Tillage – mechanical impact on the soil by tillage machines and implements in order to create optimal soil factors of plant life, as well as the destruction of weed vegetation and soil protection from erosion processes. It is the main agrotechnical means for regulation of soil regimes, intensity of biological processes and phytosanitary condition. Quality, timely, scientifically grounded tillage is the means of increasing fertility, crop yields and an integral part of intensive effective resource-saving farming systems.
- The importance of tillage
- Developments in the science of tillage
- Scientific basis of tillage
- Technological operations of tillage
- Soil physical and mechanical properties and their influence on tillage quality
- Interaction of wedge with soil
- Tillage methods
- Tillage system
- Minimum tillage
- Deepening and cultivation of the arable layer of different soil types
- Tilling of soils prone to water erosion
- Tillage of soils prone to wind erosion
- Tillage of meliorated land
- Evaluation of the quality of fieldwork
- Current problems of tillage
- Main tillage
- Surface and shallow tillage
- Sowing (planting)
- Post-sowing tillage
- Special methods of main tillage
- Tillage system
- Minimum tillage
- Deepening and improvement of the arable layer
- Tilling of soils prone to water erosion
- Tillage of soils prone to wind erosion
- Tillage of reclaimed land
- Evaluation of the quality of fieldwork
- Problems of energy conservation and soil compaction
- Main tillage
- Surface and shallow tillage
- Sowing (planting)
- Post-sowing tillage
- Special methods of main tillage
- Tillage system
- Minimum tillage
- Deepening and improvement of the arable layer
- Tilling of soils prone to water erosion
- Tillage of soils prone to wind erosion
- Tillage of reclaimed land
- Evaluation of the quality of fieldwork
- Problems of energy conservation and soil compaction
The importance of tillage
Objectives of tillage:
- giving the soil a fine lumpy structure and creating optimum texture in density, porosity, etc., at which optimum conditions are created for the growth and development of plants and microflora;
- maintaining a good phytosanitary condition;
- prevention of erosion processes, overcompaction, reduction of washing away and unproductive losses of water, humus and nutrients.
Tillage is necessary for reproduction and re-cultivation by deepening and increasing the thickness of the arable layer, loosening of the plow pan in the subsoil layer, incorporation of organic and mineral fertilizers and ameliorants.
Tillage allows to improve soil aeration, increase moisture supply for plants and activate the vital activity of microorganisms. Well and deeply cultivated soil allows plants to create a powerful root system. Quality loosening and leveling of the surface during pre-sowing cultivation – allows you to create favorable conditions for seed germination and emergence of seedlings.
Deep loosening in the steppe arid conditions and on sloping lands allows to regulate water regime, accumulating moisture of atmospheric precipitation in root-inhabited layer, or, on the contrary, withdrawing excessive water from the field that indirectly influences other soil regimes.
Tillage tasks differ significantly depending on soil and climatic conditions and biological features of crops.
It is worth noting that the tillage can have negative consequences: violation of the dynamic equilibrium in the system soil – plant – environment. Thus, intensive treatment activates the vital activity of soil microflora, accelerating the mineralization of humus and increasing its unproductive losses. Decomposition of turf and dispersion of the top layer in areas at risk of wind erosion creates the preconditions for soil destruction and erosion.
Repeated passes of agricultural machinery lead to strong over-compaction of the arable layer, worsening the properties, intensifying water runoff and soil drift. Tillage is an energy consuming process, requiring up to 10-15 thousand MJ of energy per 1 ha, which is not always paid back by the harvest.
The results of long-term studies of Russian and foreign scientists indicate that the high level of intensification of agriculture through the use of fertilizers, herbicides, ameliorants, irrigation, etc., change the function of tillage, reducing its share in the formation of yields to 8-12%. This is especially characteristic of soils with high potential fertility and favorable agrophysical properties. In these conditions excessive influence is inexpedient, and the role of tillage can be reduced to technological functions: filling of fertilizers, herbicides, ameliorants, seeds, etc. The main tasks in this case become reproduction of fertility, regulation of water regime and protection against erosion.
On the contrary, at low level of farming intensification, insufficient application of fertilizers, plant protection agents, etc. the importance of tillage increases and consists in mobilization of potential fertility, increasing the share of available forms of nutrients, maintenance of optimal structure and phytosanitary condition.
Developments in the science of tillage
Tillage is one of the earliest occupations of the farmer, having arisen at the same time as the beginning of plant cultivation.
Considerable progress in tillage was made in 1797 with the appearance of the first iron ploughs in England and later in Belgium. Subsequently, in 1863, the plow was improved by the German farmer Rudolf Sack, who used for plowing the plow with a skimmer, which allowed the first to learn the benefits of deep tillage.
In Russia the first recommendations for deep tillage were given in the works of Professor I.M. Komov in 1788, who proposed the double plowing of the soil from under perennial grasses, with the first plowing the depth was 8-10 cm, the second – 10-20 cm.
Significant contribution to the development of the basics of 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 tillage is, among other things, to change the structure of the soil, to give it such a texture, which is most favorable for the growth of plants.”
In his work “On the issue of fertilization and tillage of chernozem soils” (1886), he justified shallow plowing of early fallow in dry years to improve turf decomposition. On the contrary, P.A. Kostychev suggested deep autumn plowing on soils not covered with grass.
In the first half of the XX century, research in the theory of tillage was aimed at justification of cultural plowing with plow with skimmer and thickness of the arable layer. Much credit for this belongs to W.R. Williams. The need for cultural plowing is based on the fact that by the end of the growing season of annual plants 10 cm layer of soil is dispersed, loses structure from the mechanical effects of tools, physiological and biochemical reasons, which generally leads to a decrease in fertility. This is caused by aerobic conditions formed in the upper layers of the soil, increasing the decomposition of humus, the difficulty of oxygen penetration into the deeper horizons. To prevent the negative impact, it was proposed to repeat annual plowing to give the soil a lumpy structure.
