Soil erosion is the destruction of soil by water and/or wind. The word “erosion” comes from the Latin “erosio,” which means erosion or destruction.
In the history of agriculture there are many facts of destruction and degradation of soils. According to various estimates, about 2 billion hectares of arable land have been destroyed by erosion in the last 200 years, which exceeds the currently cultivated area of about 1.5 billion hectares.
A distinction is made:
- depending on the factor of destructive impact:
- water erosion;
- wind erosion, or deflation;
- combined erosion which combines water and wind erosion.
- depending on the speed of the process:
- normal, or geological, or natural;
- accelerated, or destructive, or anthropogenic.
Contents
- Distribution areas
- Factors of erosion development
- Mechanism of water erosion development
- Irrigation erosion
- Mechanism of wind erosion development
- Mechanism of combined action of water and wind erosion
- Classification of soil erodibility
- Erosion control measures
- Soil-protecting complexes
- Damage caused by soil erosion
- Sources
Irrigation erosion is possible in areas of artificial irrigation and mudflows in mountainous areas.
Normal erosion is characteristic of areas with natural vegetation cover, where soil losses can be restored in the course of soil formation. Accelerated erosion occurs when natural vegetation is removed, improper use of land is observed in areas with dissected relief, more often in the steppe and forest-steppe zones, where special anti-erosion measures are neglected.
The most dangerous type of water erosion is gully erosion, which leads to the formation of ravines with loss of area. Among wind erosion are dust storms, or black storms, which destroy crops and sweep away the top layer of soil in a few hours, capable of filling irrigation networks and reservoirs.
In the forest-steppe and often in the steppe zones of Russia, the simultaneous manifestation of water and wind erosion – combined erosion is possible. Combined erosion manifests itself in the following aftermath:
- runoff and washout of the soil in the spring period,
- desiccation,
- spraying, especially with repeated tillage,
- deflation (blowing out, scattering, carry-over) or severe spraying in dry years
- with repeated tillage,
- stormwater runoff in summer,
- severe washout and erosion of soil.
There may be cases when arable layer is almost completely washed away by water and carried away by wind. On heavily sprayed fields, wind erosion of the topsoil can be observed in a few hours after precipitation.
Distribution areas
The northern border of the wind erosion zone runs along the line Voronezh – Samara – Chelyabinsk – Petrozavodsk – Omsk – Novosibirsk and further in Eastern Siberia: Khakassia, Buryatia, Tuva, Chita region. Therefore, all arable lands and pastures located to the south apply soil protection measures against wind erosion. Regions with a high risk of wind erosion development: the Volga region, the North Caucasus, the Urals, Siberia. The total area of agricultural land at risk of wind erosion is more than 45 million hectares, of which 28.7 million hectares is arable land.
According to the data of land balance in the Russian Federation, there are 36.5 million hectares of agricultural land subject to water erosion, including 24.7 million hectares of arable land. Water erosion caused by melt and storm water is mainly manifested in the forest-steppe zone. Areas of Central Black Earth zone, Volga region, Central region, Northern Caucasus are most exposed to water erosion. Meltwater runoff here reaches 80-100 mm (l/m2).
In the Non-Black Earth zone, much of the agricultural land is located on sloping lands. According to the estimates of the Russian Research Institute of Farming and Soil Erosion Protection 34% of arable lands in this zone are situated on slopes less than 1 degree, from 2 to 3 degrees – 3%, from 3 to 5 degrees – 17%, from 5 to 7 degrees – 7%, more than 7 degrees – 3%. 38% of the arable land is eroded and 62% is in erosion hazardous condition.
It is known quite a lot of examples when the spreading of erosion took place on vast territories rather quickly and led to soil depletion and land destruction. Erosion is causing significant damage to land in Canada, China, India, Australia, most countries in Africa, Europe and Asia. For example, 300 years ago the southern boundary of the Sahara Desert was 400 km north of where it is today.
About 40 million hectares of arable land in the U.S. from erosion by the mid-50s was destroyed, 20 million hectares of which were withdrawn from use. At present, about 115 million hectares of arable land in the United States are completely destroyed or seriously damaged, and 313 million hectares are subject to varying degrees of erosion processes.
