Unit 3: Tillage PDF

Unit 3, SOL-214 Tillage It is a mechanical manipulation of soil to provide favorable condition for crop production. Soil tillage consists of breaking the compact surface of earth to a certain depth and to loosen the soil mass, so as to enable the roots of the...

Unit 3, SOL-214 Tillage It is a mechanical manipulation of soil to provide favorable condition for crop production. Soil tillage consists of breaking the compact surface of earth to a certain depth and to loosen the soil mass, so as to enable the roots of the crops to penetrate and spread into the soil. Objective of Tillage To obtain seed bed, suitable for different type of crops. To add more humus and fertility to soil by covering the vegetation. To destroy and prevent weeds. To aerate the soil for proper growth of crops. To increase water absorbing capacity of the soil. To destroy the insects, pests and their breeding places and To reduce the soil erosion. Classification of Tillage Tillage is divided into two classes: i) Primary tillage, ii) Secondary tillage. Primary tillage It constitutes the initial major soil working operation. It is normally designed to reduce soil strength, cover plant materials and rearrange aggregates. The operations performed to open up any cultivable land with a view to prepare a seed bed for growing crops is known as primary tillage. Implements may be tractor drawn or animal drawn implements. Animal drawn implements mostly include indigenous plough and mould- board plough. Tractor drawn implements include mould-board plough, disc plough, subsoil plough, chisel plough and other similar implements. Secondary tillage Tillage operations following primary tillage which are performed to create proper soil tilth for seeding and planting are secondary tillage. These are lighter and finer operations, performed on the soil after primary tillage operations. Secondary tillage consists of conditioning the soil to meet the different tillage objectives of the farm. The implements used for secondary tillage operations are called secondary tillage implements. They include different types of harrow, cultivators, levellers, clod crushers and similar implements. These operations are generally done on the surface soil of the farm. Secondary tillage operations do not cause much soilinversion and shifting of soil from one place to other. These operations consume less power per unit area compared to primary tillage operations.  To break the big clods and to make the field surface uniform and levelled. To cut crop residues and mix them with top soil of the field. Secondary tillage implements may be tractor drawn or bullock drawn implements. Bullock drawn implements include harrows, cultivators, hoes etc. Terms Used in tillage : Tool - It is an individual working element such as disc or shovel. Implement - It is an equipment generally having no driven moving parts, such as harrow or having only simple mechanism such as plough. Machine -It is a combination of rigid or resistant bodies having definite motions and capable of performing useful work. Plough The main implement for primary tillage is plough, which is used for ploughing operations. Ploughing is the primary tillage operations, which is performed to cut, break and invert the soil partially or completely. Ploughing essentially means opening the upper crust of the soil, breaking the clods and making the soil suitable for sowing seeds. The purpose of ploughing is to achieve the objectives of the tillage. Types of ploughing : Normal Ploughing : It is the ploughing up to a depth of about 15 cm. Contour Ploughing: It is the method of ploughing in which the soil is broken and turned along the contours. Ploughing of Land The ploughing of land is to separate the top layer of soil into furrow slices. The furrows are turned sideways and inverted to a varying degree, depending upon the type of plough being used. It is a primary tillage operation, which is performed to shatter soil uniformly with partial or complete soil inversion. There are a few important terms frequently used in connection with ploughing of land. (i) Furrow - It is a trench formed by an implement in the soil during the field operation. (ii) Furrow slice- The mass of soil cut, lifted and thrown to one side is called furrow slice. (iii) Furrow wall - It is an undisturbed soil surface by the side of a furrow. (iv) Crown- The top portion of the turned furrow slice is called crown. (v) Back furrow - A raised ridge left at the centre of the strip of land when ploughing is started from centre to side is called back furrow. When the ploughing is started in the middle of a field, furrow is collected across the field and while returning trip another furrow slice is lapped over the first furrow. This is the raised ridge which is named as back furrow. (vi) Dead furrow - An open trench left in between two adjacent strips of land after finishing the ploughing is called dead furrow. (vii) Head land - While ploughing with a tractor to turn, a strip of unploughed land is left at each end of the field for the tractor to turn, that is called head land. At the end of each trop, the plough is lifted until the tractor and the plough have turned and are in position to start the return trip. The head land is about 6 metres for two or three bottom tractor plough and one metre more for each additional furrow. The Line diagram of different terminology used in ploughing is shown in Fig.11.1. Fig. 11.1 Line diagram of different terminology used in ploughing Methods of ploughing In order to provide furrows at all times on the right hand side of the plough, two method of working are used called Gathering and Castering (Fig.11.2). Gathering - Whenever a plough works round a strip of ploughed land, it is said to be gathering. Casting- Whenever a plough works round a strip of unploughed land, it is said to be casting. Ploughing of a field by casting or gathering alone is normally uneconomical. The following are a few important methods used in tractor ploughing. Fig.9.2 Line diagram if plouging methods Continuous ploughing method In normal conditions, the continuous ploughing method (Fig. 11.3) is considered very convenient and economical. This is a method usually used in which the tractor and plough never run idle for more than three quarter land width along the headland and never turn in a space narrower than a quarter land width. In this method, first the headland is marked and the first ridge is set up at three quarter of a land width from the side. The other ridges are set at full width over the field. The operator starts ploughing between the first ridge and the side land. The