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Deepening and improvement of the arable layer

Deepening and improvement (state of cultivation) of the arable layer is one of the urgent tasks of arable farming. A deep arable layer allows to accumulate more moisture, organic matter, increase the zone of active activity of soil microorganisms and the availability of nutrients.

Advantages of deep tillage were noted by V.R. Williams, T.S. Maltsev, M.G. Chizhevskii, P.M. Balev and others in their works. Academician V.R. Williams believed that no progress in agricultural production is unthinkable with the thickness of the arable layer less than 20 cm.

Advantages of deep tillage and deepening of the arable layer

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

  • Deeper penetration of the plant root system into the lower soil layers, allowing better use of water and nutrients in the root zone. 
  • Accumulation of water in the soil from precipitation and melt water. According to calculations of K.I. Boltyan, deepening of arable layer of sod-podzolic soil from 20 to 30 cm increases stocks of available water by 110 t/ha, or 11 t of water for each additional 1 cm of layer. Potential reserves of available water for plants in 10 cm illuvial layer are 16 mm (l/m2) for light loamy and 21 mm – for heavy loamy. The deepening of the arable layer allows plants to better withstand short-term spring-summer droughts.
  • Increasing the porosity and air capacity of the soil, improving gas exchange, which allows plants with a strong root system to use subsoil layers more fully.
  • Effective control of weeds, diseases and pests. Cutting the roots of weeds to a great depth contributes to their death. Deep embedding of seeds and vegetative organs of weed reproduction hinders their germination, accelerates the death of pests and pathogens, in general it allows to reduce by 60-70% of the soil infestation and improve its phytosanitary condition. 
  • Loosening of the subarable horizon and destruction of the plow pan, which is formed during the annual plowing at the same depth and which significantly worsens the water and air regimes of the subarable horizon, that is especially undesirable on clay soils. As a consequence of deepening the arable layer, water runoff, washout of soil and nutrients are reduced, the risk of erosion processes is reduced and the efficiency of fertilizers and chemicalization increases.
  • Reduced soil deformation and greater resistance to excessive compaction under the influence of the driving systems of tractors, tillage implements and transport vehicles.
  • Sustainable functioning of the agro-ecosystem due to the potential increase of organic matter and energy accumulation in 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 for itself by an increase in yield. For example, 1 kg of diesel fuel or about 500 MJ/ha is used to increase the arable layer by 1 cm.

Response of cultivated plants to deep tillage and deepening of arable layer

Plants respond differently to deep tillage. It depends on the biological characteristics of the crop, the depth of penetration of root systems and the ability to absorb hard-to-reach nutrients, the amount of precipitation and its distribution during the growing season, and the agrophysical properties of the soil. For example, winter and spring wheat on the black earth soils of the forest-steppe zone respond better to deep tillage than winter rye and barley.

On black earth and chestnut soils for winter wheat, corn and sunflower it is advisable to deep plow to a depth of 25-30 cm. Deep tillage is used more often on sod-podzolic soils, because the soil settles and compacts faster. Deep tillage is used less often on light soils with granulometric composition.

Modeling of different thickness of arable layer (20, 30 and 40 cm) of gray forest and sod-podzol soils of different state of cultivation showed that field crops respond positively to heterogeneous structure in which in the upper 20 cm part a higher degree of optimization of soil properties is achieved by making organic and mineral fertilizers, lime. The yield of cereal and row crops thus increases by 9-10%, which suggests that in the humidified areas of the Non-Black Soil zone it is rational to cultivate the upper 20 cm layer of soil.

Crops with a strong deep-penetrating root system, such as sugar and fodder beets, sunflowers and other row crops, as well as legumes, respond well to deep tillage up to 28-32 cm. These crops require good aeration, with at least 15% oxygen content in the soil air and no more than 1% carbon dioxide.

On the roots of legume crops under deep cultivation, nodule bacteria develop more intensively and nitrogen fixation activity increases. Therefore, in crop rotations deep tillage is carried out differentiated, taking into account the reaction of crops on the thickness of the cultivated layer. Peas, vetch, clover, alfalfa, fodder root crops are most responsive to deep tillage. Crops with stubby root system – flax, winter rye, winter wheat, barley and other cereals almost do not respond to deep and reclamation tillage, as they do not have special requirements for agrophysical properties of soil and poorly use nutrients of deep layers.

Techniques for deepening the arable layer on sod-podzolic and gray forest soils

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

  • gradual inclusion of the lower layer in the tillage with its mixing with the soil of the arable layer;
  • complete overturning of the arable layer with simultaneous loosening of the subsoil layer;
  • deep non-moldboard loosening of the subsoil layer.

