Various nutrients entering the soil with fertilizers undergo significant transformations. At the same time, they have a significant impact on soil fertility.
And the properties of the soil, in turn, can have both positive and negative effects on the applied fertilizers. This relationship between fertilizers and soil is very complex and requires in-depth and thorough research. Various sources of fertilizer losses are also associated with the transformation of fertilizers in the soil. This problem represents one of the main tasks of agrochemical science. R. Kundler et al. (1970) generally show the following possible transformations of various chemical compounds and the associated loss of nutrients through leaching, volatilization in gaseous form and fixation in the soil.
It is quite clear that these are only some indicators of the transformation of various forms of fertilizers and nutrients in the soil; they still do not cover the numerous ways of transformation of various mineral fertilizers depending on the type and properties of the soil.
Since soil is an important link in the biosphere, it is primarily exposed to the complex complex effects of applied fertilizers, which can have the following effects on the soil: cause acidification or alkalization of the environment; improve or worsen the agrochemical and physical properties of the soil; promote the exchange absorption of ions or displace them into the soil solution; promote or hinder the chemical absorption of cations (biogenic and toxic elements); promote mineralization or synthesis of soil humus; enhance or weaken the effect of other soil nutrients or fertilizers; mobilize or immobilize soil nutrients; cause antagonism or synergism of nutrients and, therefore, significantly affect their absorption and metabolism in plants.
In the soil there can be a complex direct or indirect interaction between biogenic toxic elements, macro- and microelements, and this has a significant impact on the properties of the soil, plant growth, their productivity and the quality of the crop.
Thus, the systematic use of physiologically acidic mineral fertilizers on acidic soddy-podzolic soils increases their acidity and accelerates the leaching of calcium and magnesium from the arable layer and, consequently, increases the degree of unsaturation with bases, reducing soil fertility. Therefore, on such unsaturated soils, the use of physiologically acidic fertilizers must be combined with liming of the soil and neutralization of applied mineral fertilizers.
Twenty years of fertilizer application in Bavaria on silty, poorly drained soils, combined with liming for grasses, resulted in an increase in pH from 4.0 to 6.7. In the absorbed soil complex, exchangeable aluminum was replaced by calcium, which led to a significant improvement in soil properties. Calcium losses as a result of leaching amounted to 60-95% (0.8-3.8 c/ha per year). Calculations showed that the annual need for calcium was 1.8-4 c/ha. In these experiments, the yield of agricultural plants correlated well with the degree of base saturation in the soil. The authors concluded that to obtain a high yield, soil pH >5.5 and a high degree of base saturation (V = 100%) are required; in this case, exchangeable aluminum is removed from the zone of greatest location of the plant root system.
In France, the great importance of calcium and magnesium in increasing soil fertility and improving their properties has been revealed. It has been established that leaching leads to depletion of calcium and magnesium reserves
in the soil. On average, the annual loss of calcium is 300 kg/ha (200 kg on acidic soil and 600 kg on carbonate soil), and magnesium - 30 kg/ha (on sandy soils they reached 100 kg/ha). In addition, some crop rotation crops (legumes, industrial crops, etc.) remove significant amounts of calcium and magnesium from the soil, so the following grain crops often show symptoms of deficiency of these elements. We must also not forget that calcium and magnesium act as physical and chemical ameliorants, having a beneficial effect on the physical and chemical properties of the soil, as well as on its microbiological activity. This indirectly affects the conditions of mineral nutrition of plants with other macro- and microelements. To maintain soil fertility, it is necessary to restore the levels of calcium and magnesium lost as a result of leaching and removal from the soil by agricultural crops; To do this, 300-350 kg of CaO and 50-60 kg of MgO per 1 ha should be applied annually.
The goal is not only to replenish the loss of these elements due to leaching and removal by agricultural crops, but also to restore soil fertility. In this case, the application rates of calcium and magnesium depend on the initial pH value, the MgO content in the soil and the fixing capacity of the soil, i.e., primarily on the content of physical clay and organic matter in it. It is estimated that to increase soil pH by one unit, lime needs to be added from 1.5 to 5 t/ha, depending on the physical clay content (<10% - >30%), To increase the magnesium content in the topsoil by 0.05%, you need to add 200 kg of MgO/ha.
It is very important to establish the correct doses of lime in the specific conditions of its use. This question is not as simple as it is often presented. Typically, doses of lime are set depending on the degree of acidity of the soil and its saturation with bases, as well as the type of soil. These issues require further, more in-depth study in each specific case. An important question is the frequency of lime application, the granularity of application in crop rotation, the combination of liming with phosphorite treatment and the application of other fertilizers. The need for advanced liming has been established as a condition for increasing the efficiency of mineral fertilizers on acidic soils of the taiga-forest and forest-steppe zones. Liming significantly affects the mobility of macro- and microelements of applied fertilizers and the soil itself. And this affects the productivity of agricultural plants, the quality of food and feed, and, consequently, the health of humans and animals.