operator continues to turn left and cast in the three quarter land until a quarter land width of ploughing is completer on each side. At this stage, it is important to lift the plough to half depth for last trip down the side land of the field. This leaves a shallow furrow where the finish comes. Fig. 11.3 Line diagram of Continuous ploughing method After this, the driver turns right and gathers round the land already ploughed on the first ridge. Gathering is continued till the unploughed strip in first three-quarter land has been ploughed and completed. This gathering reduces the first full land by a quarter. The remaining three quarter land can be treated in exactly the same manner as the original three quarter land. This process is repeated for all other lands in the field. Round and round ploughing In this method, the plough moves round and round a field. This system is adopted under conditions where ridges and furrows interfere with cultivation work. The field can be started in two ways. a) Starting at the centre A small plot of land is marked in the middle of the field and it is ploughed first. After that, the plough works round this small plot and the entire plot is completed. This is not a very economical method. b) Starting at the outer end Tractor starts ploughing at one end of the field and then moves on all the sides of the plot and comes gradually from the sides to the centre of the field. Wide diagonals are left unploughed to avoid turning with the plough. There are no back furrows in this method. Conventional ploughing is usually done by this method. One way ploughing This system requires the use of a special type of plough known as reversible plough or one way plough. Such a plough turns furrows to the left or right. After the headland has been marked, the operator plough along a straight side land mark. At the end of the first trip, he turns his tractor in a loop and returns down the same furrow. No dead and back furrows are left in the field. In gently sloping fields, this method is suitable. ************  Primary tillage implements Indigenous plough Indigenous plough is most commonly used in this country as a primary tillage implement. The shape and size of the plough varies with places and regions due to variation in soil types and tillage requirements. The bullock drawn indigenous plough is shown in Plate : 12.1. The main parts of the plough are: body, share, shoe, beam and handle. The body is the main frame to which the shoe, beam and handle are attached. The share is a narrow steel bar attached to the upper surface of the shoe longitudinally along the centre line and the handle is generally attached to the body of the plough. The share is attached to the shoe which penetrates into the soil and breaks it open. The shoe also helps in stabilizing and balancing the plough while in operation. The plough is provided with a wooden beam and a handle. The indigenous plough is made of wood except the share which is made of steel bar. Plate : 12.1 Bullock drawn indigenous plough Mould board plough A mould board plough is very common implement used for primary tillage operations and is shown in plate : 12.2.  Plate : 12.2 Two bottom fixed Mould board plough The main functions of mould board plough are: Cutting the furrow slice Lifting the soil Turning the furrow slice Pulverizing the soil. Components of mould board plough A mould board plough consists of the different parts like Share, Mould board, Land side, Frog and Tail piece. The different parts of mould board plough are shown in Fig. 12.1 1. Share: It is that part of the plough bottom which penetrates into the soil and makes a horizontal cut below the surface. 2. Mould board - It is the curved part which lifts and turns the furrow slice. 3. Land side - It is the flat plate which bears against and transmits the rear side lateral thrust of the plough bottom to the furrow wall. 4. Frog - It is the part to which other components of the plough bottom are attached. 5. Tail piece - It is an adjustable extension, which can be fastened to the rear of a mould board to help in turning a furrow slice.  Fig. 12.1. Components of Mould Board plough The share is one of the important part of the plough, which penetrates into the soil and makes a horizontal cut below the soil surface. It is a sharp, well polished and pointed component. The different parts of the share are shown in Fig. 12.2. 1. Share point : It is the forward end of the cutting edge which actually penetrates into the soil. 2. Cutting edge: It is the front edge of the share which makes horizontal cut in the soil. 3. Wing of share: It is the outer end of the cutting edge of the share. It supports the plough bottom. 4. Gunnel: It is the vertical face of the share which slides along the furrow wall. It takes the side thrust of the soil and supports the plough bottom against the furrow wall. 5. Cleavage edge: It is the edge of the share which forms joint between mould board and share on the frog. 6. Wing bearing: It is the level portion of the wing of the share, providing a bearing for the outer corner of the plough bottom. Fig. 12.2 Different parts of the share Material of share The shares are made of chilled cast iron or steel. The steel mainly contains about 0.70 to 0.80% carbon and about 0.50 to 0.80% manganese besides other minor elements. Type of Share There are four different types of shares used for the mould board plough such as Slip share, Slip nose share, Shin share and Bar point share and are shown in Fig.12.3. i) Slip share It is one piece share with curved cutting edge, having no additional part. It is a common type of share, mostly used by the farmers. It is simple in design, but it has got the disadvantage that the entire share has to be replaced if it is worn out due to constant use. ii) Slip nose share It is a share in which the point of share is provided by a small detachable piece. It has the advantage that share point can be replaced as and when required. If the point is worn out, it can be changed without replacing the entire share, effecting considerable economy. iii) Shin share It is the share having a shin as an additional part. It is similar to the slip share with the difference that an extension is provided to it by the side of the mould board. iv) Bar point share It is the share in which the point of the share is provided by an adjustable and replaceable bar. This bar serves the purpose of point of the share and land side of the plough. Fig. 12.3 Different types of share 2. Mould board The mould board is that part of the plough which receives the furrow slice from the share. If lifts, turns and breaks the furrow