Tillage is defined as changing the soil condition with a tool for the benefit of man. After the land has been cleared and plant debris removed, it is often necessary to subject it to some form of tillage before the crop is planted. Various forms of tillage may be carried out while the crop is growing on the field.
2. Purpose of Tillage
Tillage is carried out for one or a combination of the following reasons
- Seed bed preparation
- Control of weeds
- Incorporation of organic matter into the soil
- Soil and water conservation
- Improvement of the soil’s physical condition
i. Seed bed preparation
Tillage loosens the soil and result in a seed bed suitable for seed germination and development of the young seedlings. A good seed bed should be moist and should not contain large lumps of soil that may prevent close contact between the planted seed and soil particles. It should not contain large quantities of un-decomposed organic matter.
ii. Control of weeds
Often weeds growing on a fallow plot can be controlled by being ploughed under. Ploughing prior to cropping may also serve to kill the weeds present. Tillage between rows of growing crop can be an important method of weed control.
iii. Incorporation of organic matter into the soil
Organic matter and crop residues can be incorporated into the soil through tillage. Once in the soil, they decomposed rapidly thus releasing the nutrients they contain to the growing plants. The incorporation of plants residues in the soil through tillage also serve to improve soil structure.
iv. Soil and water conservation
Tillage often serves the purpose of breaking up the surface layers of the soil so that water is able to infiltrate more rapidly into the soil. This has the dual benefit of increasing the amount of water available in the soil for the crops and decreasing the amount of soil erosion caused by excessive run-off.
For these reasons, Lands that is not to be cropped immediately May even be occasionally ploughed or tilled as a soil and water conservation measures.
v. Improvement of the soil’s physical condition
The Physical condition of the soil can be improved by tillage. For example, where the surface layers of the soil have formed a hardpan, it may be beneficial to break up the hardpan through tillage so that plants roots can penetrate more deeply and water could percolate into the lower layers of the soil more easily.
vi. Increase soil aeration
Tillage opens up the soil, thus improving soil aeration which increases the oxidation of chemical compounds in the soil and make them more soluble and available for the plants roots to absorb. Improved aeration is also beneficial to soil inhabiting organism.
3. Historical development of tillage
Tillage began before the earliest written records of mankind. Primitive man uses hand tools made of wood, bone or stone as implements to chop or dig the soil. These simple hand tools were use to destroy the natural vegetation, and reduce competition from native plants and weeds growing among the crops.
The next stage of tillage development was the application of power of domestic animals, which occurred in part of the world before the dawn of history. This makes possible development of implement with a steady forward movement.
Among these were the crooked-stick plows to stir the soil and the brush drag to pulverize the surface soil. Little further progress was made for many centuries except that eventually some plows were fitted with iron shares. The development of steel in the 19th century resulted, in 1833, in a plow with sharp edges that can cut the soil layer and in a curved polished surface that permitted the plow to scour.
The straight line movement of the plow has since been supplemented with rotary movement in such implements as disk plows, harrows, the rotary hoe and various pulverizing and stirring tools.
4. Types of tillage
Grading and terracing
This is one of the most ancient and most universal forms of tillage. A shear, which is pulled along by some power device, slices its way under the soil as it goes along, Thereby loosening the soil and turning it over. The soil is left in lumps of various sizes and may require other operations in other to make a suitable seed bed.
Implements used for ploughing: Moldboard plough, Disc plough
Planting may be done on the field after ploughing, but if the lumps of soil left after ploughing are too large, they must be broken up before planting. The conventional way of breaking up soil lumps is through harrowing. There are various kinds of animal- powered and tractor-powered harrows but they all function by breaking up the lumps of soil and leaving an even soil surface.
This involves the collection of the soil into more or less conical heaps or mounds. The mounds usually vary in height from 30-100cm, but are usually of approximately the same height on a particular farm. The distance from one mound to the next also varies but it is the distance that determines how much cropping can occur in the lower-laying spaces between the mounds.
Mounding is the most common form of soil collection tillage in tropical Africa and is often associated with intercropping since it simultaneously permits two or more kinds of seed bed on the field; the top of the mounds is used for crops such as tubers which requires a deep layer of loose soil, the low- laying furrows are use for crops that have high requirement for water such as rice while the slopes of the mounds are used for intermediate crops.
Advantages of mounding
- Providing a deep, loose seed bed which is particularly suitable for the development of roots and tubers.
- Providing a variety of seed bed types on the same field, which may be advantageous to intercropping.
- Elevating the seed bed and plants roots above the water table in field with a high water table.
- Mounding improves aeration for roots and facilitates the growth and development of underground tuber and root crops and the pods of groundnuts.
- Mounding makes harvesting of tuber crops and pods of groundnuts easier.
Disadvantages of mounding
- The major disadvantage of mounding is that it has not been mechanized and would probably be extremely difficult to mechanize.
