Soil-protective crop rotations

Soil-protective properties of crops

Soil-protective crop rotations are based on the ability of certain crops to protect the soil from erosion, in combination with special methods of soil tillage and crop placement. Different crops have different soil-protective functions, depending on stand density, plant vigor, the amount of plant residues left on the field surface, the duration of stay in the field, cultivation technology, and the effect of crops on soil structure.

Perennial grasses have the greatest soil-protective capacity. Covering the soil throughout the year, they reliably protect it from erosion, although stand density decreases in autumn, winter, and spring. They are used mainly for hay and green fodder.

Annual crops of continuous sowing, for example cereals and forage crops, also show the ability to protect soils, although less than perennial grasses, covering the soil for 9–11 months of the year with maximum stand in May–July. They are supplemented by stubble, aftercut, and undersown crops so that the soil is not left bare after harvesting the main crop. Spring cereals cover the soil only for 3 months of summer, and row crops for 1–1.5 months.

When there is a risk of erosion, cultivation of row crops, which loosen and pulverize the soil, is avoided.

The effectiveness of soil protection depends on the mass of plant roots and their distribution through the soil profile. The powerful root system of perennial grasses reliably binds the soil in the upper layers, which is why their soil-protective properties are manifested. The root system mass of perennial grasses can reach 50–60% of the aboveground mass. Winter cereals and corn increase root system mass to 40% of aboveground mass, spring cereals to 28–30%, fiber flax, potato, and root crops to 18–20%.

According to soil-protective capacity, crops can be divided into three groups:

• with high soil-protective capacity — perennial grasses, winter cereals (the latter are sometimes assigned to the group with medium soil-protective capacity);
• with medium soil-protective capacity — annual grasses, spring cereals;
• with weak soil-protective capacity — row crops, industrial crops, vegetable crops, bare fallows, and fruit plantations.

This assessment allows determining the composition and structure of sown areas in soil-protective crop rotations. If the level of complete soil protection from erosion is taken as unity, the soil-protective capacity of crops is distributed as follows:

• perennial grasses — 0.91–0.98;
• annual grasses — 0.65;
• continuous-sown cereals — 0.50–0.65;
• potato and sunflower — 0.25;
• sugar beet and corn — 0.15;
• bare fallow — 0.

Designing soil-protective crop rotations

The ratio in the structure of sown areas of a crop rotation of row crops, continuous-sown crops, and perennial grasses depending on slope steepness is determined taking into account their soil-protective role.

Basic principles of designing, introducing, and mastering soil-protective crop rotations:

• detailed accounting and analysis of agronomic features of eroded lands;
• selection of crops providing the greatest soil-protective and economic effect;
• layout of fields and working plots must correspond to technical capabilities in crop cultivation;
• consideration of crop alternation, compatibility and self-compatibility, density, and erosion resistance of crops;
• biological and economic feasibility.

When a farm has flat areas and gentle slopes with a slight gradient, as well as areas at risk of erosion, it is advisable to introduce field, special, and near-farm crop rotations with maximum saturation with row crops on the former, whereas on steep slopes and eroded soils, crop rotations dominated by continuous-sown crops should be introduced. On very steep slopes, soil-protective crop rotations with perennial grasses and annual continuous-sown crops are introduced.

An important technique for increasing the soil-protective role of crop rotations is strip cropping, which is the alternation of strips of crops with different soil-protective capacities. This technique reduces the manifestation of erosion processes, excludes tillage along the slope, and creates conditions for the effective use of soil fertility. The width of strips is important in determining erosion-control effectiveness: the wider the cultivated strip, the smaller the erosion-control effect. However, narrow strips complicate field operations with machinery.

On fields subject to water erosion, strip width is determined depending on slope steepness and possible crop alternation.