M.R. Sheriff (1979) believes that the possible over-liming of soils can be judged at two levels: 1) when the productivity of pastures and animals does not increase with additional application of lime (this the author calls the maximum economic level) and 2) when liming upsets the balance of nutrients substances in the soil, and this negatively affects plant productivity and animal health. The first level in most soils occurs at a pH of about 6.2. On peat soils, the maximum economic level is observed at pH 5.5. Some pastures on light volcanic soils do not show any signs of responsiveness to lime at their natural pH of 5.6.
It is necessary to strictly take into account the requirements of cultivated crops. Thus, the tea bush prefers acidic red soils and yellow earth-podzolic soils; liming inhibits this crop. The application of lime has a negative effect on flax, potatoes (details) and other plants. Legumes that are inhibited in acidic soils respond most well to lime.
The problem of plant productivity and animal health (second level) most often arises at pH = 7 or more. In addition, soils vary in the rate and degree of their response to lime. For example, according to M.R. Sheriff (1979), to change the pH from 5 to 6 for light soils, about 5 t/ha is required, and for heavy clay soil 2 times this amount. It is also important to take into account the content of calcium carbonate in the lime material, as well as the looseness of the rock, the fineness of its grinding, etc. From an agrochemical point of view, it is very important to take into account the mobilization and immobilization of macro- and microelements in the soil under the influence of liming. It has been established that lime mobilizes molybdenum, which in excess quantities can adversely affect plant growth and animal health, but at the same time symptoms of copper deficiency are observed in plants and livestock.
The use of fertilizers can not only mobilize individual soil nutrients, but also bind them, turning them into a form inaccessible to plants. Research conducted in our country and abroad shows that the unilateral use of high doses of phosphorus fertilizers often significantly reduces the content of mobile zinc in the soil, causing zinc starvation of plants, which negatively affects the quantity and quality of the crop. Therefore, the use of high doses of phosphorus fertilizers often necessitates the addition of zinc fertilizer. Moreover, the application of one phosphorus or zinc fertilizer may not have an effect, but their combined use can lead to a significant positive interaction between them.
There are many examples that indicate the positive and negative interaction of macro- and microelements. The All-Union Scientific Research Institute of Agricultural Radiology studied the effect of mineral fertilizers and liming of soil with dolomite on the intake of strontium radionuclide (90 Sr) into plants. The content of 90 Sr in the crop of rye, wheat and potatoes under the influence of complete mineral fertilizer decreased by 1.5-2 times compared to unfertilized soil. The lowest content of 90 Sr in the wheat crop was in variants with high doses of phosphorus and potassium fertilizers (N 100 P 240 K 240), and in potato tubers - when applying high doses of potassium fertilizers (N 100 P 80 K 240). The addition of dolomite reduced the accumulation of 90 Sr in the wheat crop by 3-3.2 times. The application of complete fertilizer N 100 P 80 K 80 against the background of liming with dolomite reduced the accumulation of radiostrontium in grain and wheat straw by 4.4-5 times, and at a dose of N 100 P 240 K 240 - by 8 times compared with the content without liming.
F.A. Tikhomirov (1980) points to four factors that influence the extent of radionuclide removal from soils by plant harvests: biogeochemical properties of technogenic radionuclides, soil properties, biological characteristics of plants and agrometeorological conditions. For example, from the arable layer of typical soils in the European part of the USSR, 1-5% of the 90 Sr contained in it and up to 1% of 137 Cs are removed as a result of migration processes; On light soils, the rate of removal of radionuclides from the upper horizons is significantly higher than on heavy soils. Better supply of plants with nutrients and their optimal ratio reduce the entry of radionuclides into plants. Crops with deeply penetrating root systems (alfalfa) accumulate less radionuclides than those with superficial root systems (ryegrass).
Based on experimental data in the radioecology laboratory of Moscow State University, a system of agricultural measures has been scientifically substantiated, the implementation of which significantly reduces the entry of radionuclides (strontium, cesium, etc.) into crop production. These measures include: dilution of radionuclides entering the soil in the form of practically weightless impurities with their chemical analogues (calcium, potassium, etc.); reducing the availability of radionuclides in the soil by introducing substances that convert them into less accessible forms (organic matter, phosphates, carbonates, clay minerals); embedding the contaminated soil layer into the subarable horizon beyond the zone of distribution of root systems (to a depth of 50-70 cm); selection of crops and varieties that accumulate minimal amounts of radionuclides; placement of industrial crops on contaminated soils, use of these soils for seed plots.
