Fertilizers are substances designed to improve plant nutrition and soil fertility in order to increase crop yields and improve the quality of crop production.
The word “fertilizer” in Russian has a double meaning. First, it denotes the technological process of fertilizing the soil, and second, it denotes the substances used for this purpose. D.N. Pryanishnikov put into the concept of “fertilizer” the following meaning: fertilizer is food for plants that can increase the mobilization of nutrients in the soil, increase the energy of life processes and change the properties of the soil, that is, fertilizer has a multilateral direct and indirect impact on the soil and plants.
- Importance of fertilizers
- Physical and mechanical properties of fertilizers
- Fertilizer efficiency
- Fertilizer is a major factor in increasing yields
- Fertilizer classification
- Mineral fertilizers
- Organic fertilizers
- Microbiological fertilizers
- Fertilizer interaction with soil
Importance of fertilizers
Due to the multifunctional role of fertilizers in the agrocenosis, their importance increases with increasing agricultural productivity, which is confirmed by the experience of farming in many highly developed countries of the world.
Organic and mineral fertilizers influence the soil structure, reaction of soil solution, the rate of microbiological processes, actively participate in fertility reproduction, influence nutrition, plant growth and development, resistance to adverse external factors and, in general, the yield and its quality. For example, soils systematically fertilized with manure are characterized by lower acidity, higher content of phosphorus forms available for plants, increased amount of humus and total nitrogen, a greater degree of saturation with bases. Fertilizers are the basis for the chemicalization of agriculture.
Cultivation of crops results in alienation of nutrients with crops, loss with surface runoff and infiltration into deep layers, erosion. As a result, the balance of nutrients is changed, fertility, crop yields and product quality are reduced. Fertilizers are used to level out the deficit of nutrients in the soil.
Plants form dry matter in the process of their life by absorbing air carbon dioxide, water and soil minerals. As a result, plants accumulate certain substances that characterize the chemical composition of plants.
The most important, so-called biophilic, nutrients are nitrogen, phosphorus and potassium. The amount of nutrients absorbed by plants, contained in all organs and in the entire mass of the crop, allows us to determine their need for nutrients. The consumption of nutrients is expressed in kg per 1 ha or kg per 1 ton of marketable products, including by-products. The optimum content and ratio of nutrients in the soil under the condition of sufficiency of other factors of plant life allows you to get the highest possible yields of crops with high quality.
D.N. Pryanishnikov noted: it took 100 years for Western European countries to increase wheat yield from 0.7 to 1.6 tons per hectare by application of the fruit-change cropping system and improved tillage, and 25 years to increase the yield from 1.6 to 3 tons by application of fertilizers.
In Russia, the use of fertilizers provides up to half of the total increase in crop yields. For example, the application of fertilizers on the soils of the Non-Black Soil Zone, characterized by low natural fertility, or on the southern soils with limited moisture supply, allows a yield increase of up to 75%.
Physical and mechanical properties of fertilizers
Fertilizer losses during transportation and storage can be related to their ability to segregate (for mixed fertilizers), vapor elasticity and viscosity (for liquid forms), bulk density and the angle of natural slope (for powder forms). Organization of transportation and storage of fertilizers is also associated with fire and explosive properties, residual acidity, rate and conditions of decomposition, and toxicity. For example, potassium nitrate when mixed with sawdust is capable of forming fire- and explosive mixtures, and liquid ammonia or its aqueous solutions have a strong asphyxiant stock.
Properties of fertilizers can vary widely depending on the technical features of production, raw materials and their composition, are regulated by technical specifications (regulatory documents). For example, for urea allowable moisture is not more than 0.2-0.3%, calcium nitrate – not more than 14%, powdered superphosphate – not more than 12%, potassium fertilizers – from 1 to 6%. Failure to meet the requirements entails changes in the physical and mechanical properties of fertilizers, which makes them of little use.