Strip placement of crops and bare fallows is also used on lands subject to wind erosion. For light soils, alternation of cereal crops and bare fallow with perennial grasses in equal-width strips of 50–100 m (up to 200 m) is recommended:

• 1 — bare fallow, 2-3 — wheat, 4-8 — perennial grasses of the 1st–5th year of use, 9 — wheat, 10 — wheat or forage crops.

Strips are placed at right angles to the direction of prevailing winds.

To combat wind erosion and accumulate more snow in the steppe regions of Siberia, in addition to no-moldboard tillage, stubble coulisses with a higher cut are left on autumn-plowed land or coulisses of sunflower and mustard are sown. According to data from experimental institutions of Northern Kazakhstan, coulisse fallow accumulates 2–3 times more snow, with yield increasing by 0.4–0.7 t/ha. In the steppe part of the North Caucasus, to combat wind erosion, bare fallows are replaced by fallows occupied by corn with row spacing up to 210 cm. Such fallows protect sowings of winter wheat.

When determining strip width, soil texture, aggregation (i.e., content of fractions >1 mm in the top layer during the erosion-hazard period), average height of stubble or grass, average wind speed during dust storms, and orientation of strip placement are taken into account.

The advantage of strip cropping is its cost-effectiveness; it does not require large capital expenditures.

When designing crop rotations aimed at protection from water erosion, the following principle is followed: on flat soils and gentle slopes, crop rotations saturated with row crops are placed; on slopes of increased steepness, crop rotations saturated with continuous-sown crops are placed. On steep and eroded slopes, soil-protective crop rotations saturated up to 75% or more with perennial grasses are introduced.

The productivity of soil-protective crop rotations can be increased by introducing sowings of annual grass mixtures, catch crops, and somewhat denser sowing of cereal crops. The soil-protective role of crop rotations on slope lands increases significantly with the introduction of catch crops.

Examples of soil-protective crop rotations

In soil-protective crop rotations, perennial grasses and annual continuous-sown crops predominate:

• 1-4 — perennial grasses of the 1st–4th year of use, 5 — spring wheat, 6 — oats with undersowing of perennial grasses. In this case, perennial grasses are complex grass mixtures consisting of 2–3 legume and 2–3 cereal components.

In the European part of Russia, on slope lands with an angle greater than 5°, grass-field and grass-grain crop rotations are recommended for protection from water erosion:

• for the Non-Chernozem 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 — grain legumes, 7 — winter crops with undersowing of perennial grasses;
• for the steppe zone: 1-4 — alfalfa, sainfoin, 5 — winter crops + stubble crops, 6 — corn (in strips), 7 — spring cereals with undersowing of alfalfa and sainfoin.

On slopes from 5 to 7°, soil-protective crop rotations are introduced:

• 1-4 — perennial grasses; 5 — spring wheat; 6 — spring wheat; 7 — grain forage crops; 8 — annual grasses with undersowing of perennial grasses.

On slopes from 1 to 5°, crop rotations with occupied fallow are introduced:

• 1 — occupied fallow; 2 — spring wheat; 3 — peas; 4 — spring wheat; 5 — oats with undersowing of sweet clover.

Under conditions of water soil erosion risk on slopes with an angle greater than 7°, sodding with grass-legume mixtures of perennial grasses is carried out, for example, smooth brome (Bromus inermis) with alfalfa.

Under conditions of wind erosion, three-field forage crop rotations are recommended:

• 1 — sweet clover; 2 — spring wheat; 3 — grain forage crops with undersowing of sweet clover.

In the Kuban, a soil-protective crop rotation has been introduced:

• 1-2 — perennial grasses, 3-4 — winter wheat, 5 — barley with undersowing of perennial grasses (alfalfa, crested wheatgrass, sainfoin, brome).

In the Samara Oblast of the Middle Trans-Volga region, slope lands are protected using the following alternation: 1-4 — perennial grasses (alfalfa, crested wheatgrass), 5 — spring wheat, 6 — millet, 7 — spring cereals with undersowing of perennial grasses.