These measures can also be used to reduce pollution of agricultural products and toxic substances of non-radioactive nature.
Research by E.V. Yudintseva et al. (1980) also found that calcareous materials reduce the accumulation of 90 Sr from sod-podzolic sandy loam soil in barley grain by approximately 3 times. The introduction of increased doses of phosphorus against the background of blast furnace slag reduced the content of 90 Sr in barley straw by 5-7 times, in grain - by 4 times.
Under the influence of calcareous materials, the content of cesium (137 Cs) in the barley harvest decreased by 2.3-2.5 times compared to the control. With the combined application of high doses of potassium fertilizers and blast furnace slag, the content of 137 Cs in straw and grain decreased by 5-7 times compared to the control. The effect of lime and slag on reducing the accumulation of radionuclides in plants is more pronounced on sod-podzolic soil than on gray forest soil.
Research by US scientists has established that when Ca(OH) 2 was used for liming, the toxicity of cadmium decreased as a result of the binding of its ions, while the use of CaCO 3 for liming was ineffective.
In Australia, the effect of manganese dioxide (MnO 2) on the uptake of lead, cobalt, copper, zinc and nickel by clover plants was studied. It was found that when manganese dioxide was added to the soil, the absorption of lead and cobalt and, to a lesser extent, nickel decreased more strongly; MnO 2 had an insignificant effect on the absorption of copper and zinc.
In the USA, studies have also been conducted on the effect of different levels of lead and cadmium in the soil on the absorption of calcium, magnesium, potassium and phosphorus by corn, as well as on plant dry weight.
The table data shows that cadmium had a negative effect on the supply of all elements to 24-day-old corn plants, and lead slowed down the supply of magnesium, potassium and phosphorus. Cadmium also had a negative effect on the supply of all elements in 31-day-old corn plants, while lead had a positive effect on the concentration of calcium and potassium and a negative effect on the content of magnesium.
These issues are of important theoretical and practical importance, especially for agriculture in industrialized areas, where the accumulation of a number of microelements, including heavy metals, increases. At the same time, there is a need for a more in-depth study of the mechanism of interaction of various elements on their entry into the plant, the formation of the yield and the quality of the product.
The University of Illinois (USA) also studied the effect of the interaction of lead and cadmium on their absorption by corn plants.
Plants showed a definite tendency to increase cadmium uptake in the presence of lead; soil cadmium, on the contrary, reduced lead uptake in the presence of cadmium. Both metals at the tested concentrations suppressed the vegetative growth of corn.
Of interest are studies carried out in Germany on the influence of chromium, nickel, copper, zinc, cadmium, mercury and lead on the absorption of phosphorus and potassium by spring barley and the movement of these nutrients in the plant. Labeled atoms 32 P and 42 K were used in the studies. Heavy metals were added to the nutrient solution in concentrations from 10 -6 to 10 -4 mol/l. A significant intake of heavy metals into the plant with an increase in their concentration in the nutrient solution has been established. All metals had (to varying degrees) an inhibitory effect on both the entry of phosphorus and potassium into plants and their movement within the plant. The inhibitory effect on the intake of potassium was more pronounced than that of phosphorus. In addition, the movement of both nutrients into the stems was suppressed more strongly than the movement into the roots. The comparative effect of metals on the plant occurs in the following descending order: mercury → lead → copper → cobalt → chromium → nickel → zinc. This order corresponds to the electrochemical series of element voltages. If the effect of mercury in solution was clearly manifested already at a concentration of 4∙10 -7 mol/l (= 0.08 mg/l), then the effect of zinc was only at a concentration above 10 -4 mol/l (= 6.5 mg/l ).
As already noted, in industrialized areas, various elements accumulate in the soil, including heavy metals. Near major highways in Europe and North America, the impact on plants of lead compounds entering the air and soil with exhaust gases is very noticeable. Some lead compounds enter plant tissue through leaves. Numerous studies have found elevated levels of lead in plants and soil at a distance of up to 50 m away from highways. There have been cases of poisoning of plants in areas of particularly intense exposure to exhaust gases, for example, spruce trees at a distance of up to 8 km from the large Munich airport, where there are about 230 aircraft departures per day. Spruce needles contained 8-10 times more lead than needles in uncontaminated areas.
