No-tillage is generally defined as planting crops into soil that has remained untilled after the harvest of the previous crop. Conservation tillage includes the WHEN and HOW this tillage is done. The "when" basically refers to the moisture-state of the soil. Conservation tillage takes into account both environmental and tillage factors .This system involves opening a narrow slot only wide and deep enough to obtain proper seed coverage and with at least 30% mulch cover. Permanent, continuous no-tillage should follow, while the soil should remain covered by crop residues or green manure cover crops. Crop residues should remain undisturbed on the soil surface after seeding.

No-tillage and reduced tillage have been used since ancient times by indigenous cultures. This was because tillage to any depth required more energy and power than was generally possible with hand labour. The ancient Egyptians and the Incas in the Andes of South America used a stick to make a hole in the ground and place seeds by hand into the unprepared soil (Derpsch, 1998). Even today in some parts of the world that use shifting cultivation, seed is dropped into a hole after clearing the forest by burning. Tillage, indeed, greatly aided the enhancement of food production by creating a seedbed for easier planting and by controlling competition by weeds. However, tillage also accelerated soil loss and soil structural degradation hence leading to the current food shortage and persistent crop failure in most parts of Sub Saharan Africa.

There are a number of reasons for adopting no-tillage in addition to the effects listed above the following are the most attractive to farmers.

Reduction in the cost of production: For instance, production costs per acre (0.405 ha) of soybeans under no-tillage are reduced by US$ 27.00 in Argentina, by US$ 14.18 in the USA and by US$ 11.50 in Brazil (Derpsch, 1998). According to FAO recent studies have shown that practicing conservation tillage leads to:

• Less labour and farm power
• Up to 60% fuel savings
• Up to 50% savings in tractors
• Up to 40% savings in tractor size
• Up to 3 times longer tractor-life
• Reduction in machinery capital

Timely farm operation is easily achieved through no till. Farmers are able to plant well in good time since the focus on land preparation is mostly neither intensive nor subjective. Studies have shown that timely planting contributes up to 40% of the yield hence the ability of Conservation Agriculture to increase yield is largely drawn from this principle.

Some of the benefits of no-tillage include:

• Prevention of soil erosion
• Prevention of soil compaction
• Preservation of soil structure, soil aggregates and macro-pores
• Improvement of soil moisture and water use efficiency through mulching
• Promotion of beneficial organisms such as earthworms
• No-till mulching enhances soil microbial activity, transfers organic matter to the soil improving its nutrient status
• Less inputs of fuel, energy and labour

Despite the wealth of research information in Africa showing the benefits of no-tillage, this farming system is not yet extensively practised (Lal, 1973, 1983)

The ecological constraining factors for spreading no-tillage in Africa are:

• Effects of climate change resulting in low precipitation with low biomass production
• Short growing seasons
• Sandy soils with tendency for compaction
• Soils at risk of waterlogging

Where no-tillage is not possible, the second best choice is minimum tillage.

Before adoption of the no-tillage system following factors must be consider:

• Farmers must improve their knowledge about the system (especially weed control) before trying the technology on their farms
• The change to no-tillage should be planned at least one year before implementation
• Plan to acquire no till implements (direct seeders) and obtain proper orientation on their utilisation. The implements so acquired should match the available farm power.
• It is advisable to start with a small portion/section and advance with time (e.g. 10% of the farm)
• Soil tests should be done, and nutrient deficiencies corrected, aiming at a balanced nutrient and pH status. If soils are acidic, farmers should apply small quantities of lime each year (instead of large amounts only once)
• Avoid soils with bad drainage. It is known that no-tillage does not work on badly drained soils or if soils suffer from water-logging
• Level the soil surface, as uneven surfaces make exact seeding impossible
• Eliminate soil compaction
• Use crop rotations and green manure crops, these are basic in no-tillage system
• Produce the highest amount of mulch cover possible. Choose crops varieties/species with higher biomass than others ( e.g. maize instead of beans) and include green manure cover crops in the rotation. Crop residues and green manures must be left on the soil surface, being incorporated biologically into the soil as they decompose
• Buy a no-till seeding (planter) only after having met all requirements mentioned above
• Learn constantly and stay up to date with new developments

Reduced or Minimum Tillage System

This refers to those tillage practices where by minimum or no disturbance is effected on the soil for purposes of crop production. It involves the making of furrows or holes where seed is planted. The rest of the field remains undisturbed and crop residue is left on the surface. This practice reduces soil erosion; causes build up of organic matter in the soil, hence better chemical and physical soil fertility. Minimum tillage also implies reduced labour, energy, and reduced time demand in land preparation. Hence, cropping can be done in time at less cost. In most commercial farming, the weeding in minimum tillage systems would be done using herbicides.

