Crop rotation is a fundamental principle of sustainable crop production. Farmers need to consider a host of factors when deciding on a rotational crop in order to fit the climatic conditions and production requirements.

The oilseeds canola, sunflower and soya bean each have their own benefits. Soya bean is a valuable addition in a maize rotation as it fixes nitrogen in the soil. It also has a lot of value in its own right, since it is processed primarily for protein meal, which is widely used in animal feed rations.

As a result, demand for soya bean is driven by a growing need for animal feed as livestock sectors around the world expand.

Sunflower makes a valuable contribution to a farming business since it has low input costs and generally performs well under dry conditions. However, sunflower markets are finely balanced, and when production expands substantially, prices fall to levels that are not sustainable for most producers.

Low prices prompt farmers to reduce their sunflower plantings, which then reduces supply. This then leads to increases in prices, which then fall again if farmers respond by planting more sunflowers. This is an important consideration when making long-term decisions about including sunflower in crop rotations.

The canola industry has shown much promise over the past few years as new technologies and campaigns to boost consumption are bearing fruit. Canola remains an important rotation crop for wheat farmers, since it helps to keep weeds in the fields under control, reducing herbicide costs and consequently helping to boost yields for wheat.

Cultivars

To achieve the highest yield with the lowest risk, producers need to carefully choose cultivars for the respective crops based on climate and production techniques.

Both conventional and genetically modified (GM) soya bean seed are available in South Africa.

GM seed includes that which is herbicide tolerant, insect resistant, or both. Insect-resistant seed provides protection against African bollworm, reducing the need for pesticide applications.

Herbicide-tolerant soya bean allows farmers to control weeds chemically rather than manually, saving costs.

South Africa does not have GM canola or sunflower seed registered for use. Furthermore, a lack of high-yielding cultivars for both crops has been cited as a reason why hectares under production are stagnant.

While there are herbicide-resistant GM and hybrid canola seed cultivars available elsewhere, they are not available in South Africa. As such, the local seed industry has focused on multiplication of high-performing cultivars to improve yield potential. Yields do however lag behind that of other countries.

Sunflower producers have a choice of 199 different sunflower seed varieties. Of these, 113 are classified as high-oil hybrids with the potential of achieving higher than 40% oil content.

While the 113 cultivars are non-GM, some have resistance to specific herbicides, or have certain fatty acid compositions.

A conundrum facing the sunflower industry is that South Africa, unlike other countries, does not pay a premium for seed with a higher oil content. Thus, producers are not incentivised to prioritise oil production over yield.

A report compiled by the Bureau for Food and Agricultural Policy (BFAP) points to evidence that planting dates that are too early or too late have a negative effect on both the yield and oil content of sunflower seed, and the late plantings common in South Africa, where sunflower is mostly planted after the maize crop, may negatively influence the sunflower seed’s oil production potential.

A low oil content is detrimental to the processing industry and discussions are ongoing in the industry to introduce incentives for high oil production.

Growing sunflowers

Sunflower is a good crop to grow in marginal soils, yet is also well adapted to a wide range of soils from heavy to sandy loam. The crop prefers a warm and dry climate, making it ideal for the central parts of the country and those to the west of Gauteng.

Cool and wet conditions during the crop-ripening phase will likely lead to rust and head rot, while extremely hot conditions can cause charcoal rot. Sunflowers are planted under dryland conditions and don’t require irrigation.

Grain SA notes that since sunflower has a shorter growing season than maize and can handle frost, it can be planted later in the season, but preferably before mid-February.

Sunflowers’ tenacity presents both advantages and disadvantages. On the one hand, they can provide income to farmers who have marginal soils or who wish to add another crop to the mix after maize and soya bean plantings have been completed. On the other hand, suboptimal planting dates and care will curtail yields and oil content.

BFAP explains that sunflowers are often planted as a ‘catch crop’, which means preference is not given to optimal planting dates, fertiliser applications, soil analysis, or much of the weed or disease programmes required for optimal production. However, if these are neglected, yield potential inherent in the seed will never be reached.

Grain SA states that sunflowers should not be planted in the same field more than once every three to four years.

The Agricultural Research Council (ARC) cautions that plant population is the single most important contributor to yield potential. The council proposes a stand of 30 000 to 45 000 plants per hectare if maximum yields of up to 2t/ha are the aim.

Nursing the young seedlings through the difficult and challenging emergence stage is highly management intensive, and the ARC advises producers to score the crusty earth’s surface just prior to emergence, which is normally about three to four days after planting.

To enhance yields, the ARC notes that weed control is critical. Weeds compete aggressively for the nutrients and moisture that should benefit the sunflower plants. The plants are especially vulnerable during the first three to four weeks.

It is wise to do a final cultivation just before the tractors can no longer get into the field without harming the sunflower plants.

Insect control is important, and this requires regular monitoring of crops, looking for signs of pests from as early as egg and worm stages. If pesticides are required to control a pest invasion, the ARC advises that farmers work closely with the representatives of the chemical companies who will visit the field and advise on application rates.

