swaziland; grains; maize; inputs

Crop production: How to get an a-maize-ing harvest

To choose the best planting time for their maize farmers should consider the available heat units on their farms, in other words determine how warm or cool the area is where they farm. Also keep in mind long-term rainfall patterns.

The maize plant should have enough time to develop fully during the available growing season, which is determined by day light hours, temperature and rainfall. Research has shown that the ideal average temperature for the maize plant is 30˚C. Ideally, temperatures should not drop below 6˚C and not rise above 45˚C. Temperatures outside these parameters could harm the development of the maize plant.

It is important that the crop develops under the most favourable conditions to ensure the best possible yield with the least risk.

Besides choosing the correct cultivar, the single most important decision the maize producer has to make is probably the best planting date to suit the conditions in his area.

In South Africa the maize producing area is divided into warmer and cooler regions. Every district has its own ideal planting date determined by the number of heat units, which simply means how warm or cool it is.

A maize plant needs a certain number of heat units to mature fully and produce a crop.


In the case of fewer heat units, farmers in those areas should plant more seeds per hectare to compensate. In areas with higher heat units, farmers can afford to have a lower plant population, especially if they choose maize hybrids that develop 2 or 3 ears per plant. Under conditions of drought such hybrids will provide them with the best chance of a harvest and under favourable conditions they can look forward to above average crops.

Risks of late plantings: Late-planted crops have a higher risk of ear rot as plants take longer to reach maturity due to fewer heat units being available later in the summer.

Risks of planting too early: To sidestep the risk of drought farmers should choose their planting date in such a way that their maize plants won’t be flowering (70 days after planting) during the period when the mid-summer drought usually occurs. This is especially important in South Africa’s western production regions.

It is a good idea to study long-term rainfall patterns for your specific region. Two weeks before and after it flowers the maize plant’s need for moisture reaches a peak.


  • Some areas have adequate heat units for a long planting period.
  • The best planting dates for warmer areas are between 15 November and 15 December.
  • If planting takes place after this period, the crop runs the risk of being damaged by early frost as it has not reached maturity by the time winter sets in.
  • Some areas are subject to mid-summer droughts from late December to the second half of January.
  • With earlier planting dates one runs the risk of damage to the crop as the plants will either flower or be in the early stages of grain filling when the dry period starts.
  • In these regions the planting date should be such that the flowering date is only late in January or early in February.


  • In cooler maize producing areas heat units are limited.
  • To make use of the maximum number of heat units available farmers in these areas plant earlier than in the west.
  • Planting can start as soon as the day temperatures reach 13ºC to 15ºC.
  • In many of these production areas this is usually from about 20 August.
  • The ideal planting period is usually from mid-October to early November.
  • Maize planted after this period usually has a lower yield potential.
  • Cultivars with a medium growing season should not be planted later than 20 November.
  • With quicker growers, the planting period can be stretched by a week.
  • Seed companies have experienced personnel who can advise farmers on the best cultivars and planting dates for each production region.


It is a good idea to analyse your soils and consult an expert to determine a fertilisation programme for your maize fields. A few important factors, such as water, nutrition and heat units, determine the efficiency of the maize plant as a “starch factory”. Fertilisation is essential to ensure that the maize plant produces at its full capacity.

Each maize field should be managed and fertilised according to its nutritional status and yield potential. The creation of a soil medium that allows optimum root development forms the basis of a promising maize yield.

Furthermore the neutralisation of soil acidity plays an important role in achieving the full yield potential. Certain hybrids can tolerate acidic soils, but no hybrid is completely resistant to them. That’s why a liming programme remains a better choice than switching to a different hybrid. Besides ensuring better root development and nutrient uptake liming also supplies the essential elements of calcium (Ca) and magnesium (Mg).


Nitrogen (N), phosphor (P) and potassium (K) are essential nutrients for grain production, but usually don’t occur in sufficient quantities in the soil. The uptake of these 3 nutrients increases before and after flowering.

The higher the yield target, the more nitrogen per ton of grain is required. Nitrogen is especially important where maize is grown under irrigation and the desired yield exceeds 10 tons per hectare.


  • The most economical and efficient way of fertilisation is band placement as it inhibits the fixation of nutrients.
  • Broadcasted fertiliser is only efficient at high fertility levels and is not an economically sound practice for low fertility and low yield potential.
  • The reaction to band placement at high fertility levels is substantially less compared with the reaction at low fertility levels.
  • It is good practice to band place some of the fertiliser as it acts as a pop-up to stimulate early growth, especially where the soil temperature is still low during planting.
  • Under high potential- and irrigation conditions high soil fertility is essential to meet high yield expectations.


In general cultivars with a medium growing season have over the years shown that they involve fewer risks for the farmer. Furthermore choose hybrids that have already shown stability over many seasons.

To determine your farm’s heat units on a daily basis add the maximum temperature and the minimum temperature, subtract 10ºC from that and divide the total by 2.

As soon as the days of the year become shorter maize ears ripen. At this stage heat units will also decline, which doesn’t help the development of maize planted too late. This is why late plantings often result in disappointing yields and quality.

Also read: Maize pests – control starts with knowing the enemy

  • This article was written by Charl van Rooyen and Jacques Claassen and first appeared in Farming SA.

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