Scientific basis of crop rotations is a complex of reasons based on the experience and knowledge accumulated by science, stipulating the necessity of crop rotation.
D.N. Pryanishnikov first summarized these reasons on the basis of works devoted to:
plant nutrition – the humus theory of A. Thayer, the theory of mineral nutrition by J. Libich;
formation and accumulation of harmful substances in the soil under no-till crops by R.K. Maker, A. de Candolle et al;
symbiotic ability of leguminous crops and different influence of plants on soil properties, first of all on structure by P.A. Kostychev and V.R. Williams.
Causes of alternation are divided into:
- physical;
- chemical;
- biological;
- economic.
Many years have passed since D.N. Pryanishnikov’s generalization, the knowledge in this direction has significantly expanded, however, the four groups of causes highlighted by him remain relevant.
Crop attitudes towards permanent and repeated crops
Today’s tough market conditions dictate the requirement for the possibility of flexible changes in the structure of sown areas, both by changing crop rotations, and the use of repeated and permanent crops. Therefore, profound knowledge in the theory and practice of crop rotation in this direction allows agronomists and managers of enterprises to increase the sustainability of agribusiness.
According to the results of long-term experiments, different attitudes of crops to permanent crops have been established.
Grain crops, especially winter crops, as well as in the absence of fertilizers show the greatest sensitivity to permanent crops. Yield gains from the introduction of crop rotation are greater than from fertilizer and range from 50 to 73%.
Table. Effect of fertilizers and crop rotation on crop yields, t/ha[1]Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. - M.: Publishing house "Kolos", 2000. - 551 p.
| Winter wheat | ||||||
| Spring wheat | ||||||
| Winter rye | ||||||
| Barley | ||||||
| Oats | ||||||
| Potatoes | ||||||
| Corn for silage | ||||||
| Sugar beet | ||||||
The use of fertilizers slightly reduces the effect of permanent crops, crop rotation in this case increases the yield by 30,0-34,2% for spring cereals and by 34,2-53,4% for winter cereals, which allows the use of permanent crops on a high fertilized background and after good predecessors.
Corn for silage and potatoes are less sensitive to permanent crops. Corn increases yields from crop rotation by 10%, while fertilizer increases yields by 90%, for potatoes by 30 and 60%, respectively. The effect of increasing the yield of these crops from crop rotation regardless of soil fertilization was less significant than for cereals. Thus, in the experiments of the Moscow Agricultural Academy, the yield of winter rye and oats for 69 years (on average) in the rotation without fertilizers was higher by 93% and 76%, respectively, than in the permanent crops, while for potatoes by 16%. Similar results were obtained at the Rothamsted experimental station in England for winter wheat and in Halle (Germany) for winter rye.
For example, farms near Moscow on floodplain fertile well-heated soils were able to obtain good yields of corn for silage for 25-30 years with permanent seeding. Thus, with good fertilization and high agrotechnics, corn for silage can be grown continuously for 10-15 years without a noticeable decrease in yield.
Sugar beet also showed high sensitivity: on unfertilized background yield increase was 2-2.5 times, on fertilized one – 60-70%.
Fiber flax, leguminous, sunflower for seeds sharply reduce the yield when sown in permanent crops, with prolonged cultivation the crops can completely die.
A number of agricultural practices, such as irrigation and fertilization, reduce the impact of permanent crops. In the forest-steppe zone, sugar beet does not withstand permanent crops, dramatically reducing yields, while in the conditions of irrigated agriculture in Central Asia the reduction of yields is much lower. Similar is the attitude of cotton and rice to repeated sowing.
Vegetable crops, according to the research of the All-Russian Research Institute of Vegetable Farming, also showed different effects on permanent crops. Moreover, this influence remains within the crops of the same family, for example, nightshade: tomato, eggplant, pepper; cabbage: cabbage, radish (Raphanus sativus var. radicula), turnip, radish (Raphanus sativus L.), regardless of the sequence of rotation.
Table. Influence of permanent and repeated sowing on the yield of vegetable crops, t/ha[2]Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. - M.: Publishing house "Kolos", 2000. - 551 p.
| 1 year (crop rotation) | |||||||
| 2 years (repeat seeding) | |||||||
| 3 years (repeat seeding) | |||||||
| 4 years (permanent seeding) | |||||||
In general, all crops respond differently to permanent crops. This effect may vary depending on soil and climatic, agrotechnical and other conditions.
All crops can be divided into groups according to their relation to permanent crops.