In the works of A.N. Lebedyantsev (1905) and L.N. Barsukov (1952, 1956) differentiation of arable soil by fertility by the end of vegetation period was determined. Taking into account this discovery recommendations on combination of mouldboard and non-moldboard tillage in crop rotation were developed.
I.E. Ovsinsky in his work “New Farming System” (1899) justified tillage without ploughing, stating that chernozem soil in its natural state can accumulate sufficient amount of air and moisture, for which it is necessary to preserve its capillarity and not to allow drying. If this requirement is satisfied, 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 blade working tools were used.
Among western scientists, the theory of tillage without plow was followed by Jean (1910) in France, F. Achenbach (1921) in Germany, E. Faulkner (1959) in USA.
The system of non-moldboard tillage proposed by T.S. Maltsev, which replaces the plowing with soil turnover, can be considered the greatest achievement of agronomic science and practice. The system recommended by him includes subsurface tillage of 35-40 cm in depth every 3-5 years combined with surface tillage at 5-8 cm with the help of stubble ploughs or disc harrows as applied to cereal-fallow crop rotations.
The use of non-moldboard tillage led to an increase in weed infestation of the fields due to the lack of chemical means of weed control, which became a limitation in its application.
Soil conservation tillage was further developed thanks to the research of the All-Russian Research Institute of Grain Farming under the guidance of Academician A.I. Barayev. It is based on flat tillage with leaving stubble and crop residues on the soil surface, with complete rejection of mouldboard plows, cogging and disc tools and their replacement by subsurface (flat-cut) deep tillers, needle harrows and stubble seeders. Application of this technology allows to keep on the surface of the soil up to 70-80% of stubble, which protects moisture from evaporation, and gives soil wind resistance.
However, on heavy reconsolidated soils, subsurface (flat-cut) deep tillers do not provide high-quality loosening. Therefore, for these purposes, chisel, non-moldboard tools of paraplau type, interchangeable SibIME stands to ploughs were created and are used, which expand the possibilities of soil-protective cultivation, especially on the lands with increased erosion risk.
In the 70s in the USSR began to develop a new trend – minimization of tillage, which focuses on reducing over-compaction of soil, reducing losses of organic and nutrients from the soil, reducing energy and labor costs. Professors B.A. Dospekhov, S.A. Naumov, K.I. Saranin, A.I. Puponin and others made a significant contribution to this direction.
Minimization of tillage is achieved by reducing the number and depth of the main tillages in the rotation on soils with sufficiently favorable properties for plant growth, combining technological operations, replacement of mouldboard tillage with non-moldboard tillage, which reduces the number of passes of machinery in the field, reduces the time of work, increase productivity by 1.5-2 times and reduce energy costs by 30-40%.
The new technology has also disadvantages: the phytosanitary condition of the soil deteriorates, in particular, the weed infestation of crops, and crops infestation by diseases and pests increases. At the same time, reducing the rate of humus mineralization worsens the provision of crops with nitrogen, especially after cereal predecessors, which requires additional nitrogen fertilizers.
For sloping lands at risk of erosion, systems of soil-protective tillage have been developed, based on the use of non-moldboard chiseling; plowing with slitting, with changes in the field microrelief; mulching the soil with straw chips and reducing the cultivated surface and depth of loosening.
In the USA and Canada soil-protecting tillage technologies are widespread:
- mulching – continuous non-moldboard tillage with the use of chisel, subsurface flat-cut and disk implements;
- strip tillage – soil is cultivated before tilled crops sowing only in the row area with the help of milling machines, cultivators; weed control is carried out by a combination of mechanical and chemical methods.
For row crops sown on slopes, ridge cultivation was suggested, providing sowing on ridges 15-20 cm in height, which are making by ridge-forming cultivators across the slope of the field. Chemical methods are used to control weeds. Ridge technology allows the soil to warm up better, reducing the period of vegetation of crops. Thus, the increase in grain of corn cultivated by ridging technology was 0.35 t/ha.
Scientific basis of tillage
Creating optimal conditions in the soil for plant growth is the main task of tillage. Among the most important agrophysical indicators are the density and texture of the arable layer, structural composition and degree of crumbling, the thickness of the arable layer and others, which directly affect crop yields.
The quantitative characteristic of soil structure is density.
Equilibrium density is the density of soil that is established in natural conditions in the absence of tillage within 1-2 years and is formed under the influence of gravity, precipitation and other natural factors.
Optimum density is the density of soil at which there are the most favorable conditions for plant growth and life of soil microorganisms.
The study of plant response to the physical state of soils of different genesis allowed us to determine the intervals of optimum density values for cereals and row crops. For example, modeling the density of sod-podzolic medium-loamy soil showed that the optimum density in years with average moisture content for grain crops is 1.1-1.3 g/cm3, for row crops – 1.0-1.2 g/cm3. Equilibrium density of the same soils is 1.35-1.50 g/cm3.
Table. Equilibrium and optimum soil density for field crops (according to A.I. Puponin, 1986), g/cm3Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. - M.: Publishing house "Kolos", 2000. - 551 p.
|Swampy||Degree of peat decomposition 35-40%|
The ratio of equilibrium and optimum densities allows to determine the necessity of tillage, its intensity and depth. Thus, at plowing sod-podzolic soil its density decreases from 1.4-1.5 to 0.8-0.9 g/cm3.
Density depends on granulometric composition, humus, quantity of water-resistant aggregates and moisture.
With a heavy granulometric composition with a large proportion of silt fraction and humus soils are subjected to significant swelling in moisture and loosening, which leads to a change in the equilibrium and optimal density.
Black earth soils with high humus content have an equilibrium density of 1.0-1.3 g/cm3 that coincides with the optimum density, which allows reducing the intensity and depth of tillage. Optimal conditions for the emergence of seedlings of cereal crops, as well as reducing moisture evaporation, are in the black earth heavy loamy soils with the density of the upper 7 cm layer of 0.98-1.04 g/cm3 and the bottom at a depth of 7-30 cm – 1.18-1.20 g/cm3.To achieve this combination of densities, a combination of different deep moldboard and non-moldboard tillage with surface tillage is used.
