Optimizing soil tillage for sowing winter crops under conditions of moisture deficit

Soil preparation for winter crops is the most complex compared to tillage for other crops. It presents many challenges, the solution of which requires great flexibility and a creative approach from the specialist, as well as the ability to adapt to the dynamic conditions arising in each specific field or even part thereof.

Obviously, before proceeding to outline the methods of soil preparation for winter crops, it is necessary to consider its general tasks, the fulfillment of which will ensure the effectiveness of the techniques discussed.

An outstanding agronomist-breeder, Professor A. I. Nosatovsky, repeatedly pointed out the great importance of obtaining timely, uniform, and sufficiently dense emergence for creating a high winter wheat yield.

Dense, well-developed crops in autumn reliably protect the soil from wind erosion. The need to ensure the best conditions for winter crop emergence should be taken as the main task of the Tillage system tillage system">tillage system for these crops.

The difficulty of the task lies in finding an optimal solution for the steppe, insufficiently moistened regions of Kuban, where there is a great deficit of productive soil moisture in the plough layer after the main preceding crops of winter crops by the time of their harvesting. The main reasons for the deficit:

• a significant part of the predecessors consists of late-harvested row crops;
• in steppe regions, the probability of heavy precipitation during the sowing periods of winter crops is relatively low;
• years are infrequent when winter crops that emerged late in autumn in the northern regions of the region "recover" due to winter growing season.

The most important condition determining the emergence of seedlings of winter crops, which soil preparation for these crops must ensure, is sufficient moisture in the upper half of the plough layer.

Optimal moisture conditions for seed germination of winter wheat are created even at a humidity 2–3% lower than the capillary rupture moisture of a given soil.

It is precisely this minimum water content in the soil that tillage must ensure by the time of winter wheat sowing. Humidity above 21–24% on chernozem soils in the steppe part of the region is easy to determine organoleptically. The soil has a dark color, and when strongly squeezed in the hand, traces of the fingerprint pattern remain on the surface of the clod. This means that the soil moisture level is equal to or exceeds the one indicated above.

At the same time, tillage must completely exclude the possibility of such soil moisture at the Sowing depth depth of seed placement, which corresponds to the so-called provocative moisture. It is determined by the water content, which is 1–1.5% higher than the wilting point for a given soil. If seeds are placed in a layer with such moisture, conditions may arise that will lead to the death of the germinating grain. This usually happens when the period from sowing to emergence is prolonged due to the absence of precipitation. The death of seedlings under such conditions is particularly significant at high temperatures in autumn, drying out of the seed layer, and also as a result of fungal infection.

In years with a dry autumn and relatively high temperatures, seeds that have begun to germinate at provocative moisture, or plants that have already emerged, usually die if there was not enough precipitation.

From this, it follows that sowing wheat seeds in soil where the amount of water is only 1–1.5% higher than the wilting point is very dangerous. If sowing cannot be delayed, the soil in the seed layer should be dried using loosening tools and only then proceed to sowing.

The moisture level at the Sowing depth depth of seed placement, corresponding to provocative moisture, can be determined organoleptically with some practice. Chernozem soils of the region in this case have a color changing from dark gray to gray. When strongly squeezed, the clod poorly maintains its shape and crumbles at the first movement of the hand.

The timely appearance of uniform seedlings also depends on the structural composition of the plough layer, and especially the seed layer. At low moisture levels at the depth of seed placement, the process of their swelling and germination is influenced by the size of the surrounding structural aggregates.

At moisture close to the wilting point, smaller aggregates surrounding the seed improve the conditions for swelling and germination, ensuring better contact with the soil. That is why it is important to create a fine-cloddy state of the seed layer using tillage methods, especially when its moisture is low. However, one should be wary of soil pulverization, which increases the development of wind erosion and worsens the physical conditions in the plough layer.

With insufficient moisture, seed emergence of winter crops is also facilitated by their proper placement on the seedbed. It is also created by tillage practices. First of all, it should be noted that seeds must rest on a slightly compacted seedbed rather than "hanging" above it. Seeds placed in loose soil may die in the absence of precipitation and rapid soil drying during a hot, dry autumn.

Different results are obtained when, at low humidity, seeds are pressed or "embedded" into a compacted bed. In this case, at low soil moisture, seedlings began to appear earlier than without "embedding" into the bed. However, "embedding" seeds into a dense bed has almost no effect on the emergence of winter wheat seedlings under optimal moisture of the seed layer. Such results were obtained both on ordinary and on leached chernozems.

How to prepare a seedbed and adjust a seed drill during moisture deficit

You can obtain uniform seedlings of winter wheat during a moisture deficit by properly preparing the seedbed. To do this, carry out pre-sowing cultivation to a depth slightly less than the planned sowing depth. Adjust the coulter pressure springs so that they "embed" the seeds into the compacted bed. This improves contact of the seed material with the soil and stimulates its germination.

