GRIDLOCK ON SA SOYBEAN YIELDS CAN BE BROKEN
There are ways and means to give South African soybean yields much needed impetus. To do so, farmers will have to make some changes to how they handle their cropping systems and soils. This is according to Dr Stephano Haarhoff, an agronomist of Yara Africa Fertilizer, and Dr Pieter Swanepoel of the Department of Agronomy at Stellenbosch University (SU), in a paper in Agronomy Journal.
The paper reviews the current state of soybean production in South Africa, current practices in place and shortfalls in research. It was included in a special section of the international journal that reflects on near-term problems that stand in the way of meeting food demand on a regional level.
Two students, Lisa Matthews and Anell Lötter, received a SASCP Gold Merit Award for passing their undergraduate studies with distinction (with an average of 75% or higher). Matthews is currently pursuing MSc studies in Agronomy at SU, while Lotter is working on a wine farm between Worcester and Villiersdorp. She is putting her studies into practice by integrating diverse crops into the current operation to also include livestock and grazing options. Worldwide, soybean yields have increased over the past two decades. Unfortunately, this trend is however not seen for rainfed soybean production in South Africa, despite the release of improved soybean germplasm and modern herbicides in recent decades.Amandrie Louw presented the best student paper at the Combined Conference with a talk on the dynamics of diversification through crop rotations. Amandrie is from the Department of Conservation Ecology and Entomology and the paper was presented in conjunction with Dr Pieter Swanepoel of the SU Department of Agronomy, Dr Johann Strauss of the Western Cape Department of Agriculture and Dr Stephan van der Westhuizen from SU Department of Genetics.
According to 2020 statistics by the Food and Agriculture Organisation (FAO), total soyabean production in South Africa have increased over the past decade (from 1680 kg per hectare from 2001-2010 to 1730 kg per hectare between 2011 and 2019). However, this is due to more land being harvested and not because of greater yields.
“South Africa has the potential to sustain high soybean yields. Unfortunately, the use of modern agronomic practices in South Africa lag behind several other top soybean producing countries. It would be wise for producers to increasingly consider reducing soil tillage, to ensure more effective nutrient management, and to adopt diverse crop rotations,” Dr Haarhoff and Dr Swanepoel note.
Inconsistent rainfall patterns, high temperatures, very high levels of evaporation and soil compaction remain limiting factors across South Africa’s major soybean production regions.
Ways to improve yield and productivity:
In the paper, the two agronomists note that yield and productivity can be improved by:
• applying nitrogen fertilizer early in the season if soil nitrogen content is low;
• including soybean in maize-dominated cropping systems, preferably with other crops or grazed cover crops for improved crop rotation diversity;
• using agronomic practices that limit excessive runoff and evaporation and therefore soil water losses This includes leaving more crop residue behind following harvesting of maize, or allowing livestock to only partially feed on what is left after a harvest has come and gone;
• using less rigorous soil tillage practices such as no-tillage to help mitigate the impact of environmental stressors such as droughts and high temperatures by improving soil structure and organic matter content;
• considering diversified production systems and including livestock to control weeds and diseases in an integrated way;
• controlling machinery traffic and, where possible to prevent soil compaction and to use modern planter and/or precision technology to promote uniform seed and fertilizer placement;
• consider strategic tillage to address soil compaction on sandy soils under long-term reduced tillage or no-tillage. Its use does not necessarily have to lead to yield reduction. Carefully consider secondary effects such as erosion by wind or water following the tilling action.
More local research and data needed
“Because they have been getting inconsistent yields, many farmers are uncertain about how much nitrogen fertilizer to use, and when to apply fertilizer. The problem is that there is a lack of local scientific knowledge on the topic. If we can address this, we can start eliminating such uncertainties among farmers and field agronomists,” notes Drs Haarhoff and Swanepoel.
“We need tailored management practices and guidelines that can be adjusted according to a specific farming system. This will not only address farm-specific challenges but also take advantage of beneficial soil and crop conditions.”
Understandably, each farming system or field is unique due to prevailing soil and climatic conditions and farmer needs. Therefore, studies must be done to investigate the success or failure of specific agronomic principles and systems (such as conservation agriculture or conventional tillage) across various production regions in South Africa.
Research for instance needs to be done to:
• establish the optimal amount and timing of nitrogen, potassium and phosphorus fertilizer, and how it might differ between South Africa’s eastern and western soybean production regions.
• understand how practising conservation agriculture (for instance using no-tillage, permanent soil cover and a diversified cropping system with or without livestock integration) versus conventional tillage (soil disturbance using tines with low soil cover levels) complicates the potential success of a nutrient programme. Studies should also be conducted on how these practices are influenced by the soil chemical status and functioning such as the three-way interaction between microbes, soil, and plants and soil water husbandry associated with each.
• How nutrient management should be adapted according to farming system needs.
Challenges
A particular challenge for farmers in the western production region is maintaining a soil cover to preserve the soil and decrease evaporation losses.
“This region, which includes northern parts of Northwest and central Free State, receives 90% of its total annual rainfall between October and March. These summer months correspond with the soybean growing season. Water is the most limiting factor when it comes to soybean yield.”
In the Eastern region, which includes Gauteng, the eastern Free State, large parts of Mpumalanga and Limpopo, hail remains a threat, while early frost could destroy crops in the Eastern and the KwaZulu-Natal regions.
Drs Haarhoff and Swanepoel believe it remains wise to include soybean in current maize-dominated cropping systems. It does more than just improve the yield of crops being alternatively planted. The practice gives producers the opportunity to alternate weed control strategies. This includes the use of herbicides and tillage timing. It disrupts disease and pest cycles and improves nitrogen levels in soil by biological nitrogen fixation. Integrating cover crops into these maize-soybean crop rotation systems may also enhance soil organic matter build-up. It provides high volumes of biomass as feed for livestock and can be used as a soil cover in-between cash crops.
“We need adaptable and diverse approaches to guide farmers, field agronomists, and researchers. These will help them consider alternative agronomic management options so that long-term yield can be increased and stabilised. Such options are needed to handle adverse growing conditions, such as lengthy dry periods, high temperatures, and our nutrient-poor and easily compacted soils,” note Drs Haarhoff and Swanepoel.