The use of heavy tillage machines and transport vehicles leads to strong compaction up to 1.35-1.55 g/cm3, which deteriorates the physical and mechanical properties. That, for example, affects the germination of winter wheat seeds, which decreases from 81.1 to 60.7%. In turn, over-consolidation causes the need for deep loosening with non-moldboard, chisel implements, plows for deep loosening and other aggregates.
The structure of the arable layer
Soil structure – the ratio of solid phase, capillary and non-capillary porosity. Optimal conditions for plant growth and development are found in sod-podzol medium-loam soil with total porosity of 46-56%, noncapillary porosity – 18-25%, capillary porosity – 28-31%, and the proportion of solid phase 44-54% of soil volume.
For black earth soils optimal conditions are formed at total porosity of 51-62% and aeration porosity – 15-25%. Ultimate porosity of stable aeration, at which a decrease in grain yields is observed, is – 13-15% of soil volume. At the same time, the oxygen content in the wetted soil is not less than 20%, and CO2 is not more than 0.2-0.5%.
Treatment allows to improve the structure of the arable layer: loosening in the main and pre-sowing treatments allows to increase non-capillary porosity, and compaction of excessively loose – to reduce non-capillary porosity and reduce aeration.
Creating an optimal model of the fertility of the arable layer allows the most favorable soil regimes, which contributes to higher crop yields. Modeling of homogeneous and heterogeneous state of arable layer of sod-podzolic soil with different thickness of arable horizon showed that potatoes, corn and other field crops respond positively to heterogeneous composition of soil profile, in which in the upper 20 cm due to fertilizers and lime more optimal agrophysical and agrochemical properties are created.
Yield increase of field crops under heterogeneous structure of arable layer and introduction of high doses of fertilizers at the depth up to 20 cm for 15 years increased from 3,8 to 9,7 thousand feed units per 1 ha compared with unfertilized background. In conditions of homogeneous structure – from 3.4 to 8.9 thousand fodder units per 1 hectare. Fertilizer application on the depth up to 40 cm reduced the yield in fodder units by 10,8%, which indicates the mixing of arable layer with soil of eluvial horizon characterized by low natural fertility and not allowing to restore fertility to the initial level even for 15 years period.
Table. Yields of field crops depending on the structure of 0-40 cm layer of sod-podzolic soil, t/haFarming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. - M.: Publishing house "Kolos", 2000. - 551 p.
|Vetch-oat mixture (hay)|
|Corn for silage|
|Average for 15 years, thousand fodder units per 1 ha|
Soil structure depends on the content of water-resistant aggregates, its stability against erosion and compaction, affects soil regimes and determines the productivity of crops.
The optimum content of water resistant macrostructure, i.e. aggregates of 0.25-10 mm and more for gray forest and sod-podzolic soils is 30-45%, for chernozem soils – 45-60%. This structure allows for a long time to keep a stable structure, given to it by processing. Structured soil loses its positive properties when the amount of dust particles less than 0.25 mm in size increases to 30-40%.
The proportion of humus in the upper 10 cm layer is higher than in the depth of 10-20 cm. In the upper layer, structure restoration is faster due to the accumulation of crop residues and fertilizers. Turnover of the soil layer during plowing contributes to the structuring of the lower part of the arable layer.
Crop requirements to the degree of crumbling is determined by the granulometric composition, texture, degree of moisture, biological characteristics of the crop and the risk of erosion. For example, for grain crops in the Non-Black Soil Zone degree of crumbling, that is, the proportion of lumps with a diameter of 0.25-30 mm, sod-podzolic and gray forest soils must be at least 80% and clumpiness – no more than 20%.
Soil hardness is a property that has a strong influence on growth and root penetration. When heavily compacted when dried and the hardness increases to critical values of more than 10 kg/cm2 for grain crops, leads to reduced root growth and increased energy expenditure of plants to overcome the resistance of the soil. Deep loosening facilitates root penetration into the deep layers, which is especially important for the formation of root crops in sugar beets, carrots and potato tubers.
Soil protection tillage
Modern tillage systems in landscape farming systems have requirements for erosion protection and energy saving. On slope lands with the risk of water erosion, special soil-protective technologies on the basis of deep non-moldboard loosening, chiseling, slotting, intermittent furrowing and contour ploughing with making ridges, holes, etc. are applied. Application of these methods allows to reduce 2-2,5 times melt water and storm water runoff and 2,5-11 times soil washout. The efficiency of mineral fertilizers application increases by 10-12% and grain yield increases by 0,15-0,2 t/ha.
In the steppe and forest-steppe zones, where soils are prone to wind erosion, the soil-protective system includes mulching, strip-till and other minimum tillage with the use of loosening, but not overturning layer of working tools of machines, such as subsurface (flat-cut), chisels, paraplau, SibIME racks, direct-seeded seeders that keep stubble and stubble residues on the surface.
More phosphorus and potassium accumulate in the upper 10-cm layer. The high content of organic matter contributes to structuring and good absorption properties. This is due to the localization of phosphorus and potassium in the upper layers due to organic and mineral fertilizers. One thing, the application of excessive doses of phosphorus and potassium fertilizers can exceed the allowable load on the soil and the root system of plants, which leads to a decrease in fertility and crop yields.
At the same time, the concentration of nutrients in the upper layer with shallow surface treatments leads to depletion of the deeper layers of the root zone. Under unfavorable conditions, such as the surface layer drying out in the absence of precipitation, nutrients become unavailable. Deep periodic plowing in the crop rotation avoids these negative phenomena, which ensures the turning and mixing of the soil layers. In addition, the concentration of crop residues, which leads to the accumulation of toxic substances in the soil of decomposition products, is eliminated, except on lands at risk of erosion.
The widespread use of chemical crop protection agents necessitates the use of intensive tillage systems that aim to improve aeration and accelerate deactivation of pesticides such as promethrin.
Soil fertility is largely determined by the activity of biological processes, so tillage aimed at improving the living conditions of soil microflora contributes to improving fertility. In particular, loosening improves aeration, normalizes the soil water regime, and increases the number of saprophytic organisms.
