Influence of winter conditions on the state of the topsoil before spring sowing

Physical state of the soil: how overwintering changes the arable layer

Even high-quality autumn-tilled soil requires spring preparation for sowing. Over the winter, the structure of the arable layer changes significantly under the influence of weather, the timing of autumn ploughing, and soil type. To properly plan spring operations, an agronomist must assess soil density and the state of the soil crust immediately after the snow melts.

On average, the density of ordinary and leached chernozems remains within the optimal range for plants in spring. However, strong winds and the lack of snow cause desiccation of the arable land, which causes the density of the top layer to increase sharply. Heavy clay soils of the southern foothill zone compact more than ordinary and leached ones.

Winter precipitation directly affects the structure of arable land in spring. Rain compacts the arable layer, especially on soils with high silt and clay content. In frosty winters with little snow, erosion-prone aggregates smaller than 1 mm accumulate in the top layer (0–5 cm) of ordinary chernozems in northern and central regions. Autumn tillage cannot prevent this process — it is determined solely by winter temperatures and precipitation deficit.

Cloddiness of the arable land during spring tillage is also determined in winter. Abundant rainfall leads to an increase in the number of large clods, whereas a frosty winter contributes to soil crumbling. The accumulation of cloddy aggregates also depends on mechanical composition: carbonate and chestnut soils crumble better, forming fewer clods than leached and vertisols, grey forest or heavy meadow soils.

Soil moisture and key tasks of pre-sowing tillage

Soil behavior in spring largely depends on the rate of moisture loss. Steppe soils rarely become waterlogged over the winter and quickly reach physical ripeness. In spring, they gradually lose capillary moisture down to the level where capillary connection breaks. The period when steppe soil crumbles perfectly during tillage lasts up to several weeks.

Waterlogged clay soils of the southern foothill zone, such as vertisols, grey forest soils, heavy meadow soils, and depression chernozems, behave differently. They accumulate a lot of moisture over the winter, and in spring, they dry out extremely slowly. A thin dry layer forms on the surface, while a damp, plastic mass remains hidden beneath it for a long time. The period of physical ripeness for such soils lasts only a few days.

• Up to 80% — clay content in heavy foothill soils
• 1–1.5 kg/cm² — force required to break the crust of leached chernozems
• Up to 6 cm — thickness of the soil crust on leached chernozems
• 3–6 cm — depth of the dried layer on heavy waterlogged soils
• Less than 1 mm — size of erosion-prone soil aggregates

By the start of pre-sowing tillage on autumn-ploughed land, wintering weeds and volunteer winter crops have managed to germinate. Spring tillage must not only destroy unwanted vegetation but also prepare the soil for seed placement. Special attention should be paid to small-seeded crops: for their uniform emergence, a perfectly level arable layer is required, which will also ensure the unimpeded operation of high-speed equipment.

• Prepare a seedbed to place seeds on slightly compacted soil or "cut" them into it with the seeder's coulter.
• Level the surface of the arable land to ensure uniform seed sowing depth and optimal operating conditions for equipment.
• Create conditions to trigger maximum weed seed germination with subsequent destruction.

Conserving soil moisture, especially in its upper part in the seedbed layer, is an important task of pre-sowing preparation of the soil. One should take into account the need to conserve the amount of water optimal for seed germination specifically at the sowing depth of the seeds seed placement. It is often difficult to achieve this, especially when sowing small-seeded crops.

It should be remembered that increasing the tillage depth during the period when a coarse-cloddy or lumpy layer is formed threatens to dry out the seedbed and jeopardizes seedling emergence. The optimal humidity parameters are presented in the table:

The first step of pre-sowing soil tillage can be spring harrowing of winter-ploughed land (moisture conservation, surface harrowing). Its main task is the creation of a loose mulching layer, but this is possible only if ploughing was carried out in the autumn. In addition, the soil crust is broken, which enhances aerobic processes of nutrient accumulation.

The timing for spring harrowing of winter-ploughed land is the first day of field access, when the soil reaches physical maturity at the depth of the harrow tooth. Moisture conservation is a fast, intensive operation. It must be completed within two to three days. Both entering the field too early and delaying are harmful. Early field entry on immature soil leads to "smearing" and "damage" to the soil structure; furthermore, tractor units compact the arable land. Delaying leads to significant moisture losses. On lumpy, uneven winter-ploughed land, up to 100 m3 of water per hectare is lost daily in early spring. On heavy soils with a thick crust and compacted surface, it is necessary to use heavy spike harrows.

Light, loose soils can be worked with light harrows and levelers. For better surface leveling, levelers are often attached behind the harrows. These can be wooden beams, angle iron, or heavy chains rotating on swivels, directed at an angle to the movement. The use of harrow-cultivators with levelers allows, in the absence of perennial weeds, to replace spring cultivation and moisture conservation.