In Russia intensive soil erosion started in the second half of the 19th century. Plowing of new lands by destroying forests and herbaceous vegetation with low level of agrotechnics in conditions of plain relief led to rapid development of erosion, first of all in the Central Black Earth zone.
In 1846 in the Central Black Earth zone of Russia 41,2% of the territory was arable, 20 % – forest, 23,2% – virgin lands. By 1887 the area of arable land had grown to 69%, and the area of forests and virgin lands had fallen to 25.6%. In 1914, the share of arable land was already about 80%, the area of forests – 6-7%. Currently, in some regions the share of arable land reaches 90% and more.
According to Goskomzem (State Committee on Land Resources) on January 1, 1996 over 117 million ha of 210 million ha of agricultural land are considered erosion hazardous and exposed to water and wind erosion, 51 million ha of which are eroded, 84.8 million ha of arable land and 35.1 million ha of pastures, 28.7 million ha and 14.4 million ha respectively. Soil erosion control is the most important link in the system of agricultural production development measures.
Factors of erosion development
In constructing scientifically sound erosion control and prevention measures, it is important to understand the patterns and causes of the spread of erosion processes. The degree of manifestation of erosion depends on:
- climate,
- soil and vegetation cover,
- topography,
- geology,
- economic purpose of the land.
Climatic factors
Climatic factors of water erosion development, first of all, include atmospheric precipitation and regime of their fallout, especially heavy rainfalls, which are the most dangerous in the period of insufficient development or absence of vegetation on the soil surface.
In one downpour, depending on the intensity of rain and steepness of slope, from 1 hectare of arable land is washed away from 10 to 50 tons of soil. The whole arable layer and gully growth up to 30-50 m can be washed away.
Soil erosion from melt water runoff is widespread in the Non-Black Soil and Central Black Soil zones, in the Volga region and Western Siberia. Average annual water reserve of snow cover reaches 100 mm and more. When melting in spring, this mass of water drains from the fields in 7-10 days, destroying the soil up to the formation of ravines.
Erosion resistance
Erosion resistance of soils is a factor of erosion development, which depends on the physical-chemical, water-physical properties and granulometric composition of the soil: humus content, composition of the absorbed complex, friability of the composition, water permeability, watertight structure.
Relief
Soil washout increases directly proportional to the slope. Increase of soil slope from 2 to 4° leads to 1.8 times increase of soil washout, from 4 to 8° – 7.2 times. Slope length also influences on water erosion. According to data of A.D. Orlov, washout increases 2.9-3.7 times in case of doubling of runoff line from 50 to 100 m.
The shape and exposition of slopes have a significant influence on soil washout. For example, southern slopes are often more eroded than northern and northeastern ones. Contour tillage of soils is carried out on difficult slopes.
Vegetation cover
Vegetation cover can reduce or completely prevent the development of water and wind erosion. The stronger and more powerful the vegetation cover, the higher its anti-erosion properties. The vegetative mass protects the soil from the destructive power of raindrops, and the root systems bind the soil particles, preventing soil erosion and washout. The degree of protective properties of vegetation cover is expressed by the erosion hazard coefficient.
Perennial grasses have the best soil-protecting properties. Their developed vegetative mass and powerful root system protect the soil from erosion processes and enrich it with organic matter. Winter crops have good soil-protecting properties. Row crops and bare fallow practically do not protect the soil from erosion.
Table. Erosion hazard coefficients
| Bare fallow | |
| Row | |
| Spring cereals | |
| Winter cereals | |
| Perennial grasses |
Soil protection capacity of crops is determined by biological and agrotechnical peculiarities, as well as the rainfall regime. Thus, in areas where water erosion is caused by melt water, perennial grasses have the greatest anti-erosion value, while winter, spring and leguminous crops have good protective properties under runoff associated with summer showers.
Soil-protective role of field crops depends on the phase of plant development, which is conditioned by the state of aboveground vegetative mass and root system during erosion-dangerous periods. The more developed the green mass, fuller coverage of the soil surface, and more powerful the root system, the more reliable is the protection from erosion.