Reducing the intensity and depth of loosening leads to a slowdown in the mineralization of humus matter, which is a key factor in soil fertility. Thus, replacement of plowing with non-moldboard subsurface flat-cut tillage increases the humification of organic matter by 20-30%, on light loamy soils by 40%. Liming of acidic soils shifts the process of synthesis of humus compounds in the direction of formation of the most valuable of them.
The depth and method of tillage affect the phytosanitary potential of the soil and its weed infestation. Thus, the annual subsurface flat-cut tillage during 5-7 years increases the damage of oats by root rot by 6,9-8,3%, of barley – by 11,3-12,4%, the weediness – by 2 times. This fact leads to the necessity of alternation of non-moldboard tillage with deep tillage in crop rotations.
Fallow, half fallow and autumn tillage systems are means to improve the phytosanitary state of the soil and crops. For example, a timely system of autumn tillage serves to reduce the number of wireworms and cereal aphids. Stubble flaking and autumn plowing with a plough with a skimmer allows deep embedding of weed seeds, stubble, and together with them the larvae of Swedish and Hessian flies, caterpillars of winter moths. This kills spores of linear and brown rust, infection, root rot, septoriosis. Deepening of the arable layer, ploughing, and tillage in dry conditions reduces the weediness of fields, improves moisture supply to plants, and accelerates their growth.
Technological operations of tillage
Cutting and separating
Soil cutting by knives occurs in the vertical (Fig., I) and horizontal (Fig., II) planes. Vertical cutting produces no chips, while horizontal cutting produces and separates chips.
Separation of the layer from the soil mass occurs after it is cut (cut off) in the horizontal, inclined or vertical plane. The layer (Fig., III) in cross-section has the shape of a rectangle, triangle or other geometric figure.
Turning (overturning) is a technological operation of tillage in which there is a mutual movement in vertical direction of soil layers or horizons. Turning is rotation of soil layer in transverse plane and change of mutual vertical position of upper and lower soil layers.
The layer rotation can be complete, i.e. by angle β = 180° (Fig., I), and partial – 90° < β < 180°. Reservoir turnover by an angle of up to 135° is called a take-off (Fig., II). Rotation of the layer, where a part of the sod layer is cut off and dumped to the bottom of the furrow, is called cultural plowing (Fig. III).
When overturning, turf, plant residues, fertilizers, crumbled seeds and vegetative organs of reproduction of weeds, pathogens of diseases and pests of crops are incorporated. The necessity of overturning is caused by differentiation of arable soil by fertility, which can be strongly pronounced in humid areas with low farming culture.
Under the influence of plants, fertilizers, light, microorganisms, treatment, the top layer becomes more structured, biogenic and fertile compared to the lower layers. It contains more humus, nutrients and microorganisms. Overturning improves the fertility indicators of the lower part of the arable layer, especially it is affected by fertilizers and ameliorants. It is also promoted by the involvement of silty and finely dispersed fractions of the soil in the arable layer. On heavy, overwatered soils, overturning reduces the harmful effect of sour compounds on plants.
Overturning is not carried out in arid conditions and areas with wind erosion, as it intensifies negative processes.
The overturning is carried out by mouldboard ploughs, polydisk tiller and other implements. Turf, weeds, stubble and root residues are best incorporated during the plowing of plows with skimmers.
Loosening is a technological operation, which changes the size and relative position of soil clods or aggregates with the formation of larger pores. Loosening helps to increase non-capillary porosity, soil aeration, water and air permeability, improve thermal regime and activity of soil microflora, increase availability of moisture and nutrients, facilitate root penetration into deep soil layers and drought tolerance. Tillage crops are the most sensitive to loosened soil condition, to a lesser extent – crops of continuous sowing.
The degree of loosening is estimated by the ratio of the thickness a2 of the loosened layer to its original thickness a1. At loosening the ratio a2/a1 > 1.
Surface loosening allows you to destroy the soil crust to create a mulch layer. Loosening is carried out by passive and active working tools: mouldboard and disk ploughs, cultivators, stubble ploughs, harrows, mills, rotary hoes, etc. It is carried out on depth from 3 to 50 cm and more. For loosening the subsoil layer without wrapping, ploughs with deepeners and ploughs with cut-out bodies are used.
Crumbling is a technological operation that crushes large lumps and clumps into smaller ones. As a rule, it is carried out simultaneously with other operations.
Crumbling reduces moisture evaporation, accelerates emergence of seedlings and stimulates plant growth, and ensures uniform seed embedding. Disc harrows, rollers, etc. are used for crumbling.
Soil mixing involves changing the mutual arrangement of soil particles, crop residues, fertilizers, and trace elements. Mixing allows to create a homogeneous tilled layer of soil with uniform distribution of products of decomposition of organic matter, fertilizer.
This technique is especially important for plowing the less fertile subsoil layer. Mixing the soil with lime or gypsum increases the effectiveness of these techniques and improves the availability of nutrients to plants.
Over-mixing is carried out simultaneously with loosening and overturning with ploughs without skimmers, mouldboard and disk stubble ploughs and soil cutters.
Compaction changes the mutual arrangement of soil particles with the formation of smaller pores. Compaction is an inverse process to loosening. Compaction is a2/a1 < 1. Soil compaction reduces non-capillary porosity, increases the volume of smaller capillary pores, and results in closer contact between seed and soil.
In conditions of insufficient moisture compaction reduces soil aeration and moisture evaporation. It is performed during seedbed preparation and after sowing. In both cases, this method promotes better contact of seeds (especially small ones) with the soil and improves water inflow from the lower layers. Under conditions of lack of heat in the spring, compacted soil warms up better. Sometimes it is used for crushing large clods and in the treatment of loose peaty soils.
Compaction is carried out by rollers with different working surface and other implements.
Leveling the soil surface is a technological operation to eliminate unevenness of the soil surface. It is necessary to reduce moisture losses for moisture evaporation, to prepare the plot for irrigation, to sow seeds evenly, to perform quality work of seeding, harvesting machines and plant care.