The first group of crops that do not withstand repeated and even more so the permanent crops. These include sunflower (return to the same place not earlier than 8 years), sugar beet (not earlier than 3-4 years), flax (not earlier than 5-6 years), peas, beans, vetch, clover. Vegetable crops: tomato, eggplant, pepper, cabbage, cucumber. Periodicity of return to the same field for most crops of the group is usually not less than 3-4 years.
The second group of crops that are resistant to repeated sowing without a noticeable decrease in yields. They include barley, oats, winter and spring wheat, winter rye, millet, potatoes, buckwheat, carrots, green vegetables. Resistance of crops of this group strongly depends on the conditions of cultivation. For example, in conditions of the Non-Black Soil Zone, repeated sowing of winter wheat is undesirable, while in steppe areas of the Northern Caucasus and South-East – acceptable, or repeated sowing of spring wheat is undesirable in European Russia, but acceptable in steppe areas of Trans-Ural, Volga, Western Siberia, Altai after bare fallow.
The third group of crops weakly responsive to crop rotation and resistant to permanent crops. They include rice, corn, hemp, tobacco, and cotton. Despite the self-compatibility of crops in this group, it is recommended to alternate them periodically with leguminous, cereals, and other crops. The periodicity of intercropping corn and hemp is 4-6 years or more. Rice, cotton and tobacco, it is also desirable to change periodically with alfalfa, sugar beets, legumes, cereals, etc.
Such a division of crops is rather arbitrary, but it allows one to use it when developing crop rotations, taking into account the principle of compatibility and incompatibility of crops and the principle of periodicity of returning crops to the same field.
The use of varieties resistant to characteristic diseases and pests is a separate method of increasing the resistance of crops to repeated sowing. Chemical and biological preparations can have a similar effect. For example, the use of fusarium-resistant varieties of fiber flax, clubroot-resistant varieties of cabbage, and orobanche-resistant varieties of sunflower can reduce the period of returning to their previous location or cultivating them repeatedly. Application of nematicides – preparations to control beet nematode – allows the use of repeated sowing of sugar beet.
Chemical reasons for crop rotation
The chemical reasons for crop rotation are related to the differences in crop needs for chemical nutrients and the ability to assimilate their hard-to-reach forms.
No single crop is able to increase the accumulation of ash elements in the soil (all except nitrogen), however, crop rotation allows a more rational use of their soil reserves and increase the efficiency of fertilizers.
Thus, crops with deep-rooted system use moisture and nutrient reserves from subsoil layers, and their root residues enrich these layers with organic matter and mineral elements. Deeply penetrating root systems (up to 3 meters and more) have alfalfa, clover, lupine, gourds. At the same time, flax, buckwheat, millet, annual grasses, rape, cucumber, and onion have shallow root systems.
Chemical reasons of alternation are related to the balance of nutrients within the plant. Part of the nutrients is alienated with the harvest and fodder, the other – in the form of plant remains returns back with straw, manure, etc. These features are taken into account when building a crop rotation.
Crops affect the balance of soil organic matter to varying degrees. By leaving plant and root residues after harvest, soil reserves are replenished. However, crops differ in the amount of residues left behind.
In terms of the amount of crop residues left in the soil, plants are arranged in the following sequence in descending order:
- Non-chernozem zone of Russia: perennial grasses – corn for silage – winter cereals – spring cereals – grain legumes – potatoes;
- Forest-steppe zone of Russia: perennial grasses – winter wheat – corn for grain and silage – spring cereals – sunflower – grain legumes – sugar beet.
By changing the structure of cultivated areas it is possible to simulate the balance of organic matter. For example, increasing the share of perennial grasses in the cropping pattern leads to an accumulation of organic matter with a slowing down of its decomposition while reducing the content of available nutrients in the soil.
On the contrary, the increase in the structure of cultivated areas of row crops and bare fallow under conditions of insufficient organic fertilizers leads to a decrease in the reserves of organic matter in the soil.
Introduction of intermediate and green manure crops, such as seradella, sweet clover, lupine, into crop rotation allows to additionally increase the supply of crop residues. In the southern regions under irrigated conditions they leave up to 10 t/ha of residues in one rotation of crop rotation, in the southwestern and central part of the Non-Chernozem region – 3-5 t/ha.
In addition to the accumulation of organic matter, plant residues leave 21.5-51.5% of nitrogen, 1.7-48.1% of potassium, 18.5-51.7% of phosphorus of their total amount in the crop.
