GUIDELINES FOR outstanding soybean yields

November 2024

GEORGE PRINSLOO, BUSINESS MANAGER, LAEVELD AGROCHEM

THERE IS NO SIMPLE RECIPE FOR OPTIMUM SOYBEAN PRODUCTION. THE YIELD REMAINS A RESULT OF VARIOUS FACTORS THAT TOGETHER ENSURE SUCCESS. HOWEVER, THIS ARTICLE ATTEMPTS TO HIGHLIGHT JUST A FEW IMPORTANT PRINCIPLES THAT CAN CONTRIBUTE TO ENSURING THE BEST POSSIBLE RESULTS.

Before one can look at what the principles are, a few non-negotiable critical prerequisites must first be in place to be able to plant soybeans:

1. Soil structure and drainage: The soil structure and drainage must be in place before even considering to plant soybeans. It will be very difficult for plants to produce a decent crop if they either suffocate or are waterlogged in the soil.
2. Soil acidity, potassium and phosphorus: It is very important to know what is happening in the soil, especially regarding the pH of the soil and the base level of phosphorus (P) and potassium (K) currently available and absorbable in the soil. This is why a soil analysis is always recommended, especially soil chemistry and soil mapping. Accurate predictions can then be made for the next season. Consult your fertiliser advisor about options.
3. Weed and pest control programme: Thirdly, a well-planned weed and pest control programme is essential. The previous year’s pests and weeds should be taken into consideration. A well-designed chemical programme will sort out problems even before they appear.

WHAT INFLUENCES SOYBEAN PRODUCTION?
Soybean production is the sum of the plants per hectare, number of pods per plant, number of kernels per pod and kernel weight (Figure 1). All the variables are driven by several factors such as the planting date, cultivar, growth length, foliar feeding, seed treatment, insect control, fungal control, soil status (chemical and physical), tillage, soil pH and plant condition, to name but a few. Each of the individual factors plays a role in ensuring an optimal yield.

Figure 1: Soybean yield is a function of yield components.

Plants per hectare
The first way to achieve an optimum yield is to optimise the plants per hectare. The choice of a cultivar that can grow optimally in the relevant geographical area is the essential first step. The cultivar must be able to handle stressful conditions such as heat and moisture restrictions well. Therefore the seed producers must be thoroughly consulted in the selection of cultivar for your specific farm.

Planters also play a critical role in the plants per hectare. It often happens on farms that the estimated plant population in the field differs from what is actually achieved. A differentiation of up to 20% is quite common. This difference can be directly correlated to the planter efficiency and this influences the yields directly.

Inoculation
There is no substitute for the best possible inoculant in soybean production. The inoculant must provide the largest amount of nitrogen for the plant’s needs and poor nodulation cannot be corrected with fertiliser. In South Africa, farmers have access to some of the best international inoculants that have been tested to ensure optimum inoculation in the hot and dry conditions.

On-seed survival of the inoculant is not a given, especially if it is retained seed that is also treated on the farm for fungi and insects. So, make sure you use the best possible inoculant. Double inoculation on the seed and in the furrow did better in most trials compared to single inoculation, especially on virgin soils where soybeans were not planted before.

Two other factors that can also contribute to poor nodulation are very low pH soils, which leads to aluminium toxicity, as well as high levels of nitrogen. So make sure your soil status and pH are in place. 

Pods per plant
Another way to speed up the yield is to grow more pods per plant. This means that the full growing season and optimum daylight length must be utilised. In most cases, the optimum planting date is one of the biggest requirements for maximum pods per plant.

A typical soy plant has about 20 nodes, of which 16 can normally bear flowers and then pods. However, each node can carry more than one pod. Adding just one extra pod per plant can potentially add an average yield of 130 kg per ha. 

An average pod has three seeds, but several genetics are available that can also produce four to five seeds. A soybean kernel’s average weight is about 150 mg. Raising the kernel weight by 6 mg has the potential to produce 200 kg/ha more soybeans.

Leaf protection: The golden rule to keep in mind when striving for optimal soy production is the protection of the plant factory. Leaf protection, especially in the critical time from flowering to seed filling, is essential to ensure an optimum number of pods and seed weight. About 60% of soybean production comes from nodes 7 to 13, which are in the middle of the plant. The nodes must therefore be protected, especially against fungi and insects, in the reproduction growth phase. The use of fungicides during flowering and pod formation forms an integral part of protecting the leaves. 

Nutrition also plays a very big role in the number of pods per plant. 

• Sometimes farmers forget to manage the amount of nitrogen (N) required by a soybean plant. To achieve higher yields, the soybean plant needs higher amounts of N. The inoculant cannot always provide the large quantities of N that are required – therefore N fertilisation is sometimes necessary. Remember the principle, to measure is to know, so a leaf sample will be the only way to know.
• The role of boron (B) in optimum production is essential, as it plays a role in pollination, cell wall and cell membrane integrity and root growth. Soybeans’ B requirement is much higher than, for example, that of maize, and therefore it responds very well to well-formulated foliar nutrition. Not all B foliar feeding is formulated to translocate well throughout the entire plant. Many B formulations are trapped only in the leaf structure and are not available to the whole plant. A leaf sample alone can be misleading. The yield is the final indication of whether the B formulation is working. Sufficient B during flowering to pod formation can also limit the number of flowers and pods that are weaned.

Sufficient boron during flowering to pod formation can limit the number of flowers and pods that are weaned. Photo: Gerda de Kock

Seed weight
Potassium (K) is particularly important to ensure the optimum seed weight and also plays an important role in heat regulation. This is especially applicable in K foliar feeds, supplementing enough K in the soil to push a good crop into a top crop.

In ‘non-Intacta^® gene’ cultivars, the protection of pods against insects as a preventive strategy is non-negotiable. If you act reactively, the damage is already there, which can also lead to secondary fungal infections. The use of insecticides that have residual working provides better protection than just a contact product.

Harvesters that are not properly calibrated, can also lead to a yield loss of between 5% and 20% of the yield. It is not only your yield that is lost, but it will also increase the chemical spend to control volunteer soybeans in the follow-up crop.

Be committed to optimise your soybean yield by doing the right thing at the right time. Laeveld Agrochem is committed to optimise soybean yields.

Publication: November 2024

Section: Pula/Imvula