Surface leveling is carried out by float, scrubber, harrows, rollers, mala (heavy scrubber). In conditions of irrigated agriculture graders, bulldozers and levelers are used.
Cutting weeds is an agrotechnical method of weed control. It is carried out simultaneously with loosening, overturning and mixing the soil during plowing, cultivation, husking or using special knife, boom, cultivators, as well as special cultivators with double-sided or single-sided razor blades.
Creation of micro-relief, such as furrows, ridges, slots, holes, microlimans, etc. on the soil surface. This technique is necessary to regulate and create the most optimal water, air, nutrient, thermal regimes on sloping lands subjected to water erosion. Microrelief prevents water runoff and along with it soil washing away. The furrows help to divert excessive water. To create micro-relief use furrow breakers, sweep hilling, ridge breakers adapted to plows, hole breakers, and slitters.
In areas with insufficient moisture to increase the amount of water in the soil at the expense of autumn and winter precipitation and spring meltwater microrelief is created by intermittent furrowing of autumn arable land, trenching, slotting, etc.
When stubble is retained on the soil surface under conditions of erosion risk, the use of flat-cut cultivators, needle harrows, stubble seeders, deep subsurface flat-cut deep tillers, etc.
Soil physical and mechanical properties and their influence on tillage quality
Physical and mechanical properties – properties of soil, characterizing the physical state and relationship to external and internal mechanical influences:
- physical ripeness,
- shrinkage, etc.
Physical and mechanical properties determine the quality of technological operations of soil processing and the degree of its deformation during the operation of agricultural machinery.
They have a significant impact on the conditions of plant growth and development and depend on moisture, granulometric composition, content of organic matter and composition of absorbed cations.
Hardness is the property of soil in natural conditions to resist the action of wedging forces. Hardness is affected by humidity, texture, and granulometric composition. Hardness increases with drying. High hardness negatively affects the growth of plant roots, increases energy costs for processing and wear and tear of working elements of machinery.
The unit of measurement of soil hardness is N/cm2 or kg/cm2. To determine soil hardness, first measure with density meters the resistance force of soil to vertical penetration into it by the tip of the device of various shapes (plunger, cone, ball, cylinder), and then divide this force by the cross-sectional area of the penetrated body.
Black earth and structured soils have the least hardness. Optimal hardness of black earth at moisture content 0.7 of the lowest moisture content for grain crops is 7-9.9 kg/cm2, for corn – 5.2-7.2 kg/cm2, for potatoes – up to 5 kg/cm2.
Cohesiveness is the property of soil to resist loosening action. Heavy clay soils and solonetz in a dry state have the greatest cohesion, which is manifested in poor crumbling, clumpiness and increased energy costs for tillage. When wet, these soils adhere strongly to the working tools of machines. Light and well-structured soils have the least cohesion, which allows to handle them in a wide range of moisture.
The cohesiveness increases resistance to erosion.
Plasticity is the ability of the soil in the wet state to change and retain the shape under the action of external forces and deform without the formation of cracks. Plasticity depends on the granulometric composition, the composition of the colloidal fraction and absorbed cations, humus content. Plasticity is manifested in a certain range of soil moisture. Upper limit of plasticity is determined by lower limit of fluidity.
Lower limit of plasticity is manifested at humidity, at which the soil passes from semi-solid consistency to viscoplastic consistency, such as rolling out into a cord. The ratio between the upper and lower limits of plasticity is measured by the number of plasticity, equal to 0 to 7 for sandy loam soils, 7 to 17 for loamy soils, and more than 17 for clay soils. The most plastic soils are clayey, loamy and solonetz soils.
Stickiness of soils characterizes the ability of its particles to stick and adhere to the working bodies and wheels of agricultural machinery. It is manifested when a certain level of soil moisture is exceeded.
Stickiness is measured in N/cm2. To determine the stickiness of the soil the force required to tear off the steel plate stuck to the soil is divided by the sticking area.
Stickiness depends on humidity and dispersity of soil. At constant normal pressure, stickiness grows with increase of soil humidity up to maximum value, and then, as a result of increase of water film thickness on sticking surface, it decreases. Stickiness of implements increases with increase of soil dispersibility (atomization).
Clayey soils have the highest stickiness. In atomized, i.e. unstructured, soil stickiness begins to appear at relative humidity of 40-50%, whereas in structured soil – at 60-70%. Therefore, it is necessary to preserve and restore the soil structure, which creates optimal fertility conditions and reduces stickiness of implements.
To reduce stickiness, measures aimed at increasing fertility and restructuring are promoted: application of organic fertilizers, liming or plastering, drainage of over-moistened areas, covering surfaces of working tools with polymeric materials, use of slatting blades on plough bodies, etc.
Physical ripeness is an optimal interval of moisture for tillage, at which physical and mechanical properties have the best qualities for carrying out technological operations.
For loamy soils physical ripeness corresponds to 40-60% of the smallest moisture capacity, for light soils – 40-70% of the smallest moisture capacity. In view of compaction under the action of heavy machinery processing is accepted to conduct at 60-70% of the smallest moisture capacity.
High quality of processing with the least traction resistance is achieved with 14-18% moisture.
Carrying out processing of dry soil is undesirable because of poor crumbling, strong clumping, dispersion and compaction.
The best quality of loosening is reached when the soil is physically ripe in the spring to the depth of harrowing and cultivation of 6-10 cm, in the spring plowing – 16-20 cm.
Tillage of unripe soils increases traction force and fuel consumption: on dry soils – because of increased cohesion, and on over-wet soils – because of increased stickiness.
Humidity determines the choice of tillage implements. Disc and milling implements are used for tillage of soils with 2-3% higher moisture content, aggregates with lancet, flat-blade or chisel-like working tools – with lower moisture content.
Increasing movement speed of units, for example, when plowing, up to 2.50-3.33 m/s the interval of optimum moisture is extended and the soil is allowed to handle at moisture 18-20% of the smallest moisture capacity, without compromising the quality of crumbling.