slice. To suit different soil conditions and crop requirements, mould board has been designed in different shapes. There are four types of mould board used such as : General purpose, Stubble, Sod or Breaker and Slat. General purpose It is a mould board having medium curvature lying between stubble and sod. The sloping of the surface is gradual. It turns the well defined furrow slice and pulverizes the soil thoroughly. It has a fairly long mould board with a gradual twist, the surface being slightly convex. The general purpose mould board is shown in Fig.12.4 Fig. 12.4 General purpose mould board Stubble type It is short but broader mould board with a relatively abrupt curvature which lifts breaks and turns the furrow slice used in stubble soils. Its curvature is not gradual but it is abrupt along the top edge. This causes the furrow slice to be thrown off quickly, pulverizing it much better than other types of mould board. This is best suited to work in stubble soil that is under cultivation for years together. Stubble soil is that soil in which stubble of the plants from the previous crop is still left on the land at the time of ploughing. This type of mould board is not suitable for lands full of grasses and is shown in Fig. 12.5.  Fig. 12.5 Stubble mould board Sod or Breaker type It is a long mould board with gentle curvature which lifts and inverts the unbroken furrow slice. It is used in tough soil of grasses. It turns over thickly covered vegetable of the soil. This is very useful where complete inversion of soil is required by the farmer. This type has been designed for used in sod soils. The sod or breaker type mould board is shown in Fig. 12.6. Fig. 12.6 General purpose mould board Slat type It is a mould board whose surface is made of slats placed along the length of the mould board, so that there are gaps between the slats. This type of mould board is often used, where the soil is sticky, because the solid mould board does not scour well in sticky soils and is shown in Fig.12.7. Fig. 12.7 Slat mould board 3. Land side It is the flat plate which bears against and transmits lateral thrust of the plough bottom to the furrow wall. It helps to resist the side pressure exerted by the furrow slice on the mould board. It also helps in stabilizing the plough while it is in operation. Land side is fastened to the frog with the help of plough bolts. The rear bottom end of the land side is known as heel which rubs against the furrow sole. 4. Frog Frog is that part of the plough bottom to which the other components of the plough bottom are attached (Fig.6 ). It is an irregular piece of metal. It may be made of cast iron for cast iron ploughs or it may be welded steel for steel ploughs. 5. Tail piece It is an important extension of mould board which helps in turning a furrow slice. Plough accessories There are a few accessories, which are used to increase the efficiency of ploughing. The different accessories used are Jointer, Coulter, Gauge wheel, Land wheel and Furrow wheel. 1. Jointer It is a small irregular piece of metal having a shape similar to an ordinary plough bottom. It looks like a miniature plough. Its purpose is to turn over a small ribbon like furrow slice directly in front of the main plough bottom. This small furrow slice is cut from the left and upper side of the main furrow slice and is inverted so that all trashes on the top of the soil are completely turned down and buried under the right hand corner of the furrow. 2. Coulter It is a device used to cut the furrow slice vertically from the land ahead of the plough bottom. It cuts the furrow slice from the land and leaves a clear wall. It also cuts trashes which are covered under the soil by the plough. The coulter may be (a) Rolling type disc coulter and (b) Sliding type knife coulter. a. Rolling type disc coulter It is a round steel disk which has been sharpened on the edge and suspended on a shank and yoke from the beam. The edge of the coulter may be either smooth or notched. It is so fitted that it can be adjusted up-down and side ways. The up-down adjustment takes care of depth and sideways adjustment is meant for taking care of width of cut. b. Sliding type knife coulter  It is a stationary knife fixed downward in a vertical position on the beam. The knife does not roll over the ground but slides on the ground. The knife may be of different shapes and sizes. 3. Gauge wheel It is an auxiliary wheel of an implement to maintain an uniform depth of working. Gauge wheel helps to maintain uniformity in respect of depth of ploughing in different soil conditions. It is usually placed in hanging position. 4. Land wheel -It is the wheel of the plough which runs on the unploughed land. 5. Furrow wheel – There are two types of furrow wheel. Front furrow wheel - It is the front wheel of the plough which runs in the furrow. Rear furrow wheel - It is the rear wheel of the plough which runs in the furrow. Adjustment of mould board plough For proper penetration and efficient work by the mould board plough, some clearance is provided in the plough. This clearance is called suction of the plough. Suction in mould board plough is of two types (i) Vertical suction and (ii) Horizontal suction. Vertical suction (Vertical clearance) It is the maximum clearance under the land side and the horizontal surface when the plough is resting on a horizontal surface in the working position. It is the vertical distance from the ground, measured at the joining point of share and land side. It helps the plough to penetrate into the soil to a proper depth. This clearance varies according to the size of the plough. The vertical clearance is shown in Fig.12.8. Fig. 12.8 Vertical suction of mould board Horizontal suction (Horizontal clearance) It is the maximum clearance between the land side and a horizontal plant touching point of share at its gunnel side and heal of land side. This suction helps the plough to cut the proper width of furrow slice. This clearance varies according to the size of the plough. It is also known as side clearance and is shown in Fig.12.9. Fig. 12.9 Horizontal suction of mould board Throat clearance It is the perpendicular distance between point of share and lower position of the beam of the plough. The throat clearance of mould board plough is shown in Fig. 12.10. Fig. 12.10 Throat clearance of plough Vertical clevis It is a vertical plate with a number of holes at the end of the beam to control the depth of operation and to adjust the line of pull. The vertical clevis and line of pull is shown in Fig.12.11. Fig. 12.11. Vertical Clevis and line of pull Horizontal clevis It is a device to make