilizers;
- manganese fertilizers;
- molybdenum fertilizers;
- zinc fertilizers;
- cobalt fertilizers;
- selenium-containing fertilizers;
Application of microfertilizers in agriculture
The results of research on promising types and forms of microfertilizers show the feasibility of production and application of microelement-enriched fertilizers, including complex ones. Tests of experimental and pilot batches of basic fertilizers enriched with microelements have shown that, for example, at the expense of boron in nitroamphoska applied to leached chernozem and sod-podzolic soils, additional yield increases are obtained: 3-4 t/ha of sugar beet roots, 0.23-0.29 t/ha of cabbage seeds, 0.21-0.37 t/ha of pea seeds.
Addition of molybdenum-enriched superphosphate to sod-podzolic soils provides additional 0.5-0.6 t/ha of legume grass hay. Under conditions of severe copper deficiency, for example, on drained peat-bog soils of lowland type, against the background of basic fertilizers, spikelets almost do not yield grain, whereas potassium chloride enriched with copper allows to receive 2.5-3.0 t/ha of barley grain, 15-18% increase grass yield and 20% increase vegetable yield.
According to forecasts, the demand of agriculture in microelements must be provided by 60-70% by basic fertilizers enriched with microelements and by 30-40% by technical salts used for foliar dressing and pre-sowing seed treatment.
Some industrial wastes, such as metallurgical slags, pyrite slag, sewage sludge, etc., can be used as a source of trace elements. Fertilizers of this type do not always contain nutrients in a form accessible to plants and often contain toxic impurities.
Micronutrient fertilizers “MiBAS” developed on the lignin base and made from the wastes of pulp and paper industry, printing, electronic, machine-building and other industries can be promising. The technologies developed for utilizing this waste allow us to extract microelements in a pure form and obtain environmentally safe fertilizers. At the same time, lignin-containing waste from pulp and paper production and metal-containing waste are utilized.
The distinctive feature of the new fertilizers is the lignin base, which creates a polymer film on the surface of, for example, seeds, and reliably adheres to this surface. The composition of microfertilizers “MiBAS” includes copper, zinc and cobalt-containing components. Fertilizers “MiBAS” are technologically advanced in use, they are not dusty and are compatible with plant protection products. The effectiveness of these microfertilizers has been established by field and production experiments.
Lignin-based microfertilizers are available in a granular form with a prolonged action for basic application and a liquid concentrate for pre-sowing seed treatment. The content of trace elements in granular form is 10±5%, in the concentrate, which is diluted 3-fold before treatment, 1.3±0.3%. Consumption of granular fertilizer is 50-150 kg/ha, liquid concentrate in diluted form – 10-20 kg/t seed.
Timing and methods of microfertilizer application
It is better to apply microfertilizers to the soil as part of the main mineral fertilizers. It is promising to introduce microelements as part of slow-acting fertilizers, as well as to apply them with irrigation water.
Based on the information about the content of trace elements in the soil and plants to determine the doses of trace elements needed for application. Doses of microfertilizers vary depending on soil and climatic conditions, biological characteristics of crops. Approximate doses for individual crops are given in the table.
Table. Doses and applications of microfertilizers for different crops (CINAO, 1987)
Table. Doses and methods of application of various microfertilizers for major cropsAgrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
For the conditions of the North Caucasus region, recommendations on the rates of microfertilizers for field crops depending on the methods of application and the content of trace elements in the soil (Podkolzin, Demkin, Burlay, 2002) were developed.
Table. Doses and methods of microfertilizers for field crops depending on the content of trace elements in the soilAgrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. - 854 p.
Microelements (boron, molybdenum, copper, manganese, zinc, cobalt) are important in protected ground conditions. Methods of application: pre-sowing application to soil, pre-sowing seed treatment and foliar feeding. You should use 2-3 liters of solution per 100 kg of seeds. Seedling watering at the rate of 10 liters per frame. Soaking the seeds – up to 24 hours at a ratio of seed weight to solution 1:2. Non-root feeding is carried out at the rate of 300 liters per 1 ha.
Table. Doses of microfertilizers for vegetable crops in protected ground (greenhouses) Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. - 854 p.