One of the properties of fertilisers that greatly affects their use is hygroscopic properties, i.e. their ability to absorb moisture from the air. Among the highly hygroscopic fertilizers are calcium nitrate (9.5 points out of 10 possible) and ammonium nitrate (9.3 points), potassium chloride 3.2-4.4 points, potassium sulfate 0.2 points. Conditions for storage, transportation and packaging of fertilizers are determined by this property. Strongly hygroscopic fertilizers are stored and transported in sealed containers, often in polyethylene bags.
Friability – the suitability of fertilizers for mechanical spreading with fertilizer spreaders, depends on the moisture capacity. The maximum moisture content of mineral fertilizers corresponds to the maximum moisture content, at which the ability to disperse with fertilizer sowing machines is retained.
Fertilisers may cake if stored or transported for an extended period of time. Fertilisers that are caked on the ground require more grinding before spreading. The amount of caking depends on hygroscopicity, moisture, particle size distribution, storage conditions and duration. Traceability is estimated on a 7-point scale and is determined by the resistance to breakdown of caked fertilizer. Simple powder-like superphosphate (7 points), fine-crystal potassium chloride (6 points) are prone to strong caking, ammonium sulfate is weak (2-3 points), resistant to caking potassium sulfate, potassium magnesia (1 point).
Physical and mechanical properties of mineral fertilizers associated with granulometric composition, i.e. particle size. It is determined by the method of sieves. Granulometric composition affects the uniformity of application over the area of the field. Homogeneous granulometric composition when spreading with centrifugal spreaders provides uniform distribution across the width of the machine. When the grain size distribution is not uniform, separation, i.e. scattering of fertilizer particles of different sizes and weights at different distances from the fertilizer spreading unit is observed: larger and heavier particles are thrown at a greater distance, which creates an uneven distribution.
Preservation of granulometric composition during storage, transportation and application in the soil depends on the strength of granules, which is characterized by the mechanical crushing strength (in kgf/cm3) and abrasion (in %). The strength of granules is related to humidity, size and shape of the particles, the presence of hydrophobic additives, the density of fertilizer packaging, and the duration of storage.
Fertilizer spreadability, or flowability, is the mobility of fertilizer particles at their application with fertilizer seeders. Fertilizer spreadability is evaluated with a 12-point system.
When transporting fertilizers and calculating the size of storage space, we take into account the density of fertilizers, that is, the volume per unit mass (1 t/m3) and weight per unit volume. The least dense are ammonium chloride and urea (0.58-0.65 t/m3), heavy – tomaslak, limestone and phosphate rock (2.01-1.62 t/m3).
Some fertilizers with good physical and mechanical properties, such as ammonium sulfate, potassium sulfate, allowed to transport and store bulk – in bulk. When storing them take into account the angle of natural slope (rest), which is formed by the horizontal plane (surface) and the slope line of the fertilizer heap.
Fertilizer application timing and incorporation methods influence efficiency and rational use of fertilizer.
Table. Yield increment of sugar beet (t/ha) depending on the time of application and methods of fertilization
The efficiency of mineral fertilizers increases under conditions of irrigation or sufficient moisture due to precipitation.
A deficit of moisture in the soil reduces the effectiveness of fertilizers, but excessive moisture also has a negative impact on efficiency due to leaching of nutrients.
Soil fertility is another factor in fertilizer efficiency. High weed infestation, poor tillage, violation of agrotechnical requirements reduces the effectiveness of fertilizers. For example, an increase in grain yield per 1 kg of the active substance of fertilizers on average more than 4 kg of grain. Depending on nutritional conditions it varies for different crops: winter wheat – 3,2-5,8 kg, spring wheat – 2-6,2 kg, corn – 3,3-7,6 kg of grain, sugar beet – 19,3-37,8 kg of root crops, potatoes – 25-37,6 kg of tubers.
The effectiveness of the fertilizer depends on:
- type and form of fertilizer;
- optimal dosage;
- ratio of the nutrients to be applied;
- timing of application;
- methods of application.
