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Bare fallow

Bare (clean) fallow – a field of crop rotation, free of crops during the growing season. Bare fallow is cultivated during the whole warm period of the year, keeping the soil loose, conducting extermination measures against weeds, pests and pathogens of crops, carry out reclamation work. A fallow field does not produce agricultural products, it prepares the soil for cultivation of subsequent crops.

The importance of bare fallow in the crop rotation

Bare fallows allow:

  • accumulate moisture, conserve and sustainably use soil moisture;
  • mobilize nutrients in the soil;
  • to carry out activities to control weeds, pests and pathogens of crops.

The whole complex of agronomic practices allows to improve the fertility of fallow soils and to create optimal conditions for the growth and development of plants, making them the most valuable predecessor for all crops, especially for the most demanding cereals – winter and spring wheat and winter rye.

Bare fallow, on the one hand, leads to intensive decomposition of soil organic matter, on the other hand, enriches it with nutrients in available forms for plants, provided there are no weeds. This is especially important in the deficit of fertilizers, especially phosphorus, which is poor in chestnut and chernozem soils of the steppe zone.

Bare fallow perform a phytosanitary function in controlling weeds, pests and pathogens of crops (for example, defeat wheat root rot decreases by several times), increase soil biological activity, accelerating the mineralization of organic matter.

Bare fallows due to their positive role allow to obtain high sustainable yields of wheat (winter and spring) of good quality, especially in the steppe regions: the Volga region, the North Caucasus, the South-East of Russia, where the wheat yield after a bare fallow increases by 1.5-2 times compared with other predecessors; and in the arid steppe and forest-steppe regions of the Southern Urals, Volga, Trans-Urals, Altai and Western Siberia – by 30-50%.

Types of bare fallows

Bare fallows can be:

  • black;
  • early;
  • late.

Black fallow is a bare fallow, the main tillage of which is carried out in autumn after harvesting the preceding crop.

Early fallow is a bare fallow, the main tillage of which is carried out in spring, in the year of fallow. It is used in areas where the autumn period is short or there is no time to till the soil after harvesting spring crops, for example, in Northern Kazakhstan and Siberia. In addition, leaving stubble, reduces the effect of wind erosion and increases snow accumulation.

Black fallows almost always have an advantage over early fallows, as it allows the accumulation of more moisture due to the fall-winter and spring period, as well as a longer application of extermination measures.

Strip fallow is a black or early fallow in which tall crops such as sunflowers, corn, mustard, and other plants with strong stems are planted in strips. They are most often used in arid steppe areas with strong winds. 

Strip fallow performs three functions: snow retention, protection of winter crops from unfavorable conditions in winter in low-snow and arid areas, and soil protection from wind erosion.

The strips are placed across the direction of the prevailing winds, with a distance between them equal to 3-5 times the working width of seeders or 8-24 m. Cultivated crops are sown during fallow cultivation, for example, by cultivators aggregated with seed drills. If the summer sowing dates of the sward (for arid areas – late June – early July), they do not have time to gain sufficient height, which allows to sow winter crops across the sward. Damage to plants by the passage of seeders is relatively small, they have time to strengthen enough before winter and give a stable stem at the onset of frost.

The strips allow to retain even the first snow, while snow rolls can be made only when the snow cover height is 12-15 cm. Increasing the thickness of snow cover contributes to the accumulation of moisture, protecting winter crops from freezing and sharp fluctuations in temperature during the spring period, and preventing wind erosion.

Late, or peasant, fallow was a bare fallow that was used in the three-field farming system of Russia in the spring and summer period for the pasture of cattle. On peasant farms which lacked efforts and means for the simultaneous spring-summer field work and tillage of bare fallow, the late fallow was cultivated only in the second half of summer, before sowing the winter crops. For this reason, its efficiency is much lower than black or early fallow, and it is rarely used in modern agriculture.

Tillage of bare fallow

Deep tillage in a bare fallow allows to increase absorption and retention of moisture of atmospheric precipitation and melt water. 

Surface tillage with fallow cultivators allows to keep the top layer in a friable state, which promotes intensification of microbiological soil processes and accumulation of nutrients. Destruction of the surface crust, prevents moisture evaporation from deep layers.

Repeated trimming of weeds with the help of fallow cultivators allows to sharply reduce the infestation of fields, including vicious weeds related to root-shoot and tap-root weeds, provoking their sprouting with the subsequent elimination. The weed seed bank is also greatly depleted.

In addition to agronomic techniques to control weeds and pests, chemical and biological methods are used.

Bare fallow is suitable for the introduction of organic and mineral fertilizers, lime or gypsum soils.

Cereal crops may account for 30-50% of arable land in cereal crop rotations. Less land is allocated to bare fallow, so often repeated seeding is resorted to, the remaining share of cereals is placed on annual and perennial grasses, legumes, corn for silage and some other crops.

Geographic features

There is a certain geographical regularity in intensity of bare fallow use in crop rotations, in which the decisive role is given to water: as the amount of atmospheric precipitation changes, the leaching regime of soils changes to nonleaching and as the continental climate increases, the share of bare fallow in the cropping pattern increases to 10-20% and more. This increase is observed from west to east and southeast Russia.

Bare fallows allow the accumulation of significant moisture reserves in the upper meter layer, allowing to obtain stable wheat yields, which is especially important in the arid regions of Russia: the Volga region, the steppe zone of the South-East, the North Caucasus, the Trans-Urals, the Southern Urals, Western Siberia, Altai and others.

For example, in the steppe zone 1.5-2.5 times more water is accumulated in the one-meter layer of soil after a bare fallow compared with the non-fallow predecessors. In the forest-steppe zone – up to 1.3-1.4 times, in areas of the Non-Chernozem zone with sufficient moisture there is practically no increase. For example, in Nizhny Novgorod region under winter wheat crops after bare fallow, moisture reserves were the same as after seeded (occupied) fallows (lupine and vetch). There was no significant difference in wheat yield in these fallows (3.83 and 4.1 t/ha).

On the contrary, under the conditions of the dry steppe zone in Western Siberia (Omsk region) reserves of productive moisture in the soil layer after black fallow before sowing of spring wheat amounted to 143 mm with a grain yield of 2.11 t/ha whereas under permanent sowing reserves of moisture were only 76 mm with a yield of 1.1 t/ha.

Bare fallow has a positive impact on soil water regime not only for the first, but also for subsequent crops of crop rotation. For this reason in the steppe zone crop rotations alternating bare fallow with repeated crops of wheat are widespread:

  • in the eastern part of the steppe zone of Russia: 1 – bare fallow, 2 – spring wheat, 3 – spring wheat;
  • in the European part: 1 – bare fallow, 2 – winter wheat, 3 – winter wheat;
  • in the Volga region (transition zone): 1 – bare fallow, 2 – winter wheat, 3 – spring wheat.

Under the conditions of unstable moisture in the steppe zone of the North Caucasus (Krasnodar and Stavropol regions, Rostov region), the reserve of moisture in the upper 20 cm layer before sowing is of great importance for stable high yields and good overwintering of winter wheat. Bare fallows allow to increase moisture reserve by 15-25% in comparison with non-fallow predecessors.

In order to increase moisture reserves due to melt water, I apply strips in the fallow field. For example, in Altai Krai, the strips allow increasing the thickness of snow cover by 3 times, which contributes to increasing moisture reserves by 20-25%.

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.