When determining the method take into account the thickness of the arable layer, its humus content and the presence of podzolic layer.On light gray loams with a tilled layer depth of less than 20 cm and the presence of podzolic layer, use the method of gradual deepening of plowing by 3-4 cm, capturing the subsoil layer, with the simultaneous introduction of organic and mineral fertilizers, as well as liming. On such soils it is desirable to conduct firstly non-moldboard loosening of subsoil layer to improve its properties, and then its plowing. As a result, in subsequent years, the thickness of the arable layer increases to 26-28 cm.

On gray and dark gray forest soils, the thickness of humus horizon which is 25-45 cm with humus content 3-5%, and subsoil layers are more humusy and structured compared with sod-podzolic soils, use single deepening to 25-27 cm, and then to 30 cm. Frequency of deep tillage in the rotation is 3-4 years. It is carried out in the system of autumn tillage bare and seeded fallows or under row crops.

According to the Ryazan State Agricultural Academy, the most effective comprehensive improvement of the state of cultivation of gray forest soils, in which a one-time deepening of the arable layer to 30 cm with the introduction of organic and mineral fertilizers, lime and sowing perennial leguminous grasses. Crop yields in the cereal-grass-row crop rotation on the background of high doses of fertilizers on the average for 15 years increased by 1.19-1.32 t of fodder unit per 1 hectare. In addition to the improvement of the state of soil cultivation, the stability of yields is increased, especially in extreme wet years.

Table. Crop yields at different thickness of the created arable layer on gray forest soils, 100 kg fodder unit. (average for 1971-1985; L.V. Ilyina)

Techniques for the creation of the arable layer in the crop rotation*
Without fertilizer
Manure + NPK
from fertilizers
from deepening
Plowing at 20-22 cm
Plowing at 28-30 cm
Plowing 28-30 cm + deepening to 38-40 cm
Plowing at 28-30 cm + three-tier plowing at 38-40 cm

Thus, in the Non-Black Soil zone the conditions for deepening and improving the state of cultivation of the arable layer are the introduction of organic and mineral fertilizers, liming, the introduction of perennial leguminous grasses in the crop rotation. First of all deepening methods should be used on well-cultivated soils for sowing crops, positively responding to deepening, as well as on sloping lands. On low fertile soils it is necessary to increase fertility in the 20-centimeter arable layer.

Due to high material and energy costs, methods of deepening the arable layer are not widely enough used in the Non-Black Soil zone, so they are used in laying fruit nurseries, orchards and forest plantations.

Gradual inclusion of the underlying layer in the tillage, followed by its mixing with the soil of the arable layer

Gradual inclusion of the underlying layer into tillage is carried out by conventional ploughs with skimmers in the system of autumn tillage for row crops and in seeded fallows. In this case part of podzolic or mixture of illuvial and podzolic horizon is included in tillage. Thickness of included layer depends on properties of subsoil horizon and state of cultivation of arable layer. As a rule, 3-4 cm are plowed, but no more than 1/5 of the thickness of the arable layer.

When implementing the technique because of the strong dilution of the humus layer of soil subsoil horizon, this plowed 300-600 t/ha, reduced fertility.Therefore, the deepening of organic and mineral fertilizers from the calculation of 8-10 t/ha organic per 1 cm included in the layer. Therefore, the deepening of organic and mineral fertilizers from the calculation of 8-10 t/ha organic for every 1 cm included layer. Liming is used after plowing of the plowed layer on the surface with the following mixing for more effective neutralization of acidity.

Deepening of sod-podzolic, gray forest and saline soils is better to perform during autumn plowing of black fallow and in spring for early fallow. In the absence of bare fallow in the rotation, deepening is carried out before row crops. Deepening is not carried out before winter and spring crops, as it reduces the yield in the year of sowing.

Complete overturning of arable layer with simultaneous loosening of subsoil horizon

It is carried out by ploughs with deepeners, notched bodies or ripper ploughs, for example, ПРК-4-4,0 and ПРУ-7-40. Notched body allows loosening the working width of 35 cm, and the deepening plough only to the working width of the tine – 17 cm. For this reason, cross loosening is performed in subsequent years. The depth of subsoil loosened layer is 8-10 cm. The method is effective on podzolic soils with strong compaction of the subsoil layer, soils of temporary overwatering with gleyed horizon and sloping soils with medium-washed soils.

This method of deepening is combined with the application of organic fertilizers and lime prior to its implementation for better mixing.