Soil protection capacity of cultivated crops is calculated by the weighted average value of projective coverage in erosion hazardous period according to the formula:
Pa/w = 100(P1S1 + P2S2 + P3S3 + … + PnSn),
where Pa/w – weighted average projective soil coverage by crop of the rotation, P1, P2, P3, Pn – projective soil coverage by each crop, S1, S2, S3, Sn – area occupied by each crop, % of total area of crop rotation or arable land.
Thus, average weighted projective soil coverage by crops by ten-days or months of the growing season, taking into account the precipitation regime and the phase of plant development are determined.
Geological factors
Geological factors of the territory determine the potential possibility and character of erosion. They include the stability of rocks, the specificity of their occurrence, and the manifestation of various exogenous and endogenous processes. For example, loess-like loams of Altai Priob’ye, on which the soil cover lies, are easily eroded and destroyed by water flows. Large gullies, ravines, depressions and canyons can be formed in a short period of time.
Granulometric composition, genesis, soil type, as well as humus content, composition, structure and water strength of soil are the factors determining the development of erosion processes.
Black earth and sod-podzolic loamy soils are more resistant to water and wind erosion.
The natural conditions for the development of wind erosion under improper land use include light granulometric composition, poor texture and low moisture content of the upper soil layer.
Table. Threshold wind speeds at 0-15 cm (by A.I. Baraev and E.F. Gossen)[1]Fundamentals of agricultural production technology. Farming and crop production. Edited by V.S. Niklyaev. - Moscow: "Bylina", 2000. - 555 p.
Economic activity
Human economic activity determines the condition of the soil cover, fertility, and the susceptibility of cultivated land to erosion. Economic factors include the following:
- general organization of the territory: the placement of fields and the structure of cultivated areas, road network, forest strips, production facilities;
- applied methods of basic and pre-sowing tillage and cultivation technologies, such as mouldboarding or non-moldboard tillage along or across the slope, degree of soil compaction and spraying, care of crops and fallows;
- degree of application of preventive anti-erosion and soil protection measures, such as soil-protective crop rotations, sowing of perennial grasses, minimization of tillage, agro-forestry, hydraulic and other anti-erosion constructions;
- reclamation works: construction of reclamation systems, dams, ponds, reservoirs, road network, backfilling of ravines, quarries, etc.
Human activity can both improve and deteriorate the condition of the land area and landscape. Not taking into account the laws of nature and irrational use of land can lead to desolation of many areas, making them unsuitable for agriculture. For example, the burning of forests on the mountain slopes by Cuban planters has led to severe water erosion. Within a generation, heavy tropical downpours washed away the unprotected top fertile soil layer, leaving exposed rocks.
The causes of water erosion caused by human activity are destruction of vegetation on slopes, overgrazing, clear-cutting of forests and bushes, and soil tillage that does not correspond to the relief.
One of the main causes of wind erosion in the steppe areas caused by human activity is imperfect tillage technology: annual plowing with stubble embedding, use of disc-tillers and smooth rollers.
In O. Owen’s book “The Protection of Natural Resources”, there are examples of ancient civilizations in Asia, Africa and the Mediterranean of Europe, which used the most valuable land resources irrationally. The soils of these areas were at one time the basis of a flourishing agriculture. Gradually, however, barbaric attitudes toward land exploitation led to severe erosion, rendering them unusable and causing the mass migration and starvation of peoples of entire empires.
Many of the world’s deserts serve to illustrate how society, if developed spontaneously rather than directed consciously, leaves deserts behind.
On the contrary, relying on the laws of nature, farming, and understanding the factors of erosion processes, people can control these processes, preventing the development and spread of erosion and creating conditions for sustainable and productive farming.