However, spring harrowing of winter-ploughed land, the main task of which is to reduce water losses, does not always achieve this. On heavy clay and loamy soils of the Kuban region, there is no difference in humidity between harrowed and non-harrowed plots in the first days after the start of field operations.

Later, after 5–10 days, moisture losses increase significantly on non-harrowed plots due to the appearance of cracks. The drying front moves downward in parallel with their formation, covering the entire plough layer.

Table 14 – Effect of spring harrowing of winter-ploughed land on soil moisture, % (training farm "Krasnodarskoye" of KubSAU)

              After 5 days      After 10 days     After 14 days
 Depth,
   cm       harrow-   soil     harrow-   soil     harrow-   soil
              ing    crust       ing    crust       ing    crust
   5–10      27,7      27,5     23,6      22,9      26,6     17,8
  10–15      29,7      29,4     28,5      28,7      26,3     22,6
  15–20      28,5      28,9     29,3      29,6      28,4     25,4

The reason for the ineffectiveness of spring harrowing of winter-ploughed land on heavy soils should be sought in the specific nature of their physical drying. In these soils, which are rich in silt and clay, water is significantly bound by sorption forces, and its loss is hindered.

Usually, in spring, a thin layer of 4–6 cm dries out, under which a fairly high moisture content is maintained for a long time. During this time, water losses on harrowed and non-harrowed plots occur in almost the same way.

Pre-sowing soil preparation for early spring crops is carried out during the so-called February windows and at the very beginning of spring. Due to the fact that early spring crops react very strongly to the sowing date, all tillage operations should be carried out at an intensive pace so as not to delay the sowing date, which usually falls at the beginning of spring field operations.

There can be several variations of this tillage depending on the crop, winter and spring conditions, and the general situation in the field.

If the winter-ploughed land is leveled and well-prepared from the autumn, and during a harsh, frosty winter, no winter crops or overwintering weeds have developed on it, then pre-sowing tillage may consist of harrowing the winter-ploughed land when the soil is at its maturity, to the depth of the harrow tooth.

For better leveling of the arable surface, harrowing can be combined with leveling. This option is often used when sowing early spring crops during February windows.

If the winter-ploughed land is well leveled from the autumn, but a few poorly developed annual weeds have appeared on it, the spike harrow should be replaced by a harrow-cultivator, or the soil tillage should be replaced by the application of a herbicide. Such a system is increasingly being used when sowing sugar beet.

If, however, many strongly developed weeds grew on the field during the winter, then the first pre-sowing tillage must be performed with a cultivator, with thorough leveling of the arable surface using harrows and levelers.

Preference should be given to cultivators with flat-cutting working parts that barely turn the soil, thereby drying out the tilled layer to a lesser extent. Field cultivators with universal sweep shares should be used during soil preparation for early spring crops only in exceptional cases:

• when there is heavy winter weed development and tools with flat-cutting shares cannot be used;
• on very ridged winter-ploughed fields.

Techniques for sowing early spring crops and sugar beet: the battle for moisture

During pre-sowing soil tillage for early spring crops, it is important to keep the loosening depth strictly at the level of the seeding depth seeding depth. If the field is infested with perennial weeds, there is a need for field cultivators. To avoid drying out the seedbed, operate them only in combination with harrows and levelers.

Sugar beet places special requirements on the quality of soil preparation. Its seeds must be placed on a compacted seedbed to ensure contact with moist soil for the swelling of the woody fruit clusters. The field surface must be perfectly leveled by the time of sowing, and the structure of the seedbed must be fine-crumbly.

• Soil preparation period for medium sowing — 15–20 days
• Soil temperature for beet sowing — 7–8 °С
• Soil moisture in the beet seed row — at least 22–24 %
• Soil temperature for sunflower sowing — 10–12 °С

When preparing soil for beet, avoid deep loosening, otherwise, the seeds will "hang" in the loose layer and will not receive moisture from the lower horizons. According to field trials, the maximum root crop yield is obtained when the cultivation depth does not exceed the seeding depth. In fields without perennial weeds and winter compaction, preparation is carried out according to the standard scheme.

1. Spring moisture conservation with harrows and levelers.
2. Pre-sowing cultivation with flat-cutting shares immediately before sowing.
3. Sowing of small seeds without a time gap.

For soil tillage before beet sowing, flat-cutting shares are used, followed by processing with harrows and levelers. First, heavy harrows are used, then light ones with more frequent tooth placement, and for leveling the surface, hardwood leveling bars are applied. Using a harrow-cultivator instead of a standard cultivator allows reducing the number of implement passes by one. This reduces the compacting impact of the tractor's running gear, which causes a noticeable drop in beet yield in wheel tracks.