Optimal humidity corresponding to physical ripeness, in which the compaction effect of heavy agricultural machinery is minimal for the black earth soils is in the range of 15-24% of the smallest moisture capacity, sod-podzolic – 12-21% of the smallest moisture capacity, gray forests – 15-23% of the smallest moisture capacity.
Table. Intervals of soil moisture for quality tillage (by Pronin), %Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. - M.: Publishing house "Kolos", 2000. - 551 p.
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The sliding friction of the soil on the surface of the implement is called external friction. It is estimated by the force F of resistance of the soil to movement on the working surface. This force is proportional to the force of normal soil pressure on the implement:
F = fN.
The coefficient of proportionality f, or friction coefficient, depends primarily on the particle size distribution and moisture content of the soil. On sandy granular soils the coefficient by steel varies from 0.25 to 0.35; on sandy loamy soils from 0.5 to 0.7; on medium loamy soils from 0.6 to 0.9.
From the production point of view, friction during plowing is a negative factor. Force of friction on ploughshare and mouldboard surface makes 30-40% of total resistance of plough.
Several methods are used to reduce friction:
- the use of vibration and active working tools;
- creation of boundary layer of water and air over contact surface of soil with working body;
- polishing the moldboards, covering them with different materials;
- changing the geometry of the working elements;
- replacement of soil sliding by rolling on rollers.
Resistance to deformation
Resistance to deformation characterizes the strength of the soil. When cultivating the soil with different working tools it experiences deformation of compression, tension, shear, torsion and their combinations. Temporal resistance of soil (before crumbling) under different types of deformation varies within a wide range. So, loamy soil at absolute moisture of 21-28% has temporary resistance to tension 5-6 kPa, shear 10-12 kPa, compression 65-108 kPa. Therefore, loosening the soil with minimum energy consumption is possible with the use of working tools, providing stretching of the soil layer.
Abrasiveness of soil
Abrasiveness of soil is evaluated by its content of physical sand with a large number of stony inclusions of 0.25-3 mm in size, which are the cause of increased abrasion (wear) of working tools.
According to the criterion of abrasion wear soils are subdivided into groups:
- with low wear ability with sand content up to 80 %;
- medium wear capacity with sand content up to 80-95%; – medium wear capacity with sand content up to 80-95%;
- increased wear ability with sand content up to 95-100%.
Abrasive wear of blades at ploughing 1 ha of soils of the first group makes 2-30 g, of the second group – 30-100 g, of the third group – 100-450 g.
Specific soil resistance
Specific soil resistance is a generalized characteristic of the difficulty of tillage. The coefficient Kc of soil resistance during plowing is determined by measuring the traction resistance of the plough P and dividing it by the cross-sectional area of the lifted layer:
Kc = P / (abn),
where a – ploughing depth, cm; b – width of body penetration, cm; n – number of bodies.
According to the specific resistance of the soil are divided into:
- light (Kc < 3 N/cm2);
- medium (Kc = 3-5 N/cm2);
- medium – heavy (Kc = 5-7 N/cm2);
- heavy (Kc = 7-12 N/cm2);
- very heavy (Kc > 12 N/cm2).
Soil resistance coefficients for cultivation, harrowing, packing and other similar operations are determined by dividing the traction resistance of the machine by its working width.
Interaction of wedge with soil
According to geometrical form, working elements of plough and other tillage implements are made as flat or curvilinear wedges. Flat wedges include ploughshares, knives, cultivator tines, harrow teeth; curvilinear wedges include spherical discs of harrows, huskers, plough blades, and ridgers. The wedge shape is also characteristic of seeders and planters coulters.
The soil is deformed under the influence of the flat wedge, the character of which depends on the technological properties of the soil and the angle α of the wedge against the horizontal.
Low cohesion soils. The main type of deformation of low cohesion soils is shear. When the wedge moves from position I to position II, soil particles a, б (Fig., a) are pressed into the not yet deformed mass and pass into position a’, б’, i.e. the material is compacted. The buckling stress at point a is greater than at point б, because аа’ > бб’. As soon as the buckling stress exceeds the temporary shear resistance of the soil, the shear plane OA appears in front of the wedge’s blade, directed at an angle ψ to the furrow’s bottom, and a prism-like block OABa’ is detached from the bed.
After shearing, the blocks slide along the surface of the flat wedge without undergoing new deformations, and therefore do not disintegrate. The size of the clumps that break off depends on the thickness of the formation, i.e. the depth of processing. A thin layer breaks up into smaller clumps than a thick one.
Medium- and highly cohesive (loamy and clayey) soils of optimum moisture content. At the very beginning of the introduction of the wedge, the ОС crack is formed (Fig., б), which expands, and the АОС element is detached from the stratum. During further movement (from position I to position II) the wedge at first cuts a chip of variable thickness along the line ОО’ (it clears the bottom of the furrow), then it forms a new crack О’С’ and tears off the next layer element.
Hard and dry soils. The fracture extends downward (Fig., в), so the bottom turns out uneven, and the detached clump of the stratum turns out irregularly shaped.
Strongly sodded and moist loamy soils break in a wedge along the line of blade movement. The cracks arising in the bending of the layer do not reach the surface, thus the layer is not divided into separate elements and represents a continuous band (Fig., г).
The surface of the curvilinear wedge continuously deforms the formation (Fig., д), and it disintegrates into small parts.
The deformation of the formation is influenced by the intensity of change (increase) of the angle α along the height of the wedge. The greater is the difference between the angles α1 and α2, the stronger is the formation crumbling. However, at α = 45-50° the soil ceases to slide upwards on the working surface and, instead, is huddled in front of the wedge.
Depending on direction of movement and location of blade in relation to horizontal and vertical planes the character of influence of dihedral wedge on the ground changes.
Dihedral wedge with an angle α (Fig., I) separates the layer from the bottom of the furrow, lifts it, compresses it in the vertical plane and splits it into separate clumps.
The dihedral wedge with angle γ (Fig., II) separates the layer from the furrow wall, moves it aside and compresses it in the horizontal plane.