Deep non-moldboard loosening of subsoil layer

Deep non-moldboard loosening involves leaving the fertile humus horizon and some plant residues on the surface of the field to create a mulch layer. With deep loosening there is a slight mixing of humus horizon with the subsoil layer. The degree of soil mixing is influenced by tool design. Good loosening to a depth of 30-40 cm are provided by chisel tools, such as ПЧ-2,5, ПЧ-4,5 and ripper plows. For non-moldboard deepening, ploughs of T.S. Maltsev design, ploughs, subsurface (flat-cut) deep tillers type paraplau, ploughs with removed mouldboards and others are also used. The greatest effect of non-moldboard loosening is achieved when it is carried out for winter crops, corn, potatoes, vegetable and other crops. On slopes this method improves water permeability and water absorption, reduces water runoff and soil washout. For winter crops the depth of loosening is 25-27 cm, for row crops – 30-40 cm.

Tiered plowing

The techniques of radical improvement of sod-podzolic and gray forest soils include two- and three-tier plowing, mutually shifting adjacent layers in depth respectively. For this purpose, two- and three-tier ploughs are used, for example, ПТН-3-40.

Methods of deepening the arable layer of black earth and chestnut soils

Black earth soils

The condition for the rational use of the high potential of natural fertility of black earth soils is to create a thick to 30-35 cm arable layer.

Deepening and improvement of the state of cultivation is more necessary for podzolized and leached black earths. Significant compaction of these soils, the equilibrium density of which reaches 1.25-1.30 g/cm3, leads to deterioration of aeration, reduction of activity of microbiological processes, worsens nutritive and water regimes.

Ploughing with ploughs with deepeners, notched bodies, and non-moldboard deep loosening, i.e. methods that do not bring the soil with unfavorable properties for plant growth to the surface, are used for deepening on podzolic and leached black earths. The depth of loosening of subsoil layer depends on its properties and is 8-12 cm.Using plows with skimmers and deepeners or notched bodies allows good mixing of the upper humus layer and fertilizers with the soil subsoil layer.

Deep non-moldboard loosening at a depth of 25-27 cm with stubble remaining on the surface with the help of subsurface (flat-cut) deep tillers such as КПГ-250А, КПГ-2-150, ПГ-3-5, ПГ-3-100, as well as chisel tools, ploughs with SibIME tines, paraplau and others are used on sloping lands.

On typical and common black earth soils with a thicker humus layer use single deepening by plowing with plows without skimmers to a depth of 30-32 cm. The soil is pre-tilled with heavy disc-tillers to a depth of 10-12 cm, which provides better mixing of fertilizers and soil included layer.

The beneficial effect on the fertility of typical and ordinary black earth is produced by two-tier plowing by ploughs ПНЯ-4-40, ПНЯ-6-40 to the depth of 32-35 cm for sunflower, sugar beet and other row crops. The two-tier plough ПНЯ-6-40 is equipped with six pairs of bodies, which are arranged in two tiers: the bodies of the upper tier are equipped with half-screw mouldboards, and the bodies of the lower tier – with cultivation mouldboards. Due to such construction the double tier ploughing allows turning of the upper 0-20 cm layer with simultaneous loosening and overturning of the lower one.

The deep non-moldboard loosening techniques with the use of subsurface (flat-cut) deep tillers, tools of paraplau type with leaving stubble on the surface of the field positively affect the agro-physical properties of black earth soils. For embedding organic fertilizers in the upper part of the arable layer heavy disc-tillers are used to create a mulching layer.

Frequency of deep tillage on black earth soils is 4-5 years.

Chestnut soils

Chestnut soils are typical for dry steppe zone and are formed in hot climate conditions. They are close to black earths by their physical and water properties, first of all by moisture capacity, value of total porosity, ratio of intra-aggregate and inter-aggregate porosity.

Dark chestnut soils are characterized by the content of more than 3-4% of humus and the depth of the humus horizon up to 20-40 cm. On such soils it is advisable to deepen the arable layer once by plowing to a depth of 25-27 cm.

Light chestnut soils are characterized by less favorable water and physical properties: humus content is less than 3%, thickness of humus horizon is less than 20 cm. Therefore, these soils need deepening and improvement of the state of cultivation. The most effective way of deepening is plowing to the depth of humus horizon with loosening of subsoil layers by 8-10 cm with simultaneous application of organic and mineral fertilizers.

On solonetzic chestnut soils gypsum of plowed soil to remove excess of exchangeable sodium is preliminarily carried out. On meadow chestnut saline soils the plowing is carried out to the depth of over-saline layer, with simultaneous loosening of subsoil horizon to the depth of 32-35 cm.