Nitrogen
Permanent crops of some crops that consume large amounts of soil nitrogen, such as sugar beets, corn for silage, cabbage, cotton can lead to nitrogen depletion of the soil.
Other crops that promote nitrogen fixation processes by nodule bacteria, primarily legumes (peas, vetch, alfalfa, clover, lupine, seradella, chinna, sainfoin, chickpeas, vigna), on the contrary, are able to accumulate nitrogen annually. For example, annual legumes (peas and vetch) under favorable conditions accumulate up to 50-70 kg of nitrogen per 1 ha; perennial leguminous grasses (clover, alfalfa, sainfoin) accumulate up to 120-150 kg of nitrogen per 1 ha, which is equivalent to the application of 400 kg of ammonium nitrate.
However, repeated and permanent sowing of legumes leads to leaching of accumulated and unused nitrogen from soil to groundwater, as well as to the accumulation of phytotoxic substances, i.e. soil fatigue, resulting in a sharp decrease in yields.
Therefore, alternating legume crops with nitrogen-absorbing crops such as cereals or row crops eliminates the negative effects of permanent cultivation, which ensures the rational use of accumulated nitrogen.
Phosphorus
Potatoes, legumes and winter cereals are distinguished by high phosphorus removal with the harvest.
Crops exhibit different ability to assimilate hard-to-reach forms of soil phosphorus and fertilizers. The greatest ability to absorb hard-to-reach forms is noted in lupine, oats, buckwheat, potatoes, mustard, sugar beets, Hungarian sainfoin, which due to root excretions convert hard-soluble phosphates of soil and phosphate meal into soluble forms.
The alternation of these crops allows a more efficient use of soil phosphorus reserves.
Potassium
The greatest need for potassium is observed in sugar beets – up to 200 kg K2O at a yield of 30 t/ha, potatoes – up to 300 kg K2O at a yield of 30 t/ha, grain crops – up to 50-60 kg K2O at a yield of 3 t/ha, as well as forage root crops, cotton and vegetable crops.
Other nutrients
Physical reasons for crop rotation
Physical reasons of crop rotation are caused by the influence of crops on the texture, density, structure, water regime of soils and resistance to erosion processes. The causes of such influence are biological and morphological properties of crops, primarily the mass, distribution of roots and decomposition of plant residues, as well as the peculiarities of agrotechnics of cultivation.
The dense above-ground part, first of all, of continuous crops (legumes and cereal perennial grasses) contributes to soil protection from erosion, improvement of water and thermal soil regimes, and the organic matter formed from the decomposition of plant residues affects the agrophysical indicators of soil fertility.
Influence on the structure
In terms of the ability of crops to structure, they can be lined up in descending order: perennial grasses – annual legume-grass mixtures – winter cereals – corn – spring cereals – fibre flax – potatoes – root crops.
Perennial grasses
Perennial grasses are able to accumulate a mass of plant residues equal to the mass of the harvested crop. Their root system, penetrating to a great depth, thanks to numerous branching roots, penetrates and divides the soil into individual clumps. After the root residues die off, the clumps are enriched with organic matter, thus creating a water-resistant structure.
Deep penetration and root mass of perennial grasses affects the soil layers below the tilled layer. Clover on sod-podzolic soils enriches the underlying layers with humus and contributes to deeper cultivation of the layer. Alfalfa on saline soils loosens the dense subsoil layer with its roots, creating favorable conditions for subsequent crops.
Cereal crops
Winter cereal crops have the greatest effect of physical change of soils. Unlike spring crops with a shorter growing season, they develop a powerful root system, which in the fall and spring binds the soil and protects it with green cover from destruction by precipitation and melt water.
Tilled (row) crops and bare fallow
Small amounts of crop residues, crops with wide rows and intensive tillage in row crops in most cases contribute to the destruction of soil structure and do not provide sufficient protection against erosion, especially in repeated and permanent cultivation.
Bare fallow has an even greater negative impact on soil structure.
As the long experience of the Moscow Agricultural Academy named after K.A. Timiryazev, the negative effect of bare fallow and row crops on the structure can be reduced by the use of fertilizers, primarily organic ones.
Table. Weight of structural aggregates with a diameter of more than 0.25 mm in the arable soil layer under the permanent crops and bare fallow, % (according to Dospekhov)[3]Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. - M.: Publishing house "Kolos", 2000. - 551 p.
| Clover | |||
| Winter rye | |||
| Oats | |||
| Potatoes | |||
| Bare fallow |
Influence on the water regime of soils
Crops consume soil moisture to varying degrees. The indicator of consumption is the transpiration coefficient.
