|Retention: the action of absorbing and continuing to hold a substance. |
Swath: a broad strip or area of something.
All agricultural operations should be performed as uniformly as possible. For example:
- Depth of Tillage: Do not allow implements to ride out in hard patches nor to dig down in soft ground;
- Speed of operation: Settle for a satisfactory speed and adhere to it. This can also provide useful information for budgeting and control and;
- Application of material: e.g. Seed, fertiliser and chemicals. Periodic checks can be made, and will be discussed later, to establish whether materials are being applied accordingly or uniformly.
Most cost inputs in crop husbandry are fixed or pre-determined. Timeliness cannot be predetermined and is probably the most important factor in separating the good or bad farmer. The timing of operations in crop husbandry is critical and the earlier in a crop’s life that an error in timeliness is made, the greater the effect will be in reducing yields. Problems tend to increase from the moment of the error to the time of harvesting.
Table 1: Shows the terms that are commonly used in connection with land preparation:
|Tillage:||This is any planned disturbance of the soil.|
|Tilth:||This is the appearance of a soil which has been tilled.|
There are two systems of classification of ‘tillage’ and these are:
- Conventional Tillage: Primary tillage or heavy-duty operations: e.g. sub-soiling and ploughing. Secondary tillage is light-duty operations following primary operations: e.g. disc harrowing or rolling and;
- Conservation Tillage: reduced or minimum tillage and no tillage.
The most important thing is to understand the reason for tillage and what one achieves by using different technique. Some of the reasons are as follows:
DESTRUCTION OF EXISTING LIVING PLANTS
Ordinary commercial crops should not be planted into land with already established plants. The competition from these is too severe, and they are also difficult to eradicate once the young crop has emerged;
Soil air is an important aspect of plant nutrition and the soil needs to be loosened to allow air to penetrate. This can be done before the crop is planted or during growth. Rain tends to ‘collapse’ a soil therefore it needs a periodic loosening;
ADEQUATE TILTH FOR PLANTING
We talk about rough tilth and fine tilth. The smaller the seed the finer the tilth needs to be to establish soil to seed contact and there needs to be just enough ‘fineness’ to do this. Excessively fine tilth collapses quicker and encourages water run-off which is brought about by rain. This is reduced once a crop has grown high enough to provide a cover (canopies) for the soil;
EFFECT OF SURFACE MATERIAL
Surface material, such as, crop residues (stover) are highly desirable, preventing damage from rain drop action which causes the surface to collapse and restrict moisture penetration. The rate of lateral movement of the water is reduced which reduces soil erosion and shades the soil, cooling it and reducing the rate of evaporation which enables microbial action to increase, which subsequently improves air and moisture penetration, which helps aerate the soil;
Surface material is usually disposed of by burning or removal at it is hindered by machine- operations. There is machinery available to counter this problem like a no till planter which has been designed to cut through surface material and allows the planter to not ‘jam up’ with surface material. All this may be necessary for the control of certain fungal diseases;
A soil surface devoid of all vegetative growth is very vulnerable to soil erosion particularly as slopes increase. The object in crop husbandry should be to get all rainfall to soak in and raise the level of the soil moisture reserves. Obviously, in some circumstances the reverse is true and excess moisture has to be removed.
The rougher the tilth, the less lateral movement of water there is and better retention of water on any particular soil. This is appropriate for heavy showers whereas a light shower tends to evaporate quicker owing to the greater surface area of soil exposed to the air.
The timing of tillage is very important from a moisture conservation point of view. For maximum carry-over of moisture through the winter, the soil should be tilled to 15cm to act as mulch and be kept weed-free at the same time. Another method would be to plant cover crops so the soil is never exposed to the elements and;
LEVELNESS OF THE LAND
Higher speed operations such as spraying and cultivating, need a land smooth enough to enable the driver to work a 10-hour shift without excessive discomfort.
Machinery covering a wide swath width will sway excessively reducing the uniformity of operation. Water penetration is more uniform on a level land. This point is very important in the lower rainfall area, and some farmers have indicated noticeable increases in yield on leveled land adjacent to unlevelled land.
Low-lying areas which are subject to extended periods of water-logging every year will produce markedly lower yields.
EQUIPMENT AVAILABLE FOR TILLAGE
A Plough is designed to invert the soil. It puts the surface layers under and exposes fresh soil to the air. The plough has been the conventional form of primary tillage since man first started tilling the soil, but the plough is losing favour for economic reasons. As yet the long-term effects of this are not known. Ploughing is still the most efficient machine for destroying living material and burying trash.
Aeration occurs to the depth of ploughing. A depth of ± 250mm would normally be considered adequate. Unfortunately the tilth that a plough leaves is generally poor and a harrow or roller is needed to reduce the tilth. A roller pulled in conjunction with a plough helps to break up the clods and smooth out the surface for subsequent operations.
A disadvantage of ploughing is that a hard ‘plough pan’ may form immediately below the plough zone and may require periodic breaking up by a sub-soiler.
Figures 1 and 2: Show a mouldboard plough in field.
Source: rg-contracting Source:manufacturer
Sub-Soiler Or Ripper
This is usually a single-tine or twin-tine machine (in some cases there may be more) which is capable of penetrating to a depth of 600mm. Its primary use is to break up the hard ‘plough pan’ and allows for soil aeration and water penetration. It is useful for pulling up roots after stumping virgin land and drainage (using a mole attachment) in wet soils.
Figure 3: Shows a sub-soiler or a ripper.
This is a multi-tine implement, with 5 tines or more and used for primary tillage instead of a plough. Tines are normally set at a depth of 200 – 300mm and a maximum of 450mm. This gives deeper aeration and eliminates any hard pan at the same time.
