Soil-protective crop rotations are those intended to protect soils from water erosion on slopes of more than 5°, where soil wash-out can reach 15 t/ha per year, and wind erosion, for example in open steppe, where wind speed near surface is more than 3-4 m/s.
In modern agrolandscape farming systems, crop rotations are required to ensure soil protection and conservation functions, especially on lands at risk of water or wind erosion.
Soil-protective crop rotations are based on the properties of some crops to protect the soil from erosion, combined with special methods of tillage and crop placement.
Soil protection properties of crops
Different crops have different soil-protective properties, which depend on the density of herbage, the power of plant development, the amount of crop residues left on the surface of the field, the duration of stay in the field, cultivation technology and the impact of crops on soil structure.
Perennial grasses have the greatest soil-protecting ability. Covering the soil during the whole year, they reliably protect it from erosion, although the density of grass stand decreases in autumn, winter and spring periods. It is mainly used for hay and green fodder.
Annual crops, such as cereals and forages, are also capable of protecting soils, although less so than perennial grasses, covering the soil for 9-11 months of the year with a maximum of herbage in May-July. They are supplemented by stubble, post-mowing, and undersowing crops so as not to leave the soil open after the main crop is harvested. Spring cereals only cover the soil for 3 months of the summer and row crops for 1-1.5 months.
Cultivation of row crops that loosen and disperse the soil is avoided if there is a risk of erosion.
The effectiveness of soil protection depends on the mass of plant roots and their distribution in the soil profile. The powerful root system of perennial grasses reliably grips the soil in the upper layers, so that their soil-protective properties appear.
The weight of the root system of perennial grasses may reach 50-60% of the weight of the above-ground part. Winter cereals and corn increase the mass of root system up to 40% of the mass of above-ground part, spring cereals – 28-30%, fiber flax, potatoes, root crops – 18-20%.
According to soil-protecting ability agricultural crops can be divided into three groups:
- with high soil-protecting ability – perennial grasses, winter cereals (the latter, sometimes referred to the group with medium soil-protecting ability);
- with medium soil-protecting ability – annual grasses, spring cereals;
with poor soil-protecting ability – row crops, technical crops, vegetable crops, bare fallows and fruit plantations.
The given assessment allows to determine the composition and structure of sown areas of soil-protective crop rotations.
If we take the level of complete protection of soil from erosion as a unit, the soil-protecting capacity of crops is distributed as follows:
- perennial grasses – 0.91-0.98,
- annual grasses – 0.65,
- continuous cereals – 0.50-0.65,
- potatoes and sunflowers – 0.25
- sugar beets and corn – 0.15,
- bare fallow – 0.
Building soil-protective crop rotations
The ratio in the structure of crop rotations of row crops and perennial grasses depending on the slope of the slope is determined taking into account their soil-protective role.
The basic principles of the design, introduction and development of soil-protective crop rotations:
- detailed consideration and analysis of agronomic features of eroded lands;
- selection of crops that provide the most soil-protective and economic effect;
- delineation of fields and working plots must comply with technical capabilities in cultivation of crops;
- consideration of crop alternation, their compatibility and self-compatibility, compaction and anti-erosion stability of crops;
- biological and economic expediency.
If the farm has flat areas and gentle slopes with low gradient and areas at risk of erosion, it is advisable to introduce field, special and on-farm crop rotations with maximum saturation with row crops, whereas on steep slopes and eroded soils – crop rotations in which crops of continuous seeding prevail. On very steep slopes, soil-protective crop rotations with perennial grasses and annual crops of continuous sowing are introduced.
An important method of increasing soil-protective role of crop rotations is strip planting of crops, which is the alternation of strips of crops with different soil-protective ability. This method allows to reduce manifestation of erosion processes, exclude tillage along the slope and create conditions for effective use of soil fertility.
The width of strips is important in determining the anti-erosion effectiveness: the wider the cultivated strip, the less the anti-erosion effect. However, narrow strips make it difficult to carry out field work using machinery.