The simultaneous action of wedges with angles α and γ contributes to the destruction of the formation in two directions. Further crumbling of the chipped pieces during their movement along the surface of the wedges stops, since the angles α and γ have a constant value. For more intense crumbling of the layer set one after another a number of simple wedges with gradually increasing angles α and γ, ie a simple flat wedge is replaced by a curved one.
A dihedral wedge with an angle β (Fig., III) tilts the formation sideways. However, to transfer layer from horizontal to inclined position, it is necessary not one but a number of wedges with increasing from 0 to 90° angle β, arranged one after another. For reservoir turnover, the angle should be more than 90°.
The triangular wedge allows to replace the influence of three dihedral wedges acting successively on the formation. The trihedral wedge is an AMBO tetrahedron (figure above, IV) with three mutually perpendicular faces BOM, AOM and AOB. When the trihedral wedge moves along the x-axis, edge AB cuts the soil layer from the bottom of the furrow, edge BM cuts it from the furrow wall, and edge ABM takes the layer aside, crumbles it and turns it around.
If the angles α, γ and β are continuously changed in height, the flat trihedral wedge is transformed into a curvilinear surface. The impact of such a surface on the formation depends on its location relative to the bottom and wall of the furrow and the intensity of change (development) of angles α, γ and β along the height. If the angle α is strongly developed, the formation is crumbling intensively; if the angle γ is developed, the formation is more shifted to the side; if the angle β is strongly developed, the working surface well wraps the formation. Such surfaces, called “mouldboards”, are used on ploughs, ploughs, furrow cutters, ridgers, bulldozers and other machines, the working process of which is connected with movement of soil or soils.
Tillage methods are divided into:
- methods of main tillage;
- methods of surface and shallow tillage;
- special methods of tillage;
- post-sowing tillage, or plant care.
Main tillage is deep and continuous tillage carried out for a particular crop of crop rotation and changing the density of the arable layer and mixing layers or horizons of soil.
The main tillage methods include plowing, non-moldboard tillage, chiseling, subsurface flat-cut tillage and milling.
Shallow tillage – tillage to a depth of 8-10 to 16-18 cm. Surface tillage – tillage to a depth of 8-10 cm.
Surface and shallow tillage allow to prepare the soil for sowing, take care of fallows and plants, destroy weeds and create conditions for tillage at higher speeds and quality harvesting.
Surface and shallow tillage techniques include: disking (husking), cultivation, hilling, harrowing, rolling, leveling.
The methods of special tillage include: two- and three-level plowing, plantation plowing, slotting, mole cutting.
Post-sowing tillage is a complex of practices of crop care, aimed at creating favorable conditions for the germination of seeds, the emergence of seedlings and provide optimal conditions for plant growth and development.
Post-sowing tillage techniques include: rolling, pre- and post-growing harrowing, inter-row loosening, hilling and thinning.
Tillage system is a set of scientifically justified methods of soil treatment, consistently performed during the cultivation of a crop or in the fallow field of crop rotation, to ensure optimal soil conditions for plant growth and development.
Tillage systems regulate soil regimes and phytosanitary conditions, increase the thickness of the arable layer, and prevent the development of erosion. Tillage methods may consist of one or more technological operations, for example, chiseling allows loosening, crumbling and partially mixing the soil.
The tillage system determines the farming culture of the field and, as a consequence, the level of fertility and crop yields. The tillage system must be soil-protective, energy-saving, economically justified and environmentally friendly. Fulfillment of these requirements is connected with reasonable choice and optimum combination of applied machines, their correct adjustment and aggregation.
The choice of techniques that make up a particular tillage system is determined by landscape conditions, soil type and condition, zonal climatic features, weediness of fields, preceding crops and their biological characteristics, the fertilizer system in the crop rotation. It should provide optimal timing and high quality of work.
Currently the following systems of mechanical processing are used:
- The tillage system for spring crops is determined by the preceding crop, e.g. annual non-row crops of continuous seeding, row crops, seeded perennial grasses, bare or strip fallows, tillage for intermediate crops and after their harvesting.
- Tillage system for winter crops includes tillage of bare, strip or seeded fallows and tillage after non-fallow predecessors
Crop-specific tillage systems are combined into technological complexes or systems of tillage in the rotation.
In addition to the above, depending on soil and climatic conditions and cultivation technology of crops can be used mouldboard, no-till and tier systems.
The mouldboard system provides turnover of the soil layer, which provides embedding of crop residues, seeds of weeds and pathogens in the deeper arable layers. In this case the crop residues are quickly decomposed by aerobic microorganisms with the formation of mineral compounds, and weeds, pest larvae and pathogens are killed. The no-till system is widely used in areas of sufficient and excessive moisture.
The no-mouldboard system eliminates the turnover of the soil layer, instead, deep loosening is carried out with preservation of the stubble, protecting the soil from wind erosion. This system of tillage is used in steppe areas where there is a high risk of erosion processes, as well as in areas with insufficient moisture as a way to accumulate and store moisture in the soil.
The tiered system is accompanied by separate cultivation of the upper, middle and lower layers of soil having a pronounced tier structure. For example, when cultivating saline soils, the upper layer is wrapped and the second and third layers are loosened and mixed.
Depending on the number of treatments there are intensive, minimal and no-till systems.
Intensive system includes several technological processes in preparation of the soil for sowing, accompanied by multiple passes of aggregates, compaction and loosening of the soil.
Minimal system involves reducing the number of treatments and their depth, the combination of several technological processes in one pass of the unit. This system is used in different areas to reduce compaction and spraying of the soil by tractor engines and wheels of agricultural machinery, and reduce the time of preparation of the soil.
In some cases, not the entire surface of the field is cultivated, but only narrow strips, in which the seeds are then sown. Such tillage is called zero tillage. Tillage accompanied by covering its surface with plant residues is called mulching.
Tillage with formation of water-retaining microrelief (furrows, wells, etc.) or leaving and preservation of wind-retaining crop residues on the surface of arable land is called anti-erosion tillage.
In the conditions of ecological soil-protective farming more economical energy-saving technologies of minimum tillage are widespread.
