Soil Tillage

Importance of Soil Tillage

Objectives of soil tillage:

• giving the soil a fine crumb structure and creating an optimal constitution in terms of density, porosity, etc., under which optimal conditions are formed for the growth and development of plants and microflora;
• maintaining a good phytosanitary condition;
• preventing erosion processes and overcompaction, reducing washout and unproductive losses of water, humus, and nutrients.

Soil tillage is necessary for the reproduction and improvement of fertility by deepening and increasing the thickness of the arable layer, loosening the plow pan in the subarable layer, and incorporating organic and mineral fertilizers and ameliorants.

Soil tillage makes it possible to improve soil aeration, increase the moisture supply of plants, and activate the vital activity of microorganisms. Well and deeply tilled soil allows plants to form a powerful root system. High-quality loosening and leveling of the surface during pre-sowing tillage create favorable conditions for seed germination and seedling emergence.

Deep loosening in dry steppe conditions and on sloping lands makes it possible to regulate the water regime by accumulating atmospheric precipitation moisture in the root zone or, conversely, draining excess water from the field, which indirectly affects other soil regimes.

The tasks of tillage differ substantially depending on soil-climatic conditions and the biological characteristics of crops.

Tillage can have negative consequences: disruption of the dynamic equilibrium in the soil–plant–environment system. Thus, intensive tillage activates the vital activity of soil microflora, accelerating the mineralization of humus and increasing its unproductive losses. The decomposition of sod and pulverization of the top layer in areas at risk of wind erosion create prerequisites for soil destruction and the onset of erosion.

Repeated passes of agricultural machinery lead to severe overcompaction of the arable layer, worsening its properties and intensifying water runoff and soil removal. Soil tillage is an energy-intensive process requiring up to 10–15 thousand MJ of energy per 1 ha, which is not always paid back by the yield.

The results of long-term studies by domestic and foreign scientists indicate that a high level of agricultural intensification through the use of fertilizers, herbicides, ameliorants, irrigation, etc., changes the functions of tillage, reducing its share in crop formation to 8–12%. This is especially characteristic of soils with a high potential level of fertility and favorable agrophysical properties. Under these conditions, excessive impact is inadvisable, and the role of tillage can be reduced to technological functions: incorporation of fertilizers, herbicides, ameliorants, seeds, etc. The main tasks then become reproduction of fertility, regulation of the water regime, and protection from erosion. Conversely, at a low level of agricultural intensification, insufficient application of fertilizers, plant protection products, etc., the importance of tillage increases and consists in mobilizing potential fertility, increasing the share of available forms of nutrients, and maintaining optimal structure and phytosanitary condition.

Development of the Doctrine of Soil Tillage

Soil tillage is one of the oldest occupations of the farmer, arising simultaneously with the beginning of plant cultivation.

Significant progress in soil tillage was achieved in 1797 with the appearance of the first iron plows in England, and then in Belgium. Later, in 1863, the plow was improved by the German peasant Rudolf Sack, who used a plow with a skimmer for plowing, which made it possible for the first time to learn about the advantages of deep soil tillage.

In Russia, the first recommendations on deep soil tillage were given in the works of Professor I. M. Komov in 1788, who proposed double plowing of soil after perennial grasses, with the first plowing to a depth of 8–10 cm and the second to 10–20 cm.

A significant contribution to the development of the foundations of soil tillage was made by Russian scientists P. A. Kostychev, V. R. Williams, A. G. Doyarenko, T. S. Maltsev, and others. P. A. Kostychev wrote: The purpose of soil tillage is, among other things, to change the structure of the soil, to give it a structure most favorable for plant growth.

In his work On the Fertilization and Tillage of Chernozem Soils (1886), he substantiated shallow plowing of early fallow in dry years to improve the decomposition of sod. Conversely, on non-soddy soils, P. A. Kostychev proposed deep autumn plowing.

In the first half of the 20th century, research in the theory of soil tillage was aimed at substantiating cultural plowing with a moldboard plow with a skimmer and the thickness of the arable layer. A great merit in this belongs to V. R. Williams. The need for cultural plowing is based on the fact that by the end of the growing season of annual plants, the 10-cm soil layer is pulverized, loses structure due to the mechanical action of implements, physiological and biochemical causes, which generally leads to a decrease in fertility. The reason for this is the aerobic conditions developing in the upper soil layers, enhancing humus decomposition and hindering oxygen penetration into deeper horizons. To prevent the negative influence, it was proposed to repeat plowing annually to give the soil a cloddy structure.

In the works of A. N. Lebedyantsev (1905) and L. N. Barsukov (1952, 1956), the differentiation of the arable layer by fertility by the end of the plant growing season was determined, with its increase in the upper 10-cm layer and decrease in the lower part. Taking this discovery into account, recommendations were developed for combining moldboard and nonmoldboard tillage in crop rotation.