On fields subject to water erosion, the width of strips is determined depending on the steepness of the slope and possible alternation of crops.
Table. Changes in band width depending on slope steepness (according to Zaslavsky and Kashtanov, 1986)
Strip placement of crops and bare fallow is also used on lands prone to wind erosion. For light soils, it is recommended to alternate grain crops and bare fallow with perennial grasses in 50-100 m (up to 200 m) strips: 1 – bare fallow, 2-3 – wheat, 4-8 – perennial grasses of 1-5 years of use, 9 – wheat, 10 – wheat or forage. The strips are placed at right angles to the direction of prevailing winds.
To combat wind erosion and accumulation of more snow in the steppe regions of Siberia, in addition to non-moldboard tillage, stubble strips with a higher cut or sown strips of sunflower and mustard are left in the fall tillage. According to the data of the experimental institutions of Northern Kazakhstan, the strip fallow accumulates 2-3 times more snow while increasing the yield by 0.4-0.7 t/ha.
In the steppe part of the Northern Caucasus to combat wind erosion bare fallows are replaced by seeded corn with row spacing up to 210 cm. Such fallows protect winter wheat crops.
When determining the width of strips, the granulometric composition of soil, clodding, i.e. content of fractions over 1 mm in the upper layer during erosion hazardous period, average height of stubble or grass, average wind speed during dust storms, and orientation of strips placement are taken into account.
The advantage of strip-till placement is its cost-effectiveness, it does not require large capital expenditures.
When building crop rotations, aimed at protection against water erosion, adhere to the following principle: on flat soils and gentle slopes place crop rotations with saturation of row crops, on slopes of high steepness – crop rotations with saturation of crops with continuous seeding. On steep and eroded slopes, soil-protective crop rotations saturated with perennial grasses up to 75% and more are introduced.
Table. Ratio of areas in the crop rotation (%) of crops with different soil-protecting ability, depending on the steepness of the slope
Soil-protective role of crop rotations on sloping lands significantly increases with the introduction of intermediate crops.
Examples of soil-protective crop rotations
Perennial grasses and annual crops in continuous crops prevail in soil-protective crop rotations: 1-4 – perennial grasses of the 1st-4th years of use, 5 – spring wheat, 6 – oats with undersowing of perennial grasses. Perennial grasses are complex grass mixtures consisting of 2-3 legumes and 2-3 cereals.
In the European part of Russia, grass-field and grass-cereal crop rotations are recommended for protection against water erosion on sloping lands with an angle of more than 5°:
- for the Non-Black Soil Zone: 1-4 – perennial grasses, 5 – winter rye, 6 – annual grasses with undersowing of perennial grasses;
- for the forest-steppe zone: 1-3 – perennial grasses, 4 – winter wheat, 5 – corn (in strips), 6 – leguminous, 7 – winter crops with undersowing of perennial grasses;
- for the steppe zone: 1-4 – alfalfa, sainfoin, 5 – winter wheat; 6 – corn (in strips); 7 – spring cereals with undersowing of alfalfa and sainfoin.
On slopes of 5-7°, soil-protective crop rotations are applied: 1-4 – perennial grasses; 5 – spring wheat; 6 – spring wheat; 7 – grain forage; 8 – annual grasses with undersowing of perennial grasses.
On slopes of 1-5° crop rotations with seeded fallow are applied: 1 – seeded fallow; 2 – spring wheat; 3 – peas; 4 – spring wheat; 5 – oats with undersowing of sweet clover (melilot).
At risk of water erosion on slopes with an angle of more than 7° grass-legume mixtures of perennial grasses, such as awnless brome with alfalfa are grassed.
Under conditions of wind erosion, three-field fodder crop rotations are recommended: 1 – melilot; 2 – spring wheat; 3 – forage crops with undersowing of melilot.
Soil-protective crop rotation was introduced in Kuban: 1-2 – perennial grasses, 3-4 – winter wheat, 5 – barley with undersowing of perennial grasses (alfalfa, haydock, Hungarian sainfoin, awnless bromegrass).