Soil preparation for sunflower and weed control

When preparing soil for sunflower and other oil crops, it is also important to minimize the number of machinery passes. On ordinary and leached chernozems, pre-sowing tillage can be limited to one cultivation with harrowing or leveling. At the same time, single-pass soil preparation on spring-untilled winter-ploughed land helps to clear the field of weeds more effectively.

Early harrowing and cultivation reduce the thermal conductivity of the soil, causing it to warm up more slowly. On untilled winter-ploughed fields, the temperature at a depth of 10–12 cm is higher, which stimulates rapid and mass germination of weeds. In experiments on such plots, twice as many weeds emerged during the pre-sowing period, which were then completely destroyed by cultivation just before sowing.

The depth of pre-sowing cultivation for sunflower should not exceed the seeding depth. In steppe regions, there is usually no need to loosen the soil deeply in spring: the density of the tilled layer of winter-ploughed fields fluctuates within 1–1.15 g/cm³, which is optimal for the crop's development. Reducing the number of tillage operations to one lowers cultivation costs without yield loss.

Depth of spring tillage and soil ripeness

Sowing of late spring crops — corn, soybean, millet, sorghum, and Sudan grass — begins when the soil at seeding depth warms up above 12 °C. The period from the start of field work to sowing lasts about three to four weeks. This time should be used as efficiently as possible: to provoke the germination of weeds and destroy both early and late spring weeds.

In the fields of the steppe zone free of perennials, pre-sowing tillage is carried out with cultivator harrows. However, this method will only work if the autumn preparation of the winter fallow was of high quality. On heavy loamy and clayey soils in the central and southern foothill zones, it is better to abandon spring harrowing of the winter fallow altogether.

On heavy soils in the southern foothill zone, deep loosening of the spring winter fallow to a depth of 18–22 cm is effective for corn and other late crops. According to field trial data, tilling ripe, well-crumbling soil provides an average increase in corn grain yield of 6 centners/ha. If there is no possibility to perform deep mouldboard loosening or use a chisel on areas compacted over the winter in the southern foothill zone, make one of the pre-sowing cultivations deep. On fields without perennial weeds, a cultivator with loosening chisel sweeps is suitable for this purpose.

In steppe regions, deep spring tillage for late spring crops should be avoided. Ordinary, typical, and leached chernozems retain sufficient looseness by spring with a density of no more than 1–1.1 g/cm³, so there is no need to loosen them further. Deep passes in this zone will only lead to the desiccation of the plough layer.

The use of mouldboard harrows is undesirable here and is justified only in cases of mass infestation of perennial weeds. The optimal choice for the steppe is a cultivator with flat-cutting working tools in an aggregate with harrows and drags.

Minimizing tillage and combating over-compaction

In the cultivation technology for late spring crops, it is important to reduce the number of machinery passes across the field. On leached chernozems, a spring tractor pass compacts the soil in the wheel tracks to a depth that exceeds the limits of the plough layer. This directly reduces crop productivity.

Field experiments on typical chernozems have shown that when growing corn, it is possible to reduce the number of tillage operations from three (spring harrowing and two cultivations) to one pre-sowing cultivation. In fields free of perennials, this does not increase weediness and does not change soil density during the growing season, while the yield remains at the level of plots with triple tillage. Similar results were obtained on ordinary chernozems of the northern zone and leached chernozems of the central zone: one pre-sowing cultivation completely destroys weeds that have germinated on un-tilled winter fallow.

Good results are obtained from pre-sowing preparation for late crops in a single pass of a rotary tiller. Milling ripe, moist soil ensures high-quality crumbling without dust formation on heavy loams and prevents the emergence of clods.

In northern regions, for fields with autumn soil-protective tillage, the following scheme of spring soil preparation for corn is used:

1. Conserve moisture with a needle harrow. This will keep stubble on the surface and loosen the top layer of soil.
2. Upon the appearance of weed vegetation, carry out treatment with a flat-cutting cultivator.
3. In the second half of April, when the risk of dust storms decreases, switch to soil preparation using standard cultivators.

• Soil temperature for sowing — more than 12 °C
• Depth of spring loosening of winter fallow — 18–22 cm
• Density of chernozems by spring — no more than 1–1.1 g/cm³
• Harvest losses from loosening unripe soil — 8 centners/ha

In which cases is it recommended to perform deep ploughing?

What kind of tillage is recommended for heavy-textured soils?

What should be considered when choosing the depth of primary tillage?

What conditions are necessary for the application of minimal tillage?

What kind of tillage should be carried out for spring crops after row-crop predecessors?

Features of soil-protective tillage in areas of wind erosion?

Soil-protective tillage of sloping lands in the southern foothill zone?

Pre-sowing tillage and the tasks it faces?

What methods of pre-sowing soil preparation are distinguished?

What options for pre-sowing soil preparation are possible?