lateral adjustment of the plough relative to the line of pull. Plough size The perpendicular distance from wing of the share to the line jointing the point of the share and heel of land side is called size of plough. The size of the mould board plough is expressed by width of cut of the soil. Tractor Drawn Implements Tractor drawn implements possess higher working capacity and are operated at higher speeds. These implements need more technical knowledge for operations and maintenance work. Tractor drawn implements may be either trailed type or semi-mounted type or mounted type. Trailed type implement It is one that is pulled and guided from single hitch point but its weight is not supported by the tractor. Semi-mounted type implement This type of implement is one which is attached to the tractor only to the lower link of the hydraulic system. It is controlled directly by tractor steering unit but its weight is partly supported by the tractor. Mounted type implement A mounted implement is one which is attached to the three point linkage of hydraulic system, which can be controlled directly by the tractor steering unit. The implement is carried fully by the tractor. It can be raised, lowered and hold in any position. Terms used in ploughing Centre of power: It is the true point of hitch of a tractor. Centre of resistance: It is the point at which the resultant of all the horizontal and vertical forces act. The centre lies at a distance equal to 3/4th size of the plough from the share wing. Line of pull: It is an imaginary straight line passing from the centre of resistance through the clevis to the centre of pull. Pull : It is the total force required to pull an implement. 1) Fixed type (one way) mould board plough One way plough throws the furrow slice to one side of the direction of motion and is commonly used everywhere. It may be long beam type or short beam type. There are single bottom, two bottom, three bottom, four bottom and five bottom fixed mould board ploughs are available which are based on the power source horse power. Plate : 12.3 Two bottom fixed mould board plough 2) Two-way or Reversible plough It is a mould board plough which turns furrow slice to the right or left side of direction of travel as require. Such ploughs have two sets of opposed bottoms. In such plough, all the furrow can be turned towards the same side of the field by using one bottom for one direction of travel and the other bottom on the return trip. Two sets of bottom are so mounted that they can be raised or lowered independently or rotated along an axis. Two way ploughs have the advantages that they neither upset the slope of the land nor leave dead furrows or back furrows in the middle of the field. Plate : 12.4 Single bottom reversible mould board plough  Disc plough Disc Plough It is a plough which cuts, turns and in some cases breaks furrow slices by means of separately mounted large steel discs. A disc plough is designed with a view of reduce friction by making a rolling plough bottom instead of sliding plough bottom. A disc plough is shown in Plate 13.1. A disc plough works well in the conditions where mould board plough does not work satisfactorily. Plate : 13.1 Disc plough Advantages of disc plough A disc plough can be forced to penetrate into the soil which is too hard and dry for working with a mould board plough. It works well in sticky soil in which a mould board plough does not scour. It is more useful for deep ploughing. It can be used safely in stony and stumpy soil without much danger of breakage. A disc plough works well even after a considerable part of the disc is worn off in abrasive soil. It works in loose soil also (such as peat) without much clogging. Disadvantages of disc plough  It is not suitable for covering surface trash and weeds as effectively as mould board plough does.  Comparatively, the disc plough leaves the soil in rough and more clody condition than that of mould board plough.   Disc plough is much heavier than mould board plough for equal capacities because penetration of this plough is affected largely by its weight rather than suction. There is one significant difference between mould board plough and disc plough i.e. mould board plough is forced into the ground by the suction of the plough, while the disc plough is forced into the ground by its own weight. Types of Disc Plough Disc ploughs are of two types’ viz., Standard disc plough and Vertical disc plough. (i) Standard disc plough It consists of steel disc of 60 to 90 cm diameter, set at a certain angle to the direction of travel. Each disc revolves on a stub axle in a thrust bearing, carried at the lower end of a strong stand which is bolted to the plough beam Fig.13.1. The angle of the disc to the vertical and to the furrow wall is adjustable. In action, the disc cuts the soil, breaks it and pushes it sideways. There is a little inversion of furrow slice as well as little burying of weeds and trashes. The disc plough may be mounted type or trailed type. In mounted disc plough, the side thrust is taken by the wheels of the tractor. Sometimes a rear wheel is fitted to take side thrust of the plough to some extent. In trailed type, side thrust is taken by the furrow wheel of the plough. Disc is made of heat treated steel of 5 mm to 10 mm thickness. The edge of the disc is well sharpened to cut the soil. The amount of concavity varies with the diameter of the disc. The approximate values being 8 cm for 60 cm diameter disc and 16 cm for 95 cm diameter. A few important terms connected with disc plough is explained below. Fig. 13.1 Standard disc plough Disc - It is a circular, concave revolving steel plate used for cutting and inverting the soil. Disc angle - It is the angle at which the plane of the cutting edge of the disc is inclined to the direction of travel.. Usually the disc angle of good plough varies between 42° to 45°. Tilt angle - It is the angle at which the plane of the cutting edge of the disc is inclined to a vertical line. The tilt angle varies from 15° to 25° for a good plough. The disc and tilt angles of disc plough are shown in Fig. 13.2. Scraper – It is a device to remove soil that tends to stick to the working surface of a disc. Concavity - It is the depth measured at the centre of the disc by placing its concave side on a flat surface. Fig. 13.2 Angles of disc plough Draft of disc plough The disc plough is lighter in draft than the mould board plough, turning same volume of soil in similar conditions. In very hard soil, some extra weight is added to the wheel which increases the draft. The bearings and scrapers of the disc plough also affect the draft. Special purpose ploughs 1. Rotary tiller (Rotovator) The rotary cultivator is widely considered to be the most important tool as it provides fine degree of pulverization enabling the necessary rapid and intimate mixing of soil besides reduction in traction demanded by the tractor driving wheels due to the ability of the soil working blades to provide some forward thrust to the cultivating outfit.  