When selecting fertilizers take into account the properties of soils and climatic conditions, biological and varietal characteristics of crops grown. When choosing the form of fertilizer – the attitude of plants to its ionic composition, the physiological reaction of fertilizer, the ability of the root system to absorb nutrients from the hardly soluble forms.
Proper determination of fertilizers requires knowledge of the nature of the interaction of the fertilizer in the system soil – plant – fertilizer – environment.
For effective use of fertilizers, it is important conditions of transportation, storage, preparation for application to the soil. Therefore it is necessary to consider the physical, mechanical and chemical properties of fertilizers, such as solubility, hygroscopicity, caking, moisture capacity, dispersibility, granulometric composition, the strength of granules.
The use of fertilizers is in most cases economically profitable. According to calculations, 1 ruble spent on mineral fertilizers provides an increase in yield at an average cost of 2.2 rubles. The share of economic costs for the purchase and use of mineral fertilizers in the country as a whole until 1990 was 15-17% of all crop production costs.
The economic return of fertilizers depends on the natural fertility of the soil. For example, in the Non-Black Earth zone with high moisture availability, but low natural fertility for grain crops yield 3 t/ha as a result of fertilizer is obtained 70-80% increase in yield. In the dry steppe, fertilizers account for 50% of the growth.
Fertilizer is a major factor in increasing yields
Global farming practices show that yields are related to the amount of fertilizer used.
Table. Mineral fertilizer application and cereal yield (average 1986-1988, Popov, 1999)
The relationship between grain production and the use of mineral fertilizers can be clearly seen in Russia, where there has been a sharp decline in the use of mineral fertilizers and soil fertility.
Table. Mineral fertilizer use and grain production in Russia (annual average, Popov, 1999)
|Mineral fertilizers supplied
|- million tonnes a.s.
|- kg/ha of arable land
|Gross harvest of grain, million tons
|Grain yields, t/ha
Table. Balance of nutrients in farming in Russia, kg/ha (annual average, Popov, 1999)
According to field experiments of the agrochemical service of Russia, the yield increase from the use of mineral fertilizers is: winter wheat – 0.49-1.27 t/ha; winter rye – 0.48-1.08 t/ha; spring barley – 0.32-1.29 t/ha; corn (grain) – 0.65-2 t/ha; potatoes – 4.9-9.1 t/ha; sugar beet – 5-14.4 t/ha; corn for silage – 2.3-18.1 t/ha; natural grass for hay – 0.6-3 t/ha.
Intensification of farming leads to a further increase in yields, accelerates the removal of nutrients from the soil and the mineralization of humus. The regulation of these processes becomes possible through the application of fertilizers. In the 80s, about 60% of the nutrients were introduced into the soil with mineral fertilizers, and the use of organic fertilizers amounted to more than 4 tons per 1 ha per year. In the 90s, the application of organic fertilizers decreased by more than 5 times, and mineral fertilizers – 10 times. The deficit of humus was 0.52 t per 1 ha of arable land, the need for manure to cover the deficit was 6.5 t/ha.
In the middle of the XX century, the so-called “green revolution” took place, the foundations of which were laid by Norman Borlaug. Countries with a high level of chemicalization of agriculture are characterized by higher yields, the increase of which is based on new varieties of intensive type and progressive farming techniques.
According to summarized data of Russian Academy of Agricultural Sciences academician V.F. Ladonin (1999) grain production in the world grew 3 times: from 630 million tons in 1950 to 1970 million tons in 1990 During the same period application of mineral fertilizers grew 10 times: from 14 up to 140 million tons. At the same time, grain production increased due to the intensification of farming rather than the expansion of cultivated areas. Grain yields in the second half of the XX century increased 2.5 times, an average of 2.1% per year.
In developed countries from 1970 to 1990 fertilizer use increased from 26 to 83 kg/ha, in East Asia and the Pacific from 36 to 190 kg/ha, in Europe from 88 to 142 kg/ha, in the former USSR and China from 46 to 110 kg/ha. In 1990 the grain yield in the DPRK was 4.2 t/ha. The world records for wheat were more than 16 t/ha and for corn more than 22 t/ha.
