Soil tillage has a huge influence on crop production, and is one of the most expensive input costs. Decisions about proper methods cannot, therefore, be hit or miss.

A crop farmer’s decision about the correct tillage method to use should be based on information that leads to objectives – not on “recipes”.

Before making the decision, the farmer should note that there are three main schools of thought: residue-free systems, stubble-mulch systems and no-till.
Each has its own advantages and disadvantages.

RESIDUE-FREE SYSTEMS

• These tillage practices leave the soil surface uncovered, because they turn the soil, using a mouldboard plough, nardi, disc-plough and disc or one-way.
• Several diseases, such as ear rot in maize and Sclerotinia in sunflower and other broadleaf crops, are better controlled in a residue-free system.
• The movement of lime into the soil is very slow when it is simply applied to the soil surface. The most effective way of incorporating lime into the soil is by discing as well as ploughing.
• It is also better to cultivate certain crops, such as groundnuts, on a stubble-free field, because of the lower pressure from plant diseases.

STUBBLE-MULCH SYSTEMS

• In these systems, the soil is tilled in a way that leaves the residue on the soil surface.
• Tillage is carried out using a variety of tined (pronged) implements, at different working depths.
• The occurrence of ear rot is usually associated with maize mulch on the soil surface and monoculture maize production systems.
• Deep-ripping actions are usually effective for fields prone to the formation of compacted layers.

NO-TILL SYSTEM

• There is no primary or secondary soil tillage in a no-till system and planting is directly into undisturbed soil.
• Weed control is carried out chemically and/or biologically.
• Soil types that have a higher clay content can usually be tilled more shallowly; even no-till can be successful.
• The degree to which soil is prone to compaction correlates strongly to its clay and silt content: the sandier the soil, the more prone it is to compaction and the deeper it usually compacts.
• Soil types that differ in terms of the appropriate tillage system, should preferably be grouped in separate fields.

Also read: Do not neglect weed control

FACTORS TO CONSIDER

The best soil tillage method for a specific field, for a specific season, is determined by:

• Crop preferences.
• The field’s dominant soil types.
• The probable occurrence of compacted layers in the soil and the depth of occurrence.
• The weed pressure and the weed species that occur. (In fields where lots of weeds emerge during the crop season, the tillage system should be aimed at preventing weeds growing and producing seed. Weeds should be controlled within two weeks after they emerge).
• Liming and fertilisation.
• The occurrence of plant diseases.

The information derived leads to the setting of objectives. And after that has been done, the appropriate tillage system is put together to meet the objectives.

CAPACITY

The farmer’s mechanisation capacity also plays a major role in choosing the appropriate tillage system.

If he has relatively few tractors and implements, he should cultivate some of his fields during autumn and winter, so that he will be able to cultivate the remaining fields easily during spring or summer when the climate forces him/her to.

OBJECTIVES

When evaluating the information about these aspects, the required objectives must be clearly stated. And these must be aimed at optimising the growth of the crops.

The most common objectives of soil tillage practices are the following:

• Creating a favourable top soil structure for root development and aeration, and creating a temporary structure to combat wind erosion.
• Creating a favourable sub-soil structure through using deep ripping for deeper root penetration.
• Incorporating crop residue, lime and fertilisers in soil.
• A fine, firm seed bed.
• Weed control.
• Controlling plant diseases.

DECIDING ON A SYSTEM

Having obtained information regarding the soil properties and having set the objectives for each field, the farmer now has to decide on the appropriate cultivating system in order to reach the objectives.

Finally, he has to incorporate control measures so that he can obtain the stated objectives.

CONCLUSION

Standard “recipes” may make farming easier, but then there are no regular inspections and soil problems could occur without the farmer knowing about them.

Information about soil types and production problems should be established first, before setting cultivation objectives.

Only after that can a decision be taken about the appropriate soil tillage system, taking into account the farmer’s mechanisation capacity.

• This article was written by Martiens du Plessis and first appeared in Farming SA.