Compounds of other metals (copper, zinc, cobalt, nickel, cadmium, etc.) significantly affect plants near metallurgical plants, coming both from the air and from the soil through the roots. In such cases, it is especially important to study and implement techniques that prevent excessive intake of toxic elements into plants. Thus, in Finland, the content of lead, cadmium, mercury, copper, zinc, manganese, vanadium and arsenic was determined in the soil, as well as in lettuce, spinach and carrots grown near industrial facilities and highways and in clean areas. Wild berries, mushrooms and meadow grasses were also studied. It was established that in the area of industrial enterprises the lead content in lettuce ranged from 5.5 to 199 mg/kg of dry weight (background 0.15-3.58 mg/kg), in spinach - from 3.6 to 52.6 mg /kg dry weight (background 0.75-2.19), in carrots - 0.25-0.65 mg/kg. The lead content in the soil was 187-1000 mg/kg (background 2.5-8.9). The lead content in mushrooms reached 150 mg/kg. As we moved away from highways, the lead content in plants decreased, for example, in carrots from 0.39 mg/kg at a distance of 5 m to 0.15 mg/kg at a distance of 150 m. The cadmium content in the soil varied within 0.01-0 .69 mg/kg, zinc - 8.4-1301 mg/kg (background concentrations were 0.01-0.05 and 21.3-40.2 mg/kg, respectively). It is interesting to note that liming of contaminated soil reduced the cadmium content in lettuce from 0.42 to 0.08 mg/kg; Potassium and magnesium fertilizers did not have a noticeable effect on it.
In areas of heavy pollution, the zinc content in herbs was high - 23.7-212 mg/kg dry weight; arsenic content in soil is 0.47-10.8 mg/kg, in lettuce - 0.11-2.68, spinach - 0.95-1.74, carrots - 0.09-2.9, wild berries - 0 .15-0.61, mushrooms - 0.20-0.95 mg/kg of dry matter. The mercury content in cultivated soils was 0.03-0.86 mg/kg, in forest soils - 0.04-0.09 mg/kg. There were no noticeable differences in the mercury content of different vegetables.
The effect of liming and flooding of fields on reducing the entry of cadmium into plants is noted. For example, the cadmium content in the topsoil of rice fields in Japan is 0.45 mg/kg, and its content in rice, wheat and barley on uncontaminated soil is 0.06 mg/kg, 0.05 and 0.05 mg/kg, respectively. . Soybean is the most sensitive to cadmium, in which a decrease in the growth and weight of grains occurs when the cadmium content in the soil is 10 mg/kg. The accumulation of cadmium in rice plants in an amount of 10-20 mg/kg causes suppression of their growth. In Japan, the maximum permissible concentration of cadmium in rice grain is 1 mg/kg.
In India, there is a problem of copper toxicity due to its high accumulation in soils located near copper mines in Bihar. Toxic level of citrate EDTA-Ci > 50 mg/kg soil. Indian scientists also studied the effect of liming on the copper content in drainage water. The lime rates were 0.5, 1 and 3 of those required for liming. Studies have shown that liming does not solve the problem of copper toxicity, since 50-80% of the precipitated copper remained in a form accessible to plants. The content of available copper in soils depended on the rate of liming, the initial copper content in drainage water and soil properties.
Research has established that typical symptoms of zinc deficiency were observed in plants grown in a nutrient medium containing 0.005 mg/kg of this element. This led to suppression of plant growth. At the same time, zinc deficiency in plants contributed to a significant increase in the adsorption and transport of cadmium. With an increase in the concentration of zinc in the nutrient medium, the intake of cadmium into plants sharply decreased.
Of great interest is the study of the interaction of individual macro- and microelements in the soil and in the process of plant nutrition. Thus, in Italy, the effect of nickel on the supply of phosphorus (32 P) to the nucleic acids of young corn leaves was studied. Experiments showed that a low concentration of nickel stimulated, and a high concentration suppressed the growth and development of plants. In the leaves of plants grown at a nickel concentration of 1 μg/l, the entry of 32 R into all fractions of nucleic acids was more intense than in the control. At a nickel concentration of 10 μg/L, the entry of 32 P into nucleic acids decreased noticeably.
From numerous research data, we can conclude that in order to prevent the negative impact of fertilizers on the fertility and properties of the soil, a scientifically based fertilization system should include the prevention or weakening of possible negative phenomena: acidification or alkalization of the soil, deterioration of its agrochemical properties, non-exchangeable absorption of nutrients, chemical absorption of cations , excessive mineralization of soil humus, mobilization of an increased amount of elements, leading to their toxic effect, etc.
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Kuban State University
Department of Biology
in the discipline "Soil Ecology"
"The Hidden Negative Effects of Fertilizers."
Performed
Afanasyeva L. Yu.
5th year student
(speciality -
"Bioecology")
I checked Bukareva O.V.