I. E. Ovsinsky in his work The New System of Farming (1899) substantiated plowless soil tillage, asserting that chernozem soil in its natural state can accumulate sufficient air and moisture, for which it is necessary to preserve capillarity in it and prevent drying out. If this requirement is met, it is possible to replace plowing with shallow loosening of the topsoil to a depth of 5–6 cm. For this purpose, horse-drawn cultivators with flat-cutting working parts were used. Among Western scientists, the theories of plowless soil tillage were supported by Jean (1910) in France, F. Achenbach (1921) in Germany, and E. Faulkner (1959) in the USA.

The largest achievement of agronomic science and practice can be considered the system of nonmoldboard soil tillage proposed by T. S. Maltsev, replacing plowing with turning of the furrow slice. In the system he recommended, nonmoldboard loosening of the soil to a depth of 35–40 cm, carried out once every 3–5 years, should be combined with surface treatments to 5–8 cm using stubble cultivators or disk harrows as applied to grain-fallow crop rotations. The use of nonmoldboard tillage led to an increase in field weed infestation due to the lack of chemical means of weed control, which became a limitation of its use.

Soil-protective tillage was further developed thanks to research by the ARRI of Grain Farming under the leadership of Academician A. I. Barayev. It is based on flat-cutting tillage with stubble and plant residues left on the soil surface, with a complete rejection of moldboard plows, tine and disk implements, and their replacement by flat-cutting subsoilers, needle harrows, and stubble seeders. The use of this tillage technology makes it possible to preserve up to 70–80% of stubble on the soil surface, protecting moisture from evaporation and giving the soil wind resistance.

However, on heavy, overcompacting soils, flat-cutting subsoilers do not provide high-quality loosening. Therefore, for these purposes, chisel, nonmoldboard implements such as the paraplow, replaceable SibIME tines for plows have been created and are used, which expand the possibilities of soil-protective tillage, especially on lands with an increased risk of erosion.

In the 1970s in the USSR, a new direction began to be developed—minimization of soil tillage, which focuses on reducing soil overcompaction, reducing losses of organic and nutrient substances from the soil, and reducing energy and labor costs. A significant contribution to this direction was made by professors B. A. Dospekhov, S. A. Naumov, K. I. Saranin, A. I. Puponin, and others.

Minimization of soil tillage is achieved by reducing the number and depth of primary tillages in crop rotation on soils with sufficiently favorable properties for plant growth, combining technological operations, and replacing moldboard tillage with nonmoldboard tillage. These approaches make it possible to reduce the number of machinery passes over the field, shorten work completion times, increase labor productivity by 1.5–2 times, and reduce energy costs by 30–40%.

The new technology also has disadvantages: the phytosanitary condition of the soil worsens, in particular, weed infestation of crops increases, and crops are more affected by diseases and pests. A decrease in the rate of humus mineralization worsens the supply of cultivated plants with nitrogen, especially after grain predecessors, which requires additional application of nitrogen fertilizers.

For sloping lands at risk of erosion, soil-protective tillage systems have been developed based on the use of:

• nonmoldboard chisel tillage;
• plowing with slotting, with changes in the field microrelief;
• mulching the soil with straw chaff;
• reducing the treated surface and loosening depth.

In the USA and Canada, soil-protective tillage technologies have become widespread:

• mulching—continuous nonmoldboard soil tillage using chisel, flat-cutting and disk implements;
• strip—the soil is treated before sowing row crops only in the row zone using rotary tillers, cultivators; weed control is carried out by a combination of mechanical and chemical methods.

For row crops sown on slopes, ridge tillage was proposed, providing for sowing on ridges 15–20 cm high, cut by ridge-forming cultivators across the field slope. Weed control is carried out by chemical methods. Ridge technology allows the soil to warm up better, shortening the growing season of crops. Thus, the grain yield increase of corn cultivated using ridge technology was 0.35 t/ha.

Scientific Foundations of Soil Tillage

Biological Foundations

Soil tillage aimed at improving the living conditions of soil microflora helps increase fertility. In particular, loosening improves aeration, normalizes the soil water regime, and increases the number of saprophytic organisms. A decrease in the intensity and depth of loosening leads to a slowdown in the mineralization of humus substances.

Fallow, semi-fallow, and autumn tillage systems are means of improving the phytosanitary condition of the soil and crops. For example, timely autumn tillage makes it possible to reduce the number of wireworms and cereal aphids.

Technological Operations of Soil Tillage

Cutting and Separation

Main operations of mechanical soil tillage:

I — vertical cutting; II — horizontal cutting; III — separation of the furrow slice.

Cutting of soil by knives occurs in vertical (Fig., I) and horizontal (Fig., II) planes. During vertical cutting, no slice is formed, while during horizontal cutting, a slice is formed and separated.