Crop yield increases of 50% are determined by fertilizers, the remaining 50% come from other factors. According to studies in the U.S., yield increases in the postwar years were 41% due to mineral fertilizers, 15-20% to herbicides and crop protection chemicals, 15% to agronomic practices, 8% to hybrid seeds, 5% to irrigation, and 11-18% to other factors.
Increasing yields lead to increased nutrient uptake by plants, so the higher the planned yield of a crop, the more fertilizer is needed. However, the yield increases in direct correlation with increasing fertilizer doses to a certain level, at which the maximum payment per unit of fertilizer received agricultural products is achieved.
Increasing fertilizer doses is economically justified until the cost of applying additional fertilizers fully recoups the increase in yield.
Effective fertilizer application is possible with a high degree of agronomic technique.
Table. Effect of the complex of agricultural practices on the yield of potatoes on sandy soils
|Without fertilizer, late planting, small tubers, insufficient care
|Improved farming techniques, without fertilizers
|Improved farming techniques, with fertilizer
Numerous experiments in different soil and climatic conditions proved the influence of doses and forms of nitrogen fertilizers on grain quality, especially the protein content of winter wheat grain.
Chemical farming does not replace organic fertilizers. D.N. Pryanishnikov believed: the wrong attitude towards manure is the wrong attitude towards the nutritional elements of mineral fertilizers. Organic fertilizers are one of the basic elements of the fertilizer system.
For example, in the Non-Black Earth zone 20-30 tons of manure per hectare, give an increase in grain yield 0.6-0.7 t / ha, potatoes 6-7 t / ha, root crops to 15 t / ha, silage crops 15-20 t / ha. The effect of manure lasts for 4-5 years. During this time, one ton of manure gives 0.1 tons of increased production in terms of grain.
In experiments Dolgoprudny station introduction of 36 t/ha of manure on four crops of rotation allowed to obtain 3.4 t/ha of additional production in terms of grain.
Table. Yield increments in the crop rotation from the application of 36 t/ha of manure (average for 15 years)
|Fodder beet (roots)
According to the nature of the impact on the soil
According to the nature of the impact on the soil and plant nutrient regime fertilizers are divided into direct and indirect.
Fertilizers of direct action – fertilizers that improve plant nutrition by nutrients. This group includes all kinds of minerals, respectively, nitrogen, phosphate, potash, etc., and organic fertilizers.
Indirect fertilizers improve soil properties, mobilize available reserves of nutrients. The indirect include means of chemical reclamation of soils (lime, gypsum), bacterial fertilizers.
Division of fertilizers into direct and indirect conventional, as each of them can have both direct and indirect effects. Getting into the soil, fertilizers improve the mineral nutrition of plants and affect the agrochemical properties. For example, lime or gypsum eliminate excessive acidity or alkalinity of the soil and are at the same time a source of calcium for plant nutrition.
According to the chemical composition
According to the chemical composition, or origin, fertilizers are divided into:
- mineral (nitrogen, phosphate, potash, complex, microfertilizers);
- organic (manure, compost, slurry, poultry manure, straw (for fertilizer), green fertilizer (green manure));
Mineral fertilizers, depending on their composition, are divided into:
- single-component, or simple, or one-sided – containing only one nutrient element;
- complex – containing two or more nutrients.
According to the types of nutrients, mineral fertilizers are divided into nitrogen, phosphorus, potassium, zinc, etc. In turn, each type can be subdivided according to forms, for example, nitrogen includes nitrate, ammonium, ammonium-nitrate and amide forms.
Depending on the main component, fertilizers are subdivided into macro- and micro-fertilizers.
According to the effect on the reaction of the soil solution mineral fertilizers are distinguished:
- physiologically acidic;
- physiologically alkaline;
- physiologically neutral.
Physiologically acidic fertilizers include fertilizers, cations of which are absorbed by plants to a greater extent than anions. Correspondingly, physiologically alkaline fertilizers are fertilizers, the anions of which are more absorbed by the plants. Physiologically neutral mineral fertilizers have no effect on the reaction of the soil solution.