It differs from traditional tillage by having one or more of the following components:

• Less operations
• Less soil disturbance
• Requires less power
• Seedbed is prepared only where the seeds are planted
• Residues remain on topsoil (are not buried)
• Reduced use of several types of equipment

Only the necessary operations to optimise soil conditions for seed germination and crop establishment and growth are performed, minimise human and machine traffic and thus avoid soil compaction and destruction of soil structure, to avoid soil erosion; to conserve soil moisture, and to use less labour and mechanical energy.

1. Dibble stick planting

Planting stick or machete can be used to create holes to plant the seed in an un-ploughed field with stubble/crop residue. The cut hardwood stick from the bush is sharpened at one end and used to make planting holes. The holes are made in lines at evenly spaced intervals that make it easier to weed and apply fertiliser or manure.

2. Disc-plant (stubble-harrowing)

This tool is used to loosen the soil, chop up crop residues and cut weeds. Afterwards planting is done without further soil disturbance and the crop residues are left on the surface

3. Strip and spot tillage

This involves scraping out shallow planting holes in un-ploughed soil, sowing the seed in the holes, then covering. This approach is common throughout the Sahel (Mali, Niger, Chad, and other countries). The only equipment needed is the hand hoe (Jjembe) and a planting stick. You can plant in the dry or just after the rains. The following are the steps involved:

• Dig small shallow holes at the correct distance from each other. Make the holes just deep enough to plant the seeds.
• Put the correct number of seeds in the hole, and cover them with soil.
• About 2 weeks after the crop emerges, use a stick to make a hole about 10 cm away from each plant. Put fertiliser into the hole.

Advantages

• Less labour requirement compared to conventional cultivation.
• More attractive to vulnerable households due to labour factor and not a huge chunk of land is required.
• Planting done on time
• Do not require expensive equipment - just a hoe and a stick.

• Weed control may be difficult
• Do not break a hardpan caused by hoeing at the same depth year after year.
• Crop roots may not grow well as with planting basins, and less water will infiltrate into the soil.

A ripper is a chisel-shaped implement pulled by animals or a tractor. It breaks up surface crusts and opens a narrow slot or furrow in the soil, about 5 - 10 cm deep. Many conservation tillage systems use a ripper with a single chisel fixed to a plough or ridger frame. In ripping, only shallow parallel furrows are cut using a ripper without disturbing the soil between the planting rows. The ripper should cut regular lines to facilitate subsequent weeding with ox-drawn weeders. Planting is usually done at the same time. The distance between the furrows depends on the recommended spacing for the crop. Ripping can reduce or eliminate the need for ploughing.

The ripper is faster than ploughing, as tillage is limited to only a thin opening for planting. Because of this narrow working width, pulling a ripper requires about half the draught force of that needed for pulling a conventional single-furrow plough. The ripper is smaller and lighter than a plough, and is easier to operate. The farmer can also use smaller animals, or animals that may be weaker at the end of the dry season. The ripper is also cheaper to buy and cheaper to maintain. As a result of these advantages, the farmer can work larger acreages each season, and achieve timeliness in operations, thus taking advantage of the early rains. This is important, especially in seasons of lower-than-normal rains or, generally, for marginal-rainfall zones. The weed problem can be serious in a rip tillage system. Therefore, action should be taken to lessen the problem over the longer term. The ripper (e.g. the Magoye ripper) is a useful weeding tool.

Advantages

• Ripper attachments fit on a normal plough beam hence cheaper than complete implements.
• Can be used to make planting slots in dry soil allowing early planting.
• Disturbs the soil less than ploughing hence reduces soil erosion and encourages water infiltration into the soil.

Disadvantages

• Difficult if there is a lot of residue on the surface because the residue wraps around the ripper shaft.
• Disturbs up to 30% of the soil surface.
• Quite difficult to use on fields with tree stamps.

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