Deepening and Improvement of the Arable Layer of Various Soil Types

Advantages of Deep Tillage and Deepening of the Arable Layer

Increasing the thickness of the arable layer and improving its physical properties and aeration during deepening contribute to:

• Deeper penetration of plant root systems into lower soil layers, which allows better use of water and nutrients in the root zone.
• Accumulation of water in the soil from atmospheric precipitation and meltwater. Deepening the arable layer of soddy-podzolic soil from 20 to 30 cm increases reserves of available water by 110 t/ha, or 11 t of water for each additional 1 cm of layer (calculation by K. I. Boltyan). Potential reserves of plant-available water in a 10-cm layer of the illuvial horizon are 16 mm for light loamy and 21 mm for heavy loamy soils. Deepening the arable layer allows plants to better withstand short-term spring-summer droughts.
• Increased porosity and air capacity of the soil and improved gas exchange, which allows plants with a powerful root system to make fuller use of subarable layers.
• Effective control of weeds, diseases, and pests. Cutting the roots of weeds at a greater depth promotes their death. Deep incorporation of seeds and vegetative organs of weed propagation hinders their germination, accelerates the death of pests and pathogens; on the whole, this makes it possible to reduce soil weed infestation by 60–70% and improve its phytosanitary condition.
• Loosening the soil of the subarable horizon and destroying the plow sole, which forms during annual plowing to the same depth and significantly worsens the water and air regimes of the subarable horizon, which is especially undesirable on clay soils. As a result of deepening the arable layer, water runoff, soil and nutrient washout decrease, the risk of erosion processes decreases, and the efficiency of applying fertilizers and chemicalization agents increases.
• Reduced soil deformation and greater resistance to overcompaction under the action of running systems of tractors, tillage implements, and transport vehicles.
• Sustainable functioning of the agroecosystem due to a potential increase in the accumulation of organic matter and energy by the soil.

Disadvantages of Deep Tillage and Deepening of the Arable Layer

Despite the advantages, deep tillage is a resource- and energy-intensive technological process that does not always pay off with a yield increase. Thus, to increase the arable layer by 1 cm, 1 kg of diesel fuel or about 500 MJ/ha is consumed.

Response of Cultivated Plants to Deep Tillage and Deepening of the Arable Layer

Plants respond differently to deep soil tillage. This depends on the biological characteristics of the crop, the depth of penetration of root systems and the ability to assimilate hard-to-access nutrients, the amount of atmospheric precipitation and its distribution during the growing season, and the agrophysical properties of the soil. On soddy-podzolic soils, deep tillage is used more often, since the soil settles and compacts faster. On soils light in granulometric composition, deep tillage is carried out less often.

Modeling of different thicknesses of the arable layer (20, 30, and 40 cm) of gray forest and soddy-podzolic soils of different degrees of cultivation showed that field crops respond positively to a heterogeneous structure, in which in the upper 20-cm part a higher degree of optimization of soil properties is achieved through the application of organic and mineral fertilizers and lime. The yield of grain and row crops increases by 9–10%, which allows concluding that in humid regions of the Non-Chernozem zone it is rational to improve the upper 20-cm soil layer.

On deep tillage to 28–32 cm, crops with a powerful deeply penetrating taproot system respond well, for example, sugar and fodder beet, sunflower and other row crops, as well as legumes. These crops require good aeration, in which the oxygen content in soil air is at least 15%, and carbon dioxide is no more than 1%.

On the roots of leguminous crops under deep tillage, nodule bacteria develop more intensively and nitrogen fixation activity increases. Therefore, in crop rotations, deep tillage is carried out differentially, taking into account the response of crops to the thickness of the treated layer. The most responsive to deep tillage are peas, vetch, clover, alfalfa, fodder root crops. Crops with a fibrous root system—flax, winter rye, winter wheat, barley and other cereals—almost do not respond to deep and reclamation tillage, since they do not place special demands on the agrophysical properties of the soil and poorly use nutrients from deep layers.

Techniques for Deepening the Arable Layer on Soddy-Podzolic and Gray Forest Soils

To create a deep fertile arable layer of soddy-podzolic, gray forest, and solonetzic soils, the following methods are used:

• gradual plowing-in of the lower layer with its subsequent mixing with the soil of the arable layer;
• complete turning of the arable layer with simultaneous loosening of the soil of the subarable horizon;
• deep non-moldboard loosening of the soil of the subarable layer.