Plate : 13.2 Rotavator The functional components include tynes, rotor, transmission system, universal joint, leveling board, shield, depth control arrangement, clutch and three point linkage connection. Rotary tiller is directly mounted to the tractor with the help of three point linkage. The power is transmitted from the tractor PTO (Power Take Off) shaft to a bevel gear box mounted on the top of the unit, through telescopic shaft and universal joint. From the bevel gear box the drive is further transmitted to a power shaft, chain and sprocket transmission system to the rotor. The tynes are fixed to the rotor and the rotor with tynes revolves in the same direction as the tractor wheels. The number of tynes varies from 28 - 54. A leveling board is attached to the rear side of the unit for leveling the tilled soil. A depth control lever with depth wheel provided on either side of the unit ensures proper depth control. The following types of blades are used with the rotovator. i. 'L' type blade - Works well in trashy conditions, they are more effective in cutting weeds and they do not pulverize the soil much. i.. Twisted blade - Suitable for deep tillage in relatively clean ground, but clogging and wrapping of trashes on the tynes and shafts. i.. Straight blade - Employed on mulches designed mainly for secondary tillage. The benefits of the rotary tiller are effective pulverization of soil ensures good plant growth, stubble and roots are completely cut and mixed with the soil and proper ground levelling after the operation. 2. Chisel plough Chisel ploughs are used to break through and shatter compacted or otherwise impermeable soil layers. Deep tillage shatters compacted sub soil layers and aids in better infiltration and storage of rainwater in the crop root zone. The improved soil structure also results in better development of root system and the yield of crops and their drought tolerance is also improved. The functional component of the unit include reversible share, skids, beam, cross shaft and top link connection. Chisel plough consists of heavy chisel type tyne which is pulled through the soil normally at a depth greater than that at which conventional ploughing would be done and bursting up the underlying layers of soil without bringing the sub-soil to the surface. The tynes of the implement are sturdy and strong enough to withstand the stresses applied when they are working at depth where the soil conditions are hardened. The implement frame is also strongly constructed usually of box section steel to withstand the stresses applied. The chisel plough has a sturdy but light structure made of 3 mm thick hollow rectangular tubular mild steel sections. The share has a lift angle of 20 degree, width of 25 mm and a length of 150 mm. The implement is protected by a shear pin, which prevents damage from over loading. The implement could be used for deep tillage upto a depth of 40 cm. The coverage is 0.42 ha/hr when operated at a spacing of 1.5 m between rows. The salient features of the unit are: The implement could be used for deep tillage upto a depth of 40 cm for bursting of the sub-soil hard pan, improving the drainage and aerating the soil. Reduces the bulk density of soil Two fold increase in hydraulic conductivity of sub-soil Conserves around 30 to 40% more soil moisture Roots proliferation is improved from 40 to 45% Easily operated by any 35 to 45 hp tractor Fig. 13.3 Line diagram of chisel plough 3. Sub-Soil plough The function of the sub-soil plough also called sub soiler is to penetrate deeper than the conventional cultivation machinery and break up the layers of the soil, which have become compacted due to the movement of heavy machinery or as a result of continuous ploughing at a constant depth. These compacted areas prevent the natural drainage of the soil and also inhibit the passage of air and nutrients through the soil structure. The sub- soiler consists of heavier tyne than the chisel plough to break through impervious layer shattering the sub-soil to a depth of 45 to 75 cm and requires 60 to 100 hp to operate it. The line diagram of sub soiler is shown in Fig. 13.4. The advantages are same as that of chisel plough Fig. 13.4 Line diagram of Sub soiler ***********  Secondary tillage implements Secondary tillage Tillage operations following primary tillage which are performed to create proper soil tilth for seeding and planting are called secondary tillage. These are lighter and finer operations, performed on the soil after primary tillage operations. Secondary tillage consists of conditioning the soil to meet the different tillage objectives. The implements used for secondary tillage operations are called secondary tillage implements. They include different types of harrow, cultivators, levelers, clod crushers and similar implements. These operations are generally done on the surface soil of the farm. Secondary tillage operations do not cause much soil inversion and shifting of soil from one place to other. These operations consume less power per unit area compared to primary tillage operations. The main objectives of secondary tillage operations are : 1. To break the big clods and to make the field surface uniform and leveled for sowing. 2. To cut crop residues and mix them with top soil of the field. Secondary tillage implements may be tractor drawn or bullock drawn implements. Bullock drawn implements include harrows, cultivators, hoes etc. 1. Harrow Harrow is a secondary tillage implement that cuts the soil to a shallow depth for smoothening and pulverizing the soil as well as to cut the weeds and to mix the materials with the soil. There are several types of harrow used in India such as disc harrow, spike tooth harrow, spring tooth harrow, acme harrow, patela, triangular harrow, blade harrow, 2. Disc harrow It is a harrow, which performs the harrowing operation by means of a set, or a number of sets of rotating slat discs, each set being mounted on a common shaft. Disc harrow is found very suitable for hard ground, full of stalks and grass fields. It cuts the lumps of soil, clods and roots. Discs are mounted on one, two or more axles which may be set at a variable angle to the line of motion. As the harrow is pulled ahead, the discs rotate