Harrowing is secondary tillage operation which pulverizes, smoothens and packs the soil in seed bed preparation and/or control weeds.
There are s everal types of harrows used in India, such as: 1. Disc Harrow 2. Spring Tooth Harrow 3. Spike Tooth Harrow 4. Triangular Harrow 5. Zig-Zag Harrow 6. Blade Harrow (Bakhar) 7. Guntaka 8. Bodela 9. Bindha 10. Other Harrows.
1. Disc Harrow:
It is a harrow which performs the harrowing operations by means of a set (or a number of sets) of rotating steel discs, each set being mounted on a common shaft.
Disc-harrows are of two types depending upon the sources of power:
I. Tractor drawn
II. Animal drawn
I. Tractor Drawn Disc Harrow:
Disc harrow is found very suitable for hard ground, full of stalks and grasses. 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.
Depending upon the disc arrangements, disc harrows are divided into two classes:
(A) Single action, and
(B) Double action
(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.
(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 back gangs throw the soil in opposite directions. Thus the entire field is worked twice in each trip.
It may be of two types:
(a) Tandem, and
(b) Off-Set.
(a) Tandem Disc Harrow:
It is a disc harrow comprising of four gangs in which each gang can be angled in opposite direction.
(b) Off-Set Disc Arrow:
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.
II. Animal Drawn Disc Harrow:
Disc harrow is used for breaking clods while preparing seed beds. It has usually six or eight discs fixed in two gangs; each gang has three or four discs. There is a strong frame made of mild steel, on which gangs with the discs are mounted. An operator’s seat is also provided in the frame. Usually “transport wheels are provided for easy movement of the harrow from place to place. The size of the harrow is determined by the maximum width of cut of the soil. The weight of the disc harrow varies between 80 to 100 kg only.
The disc harrow mainly consists of:
i. Disc
ii Gang Frame
iii. Beam
iv. Gang Angle Mechanism
v. Scraper
vi. Spacer (spool)
vii. Clevis
viii. Axle
ix. Middle Tyne and
x. Bearings
i. Disc:
Disc is the main part of the harrow which cuts and pulverises the soil. Discs are arranged in two gangs. The thickness of the material used for disc is at least 3.15 mm. The cutting edge is bevelled for easy penetration. The disc has a square opening in the centre to allow the passage of the axle. The disc is usually made of steel with carbon content ranging from 0.80 to 0.90%.
ii. Gang Frame:
All the gangs are mounted on a frame, called gang frame. It is usually made of sturdy mild steel structure. The gang frame is bolted to the beam of the implement.
iii. Beam:
It is that part of the harrow which connects the implement with the yoke. The rear end of the beam has a clevis to fix its height of hitching to suit the size of animals. It is made of wood which is locally available in the area.
iv. Gang Angle Mechanism:
It is a mechanism by means of which the gang angles are adjusted. Arrangement of adjusting the width and depth of cut of the implement is done by gang angle mechanism. The lever of the gang angle mechanism is usually made of mild steel flat with a wooden handle. The gang angle can be adjusted approximately in the range from 0° to 27° only.
v. Scraper:
It is that part of the harrow which scrapes the soil from the concave side of the disc and keeps it clean for effective working of the harrow in the field.
vi. Spacer (Spool):
Spacer is used to separate the two adjacent discs and to keep them in position. It is usually made of cast iron. The spacer has a suitable square opening in the middle to allow the passage of the axle.
vii. Clevis:
Clevis is the part fitted to the beam and the frame which permits vertical hitching of the harrow.
viii. Axle:
The axle is usually 20 x 20 mm square section. The length of axle depends upon the size of the harrow.
ix. Middle Tyne:
The tyne which breaks the unbroken strip of soil left in between two gangs of the harrow during operation is called Middle tyne. This tyne is suitably fixed to the rear end of the gang frame in such a way that it is replaced easily.
x. Bearing:
There are one or two bearings either of cast iron or wood fitted at each end of the gang.
2. Spike Tooth Harrow:
It is a harrow with pegs as working part, fitted on a rigid articulated or flexible frame. The peg shaped teeth of diamond cross section is attached to a rectangular frame. It is used to break clods, stir the soil, uproot the weeds, level the ground, break the soil crust and cover the seeds. Its principal use is to smoothen and level the soil directly sifter ploughing.
Spike tooth harrows may be of two types:
i. Rigid type and
ii. Flexible type
The animal drawn spike tooth harrows are usually of rigid type. There may or may not be provision for changing the angles of spikes in operating conditions. Tractor drawn harrows are usually of flexible type. It has got advantages of being rolled up for transporting purpose.
This harrow mainly consists of- (i) Teeth, (ii) Tooth bars, (iii) Clamps, (iv) Guard, (v) Braces, (vi) Levers and, (vii) Hooks.
The teeth are made of hardened steel. The teeth may be square, triangular or circular in section. The teeth are so placed on tooth bar that no tooth is directly behind the other.