Technical crops (sunflower and sugar beet) and perennial grasses (alfalfa and Hungarian sainfoin) have the highest water consumption, which dries up the soil to a great depth, which can affect the yield of subsequent crops. Winter crops require more moisture than spring crops. Millet and sorghum consume the least water: for formation of 100 kg of dry matter millet spends 30 t of water, oats and barley – 45-50 t.
The period between harvesting of the preceding crop and sowing of the following one influences the water supply in the crop rotation. During this period, moisture is accumulated due to precipitation and melt water, which is especially important in arid regions.
Alternation of crops in the rotation with different water consumption and depth of root penetration allows to regulate water reserves in the soil.
Root penetration depth for crops:
- flax – 0.8-1 m;
- potatoes – 0,8-1 m;
- winter wheat and rye – 1,5-1,6 m;
- corn and castor beans – 2-2,5 m;
- sugar beet and sunflower – 3-3,5 m;
- alfalfa – 4-5 m.
The greatest effect of moisture accumulation is achieved by using bare fallows, which guarantees high yields of winter and spring wheat in arid areas of the steppe zone.
Biological reasons for crop rotation
Biological reasons for crop rotation are due to different attitudes to diseases, pests and weeds. This is due to the fact that each crop is characterized by its own pests, diseases and weeds. Permanent or repeated crops contribute to the exponential accumulation of characteristic disease-causing organisms, which can lead to the complete death of crops.
D.N. Pryanishnikov gave numerous examples of attempts of permanent cultivation of a number of crops, which ended unsuccessfully first of all because of accumulation of pests and diseases:
- for cotton – Mexican weevil and wilt disease;
- sugar beet – nematodes and beet weevil;
- sunflower – blight and diseases of white and gray rot, etc;
- flax – fusarium, flax weevil and extremely low competitiveness to the majority of weeds;
- clover – clover weevil, anthracnose, cancer, fusarium;
- cereal crops – root rot, Swedish fly, spittlebug, mass infestation of winter crops with broom (Apera), brome (Bromus), cornflower (Centaurea), chamomile (Matricaria);
- spring crops – infestations of wild oat (Avena fatua), barnyard grass (Echinochloa crus-galli), etc.
Specificity of these pests to particular crops makes even modern methods of pest control ineffective. That puts crop rotation in the first place.
At the same time specificity of pests makes them relatively harmless to other crops, due to which crop rotation allows to control prevalence and harmfulness of the majority of them.
Accumulation of pathogens
Accumulation of pathogens (fungi, bacteria, viruses) occurs in the soil and on plant residues. For example, flax, if it is cultivated continuously, dies because of the accumulation of the fungus that causes fusariosis. Sunflower when returned to its original place earlier than 7-8 years is affected by powdery mildew, so crop rotations with a short rotation are not suitable for its cultivation. Cultivation of corn without rotation contributes to accumulation of Fusarium and bladder blight pathogens, of winter wheat – the causative agents of brown rust and dusty mildew, and of cotton – the causative agents of wilt.
The causative agents of root rot of barley and wheat are harmless for oat crops, which is why oats are recognized as a “sanitary” crop in crop rotations. Winter rye can be greatly affected by ergot, but this disease does not harm other crops. Cabbage blight only affects plants in the cabbage family, but does not affect nightshades, umbrellas, or other families.
The main source of conservation and spreading of diseases, primarily fungal ones, is plant residues of host plants. Therefore, soil liberation from pathogens is associated with the rate of residue decomposition.
The main role in the decomposition of plant residues is played by saprophytic microorganisms, which are competitors for life factors with pathogenic fungi. Therefore, all techniques aimed at increasing the activity of soil saprophytes contribute to reducing the number of pathogens, i.e. improve the phytosanitary state of the soil. This is achieved by applying manure, application of green manure and mineral fertilizers, cultivation of legumes, loosening the soil and other methods.
Cultivation of row crops and fallowing, observance of periodicity of returning crops to the same place and refusal of repeated sowing contribute to the reduction of soil pathogens.
Flax is one of the most susceptible crops to diseases caused by pathogenic fungi, primarily fusarium. According to the All-Russian Flax Research Institute, fusarium pathogens can persist in the soil for 5-6 years, which determines the periodicity of flax returning to its previous location. The use of Fusarium-resistant varieties makes it possible to reduce the frequency of return.