According to the method of production
According to the method of production fertilizers are divided into:
- local (bone meal, wood ash, limestone, dolomites, gypsum-containing materials, sapropel);
- non-traditional (phosphate slag, phosphogypsum, defecate, shale ash, sewage sludge).
Industrial fertilizers – mineral fertilizers produced at chemical plants.
Local fertilizers – fertilizers obtained in places of application, directly in farms or near them. Local fertilizers include manure, slurry, poultry manure, compost, peat, ash, lime tuff, green fertilizer.
According to their aggregate state
According to their aggregate state, fertilizers are divided into:
- powdery, with a particle size of less than 1 mm;
- crystalline, with the size of crystals over 0.5 mm;
- granulated, with the size of granules over 1 mm;
Mineral fertilizers are industrial substances or minerals that contain one or more plant nutrients, more often in mineral form, less often in organic form. Currently, mineral fertilizers account for about 60% of the amount of nutrients applied to the soil.
The active ingredient is the nutrient contained in the fertilizer. The content of a fertilizer active substance is expressed as a percentage of weight: for nitrogen fertilizers – per N, phosphorus – on P2O5, potassium – on K2O, magnesium – on MgO, calcium – in CaO or CaCO3, in a micro fertilizer – for the corresponding microelement.
The composition of complex fertilizers is usually expressed in the content of the active substances in numbers, separated from each other by a dash or colon. The first number usually indicates the percentage of nitrogen (N), the second – phosphorus (P2O5), the third – potassium (K2O). For example, N:P:K is 17:17:17.
The ratio of active substances in complex fertilizers is commonly denoted by numbers, with the nitrogen content being taken as one. For the example above, the ratio would be 1:1:1.
The application rate or fertilizer dose is usually indicated in the active ingredient (kg/ha) as a subscript: N60P90K30.
Main article: Organic fertilizers
Organic fertilizers – fresh or biologically processed substances of complex composition of plant or animal origin, used as a fertilizer.
Main article: Microbial and bacterial fertilizers
Microbiological fertilizers – preparations containing a culture of microorganisms, the vital activity of which when entering the soil improves the composition, increasing the activity of the microbial community of the soil, thus creating favorable conditions for plant nutrition.
Fertilizer interaction with soil
When applied to the soil fertilizer as a result of interaction with the soil and under the influence of soil microorganisms is subjected to various transformations, which affects the ability to move in the soil, solubility and accessibility to plants. For example, on sandy soils, the rate of decomposition of organic fertilizers is higher than on loamy and clay soils. Phosphate meal under the influence of acidic soil reaction or acidic excreta of the root system, for example, lupine passes into soluble plant-accessible form.
Mineral fertilizers can enter into exchange reactions with soil colloids or absorbed by microorganisms, temporarily fixed in the living plasma.
The rate of fertilizer transformation processes in the soil depends on:
- the nature of the fertilizer,
- soil properties,
- climatic conditions,
- complex agrotechnical measures.
The interaction of fertilizers with the soil can be both positive and negative for plant nutrition. The positive effect of the systematic application of organic and mineral fertilizers is manifested in changes in the physical and chemical properties of soils. Thus, long-term application of manure leads to an increase in the content of organic matter in the soil, increasing the capacity of absorption, reduced exchange and hydrolytic acidity, increased degree of saturation with bases.
Negative effect from the long-term use of mineral fertilizers associated with acidification of the reaction of the soil solution due to the displacement of hydrogen and aluminum ions from the absorption complex, the use of physiologically acidic nitrogen and potassium fertilizers. Negative effects are often a consequence of improper use of agrochemicals, as the current level of scientifically sound fertilizer system can avoid negative effects. For example, a combination of mineral and organic fertilizers, liming, the use of neutralizing additives in physiologically acidic fertilizers eliminates the increase in soil acidity.
Fertilizers change soil properties: solution reaction, intensity and direction of microbiological processes, i.e. have a direct impact on soil fertility.
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