There is no inversion and surface material can hinder the operation so needs to be followed by a harrow or roller to produce tilth.
A chisel-plough can be used for system of tillage called wet ripping. This is an inter-row operation when a crop is growing and involves using one tine between each row to a depth of about 200 – 300mm.
It is useful for several reasons:
- It breaks up surface compaction through tractor or rain-drop action and thus allows rain to penetrate;
- It gives very effective inter-row weed control and;
- It can be combined with top-dressing nitrogenous fertilisers.
Figure 4: Shows a chisel plough.
Harrows can be heavy or light duty and are intended to produce tilth.
Disc harrows are the normal form of harrowing in South Africa. Disc harrows use discs to work the soil at a shallow depth of 150mm to improve the tith and level out lands. This is to ensure that there are no uneven areas on the land. Power harrows use reciprocating spikes which pulverise the clods. Spike tooth harrows are used for fine tilth and final leveling of a soil before or after planting.
Figure 5: Shows a disc harrow working the soil.
A Rotavator is a machine with small, high speed tines which cut into the surface and pulverise it which gives the soil an extremely fine tilth but can damage the structure of the soil. This soil is also more easily eroded because of its fine tilth.
Figure 6: Shows a rotavator which is used to make a very fine tilth to the soil.
- 2. SYSTEMS OF TILLAGE
Conventional: This system is the tillage operation that is standard for that area. It involves incorporating most of the crop residue into the soil and leaving the soil bare. The methods involve sub-soiling and ploughing, followed by secondary operations such as harrowing or rolling to achieve the required tilth. Some advantages of this system are effective weed removal and the disruption of the insect life cycles. Disadvantages include soil and wind erosion, damage to soil structure due to overworking the soil, high machinery costs and very high fuel costs. There are many different methods of conventional tillage and here are a few:
Figure 7: Shows a land that has been tilled with the conventional method with ploughs and harrows.
On the left hand side, maize stover has been left on the land which will be incorporated into the lands.
- Chisel Rome: The name Rome has been taken from the original heavy duty harrow made by the Rome Harrow Company of the U.S.A. and is now used to indicate almost any heavy-duty harrow used for primary tillage.
This system uses a chisel plough to loosen and aerate the soil to a reasonable depth and then a Rome harrow to break up the top 150mm of soil to a finer tilth
Figure 8: Shows a wheat land that has been planted using the tramline method.
- Wheel-Track: Under this system, a land is roughly ploughed, i.e. no roller attached, followed by a tractor, with no implement running over the ploughed land, so that the wheel tracks become the planting lines. The tractor wheels crush the clods and produce a fine planting tilth.
- Advantages of this are good rainfall penetration and no weed growth in the inter-row area as the rough clods do not allow for weed germination and;
- Tramline: Lands are permanently marked out so that operations always follow the same wheel marks, the area in between the wheel tracks being used for planting the crop. The intention here is to reduce soil compaction in the cropping area and save on expensive tillage. The cost of tillage is linked very strongly with the amount of compaction of the soil.
There are a number of methods one can use in conservation tillage. The idea is to leave the previous year’s crop residue in field before and after planting the next crop. It is essential that the soil be disturbed as little as possible. The crop residue acts as a form of protection through soil surface protection from wind and soil erosion and conserves moisture. At least 30% of the soil surface should be covered to have any form of improvement although most conservation operations leave 70% of the crop residue and plant straight into the residue.
Crop rotation and cover cropping is an important aspect in conservation agriculture. Crop rotation can include maize followed by legumes, (soya beans) in the following season as this replenishes soil nutrients and encourages soil organisms. A cover crop can be planted in the off season (winter) to keep the soil constantly covered. At the beginning of the next season one can plant straight into the winter crops residue. Advantages will include, reduced soil erosion, soil compaction, increased residue cycling, and improve soil structure and an addition of organic material.
Some benefits of conservation tillage are the reduction of soil erosion by up to 60 – 90%, preserves the moisture content, organic matter content of the soil is increased, reduces evaporation, effective in storing carbon and plays an important part in sustainable agriculture.
Some techniques include:
- Rip-Roll: This is a system which was advocated and sold by Duly & Co. but has not been too successful. It lends itself to cotton growing and a very inexpensive form of tillage. The idea is to till only the zone where planting is to occur. This system uses the Duly sub-soiler with mini-rollers following immediately behind the rip lines. An advantage is that the soil between the rows is undisturbed and does not favor weed germination; weed control can be concentrated to the in-row area;
- Reduced or Minimum tillage: The only soil disturbance is during planting and is limited to the planting strips which are generally accepted as being not more than 15% of the soil surface. This practice will leave large areas covered with crop stubble, or mulch.
The advantages of minimum tillage are the control of wind erosion, weeds and insect pests, although water erosion is difficult to manage. Machinery and fuel costs are reduced.
There is a possibility of leaf diseases being carried over from one crop to the next via the crop stubble
No-Till: This is an idea in crop production which is becoming more and more popular, especially in
U.S.A. The only time the soil is disturbed is when the seed is planted. No mechanical tillage is done and all weed control is by the use of chemical herbicides. The main advantage of this system is the very low fuel requirement. Other advantages include control of soil erosion from raindrop splash and runoff. There is a great deal of organic matter left on the surface for decomposition which in turn improves the growing quality of the soil. This improves aeration of the soil which could be a problem.
The crop residue protects the soil and allows the soil microorganisms to do their work. It is thought that, when the roots from the previous crop die off, they leave a vast network of underground tunnels which serve to aerate the soil and provide channels for the roots of the new crop.
Figure 9: Shows a land that has been planted with the strip till or the reduced till method.
Figure 10: Shows a land that has been planted using the no-till method