Complex manifestation of erosion factors
The factors of erosion and deflation manifest themselves in some combination and interaction in a complex way. The influence of the complex of factors on the development of wind erosion can be traced in detail on the example of the Kulunda steppe of Altai Krai, according to A.N. Kashtanov.
| Natural conditions | Deflation Factors |
| Climate | Droughts recurring with a frequency of 2-3 years out of 5 years. Winds with speeds of more than 5 m/s during the period of absence of vegetation and the number of days 35-50. Abrupt change in daytime temperatures and night frosts |
| Relief | Gentle-sloping or flat, creating favorable aerodynamic conditions for wind. Presence of wind-impact elevations and corridors |
| Soil cover | Chestnut soils of light granulometric composition, containing insufficient amount of wind-resistant aggregates. Low moisture capacity, water retention capacity, cohesiveness. Separate partial state (dispersion) of arable layer |
| Vegetation cover | The amount of open cultivated land is 70-90%. Predominance of annual crops, sowing of perennial grasses is 5-8%. Absence of winter crops. Lack of vegetation cover for 8-9 months. Weak plant development, low projective cover. Thinned vegetation cover of natural lands. Forest cover of the territory is 1,5-2%. |
The complex impact of these factors can make these agricultural lands unusable in a short period of time.
The combined effect of water and wind erosion is most destructive after rapid spring snowmelt and meltwater runoff, accompanied by strong washout and erosion, as well as soil dehydration. After that, there is a long (1-2 months) period of drought, during which deflation occurs. The scheme of this process: snowmelt → meltwater runoff → soil washing out and erosion → desiccation, drainage of soil cover → soil spraying under the influence of tillage, moisture loss → deflation.
Mechanism of water erosion development
Erosion processes develop under the action of water, wind, and their mutual influence. The mechanism of water erosion development was studied by Sobolev, 1948; Bennett, 1958; Hudson, 1974; Zaslavsky, 1979; Kashtanov, 1974; and others.
Raindrops and water flow are considered as acting forces of water erosion.
In modern Russian and foreign practice, rainfall erosion index is used, an index that takes into account the kinetic energy of rainfall during the period of maximum intensity of rainfall. As a rule, the period is taken equal to 30 minutes. In this case, the erosion index of precipitation is calculated by the formula:
where I30 is the maximum intensity of rain in 30 min, mm/min or l/m2 per minute; E is the kinetic energy of rain.
When assessing the erosion hazard of rain on the average annual erosion index, it is important to consider the monthly distribution of the index values. Sometimes, when the annual erosion index of rainfall is small, the risk of erosion development is higher than when it is large.
Surface water runoff can cause surface and linear erosion.
Surface, or planar, erosion is a relatively uniform washout of soil over the entire surface. Little noticeable and therefore very dangerous, it is observed on fields located on slopes of different gradients, almost annually. Depending on conditions, from 5 to 25 tons of soil is washed away from 1 ha of arable land, in some regions up to 30-50 tons/ha. Over several years, the arable layer can be reduced by half or more, taking the fields out of use. Because of its invisibility, it can remain unnoticed by the specialists of the farming enterprise.
Linear, or gully, erosion is accompanied by soil erosion under the action of jet streams of water, leading to the formation of gullies. The width of jet stream erosion can reach 2-3 m, and the depth – to the plow pan. The washouts and scour holes subsequently turn into gullies. Gully erosion is widespread in the Central Black Earth zone and the Volga region. In some cases, the annual growth of gullies is more than 10 m, up to a maximum of 300 m per year.
As a result of surface and linear erosion, washed away soils of shortened profile are formed. Depending on the thickness of the washed away layer, weakly washed away, medium washed away, strongly washed away and very strongly washed away soils are distinguished.
Depending on the form of precipitation, two types of erosion are distinguished: from rainfall runoff and from meltwater runoff. Erosion from melt water runoff, as a rule, covers large territories, stormwater erosion – locally, on separate territories. Erosion hazard period from melt water runoff is 5-15 days in spring, when there is no vegetation, and from heavy rainfall – a few hours, during summer, when there is insufficient development of crops.
A classification of water erosion has been developed based on the type of surface runoff and the form of erosion manifestation.
Surface runoff can be caused by temporary water flows, such as irrigation or outflowing groundwater.
Surface runoff of water streams that cause erosion is divided into:
- meltwater;
- rainwater;
- irrigation water;
- rising groundwater;
- wastewater.
