Ploughing is the earliest type of mechanical tillage to have been used on the soil. The earliest form of plough was simply an enlarged hoe which stirred the soil as it was dragged along and this type of implement, which is really a single-tined cultivator, is still used in India and other Eastern countries. A crude mouldboard type of plough was used in Europe in pre-Roman times, about 2 000 B.C., so the plough is about 4 000 years old. The modern type of plough was developed in the last century. The basic farming and tillage methods have not changed much over thousands of years, but the efficiency of the equipment has changed a great deal.
Reasons for Ploughing
When ploughing the top layer of soil is cut into slices, pushed sideways and turned over. The reasons are as follows:
- To turn over all the soil in a land or field, so that fresh soil is exposed to the action of the weather, wind, rain and frost.
- To expose fresh soil by the action of cultivating implements and produce soil conditions suitable for planting farm crops with the least amount of cultivation.
- To bury crop residues and any organic matter such as manure, in order to maintain or add to soil fertility.
- To control weeds by cutting deep roots and burying the whole plant.
- To bury completely a poor, non-productive crop so that a more productive crop can be grown.
- To control the water content of the soil. In temperate regions, the soil is ploughed in the autumn after the summer crop has been harvested. This helps drainage during the heavy autumn and winter rains and exposes the soil surface to the effects of frost. Frost plays a very important part in drying out and breaking down heavy clay soils and, in fact, if some clay soils in Europe are not ploughed before Winter, it is impossible to make a seed bed the following Spring.
In tropical climates such as Southern Africa, the soil should be ploughed in the Autumn as soon as the Summer crop has been harvested, but it is exactly the opposite. Instead of trying to assist water to drain out of the soil, the farmer is keeping water in the soil over the long, dry Winter period. After early ploughing, the top part of the soil dries out, but moisture is preserved in the lower soil levels. Mid-Winter or Spring ploughing disturbs the soil during the dry period and much more moisture is lost by evaporation from the soil surface. By conserving moisture in the soil, the farmer can plant earlier in the spring and his crops, particularly water-planted tobacco can get off to a much better start.
The following table gives the results of an experiment to show the difference in yields of tobacco. Land ploughed early, in February, and land ploughed late, in September. The soil was sandveld, the crop was tobacco, and 4 different levels of nitrogen fertiliser were used on the different plots.
Table 1: Shows the difference in yields from lands ploughed early and late in the season
|Time of ploughing||Yield in kg per hectare|
|12||24||36||48||Kg of N per ha|
|February||1720||2039||2109||2067||Average = 1984|
|September||1200||1639||1767||1875||Average = 1620|
Figure 1: Shows a reversible plough
2. TYPES OF PLOUGH
This is the earliest design of plough and is the type mainly used in temperate climates where soil conditions are soft and deep ploughing is not required. The Digger type of mouldboard will plough to a depth of 300 — 400mm. Single furrow mouldboard ploughs are used in Africa, mostly on small farms. The plough is drawn along by horses or oxen. Figure 2 on the following page shows a type of single furrow mouldboard plough designed for horses or oxen and the type of furrow this plough will produce under good conditions.
Figure 2: A horse or ox drawn mouldboard plough
Figure 3: Plough Parts
|A Double furrow mouldboard plough||Figure 3: A double furrow mouldboard plough|
Drawn by a tractor. On this model the coulter is a disc. All tractor ploughs have a disc coulter.
Types of Mouldboard.
The 3 types of plough mouldboard commonly used are shown below, together with the types of furrow that they produce.
This mouldboard is long with a gentle turn. The furrow is ‘set up’ and has a glazed surface. Used for ploughing grassland. The shape of the furrow requires a lot of cultivations to produce a seedbed.
A shorter and deeper mouldboard with a steeper curve. The furrow is flatter, more broken and needs less cultivation to produce a fine seedbed.
A short, curved mouldboard. The furrow is almost completely inverted, very broken and requires little working to produce a seedbed. The digger is suitable for deep ploughing and will turn a furrow as deep as it is wide.
The Skin is fitted to the disc coulter and is used when ploughing short grassland. Its function is toremove a small piece of turf which falls to the bottom of the furrow. When the furrow is turned, there will be no grass showing on the surface.
If no skin is fitted to the plough, the same effect can be obtained by tilting the disc coulter to undercut the furrow wall. When the furrow has settled no grass can be seen on the surface of the ploughed land.
Figure 4: Effects of a disc coulter
The Reversible Plough:
With a normal plough, the furrow is thrown to the right when travelling down the land. A reversible plough has 2 sets of mouldboards, 1 set throwing the furrow to the right and 1 to the left. These can be turned from the tractor, and ploughing can be done up and down land rather than round and round.
Figure 5: A 7 furrow reversisble mouldboard plough
Size of Plough:
This goes from a single furrow up to 10 furrows. Small ploughs up to 4 furrows, are fully mounted on the three-point linkage of the tractor and the depth of ploughing is controlled from the tractor. Larger ploughs are either semi-mounted with a depth control wheel at the back of the plough, or are trailer ploughs, which are towed by the tractor and all depth adjustments are on the plough.
Figure 6: Ploughing in a land
These ploughs are designed for rougher conditions than the mouldboard plough, and are used widely in Southern Africa. They will plough soils that are hard, dry and full of stones and roots. Disc ploughs do not invert the furrow as well as mouldboard ploughs, and do not bury rubbish and grass. The furrow is broken into large clods which break down easily when they are wetted by rainfall or irrigation. Disc ploughs will plough deep and can plough a large area in a day. Most disc ploughs used on large commercial farms, are reversible because of saving in time and fuel.
Figure 7: A 3 furrow reversible disc plough.
These are like large and very strong cultivators with tines that can penetrate deep into the soil. Their function is to break up and loosen the soil to allow seeds to be planted. They do not make a furrow, invert the soil or bury trash, grass or weeds. The main advantage of this type of plough is that they can cover a large area quickly and economically with a large saving of fuel.
Figure 8: A Chiesel Plough
Source: John Berends
Figure 9 and 10: Two Types of Chisel Ploughs