Reasons to consider crop rotation with soybeans

February 2025

MAGDA DU TOIT, SA GRAAN/GRAIN CONTRIBUTOR. FIRST PUBLISHED IN AFRIKAANS IN SA GRAAN/GRAIN, SEPTEMBER 2024.

ALL FARMERS STRIVE TO ACHIEVE AN OPTIMAL PROFIT PER HECTARE IN ADDITION TO GOOD YIELDS. HOWEVER, YEARS OF MONOCULTURE PRACTICES HAVE HAD DETRIMENTAL CONSEQUENCES IN THE LONG RUN. ALTHOUGH PEST AND DISEASE CONTROL WAS INITIALLY EASIER, TODAY WEEDS AND INSECTS THAT ARE DIFFICULT TO CONTROL CAUSE MAJOR HEADACHES.

CROP ROTATION OFFERS A SOLUTION
One solution is to include different crops in a crop rotation system. This practice not only contributes to biodiversity and improved soil health and quality, but also offers solutions for pest control. It is a core element in the management of cultivation risks and forms one of the cornerstones of sustainable production.

According to Hendrik van Staden, unit head of Syngenta Seed in South Africa, a crop rotation system offers the following benefits:

• Limiting plant diseases: Crop rotation can help to control plant diseases on different crops.
• Managing weed pressure: Weeds compete with crops for water, nutrients, sunlight and space, and can reduce grain yields by up to 20%. Crop rotation makes it possible to use different herbicides on different crops to control weeds. Not only is it a good practice to reduce the build-up of herbicide resistance, but effective weed control in one crop means that another crop can be grown without having to use expensive selective herbicides for it in the following season. The potential for the build-up of herbicide residues in the soil profile is also limited.
• Increased soil fertility: Crop rotation offers the opportunity to utilise the nitrogen that is captured in the soil by certain legumes, such as soybeans. It had been demonstrated in trials and other practices that wheat planted after a legume on the same field leads to a higher yield and increased protein.
• Improved profitability: The inclusion of a legume or oilseed crop in the crop rotation system can increase the profitability because yields improve in certain cases. According to a publication by the Protein Research Foundation, several local and international trials indicate that maize planted after soybean yields show a yield jump of at least 10% compared to monoculture maize (Dreyer, 2017).
• Spreading risk: Because it is difficult to predict how a season will develop, it is advisable to spread the risk as far as is practically possible. A crop rotation system offers an excellent solution.
• Van Staden warns that proper planning of a crop rotation system is essential. ‘The production risks of each crop must still be considered. It remains important for farmers to familiarise themselves with the finer cultivation aspects of alternative or rotational crops.’

SOYBEAN PRODUCTION
Soybeans are one of the most important sources of oil and protein worldwide. Over the past decade, the production of soybeans has gradually increased in South Africa.

The crop’s popularity in crop rotation systems is increasing due to soybeans’ nitrogen fixation capacity and extensive root system. When used in crop rotation, soybeans restore the soil health. This is usually visible in the yield of the next maize crop, while lower input costs and a favourable risk profile ensure that soybeans are profitable in their own right.

According to Hanlie Geldenhuys, an expert on row-crops at Syngenta South Africa, the following four aspects are important in soybean production:

• Protect the seed: Seed treatment protects the germinating seed and seedling from the outset. This ensures proper germination, good root development and vigorous seedlings that help to achieve a balanced stand.
• Weed control: Weeds compete with crops for light, water and nutrients, and can significantly reduce the soybean quality and yield.
• Insect control: Insect pests, particularly soil insects, can cause significant damage – especially at the beginning of the season. Bollworm can harm the grain quality later in the season.
• Disease control: When soybean plants begin to flower, diseases that inhibit photosynthesis in particular can adversely affect the plant and yield.

Publication: February 2025

Section: Pula/Imvula