Forms of erosion:
- soil washout, which is subdivided into:
- weakly washed away soils (surface erosion);
- medium washed away soils;
- strongly washed away soils;
- soil erosion (linear erosion), which is subdivided into:
- scour;
- ravines;
- jet erosion, which, depending on its manifestation, is classified as surface erosion or linear erosion.
Meltwater runoff is determined by water reserves of snow cover and intensity of snowmelt. It amounts to 80-90 mm in the north of the Central Black Earth zone, 40-50 mm in the south, 30-60 mm in the Volga uplands and 90-100 mm in the Central region (Tula, Moscow and Ryazan regions).
Washing away of the soil is possible already at a steepness of 1.5-2°. The steeper the slope, the more intensive the soil is washed away. Intensity of washing away depends on slope exposure and soil type. Clayey and loamy soils with strongly spreading structure are more prone to washout than sandy loamy soils with good permeability.
Table. Soil washout depending on slope steepness (Belgorod region, typical loamy black earth, southern exposure, convex slope, tilled, according to I.D. Braude)
Irrigation erosion
Irrigation erosion is a type of water erosion, which appears under the influence of irrigation water runoff during furrow irrigation in conditions of complex topography. The intensity of irrigation erosion depends on the exposure, shape and steepness of the slope, the type of watershed and its area, and soil properties.
As a result of irrigation erosion up to 100-150 t/ha of soil may be lost annually, together with which up to 0.8-1 t of humus, 100-120 kg of nitrogen and 110-165 kg of phosphorus are taken away. On soils subject to irrigation erosion, crops grow and develop unevenly, and yields are reduced. Significant areas of irrigated lands in the Volga region and Central Asia (more than 1.5 million hectares) are subject to this type of erosion.
To prevent the development of irrigation erosion they use:
- cutting irrigation furrows on the lowest slope not deeper than 10-12 cm;
- when increasing the slope from 2 to 6°, the length of furrows is reduced from 150 to 100 m, irrigation by jet – from 0.1 to 0.05 l/s;
- in cotton crops on heavy soils the slitting of inter-row spacing is carried out;
- irrigation of slopes with light soils is carried out by sprinkling;
- doses of fertilizers on washed-out soils are increased by 25-40%;
- cotton-alfalfa crop rotations with three years of alfalfa are introduced, after which on medium- and highly washed away soils, green manure crops are placed or organic fertilizers are introduced in doses up to 30-40 t/ha.
Mechanism of wind erosion development
The mechanism of wind erosion development is a physical process of interaction of air flow with the soil surface. The works of Russian and foreign scientists are devoted to the study of this mechanism, which serve as a theoretical basis for the development of soil protection techniques against deflation. The soil aggregates of the size 0,1-0,5 mm which under the influence of a wind get rotary movement with frequency 200-1000 min-1 move on a surface most easily. Aggregates with diameter from 0,6 to 1 mm move by rolling, rubbing against each other, striking, destroying, thereby increasing the number of most erosion-active 0,1-0,5 mm particles.
Erosion-hazardous particles have a great destructive power, moving by leaps and bounds, they break larger clumps, damaging crops.
To move aggregates larger than 1 mm requires a wind speed of more than 11 m/s at a height of 0-15 cm.
Table. Wind speed at which soil aggregates begin to move
Analysis of the structural composition of aeolian (sediment) deposits and in dust traps during dust storms showed that the content in fine soil of particles smaller than 1 mm is 92-95%, larger than 1 mm – 5-8%.
Particles less than 1 mm in diameter are erosion hazardous, while particles larger than 1 mm are wind-resistant. Thus, soil resistance to deflation can be assessed by the lumpiness of the surface, i.e. the presence of windproof aggregates. When the number of soil clod-resistant aggregates is less than 50% of the air-dry soil, the risk of blowing out increases greatly, so this degree of lumpiness is considered critical, or erosion hazardous. The threshold of soil resistance to wind erosion in the absence of crop residues on the surface occurs at a lumpiness of 50-55%.
Table. Structural composition of sediment and fine grains from dust traps, % (according to Baraev and Gosen, 1980)
| Aeolian sediments | |||||||
| Fine grains from dust traps | |||||||
Wind erosion can appear in the form of dust (black) storms and under the influence of constant local daily winds, or local erosion. The latter occurs in the form of overhead erosion and surface erosion (along the ground). Overhead erosion consists in trapping soil particles and lifting them upward by swirling motion. Surface erosion is the rolling of soil particles over the surface or by gradients.