Separation of the furrow slice from the soil mass occurs after it is cut in a horizontal, inclined, or vertical plane. The slice (Fig., III) in cross-section has the shape of a rectangle, triangle, or another geometric figure.

Turning

Turning of soil.

Turning is a technological operation of soil tillage in which layers or horizons of soil move mutually in the vertical direction. Inversion is the rotation of the soil slice in the transverse plane and a change in the mutual vertical arrangement of the upper and lower soil layers.

Inversion of the slice can be complete, that is, through an angle β = 180° (Fig., I), or partial—90° < β < 180°. Inversion of the slice through an angle up to 135° is called throw (Fig., II). Inversion of the slice in which part of the soddy layer is first cut off and dropped to the bottom of the furrow is called cultural plowing (Fig., III).

During turning, sod, plant residues, fertilizers, fallen seeds and vegetative reproductive organs of weeds, pathogens, and crop pests are incorporated. The need for turning is due to the differentiation of the arable layer by fertility, which can be strongly expressed in humid regions with a low level of farming culture.

Under the influence of plants, fertilizers, light, microorganisms, and tillage, the upper layer acquires higher structural state, biogenicity, and fertility compared with the lower layers. It contains more humus, nutrients, and microorganisms. Turning improves the fertility indicators of the lower part of the arable layer; fertilizers and ameliorants especially influence this. This is also promoted by the involvement of silt and fine-dispersed soil fractions in the arable layer. On heavy, waterlogged soils, turning reduces the harmful effect of reduced compounds on plants.

Turning is not carried out in arid conditions and areas with wind erosion, since this intensifies negative processes.

Turning is carried out by moldboard plows, share stubble cultivators, and other implements.

Loosening

Loosening of soil.

Soil loosening is a technological operation in which the size and mutual arrangement of soil clods or aggregates change with the formation of larger pores. Loosening promotes an increase in non-capillary porosity, soil aeration, water and air permeability, improvement of the thermal regime and activity of soil microflora, increased availability of moisture and nutrients, easier penetration of roots into deep soil layers, and tolerance of drought. Row crops are most sensitive to a loose soil state, while solid-sown crops are less so.

The degree of loosening is assessed by the ratio of the thickness a₂ of the loosened layer to its initial thickness a₁. During loosening, the ratio a₂/a₁ > 1.

Surface loosening makes it possible to destroy the soil crust and create a mulch layer. Loosening is carried out by passive and active working parts of implements: moldboard and disk plows, cultivators, stubble cultivators, harrows, rotary tillers, rotary hoes, etc. It is performed to a depth of 3 to 50 cm and more. To loosen the subarable layer without turning, plows with subsoilers and plows with cutaway bodies are used.

Compaction

Compaction of soil.

Soil compaction changes the mutual arrangement of soil separates with the formation of smaller pores. Compaction is the process opposite to loosening. During compaction, a₂/a₁ < 1. Soil compaction reduces non-capillary porosity, increases the volume of smaller capillary pores, and leads to closer contact of seeds with the soil.

Under conditions of insufficient moisture, compaction reduces soil aeration and moisture evaporation. It is performed during pre-sowing soil preparation and after sowing. In both cases, this technique promotes better contact of seeds (especially small ones) with the soil and improves the capillary rise of water from lower layers. Under conditions of insufficient heat in spring, compacted soil warms up better. Sometimes compaction is used to break large clods and in the treatment of loose peaty soils.

Compaction is performed by rollers with various working surfaces and other implements.

Environmental Problems of Soil Tillage

Intensification of agriculture leads to disruption of the dynamic equilibrium in the ecological system soil–plant–atmosphere, and to changes in the biogeochemical cycle of substances and energy in the biosphere. Mechanical soil tillage leads to the destruction of soil zoocenoses, earthworm burrows, and roots; the animal population decreases, and the soil's ability to self-loosen decreases. Frequent mechanical tillage accelerates microbiological processes of organic matter mineralization, which negatively affects soil structure and leads to significant unproductive losses of nutrients and moisture. The existing soil tillage technology over 30–40 years has led to a decrease in humus content in the arable layer of chernozem soils by 0.8–1.1%, and on slopes by more than 3.5% (ARRI of Agriculture and Soil Protection from Erosion). On average in Russia, with intensive moldboard tillage, about 1 ton of humus is mineralized annually in the arable layer per 1 hectare, which is equivalent to the loss of 10 tons of soil at 2.5% humus content.

References

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2. Niklyaev V. S. (2000). Fundamentals of Agricultural Production Technology. Farming and Crop Production. Moscow: Bylina.

3. Evtefeev Yu. V., Kazantsev G. M. (2013). Fundamentals of Agronomy: A Textbook. Moscow: FORUM.

4. Khalansky V. M., Gorbachev I. V. (2004). Agricultural Machines. Moscow: KolosS.