on the ground. The disc harrow in field operation is shown in Plate 14.1. (Courtesy: http://www.woodsequipment.com) Plate : 14.1 Disc harrow in operation Classification of disc harrow : The disc harrows are classified based on disc arrangement as Single action, Double action disc harrows, tandom disc harrows and Off-set disc harrows. Based on power source, they are classified as Tractor drawn and bullock drawn disc harrows. a) Single action disc harrow It is a harrow with two gangs placed end to end, which throw the soil in opposite directions. The discs are arranged in such a way that right side gang throws the soil towards right, and left side gang throws the soil towards left as shown in Fig. 14.1. Fig. 14.1 line diagram of disc arrangement in single action disc harrow b) Double action disc harrow A disc harrow consisting of two or more gangs, in which a set of one or two gangs follow behind the set of the other one or two, arranged in such a way that the front and rear gangs throw the soil in opposite directions (Fig. 14.2). Thus the entire field is worked twice in each trip. It may be of two types i) Tandem and ii) Off-set type. Fig. 14.2 line diagram of disc arrangement in double action disc harrow c) Tandom disc harrow It is a disc harrow comprising of four gangs in which each gang can be angled in opposite direction as shown in Fig.14.3. Fig. 14.3 line diagram of disc arrangement in tandom disc harrow d) Off-set disc harrow It is a disc harrow with two gangs in tandem, capable of being off-set to either side of the centre line of pull. Two gangs are fitted one behind the other. The soil is thrown in both directions because discs of both gangs face in opposite directions. It is very useful for orchards and gardens. It travels left or right of the tractor. The line of pull is not in the middle, that's why it is called off-set disc harrow. Off-set disc harrow is based on the basic principle that side thrust against the front gang is opposed by the side thrust of the rear gang. Hence the gangs are arranged at suitable angles so that both thrusts are counter balanced with each other. Fig. 14.4 line diagram of disc arrangement in offset disc harrow Components of a Disc harrow A disc harrow mainly consists of disc, gang, gang bolt, gang central lever, spool or spacer arbor bolt, bearings, transport wheels, scraper and weight box. Disc: It is a circular concave revolving steel plate used for cutting a inverting the soil (Plate : 14.2). Disc is made of high glass heat-treated hardened steel. Tractor drawn disc harrows have concave discs of size varying from 35-70 cm diameter. Concavity of the disc affects penetration and pulverization of soil. Usually two types of disc are used in disc harrows, plain disc and cut away disc. Plain discs have plain edges and they are used for all normal works. Most of the harrows are fitted with plain discs only. Cut away discs have serrated edges and they cut stalks, grass and other vegetation. They are not effective for pulverization of soil but it is very useful for puddling the field especially for paddy cultivation. Plate : 14.2 Different types of disc used in disc harrow ) Gang: Each set of discs that are mounted on a common shaft is called the gang. Gang bolt or arbor bolt: It is a long heavy of square headed bolt from the other end, a set of discs are mounted on the gang bolt. The spacing between the discs on the gang bolt ranges from 15 to 25 cm for light duty and 25 to 30 cm for heavy duty harrows. The angle between the axis of the gang bolt and the direction of travel is called the gang angle. Gang control lever: A lever, which operates the gang mechanisms of the disc harrow, is called the gang control lever. Spool or spacer: The flanked tube, mounted on the gang bolt between every two discs to prevent the lateral movement of the disc on the shaft is called the `spool’ or `spacer’. It is just a device for keeping the discs at equal spacing on the gang bolt. It is usually cast in special shapes and sizes and is generally made of iron. Bearing: Bearing is essential to counter act the end thrust of the gang due to soil thrust. The harrow bearings are subjected to heavy radial and thrust loads Chilled cast iron bearings are used for heavy radial and thrust loads and they are also used due to their durability. Transport wheel: In trailing type disc harrow, the transport wheels are provided for transport work on roads and for preventing the edges of the discs from damage. Mounted type disc harrows do not require wheels for transport work. Scraper: It prevents disc from clogging. It removes the soil that may stick to the concave side of the disc. Weight box: A box like frame is provided on the main frame of the harrow for putting additional weight on the implement. Additional weight helps in increasing the penetration of the disc in the soil. There are several factors which affect the penetration of disc harrow in the field. If the disc gangs are set perpendicular to the line of draft, the penetration is not adequate. Penetration can be increased by adding some additional weight on the frame of the harrow. For obtaining maximum penetration, the gangs should be set with the forward edges of the discs parallel to the direction of motion. If the hitch point is lowered, better penetration is achieved. A sharp edged disc has more effective penetration compared to blunt edged disc. It is observed that penetration is better in low speed than in high speed. The following are a few adjustments for obtaining higher penetration i. By increasing the disc angle ii. By adding additional weight in harrow iii. By lowering the hitch point iv. By using the sharp edged discs of small diameter and lesser concavity v. By regulating the speed. Spike tooth harrow It is a harrow with peg shaped teeth of diamond cross section to a rectangular frame. It is used to break the clod, stir the soil, uproot the weeds, level the ground, break the soil and cover the seeds. Its principle is to smoothen and level the soil directly after ploughing. Spike tooth harrows may be of rigid type and flexible type. The animal drawn spike tooth harrow is usually of rigid type. These may or may not have provisions for changing the angle of spikes in operating conditions. Tractor drawn harrows are usually flexible type (Fig.14.5). It has got the advantage of being turned up for transporting purpose. This harrow mainly consists of teeth, tooth bar frame, clamps, guard, braces, levers and hooks. The teeth are made up of hardened steel with square/triangular/circular in section. The teeth are so placed on tooth bar that no tooth is directly behind the other. Teeth