Heavy spraying of the top 5 cm layer of soil is often the result of excessive mechanical tillage and rubbing of soil particles by the undercarriage systems of machinery during field work.
Wind erosion can manifest itself in the form of dust storms, which destroy and carry away partially or completely the arable layer.
Dust storms are most common in Western Siberia, the North Caucasus, and the Volga region on light soils. Particularly severe storms were observed in 1892, 1928, 1960,1965, and 1969.
Wind and water erosion have different effects on agrophysical properties of soils. Wind erodes and transports top to 5-10 cm layers of soil. Water, on the one hand, dissolves and transports soil particles to deeper horizons and washes away upper layers, dissolves and carries away by washing deep into or washing away nutrients.
Soils in steppe areas subject to wind erosion are usually characterized by a deficit of phosphorus, whereas soils subject to water erosion are characterized by a deficit of nitrogen and other mobile nutrients. Losses of humus and mineral nutrients accumulate over time and depend on soil type and erosion severity.
Wind erosion can also occur during the winter. Strong winds blow away the snow cover, exposing and drying the soil. Together with snow, it is blown off the fields and forms earthen drifts elsewhere.
Mechanism of combined action of water and wind erosion
Combined erosion is most often observed in the North Caucasus, the Central Black Earth zone, the Volga region, the Trans-Urals, and Western and Eastern Siberia. The mechanism of joint action combines the processes and energy of water and wind erosion, as a consequence of which the effects are also common, characteristic of both water and wind erosion.
Combined erosion occurs when the following factors combine:
soil over-wetting – water runoff – washout;
washout – desiccation – spraying – blowing out.
In areas with stable and strong snow cover, erosion in spring and summer periods occurs according to the scheme: snowmelt – soil over-moistening – meltwater runoff – soil washing out and erosion – desiccation – spraying – deflation. In areas with little snowy winters, dry spring and wet summer period the process usually develops according to the scheme: drying and spraying – deflation – rainfall – runoff – washing out and erosion of soil.
In erosion-active years during 2-3 months of joint influence of water and wind erosion gully growth makes up to 30-50 m and more with subsequent blowing out of arable layer up to 3-5 cm.
Combined effect of water and wind erosion leads to destruction of soil cover: reduction of humus layer thickness, reduction of organic and mineral nutrients content, deterioration of structure, porosity, water permeability, moisture capacity, water retention capacity, water and nutrient regimes.
Classification of soil erodibility
The degree of soil erodibility is determined by the reduction in the depth of the humus horizon, the loss of humus and nutrients. Depending on the washout and blowing out, a distinction is made:
- slightly eroded,
- moderately eroded,
- heavily eroded,
- very strongly eroded soils.
There are several classifications based on the degree of soil erodibility and on the reduction of humus content in the upper layer. The latter is proposed by M.N. Zaslavsky:
- weakly washed away – the content of humus in the upper layer compared to unwashed soil by 10-20% less;
- moderately washed away – humus content is 20-50% lower;
- heavily washed away – humus content is 50% or more less;
- very strongly washed away – humus content is 75% or more less.
S.S. Sobolev proposed a classification depending on the degree of washed away humus horizon. According to this classification we distinguish:
- slightly washed away – up to half of the humus horizon washed away;
- moderately washed away – more than half of the humus horizon washed away;
- heavily washed away – the transitional or illuvial horizon is partially washed away;
- very strongly washed away – the humus and transitional or illuvial horizons are completely washed away; the parent rock is plowed away.
These classifications require refinement because they are not related to the arable layer.
For soils subjected to wind erosion A.F. Rodomakin proposed the following classification of erodibility:
- slightly deflated – up to 20% of the humus horizon is blown out;
- moderately deflated – 20-40% of humus horizon has been blown out;
- severely deflated – 40-60% blown out;
- severely deflated – more than 60% were blown out.