Krasnodar, 2010
Introduction………………………………………………………………………………...3
1. The influence of mineral fertilizers on soils…………………………………...4
2. The influence of mineral fertilizers on atmospheric air and water…………..5
3. The influence of mineral fertilizers on product quality and human health…………………………………………………………………………………………………………6
4. Geoecological consequences of the use of fertilizers……………………...8
5. Impact of fertilizers on the environment……………………………..10
Conclusion……………………………………………………………………………….17
List of references……………………………………………………………...18
Introduction
Soil contamination with foreign chemicals causes great damage to them. A significant factor in environmental pollution is the chemicalization of agriculture. Even mineral fertilizers, if used incorrectly, can cause environmental damage with a dubious economic effect.
Numerous studies by agricultural chemists have shown that different types and forms of mineral fertilizers have different effects on soil properties. Fertilizers applied to the soil enter into complex interactions with it. All kinds of transformations take place here, which depend on a number of factors: the properties of fertilizers and soil, weather conditions, and agricultural technology. Their effect on soil fertility depends on how the transformation of certain types of mineral fertilizers (phosphorus, potassium, nitrogen) occurs.
Mineral fertilizers are an inevitable consequence of intensive farming. There are calculations that to achieve the desired effect from the use of mineral fertilizers, global consumption should be about 90 kg/year per person. The total production of fertilizers in this case reaches 450-500 million tons/year, but currently their global production is 200-220 million tons/year or 35-40 kg/year per person.
The use of fertilizers can be considered as one of the manifestations of the law of increasing the investment of energy per unit of agricultural production. This means that to obtain the same increase in yield, an increasing amount of mineral fertilizers is required. Thus, at the initial stages of fertilizer application, an increase of 1 ton of grain per 1 ha is ensured by the introduction of 180-200 kg of nitrogen fertilizers. The next additional ton of grain is associated with a dose of fertilizer 2-3 times higher.
Environmental consequences of using mineral fertilizers It is advisable to consider from at least three points of view:
Local influence of fertilizers on ecosystems and soils into which they are applied.
Extreme influence on other ecosystems and their links, primarily on the aquatic environment and atmosphere.
Impact on the quality of products obtained from fertilized soils and human health.
1. The influence of mineral fertilizers on soils
In the soil as a system, the following occur: changes that lead to loss of fertility:
Acidity increases;
The species composition of soil organisms changes;
The circulation of substances is disrupted;
The structure is destroyed, worsening other properties.
There is evidence (Mineev, 1964) that a consequence of an increase in soil acidity when using fertilizers (primarily acid nitrogen) is an increased leaching of calcium and magnesium from them. To neutralize this phenomenon, these elements must be added to the soil.
Phosphorus fertilizers do not have such a pronounced acidifying effect as nitrogen fertilizers, but they can cause zinc starvation of plants and the accumulation of strontium in the resulting products.
Many fertilizers contain foreign impurities. In particular, their introduction can increase the radioactive background and lead to the progressive accumulation of heavy metals. Basic method reduce these consequences– moderate and scientifically based use of fertilizers:
Optimal doses;
Minimum amount of harmful impurities;
Alternation with organic fertilizers.
You should also remember the expression that “mineral fertilizers are a means of masking realities.” Thus, there is evidence that more mineral substances are removed with soil erosion products than are added with fertilizers.
2. The influence of mineral fertilizers on atmospheric air and water
The effect of mineral fertilizers on atmospheric air and water is mainly associated with their nitrogen forms. Nitrogen from mineral fertilizers enters the air either in free form (as a result of denitrification) or in the form of volatile compounds (for example, in the form of nitrous oxide N 2 O).
According to modern concepts, gaseous losses of nitrogen from nitrogen fertilizers range from 10 to 50% of its application. An effective means of reducing gaseous nitrogen losses is their scientifically based application:
Application into the root-forming zone for rapid absorption by plants;
Use of gaseous loss inhibitor substances (nitropyrine).
Phosphorus fertilizers have the most noticeable effect on water sources, in addition to nitrogen sources. The removal of fertilizers into water sources is minimized when applied correctly. In particular, it is unacceptable to scatter fertilizers on snow cover, disperse them from aircraft near water bodies, or store them in the open air.
3. The influence of mineral fertilizers on product quality and human health
Mineral fertilizers can have a negative impact on both plants and the quality of plant products, as well as on the organisms that consume them. The main such impacts are presented in tables 1, 2.
High doses of nitrogen fertilizers increase the risk of plant diseases. There is an excessive accumulation of green mass, and the likelihood of plant lodging increases sharply.
Many fertilizers, especially chlorine-containing ones (ammonium chloride, potassium chloride), have a negative effect on animals and humans, mainly through water, into which the released chlorine enters.