are fastened rigidly to the tooth bar. Clamps are rigidly fixed so as not to be loose while in operation. Fig. 14.5 line diagram of Spike tooth harrow Spring tooth harrow It is a harrow with tough flexible teeth, suitable to work in hard and stony soils. Spring tooth harrow is fitted with springs having loops of elliptical shape as shown in Fig. 14.6. It gives a spring action in working condition. It is used in the soil when obstruction like stone, roots and weeds are hidden below the ground surface. This type pulverizes the soil and helps in killing weeds. This type of harrow mainly consists of teeth, tooth bar, clamps, frame, lever and links. Usually the teeth are made of spring steel. Sometimes reversible points are provided so that one end may be used after the other end is worn out. The teeth are fastened to the tooth bar by means of tooth clamps. They are provided to give rigidity and support to the harrow. The levers are provided for setting the teeth for varying the depth of harrowing. For light harrowing, the adjustment is done in slanting position. Draft hooks on each corner of every section for hitching purpose. Fig. 14.6. Line diagram of spring tooth harrow  Cultivators, levelers, ridger and bund former Cultivator It is an implement for inter cultivation with laterally adjustable tines or discs to work between crop rows. This can be used for seed bed preparation and for sowing with seeding attachment. The times may have provision for vertical adjustments also. The cultivator can be either Disc cultivator or Rotary cultivator or Tine cultivator. Disc cultivator: It is a cultivator fitted with discs. Rotary cultivator: It is a cultivator with tines or blades mounted on a power driven horizontal shaft as shown in Plate : 15.1. (Courtesy: http://www.diytrade.com) Plate : 15.1 Rotary cultivator Tine cultivator: It is a cultivator fitted with tines having shovels. The rigid tine cultivator is shown in Plate : 15.2.  Plate : 15.2 Rigid tyne cultivator The cultivator stirs the soil, and breaks the clods. The tines fitted on the frame of the cultivator comb the soil deeply in the field. A cultivator performs functions intermediate between those of plough and the harrow. Destruction of weeds is the primary function of a cultivator. The following are a few important functions performed by a cultivator. Interculture the fields. Destroy the weeds in the field. Aerate the soil for proper growth of crops. Conserve moisture by preparing mulch on the surface. To sow seeds when it is provided with sowing attachments. To prevent surface evaporation and encourage rapid infiltration of rain water into the soil. Depending upon the type of power available for the implement, the cultivator can be classified as either Tractor drawn or Animal drawn. The tractor drawn cultivators are further classified as Trailed type or Mounted type. Trailed type cultivator It consists of a main frame which carries a number of cross members to which tines are fitted. At the forward end of the cultivator, there is a hitch arrangement for hitching purpose. A pair of wheels is provided in the cultivator. The life is operated by both wheels simultaneously so that draft remains even and uniform. The height of the hitch is adjusted so that main frame remains horizontal over a range of depth setting. The tines in each row are spaced widely to allow free passage of the soil and trash around them. The tines in subsequent rows are staggered so that the implement can cover the entire width nicely. The depth of working is set roughly by adjusting the tine in their clamps and the final depth control is done by a screw lever. Usually the tines are damaged due to turning the implement at the headland without lifting it up. Care should be taken to lift the tines off the ground before turning. Mounted type Cultivator Tractors fitted with hydraulic system operate the mounted type cultivators. A rectangular frame of angle iron is mounted on three point hydraulic linkage of the tractor. The cross members carry the tines in two staggered lines. For actual cutting the soil, different types of shovels and sweeps are used. A few important shovels and sweeps are a) Single point shovel b) Double point shovel c) Spear head shovel d) Sweep e) Half sweep f)Furrower. Depending upon the type of soil and crop, shovels are chosen for use on the cultivators. Usually tractor drawn cultivators are of two types, depending upon the flexibility and rigidity of tines (i) Cultivator with spring loaded tines (ii) Cultivator with rigid tines. Cultivator with spring loaded tines A tine hinged to the frame and loaded with a spring so that it swings back when an obstacle is encountered, is called spring loaded tine as shown in Fig.15.1. Each of the tine of this type of cultivator is provided with two heavy coil springs pre tensioned to ensure minimum movement except when an obstacle is encountered. The springs operate, when the points strike roots or large stones by allowing the tines to ride over the obstruction, thus preventing damage. On passing over the obstruction, the tines are automatically reset and work continues without interruption. The tines are made of high carbon steel and are held in proper alignment on the main frame members. This type of cultivator is particularly recommended for soils which are embedded with stones or stumps. A pair of gauge wheel is provided on the cultivator for controlling the depth of operation. The cultivator may be fitted with 7, 9, 11, 13 tines or more depending upon the requirements. Fig. 15.1 Tractor drawn cultivator Cultivator with rigid tines Rigid tines of the cultivators are those tines which do not deflect during the work in the field. The tines are bolted between angle braces, fastened to the main bars by sturdy clamps and bolts. Spacing of the tines are changed simply by slackening the bolts and sliding the braces to the desired position. Since rigid tines are mounted on the front and rear tool bars, the spacing between the tines can be easily adjusted without getting the tines choked with stubbles of the previous crop or weed growth. A pair of gauge wheel is used for controlling the depth of operation. Duck foot cultivator It is a type rigid cultivator which is used mostly for shallow ploughing, destruction of weeds and retention of moisture. It consists of steel frame and rigid tines to which sweeps are attached as shown in Plate : 15.2. The implement is attached to the tractor with three point hitch system and is controlled by hydraulic system. The sweeps are fabricated from high carbon steel. Number of sweeps can be adjusted according to requirement. Usually this cultivator is about 225 cm long; 60 cm wide with 7 sweeps.  