Minimum tillage is scientifically grounded tillage, which provides reduction of energy and labor costs by reducing the number, depth and cultivated area of the field, combining and performing several technological operations in one working process.
Deepening and cultivation of the arable layer of different soil types
Deepening and cultivation of the arable layer is one of the urgent tasks of farming. Deeper arable layer allows to accumulate more moisture, organic matter, increase the zone of active activity of soil microorganisms and availability of nutrients.
Increasing the thickness of the arable layer and improving its physical properties and aeration during deepening contribute to it:
- Deeper penetration of the plant root system into the lower soil layers.
- Water accumulation in the soil from precipitation and melt water.
- Increases soil porosity and air capacity, and improves gas exchange.
- Effective control of weeds, diseases and pests.
- Loosening of the subsoil horizon and destruction of the plow pan.
- Reduced soil deformation and greater resistance to overcompaction 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.
Tilling of soils prone to water erosion
The cause of water erosion is the runoff of rainwater and meltwater, which washes away and erodes the arable layer and destroys soil fertility. Water streams carry away the most valuable silt and colloidal fractions of soil, soluble humus and nutrients.
The main tasks of tillage of soils subject to water erosion are:
- imparting a fine crumbly structure and friable soil condition to improve water permeability and moisture absorption;
- creating a certain micro-relief on the slope surface;
- reducing soil washout with surface water runoff and its accumulation in the soil;
- deepening of the arable layer;
- destruction of plow pan.
Erosion control techniques can be divided into two groups:
- techniques increasing water permeability and filtering water;
- methods that create micro-relief on the surface to retain water runoff and soil washout.
Tillage of soils prone to wind erosion
The causes of wind erosion are high wind speed at the soil surface, a high degree of dispersion with weakly structured topsoil, its low moisture content, and the lack of protective vegetative cover. Soil erosion often occurs on cultivated lands whose tillage technology does not match the landscape conditions.
The tasks of erosion control tillage include:
loosening the soil while keeping the maximum amount of stubble and other plant residue on its surface;
Creation of optimal conditions for moisture accumulation and retention in the soil;
Avoiding soil dispersion and increasing soil aeration by minimizing tillage.
The stubble left on the field surface reduces the wind speed in the surface layer to 3-4 m/s, thus preventing the soil from being blown out. In winter it allows to retain snow, contributes to the accumulation of moisture, in the hot summer period it reduces its evaporation.
Academician A.I. Barayev laid theoretical foundations of anti-erosion tillage of soils subjected to wind erosion, which are as follows:
Soils resistant to wind erosion should be classified as soils, the content in the top layer of which is more than 50% of structural aggregates with a size of more than 1 mm.
Covering more than 40% of soil surface with crop residues and stubble allows reducing wind speed in the surface layer up to 3-4 m/sec, which reduces moisture evaporation, increases soil moistening and, as a result, increases wind resistance.
Based on these principles, the anti-erosion tillage is based on subsurface flat-cutting without overturning with retention of most of the stubble on the field surface.
Tillage of meliorated land
Meliorated land includes irrigated and drained soils, as well as soils of radical and surface improvement of hayfields, meadows and pastures. Technologies of cultivation of these lands have a number of features and are determined by crops of crop rotation, weed infestation, methods of reclamation, level of fertility.
Evaluation of the quality of fieldwork
Quality of fieldwork – the degree of compliance of quality parameters and timing of the actual performance of individual techniques with the requirements of standards or agrotechnical requirements. The quality of field work determines the yield of crops.
Quality of field work depends on the technical condition of tillage and seeding units, proper adjustment, quality of previous treatments, soil conditions, timing of work and other conditions.
Violation of agrotechnical requirements for tillage leads to:
- deterioration of growth and development conditions of cultivated plants;
- lower yields;
- reducing the effectiveness of fertilizers and chemical plant protection products;
- reduction in the effectiveness of land reclamation;
- the possibility of the development of soil erosion;
- reduction of soil fertility.
As a consequence, it is necessary to organize permanent control over the quality of field works and, in particular, over the quality of performance of individual methods of tillage.
The quality of performance of an individual technique of tillage, sowing and others is determined by a set of indicators characterizing the degree of suitability of soil for optimal growth of plants and performance of subsequent technological operations.
Current problems of tillage
Problems of energy conservation and soil compaction
Tillage is the most energy-intensive and expensive technological method of farming. Currently, it accounts for up to 40% of energy and 25% of labor costs of the total field work for growing and harvesting crops. To estimate, if we recalculate all tillage practices for plowing, 6,000 tons of soil is moved on each hectare annually.
Intensification of agriculture leads to disruption of the dynamic equilibrium in the ecological system soil – plant – atmosphere, changes in the biogeochemical cycle of substances and energy in the biosphere. Mechanical tillage leads to the destruction of soil zoocenoses, worm and root passages, zonation is reduced, the ability of the soil to loosen itself is reduced. Frequent mechanical tillage accelerates the microbiological processes of mineralization of organic matter, which negatively affects the soil structure and leads to significant unproductive losses of nutrients and moisture. According to the data of the All-Russian Research Institute of Agriculture and Soil Protection from Erosion, the existing technology of soil treatment for 30-40 years has led to a decrease in humus content in the arable layer of black earth soils by 0.8-1.1%, in the slopes – by more than 3.5%.
On average in Russia at intensive plowing about 1 ton of humus per 1 hectare is mineralized annually in the arable layer, which is equal to the loss of 10 tons of soil at 2.5% of humus content.
Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. – Moscow: Publishing House “Kolos”, 2000. – 551 с.
Fundamentals of agricultural production technology. Farming and crop production. Edited by V.S. Niklyaev. – Moscow: Bylina, 2000. – 555 с.
Fundamentals of Agronomy: Tutorial/Y.V. Evtefeev, G.M. Kazantsev. – M.: FORUM, 2013. – 368 p.: ill.
Agricultural machinery. Khalansky V.M., Gorbachev I.V. – M.: KolosS, 2004. – 624 p.: ill. – (Textbooks and tutorials for students of higher education institutions).