- Mounds impede the free movement of men and machinery through the field. For this reason, mounding is mostly confined to traditional agriculture (with intercropping) to which it is well suited.
This involves the collection of soil into elongated heaps called ridges. The distance between the ridges is variable, but is usually about one meter. Growing crops on ridges is quite common in tropical Africa .In the traditional settings, hoes and human labour are used to make ridges, but mechanicals ridgers are also available and permit large areas to be ridged in a relatively short time.
Ridging have the same advantages as mounding, but in addition ridging is an extremely useful measure for controlling erosion, particularly on sloping land. In such cases, ridging is done along the contour so that the flow of water down the slop is impeded.
The water then flows along the furrows between the ridges. In other to further discourage the rapid flow of water within the furrows, cross ridges (also called cross bunds or tie ridges) are made across the furrows at intervals to connect one ridge to the next.
Thus, ridging, when properly done, can decrease surface run-off, thereby reducing soil erosion and promoting water infiltration into the soil.
Since it has been completely mechanized, ridging finds a place in modern agriculture, where it is the most common form of soil collection tillage.
v. Bed making
This is a form of lands preparation which is more often discovered in horticultural and nursery practices than in field crop production. A bed is like a ridge in that it is elongated raised portion of the field. It is, however, usually much broader than a ridge, its top is flat and its length is usually not more than 20m.Bed making is most commonly done with hand tools.
Inter-tillage is commonly practiced with respect to crops that are planted in rows. It involves tilling the areas between the crops rows. Its objectives are usually to control the weeds between the crops rows and to promote water percolation into the soil.
vii. Grading and Terracing
These are two land preparation operations which aim at effecting changes in the gross topography of the field. Grading is most commonly done where it is desired to use furrow or some other form of surface irrigation. The land is graded in such a way that the point of water supply is the highest on the field and the field slops downwards from the water source.
Grading of the crop field is also encouraged where the farmer intends to impound water for the flooding culture of rice or taro. If the land is sloping, it is graded to be relatively level. Elevated areas or dykes are constructed around the field so that the water does not flow away once impounded.
Terracing is one of the method s of managing extremely sloping land for crop production. It creates a series of relatively flat horizontal portions alternating with vertical portions very similar to a flight of stairs.
The flat portions are used for cropping. Terracing provides erosion control measures and permits cropping on land that would have otherwise remained useless for cropping.
viii. Minimum tillage
There has been a realization in recent years that frequent tillage operations tend to impair the soil structure thus exposes the soil to adverse effect of rainfall and strong wind. These observations have led many scientists to develop the concept of minimum tillage. This means that crop production could be carried out with as little tillage or soil disturbance as possible as tillage is seen as a necessary evil which should only be sparingly indulged in.
Advantages of minimum tillage
- Preserve the soil structure.
- It is economical, since the labour and cost normally incurred in tillage operations can be saved.
5 Tillage Implements
- Ploughing implements
Plowing buries green or dried material, loosens the soil so that other implements can operate, removes or delays competition with weeds and roughen the soil surface so as to check runoff or rainfall.
- The moldboard plow
Breaks loose or shears off furrows slice by forcing a triple wedge through the soil. This action inverts the soil and breaks it into lumps. Some soil pulverization takes place.
- The disk plows
These are important for use in loose soil but also in those soils too dry and hard for easy penetration of moldboard plows. The disks vary in size from 50 to 75cm while the depth of plowing may be varied from 10 to 25cm.
i. Implement for seed bed preparation
Tillage to prepare a seed bed after the land has been plowed is accomplished with harrows, field cultivators or other machines equipped with disks, shovels, teeth, spikes, sweeps, knives, etc
Which smooth and pulverize plowed soil compact it and destroy weeds. The disk harrow cuts, Moves, and pulverizes the soil and destroys weeds.
- The hand hoe
Is still the most common tillage implement among small scale farmers
The spike-tooth harrows breaks soil clods, levels the land, and kills small weeds.
This implement makes the soil surface rough and cloddy, creating a condition necessary to check wind erosion.
ii. Implement for inter-tillage
Shovel or sweep cultivators are types most frequently used for intertillage
This consists of a series of 18-inch (45cm) hoe wheels each of which is fitted with teeth shaped like fingers. As the wheels rotate these teeth penetrate and stir the soil. This hoe is useful for uprooting small weeds by blind cultivation before the crop grows up as well as early cultivation of young corn and other row crops.
The ordinary spike-tooth harrow:
Is use, with little injury to the corn, to kill small weeds in corn when the corn plants are still small.
The lister cultivator:
This is sometimes equipped with disks or knives, or both and sometimes with disk and shovels. For the first cultivation, the disks are set to cut the weeds on the sides of the furrow, the soil being thrown away from the crop row. The shovels may be set to stir the soil near the plants.
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