Sustainable Agriculture Extension Manual

Minimum tillage

Minimum tillage is a tillage method that does not turn the soil over. There are various kinds of minimum tillage. The one described here uses two oxen-drawn pieces of equipment: a subsoiler and a ripper.

On many soils, conventional ploughing compresses a layer of soil at a depth of about 15 cm (6 inches). Over several seasons of ploughing, this compressed layer can form a hardpan. This prevents water from percolating down, decreasing the soil's moisture-holding ability and increasing the amount of water that runs off the surface.

The hardpan also stops plant roots from penetrating deep into the soil. The shallow roots of crops cannot reach nutrients below the hardpan, and the plants tend to fall over easily.

The subsoiler used in this minimum tillage method penetrates deep into the soil, breaking up the hardpan and allowing water and roots to pass through. The ripper breaks up the soil further and makes planting-furrows at the same time.

Location

This technology is applicable where hardpans exist. This is usually on light sandy loams, loams, and clay loams. It is not used in sandy or clay soils.

Advantages

Subsoiling allows water to percolate more easily and evenly into the soil. This means that the soil can be tilled earlier after the first rains, and the soil stays moist longer.
Using a ripper allows planting to be done earlier and faster than with conventional furrow planting.
Crop roots can penetrate deeper into the soil, and crops produce higher yields.

A hardpan stops water from seeping into the soil, resulting in erosion and dry soils. It also prevents crop roots from reaching down deep. Where conventional ploughs have been used, the hardpan forms at a depth of about 15 cm.

Disadvantages

At least four strong oxen are needed to pull the sub-soiler. (Only two are needed for the ripper.)
In some situations, minimum tillage can promote the growth of weeds.

Requirements

Healthy oxen.
Sub-soiler.
Ripper.

Subsoiling is done on the contour at 0.5 to 1-metre intervals. Four oxen are needed for subsoiling.

Procedure

1. In the dry season, plough the land using the subsoiler, drawn by four oxen. Plough along the contour (across the

slope, not up-and-down), leaving 1 m (3 feet) between the rows. On steeper slopes, leave 0.5 m (18 inches) between rows.

2. After the first rains, use the ripper to break up the soil and prepare furrows for planting.

3. Plant the crop.

4. Begin weeding the crop early, and weed regularly.

5. Plough with the subsoiler again after 1-2 years.

Maize grows better where subsoiling and ripping have broken the hardpan (right) than previously (left)

Do's

Use the subsoiler when the ground is dry. This will allow the hardpan to crack and shatter.
Follow the contour when subsoiling or ripping.

Don'ts

Don't use the subsoiler when the soil is wet.
Don't allow continuous grazing of cropping areas.

Promoting minimum tillage in Tanzania

The Agricultural Mechanism Management (AMM) project is promoting minimum tillage in the Arusha region in northern Tanzania. The project is working with farmers on the use of the sub-soiler and ripper in areas with 400-1200 mm of rainfall a year.

The project first visits farmers and carries out an appraisal exercise to find out if they are aware of the hardpan problem. About 20 farmers are then chosen to carry out demonstrations comparing minimum tillage with conventional ploughing. The farmers use their oxen for around 6 hours per day (in the mornings and evenings) and are able to till about 2 acres (just under 1 ha) in this time.

The farmers apply the same crop management on the minimum-till and conventionally ploughed fields. This means they can compare the results directly. The project helps organize field days so that other farmers can see and discuss the results.

The ploughs can be made locally from old implements, car chassis, and materials bought from equipment dealers. AMM can provide spare parts such as shanks, sweeps and points. By demonstrating the benefits of the technology and fostering the business infrastructure supporting it, AMM hopes that the technology will begin to spread among farmers by itself. —For more information, contact Agricultural Mechanism Management, Tanzania.

The subsoiler being used by AMM in Arusha. This digs 25-30 cm into the soil, breaking the plough hardpan. The hitch extension can be adjusted to ensure deep penetration, even in the dry season. The subsoiler attachment can also be fitted to other plough frames. The furrows should be made about 80 cm (2 feet 8 inches) apart

The Magoye-type ripper used by AMM in Arusha. It allows planting to be done at shallower depths than with conventional furrows, enabling the seedlings to emerge quickly. The ripper is especially siutable for planting maize.


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