Tooth bars are made of wood or steel. Steel bars maybe round, flat or channel shaped. All the teeth are fastened rigidly to the tooth bar. Clamps are used to fasten teeth to the tooth bars tightly so as not to be loose while in operation.
3. 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. It gives a springing action in working condition. It is best suited for hard and stony ground. It is used in the soil where obstructions like stones, roots and weeds are hidden below the ground surface. It pulverises the soil and helps in killing weeds.
This type of harrow mainly consists of- (i) Teeth, (ii) Tooth bars, (iii) Clamps, (iv) Frame, (v) Clevis, (vi) Lever and, (vii) 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 bars by tooth clamps.
Guard rails are provided to give rigidity and support to the harrow. The levers are provided for setting the teeth for varying depth of harrowing. Setting in vertical position gives maximum depth of harrowing. For light harrowing, the adjustment is done in slanting position. In order to provide straight and even pulling, Eveners are fitted in front of all harrow sections. Draft hooks made of steel are fitted on each corner of every section for hitching purpose.
4. Triangular Harrow:
It is a spike tooth harrow with a triangular frame. The frame is made of wood and pointed spikes are fitted in the frame. The teeth of spikes are fixed and not adjustable.
5. Zig-Zag Harrow:
It is a spike tooth harrow with a zig-zag frame and teeth attached at the junctions of the frame members.
6. Bakhar (Blade Harrow):
It is an implement which consists of one or more blades attached to the beam or frame, used for shallow working of the soil with minimum of soil inversion. It is used to prepare seed beds mostly in clayey soils. It works like a sweep which moves into the top surface of the soil without inverting the soil.
7. Guntaka:
It is an improved type of blade harrow. The functions of guntaka are same as that of bakhar.
8. Bodela:
It is a twin blade harrow used in the southern region of India.
9. Bindha:
It is a spike tooth harrow of local make used in a particular region.
10. Others Harrows:
Some of the harrows are explained below:
i. Acme Harrow:
It is a special type of harrow having curved knives. It is also called knife harrow. The front part of the knife compact the soil and crushes the clods. A good pulverisation is obtained by this harrow easily. It is good for mulching also. The knife is usually made of high carbon steel. The depth of penetration can be increased by putting some additional weight on the frame also.
ii. Patela:
It is a wooden plank used for smoothening the soil and rushing the clods. In certain cases, weeds can be collected with the help of the curved spikes attached behind the wooden board. It is also used for breaking clods, packing and levelling the ploughed soil and to remove the weeds. It is made of a wooden plank with a number of curved steel hooks bolted to a steel angle section which is fixed or hinged to the rear side of the plank.
The cutting edge levels and packs the soil, the curved hooks uproot and collect the weeds. The size of the patela varies in the range of 1200 to 3000 mm. The weight of Patela varies between 45 to 55 kg only.
The main components of patela are:
(a) Plank and
(b) Weeding Hooks
iii. Flexible Tine Harrow:
It is a harrow consisting of network of spring tines.
iv. Reciprocating Power Harrow:
It is a harrow fitted with rigid tines driven by the power take-off in a reciprocating, transverse or rotary motion as the machine moves forward.
v. Rolling or Rotary Harrow:
It is a harrow consisting of rigid or flexible tines, mounted on one or more horizontal or vertical shafts. It is also known as gyro harrow.
vi. Cage Harrow:
It is a rolling harrow with horizontal shafts, each fitted with star-shaped tines, joined by rods, forming the lines of cylinder.
vii. Circular Harrow:
It is a rolling harrow, consisting of a circular frame fitted with teeth and turning about a shaft slightly inclined towards the vertical.
viii. Roller Harrow:
It is a rolling harrow with consisting of a light roller with projecting teeth.
ix. Clod Crusher:
It is a rolling harrow with horizontal shafts fitted with star shaped tines.
x. Chain Harrow:
It is a harrow consisting of a frame less network of links.
xi. Roller:
It is an implement with parts mounted on a horizontal shaft, used for compacting the soil and crushing the clods.
xii. Continental Cambridge Roller:
It is a roller comprising of discs of unequal diameters and of alternating smooth and notched surface, placed on the same shaft.
xiii. Corrugated Roller:
It is a roller consisting of one or more cylinders of which the surface has corrugations in a concentric form or parallel to the axis of the cylinder.
xiv. Weeder Mulcher:
It is an implement consisting of flexible tines attached to a frame for mulching, breaking the soil crust over germinating seeds and uprooting small weeds.
xv. Cage Roller:
It is a roller consisting of a cage of metal bars arranged so as to form the shape of cylinder.
xvi. Cambridge Roller:
It is the roller comprising a number of thick discs each having the form of frustum of a cone with smooth periphery joined base to base and placed on the same shaft without gap.
xvii. Coil Roller:
It is a roller having the form of a cylindrical cage circumscribed by a spiral.
xviii. Land Packer (Culti-Packer):
It is the tandem combination in the same frame either of two cambridge rollers off-set by half a disc or cambridge and cross kill rollers.