When determining the degree of erodibility, the soil profile of the same type unaffected by erosion, i.e. full-profile soils, is taken as a reference.
In modern agriculture, a number of anti-erosion techniques have been developed and applied to protect the soil from erosion and prevent its development and spreading.
The main soil-protecting techniques:
- Measures to protect soils from water erosion:
- grassing of heavily eroded slopes;
- soil-protective crop rotations;
- contour-tillage;
- forest reclamation;
- land reclamation facilities such as dams, water regulation swale systems, and diversion ditches;
- strip rolling and snow blanketing, and use of snow retaining shields.
- Measures to protect soils from wind erosion:
- cereal-fallow, cereal-row crop rotations with a short rotation;
- buffer strips of perennial grasses;
- strip planting of bare fallows and row crops;
- strip cropping;
- flat-cutting tillage;
- sowing of cereals by stubble seeders;
- forest amelioration;
- regular irrigation.
- Measures to protect soils from combined erosion:
- soil and water conservation land management of the territory;
- grassing of heavily eroded slopes;
- cereal-grass, cereal-fallow and cereal-row crop rotations;
- strip planting of bare fallows, row crops and perennial grasses;
- flat-cutting across the slopes after cereals;
- trenching, for example, after perennial grasses and corn, ploughed soil and fallows;
- slitting of perennial grass crops;
- mulching the soil with chopped straw;
- forest reclamation;
- hydrotechnical constructions;
- agrohydromeliorative soil-protective complex in the watershed.
The leading role in erosion control is given to the systems of tillage of soils subject to water erosion and tillage of soils subject to wind erosion.
Soil-protective complex of measures – a set of science-based measures aimed at preventing and avoiding the development and spread of water and wind erosion, applied taking into account the adopted farming system.
An important condition for the creation of erosion resistant agricultural landscapes is a systematic approach, adaptability to local conditions, comprehensiveness, environmental sustainability, economic and technical feasibility, environmental and socio-economic expediency.
Due to the accumulated scientific and experimental data, for most regions of Russia and different conditions, soil-protecting complexes have been developed and successfully used, allowing to obtain high yields with a significant reduction or complete prevention of erosion processes.
Damage caused by soil erosion
Soil erosion in the absence of measures to prevent its development and spread, can cause enormous economic and environmental damage, removing land from the fund of agricultural land.
The main components of the damage caused by soil erosion are:
- reduction of the potential fertility of soils,
- deterioration of chemical and agrophysical properties,
- decline in biological activity,
- reduction of yields and deterioration of product quality,
- reduction in the effectiveness of chemicalization measures.
As far back as 100 years ago V.V. Dokuchaev noted, the decrease in the fertility of black soil, the growth of gullies, droughts and famine are a direct consequence of improper land use. He was the first to propose a scientifically sound set of measures to prevent erosion events.
Currently, erosion processes in varying degrees are observed in almost all regions of Russia. In the absence of soil-protective measures on erosion-prone lands, the total annual loss of soil from washing away can reach, according to M.N. Zaslavsky’s calculations, 7 billion tons. Losses of humus layer during dust storms are from 1 to 10 cm, while it takes more than 100 years to create 1 cm of humus layer in natural conditions.
According to V.A. Belyaev, in Russia about 5.4 million tons of nitrogen, 1.8 million tons of phosphorus and 36 million tons of potassium are lost annually from fields and pastures as a result of washout. According to the calculations of Russian Academy of Agricultural Sciences academician V.D. Pannikov, loss of 1 mm layer of southern black earth from 1 ha area causes loss of 76 kg of nitrogen, 24 kg of phosphorus, 80 kg of potassium, while for production of 1 ton of grain it is required on average 66 kg of nitrogen, 20 kg of phosphorus and 26 kg of potassium.
If we take the content in the arable layer of an average of 0.2% nitrogen, 0.2% phosphorus and 2% potassium, then the annual washout of 4 billion tons of soil, leads to a loss of about 100 million tons of nutrients.
According to U.S. researchers, as a result of erosion, 20 times more nutrients are lost than are taken out with the crop.