The negative effect of phosphorus fertilizers is mainly associated with the fluorine, heavy metals and radioactive elements they contain. Fluoride, when its concentration in water is more than 2 mg/l, can contribute to the destruction of tooth enamel.
Table 1 – Impact of mineral fertilizers on plants and the quality of plant products
| Types of fertilizers | The influence of mineral fertilizers |
|
| positive | negative |
|
| Increases the protein content in grain; improve the baking qualities of grain. | With high doses or untimely methods of application - accumulation in the form of nitrates, violent growth to the detriment of stability, increased incidence, especially fungal diseases. Ammonium chloride contributes to the accumulation of Cl. The main accumulators of nitrates are vegetables, corn, oats, and tobacco. | |
| Phosphorus | Reduce the negative effects of nitrogen; improve product quality; contribute to increasing plant resistance to diseases. | At high doses, plant toxicosis is possible. They act mainly through the heavy metals they contain (cadmium, arsenic, selenium), radioactive elements and fluorine. The main accumulators are parsley, onions, sorrel. |
| Potash | Similar to phosphorus. | They act mainly through the accumulation of chlorine when adding potassium chloride. With excess potassium - toxicosis. The main potassium accumulators are potatoes, grapes, buckwheat, and greenhouse vegetables. |
Table 2 - Impact of mineral fertilizers on animals and humans
| Types of fertilizers | Main impacts |
| Nitrogen - nitrate forms | Nitrates (MPC for water 10 mg/l, for food – 500 mg/day per person) are reduced in the body to nitrites, causing metabolic disorders, poisoning, deterioration of immunological status, methemoglobinia (oxygen starvation of tissues). When interacting with amines (in the stomach), they form nitrosamines - the most dangerous carcinogens. In children, it can cause tachycardia, cyanosis, loss of eyelashes, and rupture of the alveoli. In animal husbandry: vitamin deficiencies, decreased productivity, accumulation of urea in milk, increased morbidity, decreased fertility. |
| Phosphorus - superphosphate | They act mainly through fluoride. Excess of it in drinking water (more than 2 mg/l) causes damage to human tooth enamel and loss of elasticity of blood vessels. When the content is more than 8 mg/l – osteochondrosis phenomena. |
| Chlorine-containing fertilizers - potassium chloride - ammonium chloride | Consumption of water with a chlorine content of more than 50 mg/l causes poisoning (toxicosis) of humans and animals. |
The atmosphere always contains a certain amount of impurities coming from natural and anthropogenic sources. More stable zones with increased concentrations of pollution arise in places of active human activity. Anthropogenic pollution is characterized by a variety of types and numerous sources.
The main reasons for pollution of the natural environment with fertilizers, their losses and unproductive use are:
1) imperfection of technology for transportation, storage, mixing and application of fertilizers;
2) violation of the technology of their use in crop rotation and for individual crops;
3) water and wind soil erosion;
4) imperfection of the chemical, physical and mechanical properties of mineral fertilizers;
5) intensive use of various industrial, municipal and household wastes as fertilizers without systematic and careful control of their chemical composition.
Atmospheric pollution from the use of mineral fertilizers is insignificant, especially with the transition to the use of granular and liquid fertilizers, but it does occur. After the application of fertilizers, compounds containing mainly nitrogen, phosphorus and potassium are found in the atmosphere.
Significant air pollution also occurs during the production of mineral fertilizers. Thus, dust and gas waste from potash production includes emissions of flue gases from drying departments, the components of which are concentrate dust (KCl), hydrogen chloride, vapors of flotation agents and anti-caking agents (amines). In terms of its impact on the environment, nitrogen is of paramount importance.
Organic substances such as straw and raw sugar beet leaves reduced gaseous ammonia losses. This can be explained by the content of CaO in compost, which has alkaline properties, and toxic properties that can suppress the activity of nitrifiers.
Its losses from fertilizers can be quite significant. It is absorbed in field conditions by approximately 40%, in some cases by 50-70%, and immobilized in the soil by 20-30%.
There is an opinion that a more serious source of nitrogen loss than leaching is its volatilization from the soil and fertilizers added to it in the form of gaseous compounds (15-25%). For example, in European agriculture, 2/3 of nitrogen losses occur in winter and 1/3 in summer.
Phosphorus as a biogenic element is less lost into the environment due to its low mobility in the soil and does not pose such an environmental hazard as nitrogen.
Phosphate losses most often occur during soil erosion. As a result of surface soil washout, up to 10 kg of phosphorus is carried away from each hectare.
The atmosphere self-cleanses itself of pollution as a result of the deposition of solid particles, their washing out of the air by precipitation, dissolution in drops of rain and fog, dissolution in the water of seas, oceans, rivers and other bodies of water, and dispersion in space. But, as you know, these processes occur very slowly.
