Ploughs, chisels and subsoilers for animal traction

The plough in its different shapes as traditional ard plough or as mouldboard plough is probably the most popular land preparation tool that is used in both developing and developed countries. Compared to the plough, there is no other tool that so symbolizes agricultural development. Tillage tools might still be necessary for some specialized operations even under conservation agriculture. This is why they will be discussed briefly. However, under CA they disappear as commonly used implements.

Plate 3. 
Primary tillage to open up the soil results in moisture loss and greater weed infestation. (T.Friedrich). 

The plough is mainly used for primary tillage: opening up the soil with the aim of loosening it for good root penetration and cutting and burying weeds. The plough can be pulled by one or more pairs of donkeys or oxen.

Disadvantages of the plough include:

• At the beginning of the rainy season strong animals are needed to draw the plough while at that time most animals are weak.
• Repeated ploughing at the same depth can create plough pan or compacted layer.
• Inverting will result in loss of soil moisture through evaporation.
• Brings weed seeds from deeper soil layers to the soil surface while burying fresh weed seeds, resulting in the long term in more weed infestation in the field.

The design of the mouldboard, such as the size and curvature, determines the quantity of crop residues that are left on the surface and the part that is mixed into the soil. The bigger and more curved the mouldboard the greater the amount of residue that is inverted into the soil and thus less is left on the surface. As a first step to convert from conventional plough based farming towards conservation agriculture, farmers might opt for tined implements like chisel or cultivator.

Chisels or rippers are sharply pointed, metal tines that can be attached to the ordinary plough beam (Moeller, 1997). Usually, farmers who want to avoid ploughing in minimum or reduced land preparation activities use chisels.

Plate 4. 
Animal drawn ripper (T. Friedrich).

Plate 5. 
Magoye ripper with seeder attachment: a popular tool in South and East Africa. (J. Kienzle). 
 

It can also be used to break up plough pans or other impermeable soil layers, like crusts. 

Disadvantages include:

• Poor weed control.
• Requires an adequate soil condition (friable or dryer) to work properly.
• Residues and vegetation on the surface clog up the implement.
• Stones and clods are lifted.

The subsoiler is used to break up hard or compacted soil layers, with the aim of improving water infiltration and root penetration. It can be attached to the ordinary plough beam. It can also be used to break up dry soil. The point works beneath the compacted layer and can be used up to soil depths of 25-60 cm. With animal traction the maximum working depth of a chisel is around 30 cm. For this reason real subsoiling is not possible with animals, but shallow compacted soil strata can be broken using adequately shaped chisels.

Plate 6. 
Chisels used for deep ripping with animal traction need to be narrow and pointed. On the right: Subsoiler attachment for traditional plough, left magoye ripper attachment (T. Friedrich).