Estimated reading time: 7 minutes
- Sunflower is one of the major row crops cultivated in South Africa.
- Modern sunflower production requires a good balance of risk and reward.
- The planting depth of sunflower is one of the basics that can make a big difference in the final plant population.
- Sunflowers, like any other crop, need proper stimulation at an early growth stage to establish the foundation for a high-yielding crop. The correct application rate, type and placement of fertiliser are essential building blocks to create this foundation.
- Sunflower is heavily dependent on boron to produce optimally. The occurrence of a boron deficiency will be more prominent in sandy soils that are normally low in organic matter. Boron deficiency could also occur in acidic soils in high-rainfall areas.
Sunflower is one of the major row crops cultivated in South Africa. The history of commercial sunflower production dates back as far as the 1930s when it was planted for the first time. Sunflower was seen at the time as a potential replacement for traditional oilseed crops such as groundnuts and cottonseed. Today sunflower and soya bean are the main oilseed crops.
The focus of this article is to emphasise how small changes in general production practices can lead to big rewards. Modern sunflower production requires a good balance of risk and reward.
Maize and soya bean are normally planted from October to December; sunflower is planted at the end of the maize and soya bean planting season. Producers who plant sunflower at an earlier date and treat it the same way they do maize are often surprised the crop’s good yield and oil content.
Sunflower competes well with maize and soya bean if the following production basics are adhered to:
- Soil should be thoroughly tilled and there must be no compacted layers.
- The seedbed should be firm but not compacted.
- Plant when soil moisture is sufficient.
- Planting depth should be 3 to 5cm; however, it must be deeper (5cm) in sandy soils.
- Plant population of 25 000 to
50 000 plants per hectare is the norm, depending on soil potential.
- If a later planting date is preferred, soil temperature should be considered. High soil temperatures will negatively impact germination.
- Use nematicides on sandy soils or if nematode pressure is high.
- Fertilise according to yield potential and soil analyses.
- Placement of fertiliser should be 5cm away and 5cm beneath the seed.
- Use a rotary hoe three days after planting to break the crust, if needed.
- Use a good quality foliar micronutrient spray to increase production potential.
- Prevention of diseases and insect damage is easier than controlling the disease when it becomes visible.
- Scout fields regularly and be on the lookout for foliar diseases and insects.
The planting depth of sunflower is one of the basics that can make a big difference in the final plant population as shown in Photo 1. The plant on the left (5cm) was planted 1cm shallower than the plant on the right (6cm). The plant population was much better for the 5cm planting depth than for the 6cm planting depth.
Importance of fertiliser
Sunflowers, like any other crop, need proper stimulation at an early growth stage to establish the foundation for a high-yielding crop. The correct application rate, type and placement of fertiliser are essential building blocks to create this foundation. Photo 2 shows the difference between fertiliser applied at planting compared to no fertiliser applied at planting.
The placement of fertiliser is an important aspect of the cultivation process. Incorrect placement, in this instance too close to the seed, can cause fertiliser burn, as shown in Photo 3. If fertiliser is placed too far from the seed, the seedling will be starved of essential nutrients in the early growth stages with a negative impact on yield potential.
Early growth stimulation of sunflower roots (Photo 4) results in yield increases with a return on investment (ROI) of more than 300%. In this trial, a root stimulant was applied to the seed at planting. The plants on the left served as the control and received no root stimulant treatment; the plants on the right did receive the treatment.
The application of quality foliar sprays that complement the fertiliser programme has a positive impact on the yield of the crop. Moreover, it increases the resilience of plants to withstand stresses such as drought or excessive heat. Figure 1 shows the effect of foliar application – the result indicates that the correct foliar spray applied at the right time will have a positive impact on yield (ROI of more than 200%).
Fertiliser trials are often conducted to establish the maximum economical return on a single element such as nitrogen (N). The question remains if this is the correct way to look at plant stimulation? The synergetic effect that nutrients have on each other when used in combination is often neglected. A trial was recently conducted to better understand the effect of additional phosphate and potassium fertilisation on sunflower.
The average soil phosphate and potassium levels were between 10 to 15mg/kg and 60 to 80mg/kg, respectively. Phosphate and potassium fertiliser were applied at 16kg P/ha and 8kg K/ha. Phosphate and potassium applied in isolation do not have a significant effect on yield (Figure 2). The trial results showed that additional applications of phosphate (5,25 and 10kg P/ha) and potassium (12,5 and 25kg K/ha) in combination, had a significant effect on yield.
Sunflower is heavily dependent on boron to produce optimally. Photo 5 shows the visual symptoms of a boron deficiency. The occurrence of a boron deficiency will be more prominent in sandy soils that are normally low in organic matter. Boron deficiency could also occur in acidic soils in high-rainfall areas.
The response of sunflowers to different N sources (Figure 3) indicates that nitrate-containing products used as a top dress improved yield. The ANO top-dressed treatment received 51kg/ha N and the rest of the treatments received 60kg N/ha as a pre-plant or top-dress application. The N-Gas™ treatment showed the best pre-plant result. Products rich in nitrate N also showed a significant increase in water use efficiency.
These results indicate that well-fertilised sunflowers will deliver a good return on investment (ROI).
The continuous monitoring of any crop during the growing season is essential. Plant sap (OmniSap® analysis) or tissue analyses could indicate if the plant needs additional nutrients to achieve optimal yield. Satellite imagery is also a very good tool to detect plant growth problems. Photo 6 is an example of a satellite image used for crop monitoring.
Poor plant growth, as shown by the satellite image, should be investigated in the field to determine the cause. Poor plant growth might be the result of disease, nutrient deficiency, drought or too much water. This technology enables the grower to proactively intervene and minimise potential income losses.
The inclusion of sunflowers in a crop rotation strategy with maize, especially in the North West and Free State, has many advantages. If sunflower is treated as a main crop and well looked after, success will follow. The opposite is also true – if sunflower is treated as the third choice after maize and soya beans, it will very seldom exceed the income per hectare of maize or soya bean. – Kobus van Zyl, senior agronomist, Omnia Nutriology
For more information, contact the author at email Kobus.VanZyl@omnia.co.za.