1.3.3 Impact of mineral fertilizers on aquatic ecosystems
Recently, there has been a rapid increase in the production of mineral fertilizers and the flow of nutrients into land waters, which has created a separate problem of anthropogenic eutrophication of surface waters. These circumstances undoubtedly have a natural relationship.
Water bodies receive wastewater containing many nitrogen and phosphorus compounds. This is due to the washout of fertilizers from surrounding fields into water bodies. As a result, anthropogenic eutrophication of such reservoirs occurs, their unhealthy productivity increases, there is an increased development of phytoplankton in coastal thickets, algae, “water blooms,” etc. Hydrogen sulfide and ammonia accumulate in the deep zone, and anaerobic processes intensify. Redox processes are disrupted and oxygen deficiency occurs. This leads to the death of valuable fish and vegetation, the water becomes unsuitable not only for drinking, but even for swimming. Such a eutrophicated reservoir loses its economic and biogeocenotic significance. Therefore, the struggle for clean water is one of the most important tasks of the entire complex of environmental protection problems.
Natural eutrophicated systems are well balanced. The artificial introduction of nutrients as a result of anthropogenic activities disrupts the normal functioning of the community and creates instability in the ecosystem that is fatal for organisms. If the flow of foreign substances into such reservoirs stops, they will be able to return to their original state.
Optimal growth of aquatic plant organisms and algae is observed at a phosphorus concentration of 0.09-1.8 mg/l and nitrate nitrogen of 0.9-3.5 mg/l. Lower concentrations of these elements limit algae growth. For 1 kg of phosphorus entering a reservoir, 100 kg of phytoplankton are formed. Water bloom due to algae occurs only in cases where the phosphorus concentration in water exceeds 0.01 mg/l.
A significant portion of nutrients enter rivers and lakes with runoff waters, although in most cases the washout of elements by surface waters is much less than as a result of migration along the soil profile, especially in areas with a leaching regime. Pollution of natural waters with nutrients due to fertilizers and their eutrophication occur, first of all, in cases where the agronomic technology for using fertilizers is violated and a set of agrotechnical measures is not carried out; in general, the farming culture is at a low level.
When using phosphorus mineral fertilizers, the removal of phosphorus with liquid runoff increases by approximately 2 times, while with solid runoff there is no increase in phosphorus removal or even a slight decrease.
With liquid runoff from arable lands, 0.0001-0.9 kg of phosphorus per hectare is removed. From the entire territory occupied by arable land in the world, which is about 1.4 billion hectares, due to the use of mineral fertilizers under modern conditions, about 230 thousand additional tons of phosphorus are removed.
Inorganic phosphorus is found in land waters mainly in the form of orthophosphoric acid derivatives. The forms of existence of phosphorus in water are not indifferent to the development of aquatic vegetation. The most accessible phosphorus is dissolved phosphates, which are used almost completely by plants during intensive development. Appatitic phosphorus, deposited in bottom sediments, is practically inaccessible to aquatic plants and is poorly used by them.
The migration of potassium along the profile of soils with a medium or heavy mechanical composition is significantly hampered due to absorption by soil colloids and the transition to an exchangeable and non-exchangeable state.
Surface runoff primarily washes away soil potassium. This finds corresponding expression in the potassium content in natural waters and the lack of connection between them and the doses of potassium fertilizers.
As for nitrogen fertilizers and mineral fertilizers, the amount of nitrogen in the runoff is 10-25% of its total input with fertilizers.
The dominant forms of nitrogen in water (excluding molecular nitrogen) are NO 3 , NH 4 , NO 2 , soluble organic nitrogen and suspended particulate nitrogen. In lake reservoirs, the concentration can vary from 0 to 4 mg/l.
However, according to a number of researchers, the assessment of the contribution of nitrogen to the pollution of surface and ground waters is apparently overestimated.
Nitrogen fertilizers, with sufficient amounts of other nutrients, in most cases contribute to intensive vegetative growth of plants, development of the root system and absorption of nitrates from the soil. The leaf area increases and, as a result, the transpiration coefficient increases, the plant's water consumption increases, and soil moisture decreases. All this reduces the possibility of nitrates leaching into the lower horizons of the soil profile and from there into groundwater.
The maximum concentration of nitrogen is observed in surface waters during the flood period. The amount of nitrogen washed out from catchment areas during the flood period is largely determined by the accumulation of nitrogen compounds in the snow cover.
It can be noted that the removal of both total nitrogen and its individual forms during the flood period is higher than the nitrogen reserves in the snow cover. This may be due to erosion of the topsoil and leaching of nitrogen with solid runoff.