When determining the method, the thickness of the arable horizon, its humus content, and the presence of a podzolic layer are taken into account. On light-gray loams with an arable layer depth of less than 20 cm and the presence of a podzolic horizon, the method of gradually plowing in the subarable layer by 3–4 cm is used with simultaneous application of organic and mineral fertilizers and lime application. On such soils, it is desirable first to carry out non-moldboard loosening of the subarable layer to improve its properties, and then to plow it in. As a result, in subsequent years the thickness of the arable horizon increases to 26–28 cm.

On gray and dark-gray forest soils, whose humus horizon thickness is 25–45 cm with a humus content of 3–5%, and whose subarable layers are more humus-rich and structured compared with soddy-podzolic soils, a one-time deepening to 25–27 cm is used, and then to 30 cm. The frequency of deep tillage in a crop rotation is 3–4 years. It is carried out in the system of autumn tillage of bare and occupied fallows or under row crops.

The most effective is the comprehensive improvement of gray forest soils, in which a one-time deepening of the arable layer to 30 cm is carried out with the application of organic and mineral fertilizers, lime, and sowing of perennial leguminous grasses (Ryazan State Agricultural Academy). The yield of crops in a fruit-rotation crop rotation against the background of high fertilizer rates on average over 15 years increased by 11.9–13.2 centners of feed units per 1 ha. In addition to improving the soil, the stability of obtaining yields also increases, especially in years extreme in moisture.

Thus, in the Non-Chernozem zone, the conditions for deepening and improving the arable layer are the application of organic and mineral fertilizers, liming, and the introduction of perennial leguminous grasses into the crop rotation. First of all, deepening techniques should be applied on well-cultivated soils under crops that respond positively to deepening, as well as on sloping lands. On low-fertility soils, it is necessary to increase fertility in the 20-cm arable layer.

Due to high material and energy costs, methods of deepening the arable layer are not widely used in the Non-Chernozem zone; therefore, they are used when establishing fruit nurseries, orchards, and forest plantations.

Complete Turning of the Arable Layer with Simultaneous Loosening of the Subarable Soil Horizon

It is carried out with plows with subsoilers, cut-out bodies, or loosening plows, for example, PRK-4-4.0 and PRU-7-40. The cut-out body allows loosening to a width of 35 cm, while the subsoiler only to the width of the share—17 cm. For this reason, cross loosening is performed in subsequent years. The depth of the loosened subarable layer is 8–10 cm. The method is effective on podzolic soils with strong compaction of the subarable layer, temporarily waterlogged soils with a gleyed horizon, and sloping lands with moderately eroded soils.

Plow body with a cut-out moldboard.

Diagram of plowing with a plow with a cut-out moldboard and a skim coulter: a — upper and b — lower layer of the arable horizon, c — subarable horizon.

This deepening method is combined with the application of organic fertilizers and liming before it is carried out for better mixing.

Deep Non-Moldboard Loosening of the Subarable Soil Layer

Diagram of the operation of a chisel plow.

It involves leaving the fertile humus horizon and part of plant residues on the field surface, creating a mulching layer. During deep loosening, slight mixing of the humus horizon with the soil of the subarable layer occurs. The degree of soil mixing is influenced by the design of the implements. Good loosening to a depth of 30–40 cm is provided by chisel implements, for example, PCh-2.5, PCh-4.5, and loosening plows. For non-moldboard deepening, plows designed by T. S. Maltsev, paraplow-type flat-cutting subsoilers, plows with removed moldboards, and others are also used. The greatest effect of non-moldboard loosening is achieved when it is carried out under winter crops, maize, potato, vegetable, and other crops. On slopes, this method improves water permeability and water absorption, reduces water runoff and soil washout. Under winter crops, the loosening depth is 25–27 cm; under row crops, 30–40 cm.

Techniques for Deepening the Arable Layer of Chernozem and Chestnut Soils

Chestnut Soils

Chestnut soils are characteristic of the dry steppe zone and form under conditions of a hot climate. In their physical and water properties, primarily moisture capacity, total porosity, and the ratio of intra-aggregate and inter-aggregate porosity, they are close to chernozems.

Dark chestnut soils are characterized by a humus content of more than 3–4% and a humus horizon depth of up to 20–40 cm. On such soils, it is advisable to carry out a single deepening of the arable layer by plowing to a depth of 25–27 cm.

Light chestnut soils are characterized by less favorable water and physical properties: humus content less than 3%, humus horizon thickness less than 20 cm. Therefore, these soils need deepening and improvement. The most effective method of deepening is plowing to the depth of the humus horizon with loosening of the subarable layers by 8–10 cm while simultaneously applying organic and mineral fertilizers.

On solonetzic chestnut soils, gypsum application of the plowed soil is first carried out to eliminate excess exchangeable sodium. On meadow chestnut saline soils, plowing is performed to the depth of the above-solonetz layer, with simultaneous loosening of the subarable horizon to a depth of 32–35 cm.