Plate : 15.2 Duck foot cultivator Terms used for evaluation of an implements Theoretical field capacity It is the rate of field coverage of the implement, based on 100 per cent of time at the rated speed and covering 100 per cent of its rated width. WxS Theoretical field capacity = ---------.............................. ha/hr 10 Where, W – Width of the implement in meters (m) S - Speed of operation in Kilometers per hour (Km/hr) Effective field capacity It is the actual area covered by the implement based on its total time consumed and its actual width of operation. Field efficiency It is the ratio of effective field capacity and theoretical field capacity expressed in percent. Effective field capacity Field efficiency = Theoretical field capacity Effective field capacity is calculated as follows SxWxE C= 1000 Where, C - Effective field capacity, hectare per hr (ha/hr). S - Speed of travel in km per hour. W - Theoretical width of cut of the machine in metre, and E - Field efficiency in per cent. Problem 1: A 5 x 20 cm double action disc harrow is operated by a tractor having a speed of 5 km/h. Calculate the actual field capacity, assuming the field efficiency of 80 percent. Solution: Size of the harrow (width) = 5 x 20 = 100 cm = 1 meter SxWxE Actual field capacity, C = ----------------- 1000 = (1 x 5 x 80) / 1000 Actual field capacity = 0.4 ha/hr. Problem 2: A 3 x 30 cm plough is moving at a speed of 4 km/h. calculate how much time it take to plough 500 x 500 m field when the field efficiency is 70 %. Solution: Width of the plough = 3 x 30 = 90 cm = 0.9 m SxWxE Effective field capacity, C = ----------------- 1000 = (0.9 x 4 x 70)/ 1000 Effective field capacity, C = 0.25 ha/hr = 2500 m2/hr ( 1 ha = 10,000 m2 ) Time required = 500 x 500/ 2500 = 100 hr. Problem 3: A 4 bottom 40 cm mould board plough is operating at 5.5 km/h speed with 75 % field efficiency. Calculate the rate of doing work in hectares per hour. Solution : Width of the plough = 4 x 40 = 160 cm = 1.6 m  Rate of doing work = 1.6 x 5.5 x 75/1000 Rate of doing work = 0.66 ha/h Problem 4: An indigenous plough has a 20 cm wide furrow at the top and 10 cm depth. Calculate the volume of soil handled per day 8 hours if the speed of working is 2.5 km/h. Solution: Furrow cross section = 10 x20/2 = 100 cm2 Distance traveled in 8 hours = 8 x 2.5 x 1000 = 20,000 m Volume of soil handled = 20000 x 100/ 10000 Volume of soil handled = 200 m3 *********** Levelers In irrigated areas land leveling is an essential operation of farming. Leveled fields receive uniform penetration of irrigation water with high efficiency. The possibility of water logging and soil erosion is reduced considerably. The entire leveled field becomes ready to receive timely agricultural operations like ploughing, seeding and interculturing without any delay. Smooth fields also facilitate the operation of field equipment and are highly desirable for using mechanical harvesters. Land leveling is usually done in the slack season when the field is free from crops, and the Labours and bullocks are idle. Wooden logs or planks are the most common type of land levelers used by Indian farmers. They are operated in ploughed land to collect loose soil form high spots and to dump in into depressions. While operating in the field, the leveler is raised from the rear to take more cut and then it is tilted up side down to fill up the low spots elsewhere. The other improved type of land leveler which is used on the medium size farms, is called the leveling karaha or scraper. The scraper essentially consists of a bowl or ‘U’ shaped steel sheet made of 3 mm thick metal. Its cutting edge is generally made of high carbon steel. It is also provided with a wooden handle in the middle or two handles on the sides at the rear end. Provision is made at the front end for hitching. For taking the wear an extra steel sheet is welded underneath at the centre. The implement is pulled by a pair of bullocks. Two men are needed to operate it. One man controls the bullocks and the other man does the loading and unloading. The amount of work done in a day depends upon various factors such as hardness of the soil, transportation distance (lead) and volume of the soil cut each time. If the soil is hard, it is always helpful to loosen the soil first by ploughing or by any other means and then proceed with leveling. Tractor mounted type (plate : 15.4) or animal operated improved levelers are also used in India. The laser guided leveler operated by tractor is shown in Plate : 15.5. The laser guided leveler has a transmitter which is fitted outside the field to be leveled. The leveler is fixed with a receiver of the laser beam. It works automatically and the operator need not adjust the leveling blade. Plate : 15.4 Tractor drawn leveller Plate : 15.5 Laser guided leveler in operation  Ridges A ridger (Plate : 15.5) is an implement which cuts and turns the soil in two opposite directions simultaneously for forming ridges. It is also known as Furrower. Ridger is used to form ridges, for sowing row crop seeds and plants in well tilled soil. The ridger is also used for forming field furrows or channels, earthing up and similar other operations. Ridgers are also known ridging plough, middle buster plough and double mouldboard plough. The ridger generally has V-shaped or wedge-shaped share, fitted to the frog. The nose or the tip of the share penetrates into the soil and breaks the earth. The mouldboards lift, invert and cast aside the soil, forming deep channels and ridges of the required size. (Courtesy: http://www.scotlandfarm.co.uk ) Plate : 15.5 Tractor operated ridger in operation A Ridger required for row planted crops. It is also used for making field furrows or channels, earthing up, and similar other operations. It generally has a ‘V’ shaped share either rigidly fixed or hinged to the mould boards. The short beamed ridger is provided with a gauge wheel attached to the front end of the beam. This gauge wheel facilitates movement and control of the ridger. It may be operated by one or two pair of bullocks are a tractor. A ridger consists of beam, clevis, frog, handle, mouldboards, braces, share, and sliding shoe. Bund former It is used for making bunds or ridges by collecting the soil. Bunds are required to hold water in the soil, thereby conserve moisture and prevent run off. The size of the bund former is determined by measuring the maximum horizontal distance between the two rear ends of the forming boards. A bund former consists of forming board, beam and a handle. Plate 15.6 Bullock drawn bund former ***********