The farmer has full control over soil tillage so he must plan his actions carefully to ensure that his specific problems are solved when he tills his lands.
Favourable conditions for wheat production include creating soil in which sufficient water is stored for germination and early plant development. This is achieved by cultivation that maximises the amount of water that filters into the soil, and by reducing weeds and volunteer plants.
Unnecessary cultivation costs money, time and effort, and valuable soil water is lost in the process.
Unnecessary cultivation also causes compaction that has to be addressed later. Properly planned tillage should eliminate compaction and manage excess stubble. Traditionally, weeds were controlled by mechanical cultivation such as ploughing with a mouldboard plough (conventional tillage) or by shallow cultivation to kill weeds while retaining stubble on the surface (conservation tillage).
Another planting method, namely minimum-till (also called no-till) in which the seed is directly sown in untilled soil, has become available due to cost-effective ways of killing weeds with broad spectrum herbicides (chemical cultivation) and the availability of planting machines that can be used in high stubble conditions.
Whichever system the producer chooses, good crop establishment and economic factors remain the main issues.
Conventional tillage is recommended for a wheat-on-wheat cropping system in which the risk of root disease is high and the risk of wind and water erosion minimal. The use of a mouldboard plough causes the top soil layer to be inverted and leaves virtually no stubble on the soil surface.
It effectively kills germinated weeds but brings weed seeds from deeper layers to the surface, where they then germinate. Mouldboard ploughing should always be followed with secondary cultivation to get rid of clods and new weed infestations.
How to till conventionally:
Step 1: Harvest (December – January)
Step 2: Disc as soon as soil conditions allow. If a lot of residue is left on the surface, repeat. In years of exceptional straw (> 3.0 ton/ha grain yield), burning of the residue can be considered.
Step 3: Plough between the end of January and end of February in the drier areas, and between mid-February and the end of March in the wetter areas. The timing depends on the soil water situation. Ploughing must be done when there is still a good chance of getting good rain after the cultivation to replace water lost during the operation. At the same time, ploughing should be left as late as possible so that the minimum subsequent cultivations will be needed for weed control. If possible, the plough must be fitted with a row of small tines at the rear, or a harrow must be attached in order to seal the surface layer and break clods behind the plough.
Step 4: A sweep or harrow should be used directly behind the plough, or as soon as possible after ploughing, to break clods and to seal the surface layer to prevent evaporation.
Step 5: Shallow sweep cultivations may be used to prepare the seedbed and to control weeds, when necessary.
Step 6: Plant according to guidelines.
If possible, use a planter fitted with tines so as to achieve:
- Effective band placing of fertiliser in wet soil to enhance uptake by the roots.
- Breaking of shallow compacted soil layers caused by tillage after ploughing.
It is important to adjust the press-wheel according to the moisture content of the soil. The drier the soil, the greater the pressure that must be applied.
Conservation tillage is highly recommended in all areas where the risk of wind and/or water erosion is high, because of the low clay content of these soils. These areas are usually less prone to the root disease “Take-all”, as the rainfall is lower and the soils are well drained.
Conservation tillage can also give good results in high rainfall areas if used in a crop rotation system where wheat is alternated with different crops. Wheat should never be planted in half incorporated wheat straw in high rainfall areas and under irrigation.
Under dryland conditions farmers in the North Western Free State of South Africa producing on deep sandy soils on a shallow water table, have been implementing reduced tillage successfully for many years. A dry climate, high yield potential and resulting high residue levels are ideally suited to reduced tillage systems.
Conservation tillage may be carried out in the following way:
Step 1: Harvest (November – December)
Step 2: Weed control (if soil moisture permits) with a harrow, sweep or V-blade depending on the amount of residue required on the soil surface. Chemical weed control may be used instead of cultivations.
Step 3: Deep tillage in March or April with a tine implement (ripper/chisel plough) to break compacted layers, if needed. Timing is essential in order to reduce the number of secondary cultivations, as all further cultivation will re-compact the soil. A roller should be fitted to the
implement if possible to seal the soil surface after the operation.
Step 4: Seal the soil surface directly after or as soon as possible after deep tillage with a sweep, harrow or V-blade (if roller is not fitted to tine implement).
Step 5: Control weeds and prepare the seedbed with a shallow tillage just before planting, if necessary.
Step 6: Plant according to guidelines. If possible use a planter fitted with tines for the already mentioned reasons.
The amount of straw left on the surface at planting should be determined by the risk of water and wind erosion. In high-risk areas, as much as possible must be left on the surface in order to break wind speed and limit run-off water. However, excessive straw will cause problems at planting as it will pack between the planter units.
NO-TILL (DIRECT SEEDING)
The increasing use of crop rotation systems and the development of new technology have created new opportunities to implement direct seeding systems successfully. The current high cost of diesel and the reduction in the price of glyphosate-based herbicides, makes reduced tillage methods even more attractive.
No-till has been established successfully in many areas in South Africa, including some parts of the winter rainfall region and some irrigation schemes, especially in KwaZulu-Natal.
In the Eastern Free State the use of these systems is more problematic due to high disease pressure, but with good management these problems can be overcome.
One of the main aims of direct seeding is to minimise disturbance of the soil surface in order to prevent surfacing and germination of new weed seeds and to maximise covering of the surface by residue. This further suppresses the germination of weeds and enhances the uptake of water by the soil.
A properly functioning no-till planter is then used to open a narrow slot by pushing away crop residues from the plant row. Ideally, a tine is used for proper fertiliser placement and breaking of surface and sub-soil compaction.
- This article was written by Willem Kilian and John Tolmay and first appeared in Farming SA.