September 2018
JOHAN VAN BILJON and DR TINGMIN YU, ARC-Agricultural Engineering
The optimal use of the correct equipment and implements is necessary to optimise farming production and to maximise operational profit. All mechanisation actions need to be considered for the whole conventional farming value chain.
These actions are illustrated in Figure 1. Certain activities, like planting and harvesting, need to be done in a specific time window. Therefore, mechanisation is necessary to adhere to the time limits set.
To mechanise farming activities, one needs to consider the following factors:
- Appropriate equipment to be used for timely crop production.
- Manufacturing and availability of machine or implement parts.
- Suitable capability and capacity for maintenance.
- Effective utilisation and operation (skilled operators and technical staff must be available and affordable).
- Favourable economic and financial conditions to support mechanisation.
The planning and selection of tractors and implements for crop production can greatly impact the performance and profitability of the farming operation. The type and size of tractors and equipment used, and matching of tractor engine power and capacity of implement can also influence energy efficiency.
During the peak period of the farming process, such as planting and harvesting, time constraints are a great concern and enough tractors and implements are necessary to complete the actions within the specific time window. Too much surplus mechanisation capacity will increase the operational cost and thus reduce the profitability.
Introduction to tractors
Tractors are the powerhouse for implements and are classified according to their capacity (engine power in kW) and type. The tractor type can be two-wheel driven, four-wheel driven or track laying traction.
It is, however, important to utilise the tractor’s capacity in such a way that the tractor-to-implement match is optimised for good traction control and economic fuel consumption. It is also important to have enough capacity to do the work on time without having surplus tractors available when the operational time window is limited.
Function of a tractor
- Providing draught power for tillage tools through the drawbar or three point linked hitch system.
- Used for trailing and transportation of farm products.
- Power source – PTO, hydraulic and electrical output to drive other machines.
- Earth moving.
- Transport.
Selection of farm tractors
It is important to select the appropriate size and numbers of farm tractors according to the mechanisation plan. The following factors can influence the tractor selection:
- Farm area to be cultivated.
- Type of crops to grow.
- Mechanisation activities necessary for the various crops on the farm.
- Soil structure and condition of terrain.
- Financial capability.
Selection between 4×4 and 4×2 tractors
The 4×4 tractors have better traction performance than the 4x2s, hence better drawbar pull performance under poor terrain conditions. However, 4×4 tractors are more expensive (purchase and maintenance). It is more economical to select 4x2s for light-duty operations under better terrain conditions.
Selection of implements and farm machinery
The selection of implements and machinery will be influenced by the following factors:
- The crop and production method: CA or conventional.
- Implement performance.
- Timeliness of operations.
- Power availability.
- Operation capacity.
- Machinery selection will depend on the performance characteristics, costs, and types of operation.
Tillage implements
Tillage is the agricultural preparation of soil by mechanical agitation of various types, such as digging, stirring or overturning. Tillage implements are classified in primary tillage implements and secondary tillage implements. Furthermore, tillage implements are also classified in conventional tillage and conservation tillage. Conservation tillage (Figure 2) can also be divided into reduced tillage and no-till.
Conventional tillage practices require the most tillage operations while conservation tillage requires less or no tillage practices.
Commonly used implements for conventional tillage
Mouldboard plough
The mouldboard plough (Photo 1) is used for seedbed preparation and forms part of the primary tillage actions. It is one of the oldest of all agricultural implements and is generally considered to be the most important tillage implement in conventional tillage practices. Ploughs can be categorised into mounted and semi-mounted ploughs.
The drawbar power requirements for a four-share plough on sandy soils will be 48 kW or 12 kW/share, at a working depth of 250 mm, and a working speed of 5,9 km/h.
Disc plough
Disc ploughs (Photo 2) are most suitable for conditions under which mouldboard ploughs do not work satisfactorily, such as hard dry soils, in sticky soils where a mouldboard plough will not scour and in stony fields. Disc ploughs depend on their weight to penetrate into the ground and therefore are normally built from heavy material. Side forces are usually taken up by the land-wheel at the back of the implement.
The drawbar power requirement for a three disc plough at a working depth of 250 mm is 45 kW or 15 kW/disc at a speed of 6 km/h.
Disc harrow
Disc harrows (Photo 3) rank close to the mouldboard plough in importance as tillage implements. Heavy duty disk harrows are used for primary tillage, for controlling weeds, and for cutting and mixing stubble or cover crops with the soil. Lighter units are often used in seedbed preparation subsequent to ploughing.
The power requirement to pull a light duty, 3 m cutting width disc harrow at a working depth of 150 mm in sandy loam soil at a speed of 8 km/h, is 50 kW. The power requirement for heavy duty offset discs with a cutting width of 3 m at 8 km/h is 80 kW.
Ripper or subsoiler
A ripper or subsoiler (Photo 4) is used to break through and shatter compacted or otherwise impermeable soil layers and to improve rainfall penetration. When practicing conventional tillage and using a plough, a ripper will be used to break through the plough pan when necessary.
The power requirement to pull a three-tine ripper on average is 60 kW or 20 kW/teeth at a working speed of 7 km/h and working depth of 400 mm.
Cultivator
Cultivators (Photo 5) are used for weeding or seedbed preparation. This specific model is called a Vibro Flex tiller, and is normally used at an operation speed of 12 km/h to get the vibrating effect and therefore maximum efficiency. It is also used to loosen the top layer of soil to allow faster germination and enhance plant growth.
Depending on the working width of the implement, power requirements may vary from 40 kW to 100 kW.
Cultivator (s-tine with roller)
This implement (Photo 6) is used for light duty weeding and seedbed preparation. The roller at the back is used to break up the clots to provide a fine seedbed for planting. The power needed to pull the implement ranges between 40 kW and 80 kW, depending on the working width.
For more information contact Dr Tingmin Yu or Johan van Biljon at 012 842 4000.
Publication: September 2018
Section: On farm level