In a number of zones, the rate of erosion of arable soils is 5-15 times higher than soil formation. According to F.K. Shakirov, 0.6 t/ha of soil is formed per year, while washing out is 3-7 t/ha, reaching in some years 50 t/ha. Soil losses in orchards and vineyards can reach 30 t/ha and more, in bare fallows – 60-150 t/ha and more.
Table. Humus reserves in the 0-50 cm layer of different degrees of washing out, t/ha
| Dark gray forest | ||||
| Common black earth | ||||
| Southern black earth | ||||
| Chestnut | ||||
| Brown forest | ||||
Erosion processes lead to deterioration of agronomic properties of the soil: soil compaction, reduction of moisture retention capacity, deterioration of soil regimes, loss of clay and silt particles, which negatively affects the structure.
According to the data of the Soil Institute named after V.V. Dokuchaev, the reserves of humus of the best Russian black earth (chernozems) in the world for the last 70 years after the plowing decreased by almost 250 t/ha, the water-holding capacity decreased by 500-600 t/ha, and the potential productivity – by 0,5-0,6 t/ha of dry grain per year. At the enterprise “Kashirskiy”, Moscow region, in the potato field without anti-erosion tillage in conditions of severe erosion the soil washout for the season was 196 m3/ha, loss of humus from 1 ha – 8.7 t, nitrogen – 44.3 kg, phosphorus – 41.7 kg and potassium – 65.2 kg.
Together with the runoff of meltwater and rainwater, which amounts to 400 to 700 m3/ha, up to 50-100 t/ha of soil and 100-150 kg/ha of nutrients are washed away annually; in areas of wind erosion the same amount is blown away, respectively.
At Smolensk experimental station from sod-podzolic light loamy soil at a steepness of 4-6 ° and length up to 300 m annually washed away from 1 ha up to 5.7 tons of fine-grained soil containing 127 kg of humus, 98 kg of potassium, 24 kg of nitrogen and 10 kg of phosphorus.
Soil erosion will change the qualitative composition of humus, shifting the ratio of humic acids and fulvic acids towards the latter.
Decrease of humus content, available nutrients and deterioration of physical properties of eroded soils leads to decrease of biological activity and phytosanitary state.
Table. Microbiological activity of eroded black earth
| Unwashed | ||
| Weakly washed out | ||
| Moderate washed out | ||
| Highly washed out |
Characteristic agrophytocenosis, significantly different from plain lands, develops on eroded sloping lands. Weediness and root rot infestation increase on eroded soils.
Due to deterioration of physical properties of eroded soils, the ability to assimilate melt and rainwater decreases. As a result, runoff coefficient may increase up to 0.8-0.9, and considerable part of precipitation drains from slopes. In addition, water losses from evaporation increase. According to calculations, annual slope runoff results in the loss of up to 60-80 billion m3 of water, causing soil drought, which is supplemented by deflation.
In general, from the negative impact of erosion on the complex of agrophysical properties of soil, the yield of agricultural crops decreases. It is conventionally considered that on weakly washed away soils the crop yield decreases by 10-30%, on medium washed away – by 30-50%, on strongly washed away – by 50-70%. Washing out and erosion of pasture soils leads to reduction of hay yields by 2-3 times and more.
Table. Crop yields on soils with different degrees of erodibility, % of unwashed soil
| Winter wheat | |||
| Winter rye | |||
| Spring wheat | |||
| Barley | |||
| Oats | |||
| Corn | |||
| Peas, vetch | |||
| Sugar beets, potatoes | |||
| Sunflower | |||
| Vetch-oat mixture | |||
| Sudanese grass | |||
| Perennial grasses |
More precisely, the decline in yields depends on the degree of washout, weather
conditions, the genetic type of soil, the composition of the crops being cultivated, farming practices, and other factors. Crops can respond differently to soil erosion.
On a national scale, 1/3-1/4 of gross crop production is lost annually from eroded agricultural lands.
Damage caused by water and wind erosion also affects micro- and nano-relief, silting of rivers and lakes, reduction of productivity of forage lands, etc.
As a result of erosion processes, the productivity and sustainability of agriculture and the economic returns of agricultural production are reduced.
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.
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: Kolos, 2002. – 584 p.: ill.