The influence of mineral fertilizers on soil microorganisms and its fertility. Adding fertilizers to the soil not only improves plant nutrition, but also changes the conditions for the existence of soil microorganisms, which also need mineral elements.
Under favorable climatic conditions, the number of microorganisms and their activity after applying fertilizers to the soil increases significantly. The decomposition of humus increases, the mobilization of nitrogen, phosphorus and other elements increases.
After applying mineral fertilizers, bacterial activity is activated. In the presence of mineral nitrogen, humus is more easily decomposed and used by microorganisms. The application of mineral fertilizers causes a slight decrease in the number of actinomycetes and an increase in the fungal population, which may be a consequence of a shift in the reaction of the environment to the acidic side as a result of the introduction of physiologically acidic salts: actinomycetes do not tolerate acidification well, and the reproduction of many fungi is accelerated in a more acidic environment.
Mineral fertilizers, although they activate the activity of microorganisms, reduce the loss of humus and stabilize the level of humus depending on the amount of crop and root residues left.
The introduction of mineral and organic fertilizers into the soil increases the intensity of microbiological processes, resulting in a concomitant increase in the transformation of organic and mineral substances.
A characteristic indicator of increased microbial activity under the influence of fertilizers is the increased “breathing” of the soil, i.e., its release of CO 2 . This is the result of accelerated decomposition of soil organic compounds, including humus.
The application of phosphorus-potassium fertilizers to the soil does little to promote the use of soil nitrogen by plants, but enhances the activity of nitrogen-fixing microorganisms.
Sometimes the introduction of mineral fertilizers into the soil, especially in high doses, adversely affects its fertility. This is usually observed on low-buffer soils when physiologically acidic fertilizers are used. When the soil is acidified, aluminum compounds, which are toxic to soil microorganisms and plants, pass into the solution.
The addition of lime, especially together with manure, has a beneficial effect on saprotrophic microflora. By changing the pH of the soil in a favorable direction, lime neutralizes the harmful effects of physiologically acidic mineral fertilizers.
The effect of mineral fertilizers on yield is associated with the zonal position of soils. As already noted, in the soils of the northern zone, microbiological mobilization processes proceed slowly. Therefore, in the north there is a greater deficiency of basic nutrients for plants, and mineral fertilizers, even in small doses, are more effective than in the southern zone. This does not contradict the well-known position about the better effect of mineral fertilizers against the background of highly cultivated soil.
Natural organic fertilizers affect the soil in different ways: animals have a greater impact on its chemical composition, and plant fertilizers have a greater impact on the physical qualities of the soil. However, most organic fertilizers have a positive effect on the water-physical, thermal, and chemical properties of the soil, as well as on biological activity. In addition, it is always possible to combine several types of organic fertilizers, combining their positive properties (Kruzhilin, 2002). Organic fertilizers serve as the most important source of nutrients for plants (Popov, Khokhlov et al., 1988).
Under conditions of intensive chemicalization, it is of great importance to resolve issues of regulating the physical properties of soils, since the absorption of nutrients by plants is closely related to the water, air and thermal regimes of the soil, which in turn depend on the nature of the soil structure (Revut, 1964). The creation of water-resistant structural aggregates is largely related to the content and qualitative composition of humic substances. Therefore, the possibility of influencing the water stability of soil macroaggregates with the systematic application of manure and other organic fertilizers is of great interest to specialists. According to information available in the literature, organic fertilizers play a major role in improving these soil properties (Kudzin, Sukhobrus, 1966).
Organic fertilizers stabilize soil temperature, significantly reduce soil loss from erosion and surface runoff when manure is applied to the soil surface by 26%, and when plowed - by 10%.
With increasing doses of litter-free manure, the infiltration rate decreases, the resulting retarding infiltration layer reduces the total volume of large pores, and increases the volume of small ones, and the deposition of silt particles occurs in the pore system (Pokudin, 1978).
Almost all organic fertilizers are complete, as they contain nitrogen, phosphorus, potassium, as well as many microelements, vitamins and hormones in a form accessible to plants. In this regard, they find greatest use on soils with low potential fertility, such as podzolic and soddy-podzolic soils (Smeyan, 1963).
Thus, it has been established that the application of manure improves soil composition and increases the water strength of structural aggregates not only in the 20 cm layer, but also at great depths. Systematic application of manure improves the water-physical properties of the soil. The ability of organic fertilizers to increase absorption capacity, moisture holding capacity and other physicochemical properties is directly related to the content of organic matter in them. Therefore, bedding-free manure improves the physicochemical properties to the greatest extent (Nebolsin, 1997).