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

Deepening of arable layer and methods to improve fertility of saline soils

Saline (alkaline, also sodium) soils due to a number of unfavorable for plants agrochemical and agrophysical properties do not allow to use them for growing crops without radical improvement of fertility.

The presence of exchangeable sodium gives saline soils an alkaline reaction (pH 8-9), which contributes to dispersion and washing away of soil colloids down the profile and worsens structuring. When wetting, saline soils swell, viscosity increases, water permeability decreases, and when drying they become cemented, which greatly complicates their tillage and prevents deep penetration of root systems of plants.

To improve the state of cultivation of saline soils a set of measures for their radical improvement is applied, including:

  • deepening of the arable layer,
  • introduction of gypsum,
  • introduction of organic and mineral fertilizers,
  • sowing of salt tolerant plants,
  • measures on moisture accumulation.

Selection of measures depends on the depth of alkaline horizon, its thickness, salt composition, level of groundwater and other indicators.

Automorphic solonetz soils are most common in Russia: black earth and chestnut soils. Black earth, meadow sodic saline soils are found in the Black Earth zone, for example, in the Trans-Urals and Western Siberia, are characterized by an alkaline reaction, close to the surface groundwater level, with a risk of secondary salinization. Deep tillage and gypsum application are necessary to improve their properties.

Chestnut steppe saline soils are widespread in the zone of chestnut soils, for example, in the Middle and Lower Volga region, Eastern Caucuses, the south of Western Siberia. They are characterized by neutral reaction, deep level of groundwater, which slows down the flow of salts into the root layer. Deep tillage without the application of gypsum is sufficient to improve these soils.

On shallow and medium-columnar black earth saline soils with a depth of over-saline horizon of 10-18 cm, in the absence of gypsum horizon, periodic non-moldboard loosening at 25-28 cm is effective. Involvement in arable horizon of saline horizon sharply reduces its fertility. Therefore, gypsum, organic and mineral fertilizers are applied simultaneously. Before deep tillage, fertilizers and ameliorants are mixed with the upper over-saline soil layer with the help of disc- or milling tools to the depth of 10-12 cm. To increase the efficiency of amelioration, it is carried out in autumn, supplemented by snow retention, the introduction of strip sowing and moisture storage techniques. In subsequent years, soil with improved properties of saline horizon is plowed to the humus layer.

Saline soils cannot be ploughed deep at once, as a large amount of alkaline salts of the lower horizons when moving to the surface sharply reduce fertility. Arable layer of such soils deepen gradually with the simultaneous introduction of gypsum and organic fertilizers.

Introduced gypsum eliminates the excess of absorbed sodium, increases the coagulation of soil particles, contributing to the formation of a solid lumpy structure. The organic matter of fertilizers activates the activity of soil microorganisms. Thus, agrophysical, agrochemical and biological properties of saline soils are improved.

To activate microbiological processes and improve physical properties, tiered plowing is also used, where the arable layer remains on top and the compacted saline layer is mixed with the underlying carbonate layer.

Deep-column saline soils with location of saline layer at a depth of more than 18 cm are tilled with ploughs with skimmers and deepeners or with notched bodies with full capture of over-saline layer. At the same time a full dose of gypsum is introduced before plowing so that the ameliorant is dumped by the skimmer to the bottom of the furrow and with the help of ripper foot mixed with the saline horizon.

The effectiveness of improving the state of cultivation of saline soils increases with subsequent sowing in the rotation of salt-tolerant plants, for example, melilot, agropyron, alfalfa, sorghum, etc.

On low-salinity steppe saline soils with sodium content less than 10% deep reclamation treatments without applying gypsum are the most effective.

On chestnut steppe saline soils with low thickness of over-saline layer and shallow occurrence of gypsiferous layer in the profile it is possible to improve with deep 30-35 cm plowing with subsequent mixing of gypsiferous layer with humus layer, as well as application of organic and mineral fertilizers.

On soils with medium and deep location of saline horizon in the presence of calcium carbonate and gypsum in deep horizons, plantation or three-tier plowing at 40-45 cm is used. Thus, at three-tier plowing with ПТН-340 ploughs, the upper humus layer is overturned, and the saline layer is interchanged with illuvial layer. During further tillage in crop rotation illuvial layer, which is enriched with soil colloids and calcium salts, is included to humus layer of soil. As a result of interaction of gypsum and absorbed sodium excess alkalinity, salinity are eliminated, physical, chemical and biological properties of soil are improved.


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