Sunflower is an important oil seed crop in Southern Africa. It is grown in virtually all summer rainfall areas. It normally competes favourably and is a good alternative to other summer grain crops.
The total area under sunflower production in South Africa varies from year to year because of climatic factors and market prices.
- The sunflower is adaptable and more tolerant in heat and drought than most other grain crops such as maize.
- Its deep, branched tap-root system makes the plant more efficient at seeking out moisture.
- Even in sub-soil and heavy clay soils it uses moisture reserves far more effectively than maize.
- Because of its shorter growing season and greater cold tolerance sunflower is suitable for later planting.
- This can be an advantage when moisture is being conserved early in the season.
- Sunflower is normally planted in midsummer, which means that it grows during the cooler summer months when excessive moisture loss is limited.
- Although sunflower needs more water per unit dry matter than maize, it produces much less dry matter per hectare, with the result that it uses less water per unit area than maize.
- A warm and somewhat dry climate is considered optimal for sunflower production.
- Cool, moist weather conditions, especially during the ripening period, are unsuitable, because they encourage rust and head rot, while very hot dry conditions cause charcoal rot.
- Sunflower can tolerate cold nights and light frost better than maize, except during the pollination and early seed development stages.
- They need an annual rainfall of 650 mm to 850 mm.
- For the shorter, quicker varieties, 500 mm to 650 mm is sufficient.
- However, good yields can also be achieved with 300 mm to 400 mm of rain during the growing season.
- Deep, well-drained loam soils with a good physical condition are naturally ideal and sunflower grows much better on turf soils than maize.
- Acid, sandy soils are unsuitable because sunflower is very sensitive to aluminium toxicity.
- Eelworm-infected soils have to be avoided as the sunflower is also very sensitive to this pest.
- Young seedlings are not very strong.
- Soils inclined to crust easily have to be loosened after planting to ensure a good stand.
- Sunflowers are a valuable rotation crop on soils infected with witchweed.
- Witchweed germinates in sunflower fields, but die soon after germination because it cannot develop on sunflower.
- During and shortly after germination, sunflower is sensitive to unfavourable conditions, including weed competition.
- A fine seed bed and effective weed control are thus extremely important in ensuring a good stand.
PLANTING DEPTH AND TIME
- The heavier the soil, the shallower the recommended planting depth.
- The drier the soil, the deeper the recommended planting depth. On heavy soils the planting depth should not be deeper than 37 mm, while on lighter soils with a clay content of 15% and less, it may be planted up to 60 mm deep.
- If the soil compacts after planting and forms a hard crust, it has to be loosened as soon as possible or else the neck of the emerging seedling can break, resulting in the plant dying and a subsequent reduction in plant population.
- Sunflower is not very sensitive to date of planting and can be grown over a long period in most areas.
Normal planting times for the various areas are as follows:
• Cooler areas: November to mid-December
• Warmer areas: mid-November to early January
• Frost-free areas with a long growing season: until February/March
It has been shown in practice that populations of 30 000 to 45 000 plants/ha are best.
Lower plant population is recommended for areas with a low rainfall and at wide row spacing, while the higher plant population is preferred under high-potential conditions and with narrower row spacing.
Uneven spacing and low plant populations are undesirable as it results in excessively large heads that cause the plants to lodge before harvesting, while indications are that populations of more than 45 000/ha, even under irrigation, do not have any yield advantage.
Excessively high plant populations can even result in small heads with a poor kernel development. Exceptions to these recommendations include a number of cultivars, especially those with quick-growing seeds.
Excellent sunflower hybrids are available in the trade, including some that are high in oil content, have high yield potential, even plant height and are disease resistant. The duration of their growing seasons vary.
Oil content is very important because the producer’s price is determined accordingly.
FACTORS FAVOURING SUNFLOWER
- Marginal soils more often are used for the production of crops that are less risky and require lower production inputs. Sunflowers conform to these requirements.
- Sunflower is the ideal crop as far as oil production is concerned.
- Sunflower makes for an excellent rotation crop which can be cultivated under widely varying climatic and soil conditions.
- Since the advent of hybrid sunflower, traditional problems such as uneven height and maturity have largely been eliminated.
- The crop is now easier to handle and has become an excellent alternative to maize and sorghum.
- This article was written by Malixole Gwatyu and first appeared in Farming SA.