The use of irrigation systems on chestnut soils leads to their excessive compaction and deterioration of the physical properties of both the arable and subarable layers. Therefore, the depth of subarable loosening is increased to 35–40 cm and it is carried out every 1–2 years.

Deepening of the Arable Layer and Techniques for Improving the Fertility of Solonetzic Soils

Solonetzic soils, due to a number of agrochemical and agrophysical properties unfavorable for plants, do not allow their use for growing crops without radical improvement of fertility. The presence of exchangeable sodium gives solonetzic soils an alkaline reaction (pH 8–9), which promotes dispersion and washing out of soil colloids down the profile and worsens structure. When moistened, solonetzes swell, viscosity increases, water permeability decreases; when dried, they cement, which greatly complicates their tillage and prevents deep penetration of plant root systems.

For the improvement of solonetzic soils, a complex of measures for their radical improvement is used, including:

• deepening of the arable layer;
• gypsum application;
• application of organic and mineral fertilizers;
• introduction of salt-tolerant plant crops;
• measures for moisture accumulation.

The choice of measures depends on the depth of the solonetzic horizon, its thickness, salt composition, groundwater level, and other indicators.

In Russia, automorphic solonetzes are most widespread: chernozem and chestnut. Chernozem and meadow soda solonetzes occur in the Chernozem zone, for example, in the Trans-Urals and Western Siberia; they are characterized by an alkaline reaction, a close groundwater level, and a risk of secondary solonetzization. To improve their properties, deep tillage and gypsum application are necessary.

Chestnut steppe solonetzes are widespread in the chestnut soil zone, for example, in the Middle and Lower Volga region, Eastern Ciscaucasia, and the south of Western Siberia. They are characterized by a neutral reaction and a deep groundwater level, which slows the entry of salts into the root zone. To improve these soils, deep tillage without gypsum application is sufficient.

On shallow and medium-columnar chernozem solonetzes with an above-solonetz horizon depth of 10–18 cm, in the absence of a gypsum horizon, periodic non-moldboard loosening to 25–28 cm is effective. Incorporation of the solonetzic horizon into the arable horizon sharply reduces its fertility. Therefore, gypsum application is carried out simultaneously and organic and mineral fertilizers are applied. Before deep tillage, the applied fertilizers and ameliorants are mixed with the upper above-solonetz soil layer using disk or milling implements to a depth of 10–12 cm. To increase the effectiveness of reclamation, it is carried out in autumn, supplemented by snow retention, introduction of coulisse crops, and other moisture-accumulating techniques. In subsequent years, soil with improved properties of the solonetzic horizon is plowed into the humus layer.

Solonetzic soils cannot be plowed deeply at once, since a large amount of alkaline salts from the lower horizons, when moved to the surface, sharply reduce fertility. The arable layer of such soils is deepened gradually with simultaneous application of gypsum and organic fertilizers.

To activate microbiological processes and improve physical properties, tier plowing is also used, in which the arable layer remains on top, and the compacted solonetzic layer is mixed with the underlying carbonate layer.

Deep-columnar solonetzes with the solonetzic layer located deeper than 18 cm are treated with plows with skim coulters and subsoilers or with cut-out bodies with full capture of the above-solonetz layer. In this case, the full dose of gypsum is applied before plowing so that the ameliorant is dropped by the skim coulter to the bottom of the furrow and mixed with the solonetzic horizon by the loosening share.

The effectiveness of improving solonetzic soils is enhanced by subsequent sowing in a crop rotation of salt-tolerant plants, for example, sweet clover, wheatgrass, alfalfa, sorghum, etc.

On slightly solonetzic steppe solonetzes with a sodium content of less than 10%, deep reclamation tillage without gypsum application is most effective.

On chestnut steppe solonetzic soils with a small thickness of the above-solonetz layer and a shallow occurrence of gypsum-bearing horizon in the profile, improvement is possible by deep plowing to 30–35 cm with subsequent mixing of the gypsum-bearing layer with the humus layer, as well as application of organic and mineral fertilizers.

On soils with a medium and deep location of the solonetzic horizon, in the presence of calcium carbonate and gypsum in deep horizons, plantation or three-tier plowing to 40–45 cm is used. Thus, with three-tier plowing with PTN-340 plows, the upper humus layer is turned over, and the solonetzic layer is exchanged places with the illuvial. During subsequent soil treatments in the crop rotation, soil of the illuvial horizon, enriched with soil colloids and calcium salts, is plowed into the humus layer. As a result of the interaction of gypsum and absorbed sodium, excess alkalinity and solonetzicity are eliminated, and the physical, chemical, and biological properties of the soil improve.

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.