In Samara region of the Middle Volga region sloping lands are protected by the following alternation: 1-4 – perennial grasses (alfalfa, haydock), 5 – spring wheat, 6 – millet, 7 – spring cereals with undersowing of perennial grasses.
Seven-field soil-protective crop rotations are recommended for sloping lands of the forest-steppe regions of Tula region: 1-3 – perennial grasses of 1-3 years of use, 4 – winter cereals + stubby sowing of annual grasses, 5 – spring cereals with undersowing of winter vetch, 6 – winter vetch, 7 – winter crops with undersowing of perennial grasses. In this crop rotation about half of the sown area is occupied by mixtures of perennial grasses consisting of legumes and cereals components. The combination of perennial crops in continuous seeding with stubble and under-seeded allows to protect the soil from spring to late autumn.
The Novosilsky zonal agroforestry experimental station in the Orel region has introduced and mastered a seven-year crop rotation: 1-4 – perennial grasses of the 1st-4th years of use, 5 – winter rye for grain, 6 – buckwheat, 7 – spring cereals with undersowing of perennial grasses.
Ukrainian Research Institute of Agriculture recommends the following alternation on the sloping lands of the forest-steppe zone: 1 – vetch-oat fallow, 2 – winter crops with subsequent stubby crops, 3 – spring crops with undersowing of perennial grasses, 4-6 – perennial grasses of 1-3 years of use, 7 – winter cereals (sowing in strips combined with strips of grasses left for the 4th year of use) and stubby sowings after harvesting winter ones, 8 – Sudan grass and other annual grasses. The latter are sown in strips across the slope in combination with strips of grasses left in the 5th year of use.
In Western Siberia and Altai soil-protective crop rotation is applied: 1-2 – perennial grasses, 3 – spring wheat, 4 – forage crops with undersowing of perennial grasses. In the Altai region: 1 – annual grasses with undersowing of wheatgrass or perennial grass mixtures; 2-6 – perennial grasses. Five-field cereal-fallow-grass crop rotations with a strip arrangement across the direction of the prevailing winds are used on moderately eroded lands. Stripes of black fallow and cereals alternate with strips of wheatgrass.
In the conditions of wind erosion risk in the steppe regions and in the east of Russia, the use of perennial grasses with strip planting of crops, especially if they show weak soil-protective functions, such as corn, and strip fallow across the direction of prevailing winds (with wind erosion) or across the slope (with water erosion), as well as horizontally in complex terrain configuration is the basis of soil protective crop rotations.
Crop rotation fields are divided into several equal-area strips, ranging in width from 50 m on light soils to 100-150 m on cohesive soils. Drought-resistant wheatgrass are more commonly used as perennial grasses, whose dense cover well protects the soil from blowing out from the neighboring strips occupied by spring wheat or strip fallow.
In the absence of perennial grasses in the eastern steppe areas soil protective role in the crop rotation performs crops and stubble cereals, which are alternated by strips with strip fallow.
At the Pavlodar experimental station on protection of soils from wind erosion the five-field soil-protective crop rotation with ten-year rotation with strip placement of crops is used: 1-5 – perennial grasses, 6-7 – spring wheat, 8 – strip fallow, 9-10 – spring wheat. Strips of fallow and annual crops alternate with strips of perennial grasses. Even-numbered strips are sown with perennial grasses, such as a mixture of vetch and alfalfa or sainfoin, and odd strips are occupied by fallow and wheat.
In the Krasnoyarsk Territory, on low-powered leached medium-loamy black soil at risk of wind erosion, 5-field soil-protective crop rotation is introduced: 1-3 – perennial grasses of 1-3 years of use, 4 – spring wheat, 5 – spring wheat with undersowing of perennial grasses.
In the North Caucasus, to prevent wind erosion, soil-protective crop rotations based on perennial grasses and strip planting of crops are also introduced.
Productivity of soil-protective crop rotations can be increased by introducing the sowing of mixtures of annual grasses, intermediate crops and some thickening of cereals crops.
Sources
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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.