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Soybean farming: To measure is to know

April 2023


South Africa’s soybean production for last season was estimated at 2,2 million tons. This can be valued at over R20 billion at a price of R9 200/t at farm level. Last season’s national average yield was 2,37 t/ha from a total of 925 300 hectares planted. Dryland production yields over all areas averaged 2,25 t/ha and irrigated lands averaged 3,4 t/ha. Compare these to the yield realised with your previous harvest.

Production losses of seed formed from the reproductive phase to harvesting are estimated to be between 5% and 10% around the world; and can run as high as 15% to 20% for late combining and other factors. On a national basis, this implies a financial loss of between R1 billion and R2 billion per season. At the average yields shown above, the potential on farm financial losses is between R1 000/ha to R2 000/ha for dryland production and R1 500/ha to R3 000/ha for irrigated production.

Farmers growing 100 hectares of dryland soybeans can thus improve their income by R200 000. The current production costs are high, with an increased financial risk to insure a reasonable profit margin. It is certainly worth looking at last season’s production and harvesting methods to assess which aspects can be improved for the 2022/2023 production year.

Crop insurance

Soybean crops must be insured, as even light hail after maturity can cause huge seed losses. This is your best financial strategy to mitigate a crop income loss. It is critical that you have a good relationship with your insurer so that your crop can be made a priority for a quick hail assessment, determining the damage percentage to avoid combine harvesting being delayed any longer than necessary.

Combining on time
The cultivar choice is critical in managing future problems that can arise at harvesting. Planning in reducing potential losses begins at planting. Soybean varieties are available in different maturity classes, which means that if the different maturity class cultivars are planted on the same day the growth season for each would be hugely different. Some mature early and some later. Soybean plants flower in response to a shorter day length.

Harvesting at the right stage could differ by three weeks or more between the cultivars planted. If the rainfall pattern is early and the conditions for planting in October and early November are ideal, plant several different varieties. Choose some that you know are suitable and have been proven for yield in your farming region, as well as the soil and climatic conditions on your farm. Always record in detail the planting and harvesting dates, and the final yield for each cultivar planted on your farm. Do so for the current season if you have never kept relevant records.

One of the most important considerations coupled to the cultivar choice is to know your own combining capacity. Make sure that you have a well-maintained combine equipped correctly and set up for soybeans. Owning your own combine is the most ideal option. If not, use a very reliable combine contractor. Inform him of your planting programme and possible harvesting dates and areas to be combined. 

In many instances, soybean yields have been reduced just due to late combining. Some varieties might yield well but shatter easily after the pods are mature. Even light rain on these pods can cause it to peel open. The pods can be heard cracking in the lands while the combine operator waits for the moisture content to fall enough to start working.

Start closer inspections of your seed pods at the fifth reproductive phase (R5) stage, where the pods are almost fully formed and green. If opened, you will see the tiny young seeds. Usually, two to three seeds can be counted and in favourable conditions with effective pollination, up to four seeds per pod can be found. You can use this as a basis to do a yield determination near or at maturity. Monitor the pods until combining to be able to harvest the crop at the optimum moisture percentage. The ideal is with most of the pods being mature, with seed testing at about 13% to 15%.

The efficiency of the combining process is dependent on the condition of the crop at the time when the combine can enter the land. Be on the lookout for the following causes or categories of seed losses:

  • Preharvest losses from loose beans or beans that have already detached from the plant. 
  • Beans that are attached to the plant at harvest, but which never get into the combine. 
  • Shatter loss from loose beans and detached pods, resulting from the cutting ground speed being too fast.
  • Stubble loss with beans remaining on the pods still attached to the plants due to the cutter bar being set too high.
  • Lodged stalk loss from beans that have fallen over and the remaining in pods not cut at all. 
  • Loose stalk loss from beans remaining in pods attached to the stalk, which were cut but not delivered to the threshing mechanism on the combine. 
  • Cylinder loss from beans that pass through the combine but remain in the pod, as the cylinder spacing to bars is too large. 
  • Lastly losses occur from threshed beans which go out of the combine with the trash.

It is extremely important to monitor the settings on the combine and ability of the operator to adjust all the elements on the machine to avoid any of the problems shown above. It is advisable not to combine at night unless several people are monitoring possible breaks on the machine and the effects on harvesting efficiency. Huge unseen losses can occur from rushing to night harvesting.

Always consult you combine settings manual so that any machine error losses can be minimised. Always check the pathway behind the machine and constantly confer with the combine operator to find out how he is doing.

To do a combining efficiency check, the combine cutting and threshing pattern must be checked by analysing a cut strip well into the land at a position that is representative of the crop in a particular land. The combine is reversed after cutting the test area. The possible yield and condition of the crop are measured in front of the cutting table, below the cutting table and behind the spreaders.

The number of pods counted in each position is compared to the standing crop. As a guideline, 43 pods per square metre on the ground behind the combine is equal to a loss of about 120 kg/ha. 

Make yourself a square metre from round rod and place it at various positions to make counting and comparison easier and faster. The square metre tool can be used to do a quick yield assessment of the land in several representative places. Losses using modern combines can be limited to about 3%.

Always monitor and measure the results of combining before and after the machine has been through the land. Remeber: To measure, is to know.

Publication: April 2023

Section: Pula/Imvula