Compacting the soil around the seeds accelerates their germination when the moisture of the seed layer is no higher than 19–21%. This technique works more effectively if the top layer consists of large clods. At higher humidity, artificial compaction of the seedbed is not required.

To form a high harvest of winter wheat, it is fundamentally important to restore moisture reserves in the root zone by the beginning of spring. In chernozems, plant roots are capable of penetrating to a depth of 160–200 cm, and in some years, with complete spring wetting of the profile, even to the third meter of soil. If the soil has been wetted to the full depth of the roots in spring, plants will be able to use moisture during the critical period of development (heading – grain filling) even in the absence of precipitation in April – early May.

In the plain zone, to obtain a guaranteed average harvest, soil moisture reserves by spring must be restored to the field capacity to a depth of 180–200 cm. Only extraordinary factors can reduce grain yield at this level of moisture supply. If the spring moisture reserve is low, only abundant precipitation at the beginning of the critical period of plant development can significantly increase the harvest.

The following factors can reduce the yield of winter wheat despite a sufficient moisture reserve by spring:

• natural disasters;
• infestation of crops by diseases and pests;
• wind effect at low relative air humidity during the grain filling period.

How to conserve soil moisture and cope with cloddiness

In steppe regions, tillage must ensure maximum spring wetting of the profile. In zones with excessive winter moisture (for example, in southern foothill regions and on some river delta soils), the task is the opposite — to increase winter evaporation of moisture to avoid spring waterlogging. For arid conditions, summer-autumn precipitation remains the main reserve.

To increase the efficiency of rains falling after harvesting the predecessor, it is necessary to form a moisture-conserving layer. It will prevent excessive moisture evaporation and increase the depth of soil wetting by spring. To achieve this, the plough layer must be slightly compacted and packed, levelled, and consist of fine-cloddy aggregates without large clods.

Combating soil cloddiness is one of the main problems when preparing a field for winter crops. In chernozems, cloddiness increases sharply if humidity falls below 17–18% and total porosity becomes less than 50% due to high density under the predecessor. Preventing the appearance of large clods can be achieved through agrotechnical methods.

You can reduce the proportion of the cloddy fraction in the plough layer using the following technological practices:

• Reduce the depth of tillage to the horizon of best crumbling. In some cases, increasing the depth helps if it allows bypassing the compacted layer.
• Reduce the density of the plough layer under predecessors. To do this, reduce the number of machinery passes during the cultivation of row crops.
• Carry out shallow pre-treatment before the main ploughing or mulch tillage with a subsoiler.
• Use roller compaction, selecting their weight according to the size and cohesion of the clods.

• Productivity of summer-autumn precipitation — 30–50%
• Moisture threshold for crumbling chernozem — at least 17–18%
• Critical threshold of total porosity — 50%
• Depth of shallow preliminary tillage — 8–10 cm
• Reduction of cloddiness by rolling — by 20–35%

To reduce cloddiness in fields, implements with active working parts, such as rotary tillers, can be used. Combined tillage implements also cope with this task excellently. Depending on the current field condition, in addition to the plough, they may include disc implements, rollers, harrows, and conventional or spike harrows.

The main goal of tillage in steppe regions is to create conditions for winter crops similar to high-quality bare fallow. The field surface should be leveled, and the plough layer itself should be fine-cloddy and slightly compacted. This will ensure uniform emergence and allow moisture to penetrate deeply into the root zone in spring.

Soil moisture and density: how to activate plant nutrition

Proper tillage not only preserves structure but also activates the accumulation of available nutrients. Even with high fertilizer rates, it is important to utilize the natural soil fertility. To do this, it is necessary to maintain optimal humidity, activate microbiological processes, and conserve water during the summer-autumn period.

In steppe chernozems, beneficial microflora is most active within strictly defined humidity limits. The dynamics of available nitrogen in autumn directly follows the amount of water in the plough and sub-plough horizons. If there is no productive moisture, soil biota becomes dormant, and the process of nutrient accumulation stops.

All agricultural practices aimed at conserving summer and autumn moisture automatically improve the nutrition of seedlings. In foothill regions, tillage works in the same direction, but in a different way — by reducing the spring waterlogging of the topsoil. Besides moisture, microbiological activity is strongly influenced by the density of the tillage layer.

Weed control also directly depends on the quality of field preparation. The most reliable way to suppress annual weeds is to form a dense, well-developed, and tillered stand of winter crops from autumn. Therefore, quality tillage, which guarantees rapid and uniform emergence, serves as an effective indirect method of field cleaning.

Another effective technique is triggering weed germination in the pre-sowing period. On fields after early predecessors, one can significantly reduce the reserve of weed seed in the soil. To achieve this, it is important to perform tillage in such a way that sufficient moisture is preserved in the top layer of the ploughland.

Such predecessors include:

• cereals;
• grain legumes;
• forage crops.