Cultivation of potatoes in crop rotation reduces by 4-5 times the incidence of scab and verticillosis diseases.
Not adhering to the recommended timing of sunflower return, according to the All-Russian Research Institute of Oilseeds, increases the infestation of sclerotinia, powdery mildew, and dry rot, which reduce yields by 30-40%.
One common disease among vegetable crops that develops with repeated crops is clubroot in cabbage. Clubroot-resistant varieties have been developed that allow repeated sowing for cabbage, along with its alternation with crops of other families.
Soil fatigue
Soil fatigue is the accumulation of root excretions in the soil that suppress plant growth. Soil fatigue is also associated with the accumulation of characteristic pathogens and their products.
Weeds
Weeds, due to their property of quickly adapting to growing conditions, have become specific to certain crops. Therefore, no-till and repeated sowing leads to the accumulation of specific weeds.
For example, wild oat (Avena fatua) is a specific weed of early spring cereal crops, primarily oats. Boll (Agrostemma), larkspur (Delphinium), shepherd’s purse (Capsella), stinkweed (Thlaspi arvense), bachelor’s button (Centaurea cyanus) grow mainly in winter rye and winter wheat crops; Amaranthus, barnyard grass (Echinochloa crus-galli), mugwort (Setaria pumila), green foxtail (Setaria viridis) – in crops of rice, millet and corn.
The permanent crops of winter crops increase the number of winter and wintering weeds, the late spring crops – late spring weeds, the fields of perennial grasses – perennial, biennial, wintering and winter weeds.
Cultivated plants exhibit various competitive abilities in relation to weeds. Sowings of summer grasses, winter rye, and winter wheat show high competitiveness. Flax, sugar beet and spring wheat crops are characterized by weak competitiveness. Barley and corn crops are characterized by medium competitiveness. Some crops may exhibit high competitiveness to some weeds and low competitiveness to others.
Crops of row crops and bare and seeded fallow crops have the most favorable conditions for weed control, thanks to frequent weeding and tillage. Correct alternation with crops of continuous crops, allows to keep under control the weed infestation of fields. Increasing the proportion of continuous crops in the cropping pattern increases the weediness of fields, while increasing the proportion of row crops and fallows decreases it.
Sunflower, corn, castor bean, and hemp are capable of natural weed suppression due to wide leaves and stem height. Winter wheat and winter rye also have this ability due to rapid growth in the spring, outrunning many weeds.
Table. Weediness of winter wheat crops depending on crop rotation and fertilizers[4] Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. - M.: Publishing house "Kolos", 2000. - 551 p.
| Early potatoes | ||||
| Clover | ||||
| Corn for green fodder | ||||
| Peas | ||||
| Permanent seeding (3-4 years) | ||||
According to S.A. Vorobyov’s research, the weed infestation in the winter wheat crops in the conditions of the Moscow region was 4-5 times higher than after the predecessors.
Crop rotation makes it possible to maximize the competitive advantage to control specialized weeds of other crops. For example, spring crops crops suppress weeds characteristic of winter crops, primarily winter and biennial plants. On the contrary, crops of perennial grasses and winter crops sharply suppress early and late spring weeds.
Pests
Similarly to pathogens and weeds, favorable living conditions and distribution of pests characteristic of the crop are created in repeated and permanent crops. Thus, the reproduction of nematodes and beet weevil in repeated crops of sugar beet increases, while in millet crops – the millet weevil. Irregular crop rotation and shortening of the period of return to the previous location in spring and winter wheat crops result in accumulation of beetles, grain sawfly, Swedish and Hessian flies, lapwing beetle, and cougar beetle. Crop rotation, along with the use of pesticides, can significantly reduce the population of many pests and reduce the damage caused by them.
In cases of resistance of some pests to control means or low efficiency of pesticides, crop rotation becomes of primary importance in the struggle, especially against nematodes.
According to the data of Bashkir State Agrarian University, the area of nematode infestation of permanent crops of winter rye has increased to 66% and that of spring wheat to 91.3%. Reduction of yield during repeated sowing of sugar beet on the fields heavily infested with nematode was 60-70%.A similar situation was observed in repeated sowing of potatoes or their frequent return of potato nematode.