A combine harvester is used to cut the sunflowers, which also separates the seeds from the head and cleans the grain.

Growing soya bean

Temperature plays an important role in determining the rate at which soya bean grows, which means climate will play a vital role in determining where the crop will be planted.

The Department of Agriculture notes that yields are adversely affected when temperatures rise above 30°C, while temperatures below 13°C for long periods during the flowering stage inhibit flower and seed formation.

Although 25°C can be considered the overall optimum temperature for all growth stages, the response differs during various growth stages. At planting time, soil temperature must preferably be in the region of 15°C in order to stimulate germination.

Since soya bean is mostly cultivated on dryland, an annual rainfall of between 500mm to 900mm is required. Soil must be deep, well-drained with a good water-holding capacity, and with a fine but firm seedbed. Compacted soils must be avoided.

Soil preparation for soya bean must be done thoroughly to ensure a deep, loose seedbed. The department, however, cautions against unnecessary tillage since apart from being costly in terms of labour and money, every time soil is loosened, there will be a loss of moisture and soil structure.

Planting from early to mid-November is the most appropriate date for optimum soya bean production in South Africa. Seed should be planted at a soil depth of 3cm to 5cm. The spacing between the rows can range from 40cm to 90cm and from 5cm to 15cm between the plants.

A population of 250 000/ha to 400 000/ ha is recommended, depending on the yield potential of the area and its weather conditions.

Emergence takes place within five to seven days after planting. The department advises farmers to take proper soil samples to determine the nutrient requirements of the crop.

The nutritional requirements of soya beans are moderate to high compared to other grains, consuming more phosphorus, potassium, magnesium and calcium than maize, for example. Fertiliser can be broadcasted and ploughed into the root zone.

Since young seedlings are unable to compete with many fast-growing weeds, weed control is vital once the crop has emerged. Soya beans are also susceptible to various viral and fungal diseases, and insects. Farmers should therefore be familiar with integrated pest management techniques to maintain high yields.

Soya bean is not suited to hand harvesting, stacking or windrowing, and a combine harvester fitted with either a soya bean or wheat table is required for harvesting.

Growing canola

Canola is grown mostly in the Western Cape as a winter crop since it prefers cooler weather of around 21°C in the daytime. Canola seedlings are however tolerant to frost and temperatures as low as -4°C.

It is planted as a dryland crop and prefers clay-loam soil with good surface drainage since canola cannot tolerate waterlogged soils.

For a successful crop, rainfall between April and October should be at least 300mm for a yield of 2t/ha. Yields can drop lower than 1t/ha when rainfall is lower than 200mm during this time.

The department notes that rainfall distribution is important, with a long rainy season and cooler climatic conditions during the pod and seed development stages vital for a good harvest. Seed and soil moisture contact is critical for rapid emergence, and planting canola when the top 5cm to 7,5cm of soil has dried out is therefore not recommended.

The ideal planting density for canola is 50 to 80 plants per square metre, or 4kg to 6kg of seed per hectare. Evenly spaced plants will help to optimise yields.

The department advises producers to plant canola in April to early June to achieve the highest yields. Significant yield reduction can be expected if planting is delayed until after 15 June. Canola is very susceptible to temperatures higher than 27°C and drought stress during the flowering period.

Planting in May will reduce the risk of heat and drought stress of the crop.

Canola is similar to small grains in its response to fertiliser and soil fertility. Nitrogen and sulphur are the key elements for canola yield improvement. Canola is susceptible to boron and molybdenum deficiencies, especially when the latter is accompanied with low soil pH.

Young canola seedlings are sensitive to weed competition. The department notes that an effective weed control programme should include crop rotation, and mechanical and chemical control methods. However, once established, canola is a good competitor as its growth rate is higher than that of most weeds.

Crop rotations must be planned carefully to keep disease incidence and levels low. The two diseases of major economic importance are blackleg and Sclerotinia wilt.

From germination to seed production, the life cycle of canola takes about 3,5 months, with days to flowering varying between 70 days for late-planted (middle to end of June) and 120 days for early-planted (May) crops. Canola can be harvested with a combine harvester, and must be sorted and graded before being stored or sold.

Markets

Canola, soya bean and sunflower have multiple uses, including for vegetable oil and animal feed. Soya bean and sunflower can be traded on the Johannesburg Stock Exchange. This means that daily prices are available for these commodities, providing a good guideline for prices that can be achieved.

The market for oilseeds has been stable over the past few years since demand for vegetable oil and livestock feed remains firm. Sunflower prices are expected to move sideways in the coming year.

The profitability of canola is, however, declining, and BFAP expects prices to decrease by more than 6% in the next two years. From 2026, the canola price is expected to increase marginally, at 1,7% per annum. Nonetheless, BFAP notes that regardless of the low price, canola remains valuable in a crop rotation system.

While soya bean farmers have received high prices over the past season due to lower yields caused by the drought, prices are expected to start declining. According to Marlene Louw, senior agricultural economist at Absa, this is due to the improved production conditions owing to good rain.