Doses of microfertilizers are much lower than macrofertilizers, and the requirements for uniformity are higher. Therefore, it is more rational to use basic fertilizers enriched with micronutrients. For example, under buckwheat, sugar beets, vegetables, peas, corn, cotton, seed clover, alfalfa make boric superphosphate 300-350 kg/ha. For flax, strawberries and cucumber doses of boron superphosphate are reduced by 2 times. Bormagnesium fertilizer is best made in rows – 30-55 kg/ha or scattered – 100 kg/ha in conjunction with other mineral fertilizers.
Molybdenum superphosphate is introduced into the rows with the seeds of clover, alfalfa, peas and other legumes at a dose of 50 kg/ha.
Copper fertilizers are pyrite (pyrite) pellets (0.2-0.3 Cu), which are applied in doses of 500-600 kg/ha under autumn tillage once in 4-5 years.
Effectiveness of microfertilizers
Effective use requires:
- Knowledge of the requirements of crops for micronutrients, their content in the soil in a form accessible to plants. Optimization of nutrition should be carried out in a balanced macro- and micronutrients.
- Improving the range of microfertilizers.
- Strengthening of agrochemical and sanitary control over the use of industrial waste as fertilizer.
- Study of the influence on the formation of product quality in a balanced plant nutrition by macro- and microelements, the role of microelements in the formation of individual quality indicators.
- Study of transformation, reutilization, balanced optimization of metabolism of organic compounds in plants that characterize the quality of products and the role of microelements in these processes.
Currently, production of microfertilizers is developing in two directions: production of unilateral microfertilizers in the form of individual salts, chelates and frits; production of complex and unilateral macrofertilizers enriched with microelements.
Unilateral microfertilizers are used for crops with severe deficiency of any microelement. The disadvantage of using one-sided microfertilizer is the difficulty of application in small doses, especially in the soil, when it is difficult to achieve uniform distribution over the surface. Unilateral microfertilizers are used in the form of chelates and frits, which is especially important when applying boron, because this eliminates the impact of locally high concentrations of boron on sensitive crops.
Enriched macrofertilizers reduce application costs, have less danger of toxic effects when applying excessive doses of fertilizers, and reduce environmental pollution.
For foliar fertilization, individual salts are mainly used, e.g. manganese, zinc, iron sulfates.
The use of trace elements in combination with macronutrients in complex fertilizers or nutrient mixtures should be limited, and used in conditions of absolute nutrient deficiency in the cultivation of plants on low fertile sandy and sandy loam soils, in hydroponics or protected ground, in horticulture and ornamental floriculture.
Tasks of microfertilizer agrochemistry
In the field of agrochemistry of microelements of primary importance for practical application in agriculture, ensuring high agrochemical and economic efficiency, are the tasks on:
- development of methods for predicting the effectiveness of microfertilizers on the basis of agrochemical analysis of soils for the content of available forms of microelements and plant diagnostics;
- studying the effect of microfertilizers on the value and quality of crop yields in a network of geographical field experiments, carried out according to a single method and program, on the background of increasing doses of basic mineral fertilizers
- studies of the macro- and microelements balance in long-term field experiments with fertilizers in crop rotation in different soil and climatic zones, including fertilizer systems
- studying the interaction of macro- and microelements in the processes of nutrition and metabolism, the impact of microfertilizers on the use and uptake of major nutritional elements from soil and fertilizers.
Researches on development of methods of efficiency forecasting include definition of limiting values of the maintenance of microelements in soils and plants, development of perfect methods of definition of accessible forms in soils, establishment of scientifically proved gradations of security of soils by microelements for concrete soil-climatic zones, taking into account features of cultures, type and granulometric composition of soils, a level of application of organic and mineral fertilizers and methods of regulation of a water mode.
It is important to develop methods of rational use of industrial waste containing microelements and search for raw materials suitable for microfertilizer production.
Studies of macro- and microelements balance in long-term field experiments with crop rotations should be accompanied by research on the impact of applying high doses of organic and mineral fertilizers, methods of chemical melioration and chemical means of plant protection on the content and availability of soil and fertilizer microelements to plants.
It is promising to study agrochemical value of microelements: iodine, lithium, aluminum, vanadium, titanium, selenium, rubidium, bromine and fluorine, as well as determine the negative impact of copper, fluorine, arsenic, chromium, lead, cadmium, nickel as a result of man-made environmental pollution.
It is also necessary to study the hidden lack of trace elements without external manifestation of signs, which leads to a decrease in yield and product quality.
At the present stage of development it has become possible to take into account many factors determining the norms of macro- and microfertilizers application with the help of computer technology.
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: Kolos, 2002. – 584 p.: ill.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.