In addition to the cultivation of crops in the same location contributing to the accumulation of crop-specific pests, the effect of preceding crops on subsequent crops should also be considered. For example, crops of perennial grasses contribute to the spread of the wireworm, which strongly damages subsequent crops, such as cereals, corn, and potatoes. According to S.A. Vorobyov, in the fields of the Mikhailovskoe farm of the Timiryazev Moscow Agricultural Academy near Moscow, the number of wireworm larvae in winter wheat cultivated after corn for silage was 13 larvae per 1 m2, while 88 larvae were found after clover in the 2nd year of use.
Economic reasons for crop rotation
Economic reasons for crop rotation are conditioned by the structure of sown areas, natural and economic factors of agricultural production in order to ensure maximum profitability under the condition of stable farming.
The structure of sown areas are developed under the conditions of a particular enterprise on the basis of production plans, taking into account the productivity and economic efficiency of crops and the impact on soil fertility. Different plants in different soil and climatic conditions may give different amounts of fodder units of different quality, which is associated with their biological characteristics. For example, sugar beet or corn, in one zone can give a high yield per unit area and therefore be economically profitable, in another zone, on the contrary, give a low yield and be unprofitable.
In economic terms, crop rotation should ensure:
- maximum rational and productive use of land with simple or extended reproduction of fertility;
- demand of an enterprise (if necessary) for fodder and seeds;
- uniform use of machinery;
- the implementation of modern intensive technologies;
- effective labor organization.
As D.N. Pryanishnikov noted, economic necessity of crop rotation is connected with different quantity and distribution of labor in time necessary for cultivation of different crops in a farm.
Thus, cultivation of early and late spring crops due to different terms of sowing and harvesting allows reducing the load on people and machinery in the same period by 2 times than when cultivating only early or only late spring crops. The addition of winter crops allows even more even distribution of the intensity of field work.
The use of varieties of different maturity dates has a similar effect.
In this case, the risk of non-compliance with the optimal timing of field work is reduced.
A certain ratio of cereals, industrial and forage crops allows to build a balance of manure-forming (forage) and manure-consuming (grain, row crops) plants.
Economic reasons are related to other reasons for crop rotation, as proper crop rotation, contributes to higher economic returns of production. For example, with the help of crop rotation in combination with a number of agricultural practices it is possible to reduce the weed infestation of crops, reduce the population of pathogens and pests to the economic threshold of harmfulness, thereby reducing the cost of agrochemicals and increasing yields, which increases the profitability of production.
Ecological reasons for crop rotation
The ecological reasons for crop rotation are due to the replacement or reduction of agrochemical use through the positive impact of properly constructed crop rotations on the weed infestation of fields and populations of harmful organisms. Moreover, crop rotation plays an important role in the system of conservation agriculture.
Thanks to the use of agrotechnical and biological methods of controlling weeds and pests, the oversaturation of land with pesticides is prevented, which contributes to pollution of soils and groundwater by residual amounts of agrochemicals.
Agro-ameliorative measures aimed at protecting the soil and the environment include:
- creation of buffer strips along field boundaries;
- planting of protective forest plantations;
- creation of a network of roads on fields;
- organization of moisture retention systems for precipitation and melt water;
- construction of irrigation systems, etc.
In addition to ameliorative measures, soil protective measures include special agrotechnical methods of contour tillage and shelterbelt and kuli placement of crops.
This provision is regulated by the Federal Law of the Russian Federation “On Environmental Protection”, aimed at reducing the ecological threat associated with agricultural activities. Thus, crop rotation is an integral part of ecological land use within the boundaries of single agro-landscapes.
Prevention of water erosion of agricultural lands that are part of agrolandscape (meadows, pastures, forests) is achieved by using special contour tillage methods (plow subsurface, mole cutting, ridging). Prevention of wind erosion, for example, in steppe areas, the shelf placement of crops of crop rotation and bare fallows across the prevailing winds is used, combining them with the coulisses in the system of non-moldboard-and-ploughshare tillage. Thus, the system of crop rotations, as well as a single crop rotation, perform a soil-protecting function.
The ecological function of crop rotations is manifested in their ability to reduce the content of harmful substances, pesticides and growth regulators accumulated from industrial agricultural activities, reducing the risk of their penetration with runoff water into rivers, reservoirs and groundwater.
Sources
Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. – Moscow: Publishing House “Kolos”, 2000. – 551 с.
Fundamentals of agricultural production technology. Farming and crop production. Edited by V.S. Niklyaev. – Moscow: Bylina, 2000. – 555 с.
Fundamentals of Agronomy: Tutorial/Y.V. Evtefeev, G.M. Kazantsev. – M.: FORUM, 2013. – 368 p.: ill.