Mechanisation: How to choose a good planter

For a crop farmer, planting is probably the most important management activity. This article provides guidelines on how to choose a good planter.

Let’s say you want to plant 40 000 maize plants per hectare at a depth of 50 mm and would like to fertilise it with granular 2:3:2 at a rate of 250 kg/ha in a band that is 50 mm deeper and runs 50 mm alongside the seeds.

To comply with your needs, your planter should be able to perform the following tasks:

  • Cut through stubble (if there is stubble on the soil surface).
  • Open a slot at the desired depth for the placement of fertiliser.
  • Accurately meter out the desired quantity of fertiliser into the slot.
  • Close the fertiliser slot.
  • Open a slot 50 mm to the side and 50 mm shallower than the fertiliser slot for seed placement.
  • Accurately meter out seeds into the slot to add up to 40 000 seeds per hectare.
  • Close the seed slot with loose soil.
  • Compact the soil above the seed to establish good seed/soil contact.

The planter needs mechanisms to perform all these functions. If one or more of these mechanisms are not present, the planter will not be able to perform the corresponding actions.

It is possible to combine some of these activities in one mechanism and the farmer should look for such possibilities.

Double disc openers, for instance, will cut through stubble and open a slot for fertiliser placement. In another case a seed slot opener behind and 50 mm alongside the fertiliser opener, will close the fertiliser slot while opening the seed slot.

The following actions will now be discussed:


In no-tillage, or minimum tillage situations, stubble is left on the soil surface to reduce run-off when it rains. This reduces soil loss through erosion and also improves water penetration into the soil.

The stubble, if sufficient, will also control weed germination and act as an isolating layer on the soil to reduce soil temperature during the hot summer months.

On the other hand, the stubble can clog normal planters. Therefore the ideal planter needs to cut through the stubble in the line where slots need to be opened for fertiliser and seed placement. Coulters are used for this purpose.

There are a number of coulter designs, but the most common coulter for cutting stubble is the plain disc coulter. This is a flat coulter with a sharpened cutting edge.

An example of fluted coulters. Photo:


There should be a mechanism for opening a slot, at a depth of 100 mm – 150 mm, for the placement of fertiliser. Several options exist.

The illustration above consists of drawings A – F and shows some possibilities. Drawings A and B illustrate double plain disc openers. The fertiliser (or seed) is dropped between the discs to fall to the bottom of the slot and closers rake the soil back into the slot on top of the fertiliser or seed.

Drawings C and D illustrate shoe openers. Pipes, for dropping fertiliser or seed in the slot, are mounted at the back of the shoe.

Drawing E illustrates a single plain concave disc. The disc ploughs open a slot and the fertiliser or seed is dropped behind the disc on to the bottom of the slot.

Drawing F illustrates a tine opener. The tine draws a slot and the fertiliser or seed is placed directly behind the tine on to the bottom of the slot. All of these openers can be used for creating slots for either fertiliser or seed.

There’s a choice of several mechanisms for measuring out fertiliser, one of which is the gravity type metering mechanism where the fertiliser flow rate is controlled by adjusting the size of the opening. As these units do not deliver more fertiliser at higher speeds, they are only adequate for single speed use.

There are also gear type and auger type metering units. Gear type metering mechanisms, although adjusting delivery according to speed, tend to deliver pulsating batches of fertiliser, instead of an even fertiliser band.

Auger type mechanisms will provide more even distribution in the slots.


Seed can be metered out with conventional horizontal or inclined plate methods, finger-pickup, pressurised air or vacuum methods. The accuracy of these metering units, as well as their cost, increases in the order listed here.

Plate metering units are found in cheaper planters and are adequate where seeds are of the same size.

Once there is great variation in seed size, doubles will be metered out when two small seeds fall into one metering hole and misses will occur when seeds are too big to fit into a hole.

It is therefore important to use the right sized holes in the plate and to ensure that there is little variation in seed size.

Finger units and vacuum metering units can handle greater variation in seed size. The metering principles are shown in the illustrations below.


If the seed is placed in loose soil, the seed won’t make enough contact with the soil moisture. Compaction is therefore needed around the seed.

This seed/soil contact can be achieved either by pressing the seed firmly into the bottom of the seed slot and covering it with loose soil, or by covering the seed with loose soil and then compressing it. Illustration 7 shows a number of press wheels for this action.


Successful crop production depends on the following three factors:

  • Using the best seeds/cultivars for your particular environment.
  • Planting on optimal soils.
  • Managing the production process correctly.

It is essential to use good seed of the correct cultivar for your specific area. Inferior seed with low germination potential and possibly of a cultivar that is not adapted to the area, will produce bad stands and therefore low yields.

The farmer should ensure that he plants in a soil of acceptable soil chemistry for the crop and that soil organisms are present in sufficient quantities. Shallow soils have low moisture capacity and low potential.

Planting in arid areas is risky and other kinds of farming activities, such as livestock production, should be contemplated.

If the seed is of an acceptable type and quality and the external environment is conducive to successful cash crop farming, the rest depends on the farmer’s management skills.

Here are some guidelines:

  • Soils with compacted layers need to be broken up by ripping.
  • High acidic soils bind soil nutrients and need to be treated with lime.
  • Nutrient deficiencies must be counteracted by adding fertiliser.
  • Plant the crop at the ideal spacing and density for your specific area.
  • Weeds and pests need to be controlled.

If all these management activities are successfully undertaken and you have used the right seed in the appropriate soil and the right climate zone, you should produce a successful crop.

Also read:
Mechanisation: A short guide for new farmers
Pointers for buying a tractor

  • This article was written by Johan Van Gass and first appeared in Farming SA.

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