On slope lands in the forest-steppe districts of Tula Oblast, seven-field soil-protective crop rotations are recommended:

• 1-3 — perennial grasses of the 1st–3rd year of use, 4 — winter crops + stubble 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 legume and cereal components. The combination of annual continuous-sown crops with stubble and undersown crops makes it possible to protect the soil from spring to late autumn.

In Oryol Oblast, at the Novosil zonal agroforestry experimental station, a 7-field crop rotation has been introduced and mastered:

• 1-4 — perennial grasses of the 1st–4th year of use, 5 — winter rye for grain, 6 — buckwheat, 7 — spring cereals with undersowing of perennial grasses.

The Ukrainian Research Institute of Agriculture recommends the following alternation on slope lands of the forest-steppe zone:

• 1 — vetch-oat occupied fallow, 2 — winter crops with subsequent stubble crops, 3 — spring crops with undersowing of perennial grasses, 4-6 — perennial grasses of the 1st–3rd year of use, 7 — winter crops for grain (sowing in strips in combination with strips of grasses left for the 4th year of use) and stubble sowings after harvesting winter crops, 8 — Sudan grass and other annual grasses.

The latter are sown in strips across the slope in combination with strips of grasses left for the 5th year of use.

In Western Siberia and the Altai, a soil-protective crop rotation is used:

• 1-2 — perennial grasses, 3 — spring wheat, 4 — grain forage crops with undersowing of perennial grasses.

In Altai Krai:

• 1 — annual grasses with undersowing of crested wheatgrass or perennial grass mixtures; 2-6 — perennial grasses.

On moderately eroded lands, 5-field grain-fallow-grass crop rotations are used with strip placement across the direction of prevailing winds. Strips of black fallow and cereals alternate with strips of crested wheatgrass.

Under conditions of wind erosion risk in steppe regions and in the east of the country, soil-protective crop rotations are based on the use of perennial grasses with strip placement of crop sowings. This is especially important if crops have weak soil-protective functions, for example corn, and coulisse fallow across the direction of prevailing winds (for wind erosion) or across the slope (for water erosion), as well as along contours with a complex relief configuration.

Fields of the crop rotation are divided into several equal-area strips, from 50 m wide on light soils to 100–150 m on cohesive soils. As perennial grasses, drought-resistant crested wheatgrass is more often used; its dense cover well protects the soil from blowing from neighboring strips occupied by spring wheat or coulisse fallow.

In the absence of perennial grasses in the eastern steppe regions, the soil-protective role in the crop rotation is performed by sowings and stubble of cereals, which alternate in strips with coulisse fallow.

At the Pavlodar Experimental Station for Soil Protection from Wind Erosion, a five-field soil-protective crop rotation with a ten-year rotation and strip placement of crops is used:

• 1-5 — perennial grasses, 6-7 — spring wheat, 8 — coulisse fallow, 9-10 — spring wheat.

Strips of coulisse fallow and annual crops alternate with strips of perennial grasses. Protective even-numbered strips are sown with perennial grasses, for example, a mixture of crested wheatgrass with alfalfa or sainfoin; odd-numbered strips are occupied by fallow and wheat.

In Krasnoyarsk Krai, on thin leached medium-loamy chernozems under conditions of wind erosion risk, a 5-field soil-protective crop rotation is introduced:

• 1-3 — perennial grasses of the 1st–3rd year 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 placement of crops are also introduced.

References

1. Bazdyrev G. I., Loshakov V. G., Puponin A. I., et al. (2000). Agriculture. Textbook for universities. Moscow: Kolos Publishing House.

2. Niklyaev V. S. (2000). Fundamentals of agricultural production technology. Agriculture and crop production. Moscow: Bylina.

3. Evtefeev Yu. V., Kazantsev G. M. (2013). Fundamentals of agronomy: a textbook. Moscow: FORUM.