Plant and Soil Health: Soybean Advice for Africa

ILSoyAdvisor received a question from Willings Mulendema in Zambia on an article I wrote back in August 2014. He wrote, “This is a very important publication Dan. I am a start-up farmer and I want to grow soybeans on the new virgin land, about 125 hectares (over 300 acres) here in Zambia. I would like to get more information on the guidelines of growing soybeans. Please advise? Best regards, Willings”

Click here for the story that caught his attention, followed by my response below.

You want to grow soybeans in Zambia. I sort of know the environment. I lived and worked in Uganda to the north in the 1990s, followed by a stint in Kenya and an earlier stint in Liberia. When I was in Uganda they were testing some soybeans way back then. Don’t know the status of that today, though.

The short story on soybeans. They are very adaptable and grown from the tropics to north of the 49th parallel (U.S./Canadian border). They are broadly adapted to different environments and soil types and do equally well from the tropics (think Brazil and acid soils) to the northern temperate environments (think Canada with neutral to alkaline soils). The difference, though, is maturity groups and their adaptation to soils.

Soybeans are grown for their oil and meal. Soybeans are crushed, the oil is extracted and the by-product is high-protein soybean meal. The oil has many uses including as an edible vegetable oil. The meal is used as a source of protein in animal feed and primarily included in feed for poultry, hogs and fish. Less is used for beef, dairy, sheep or goats.

You might be wondering about soybean yield potential—it is very good when the weather cooperates (moderate temperatures and sufficient moisture) and the crop is managed correctly. In the U.S. commercial soybean fields yield from 2680 to 4355 kg per ha (40 to 65 bushels per acre). However, if you don’t have adapted, high-yielding varieties and haven’t covered the basics (see below), the more realistic yield is 1350 to 2000 kg per ha (20 to 30 bushels per acre). If your yields come in at this low range just remember that the high-end potential with good management is 6700 kg/ha (100 bu) and the U.S. record is 10,720 kg/ha (160 bu). But those farmers have years of experience and professional help to get there.

Soybeans are classed by maturity groups from triple 000 to 8, which is a based on day length. The farther north (or south) you go from the equator the shorter the maturity group. In Canada they will grow 1, 0, 00, and 000 maturity groups. In the U.S. they will grow maturity groups from 1 to 6. Get closer to the equator and the maturity group will be from 6 to 8. Soybean flowering responds to day length, so as you move closer to the equator, day length varies less and varieties are less sensitive to or dependent on day length. The other characteristic is determinate vs. indeterminate. Determinate varieties are day length insensitive and when flowering starts, they generally flower all at once. Indeterminate varieties flower over a long period, about 2 months. In the U.S. and Canada most varieties are indeterminate. In Central and South America they are determinate because they are less day length sensitive.

So the key is to select varieties that are adapted to your day length, soil type and weather environment (rainy or dry or irrigated). In the Americas the private sector seed companies have done a great job of breeding and selecting adapted and high-yielding varieties. In Africa you don’t have too many choices for seed. Look to your national breeding programs for seeds of adapted varieties or to South Africa, which has a commercial soybean industry. Another option is CIAT in Columbia or IITA in Nigeria. These International Centers may help you get good seed of good soybean varieties to get started if you can’t find any locally. Having the right variety of good quality seeds will make all the difference on whether your venture is successful or not.

Lastly, soybeans are legumes like alfalfa, clovers, cowpeas and other species. That means they fix their own nitrogen. However, to do that the soil has to have an available population of Bradyrhizobia. These bacteria infect roots and form little nodules on them that take nitrogen from the air and feed it to the plant. It is unlikely that your soils will have the right population of rhizobia to infect soybean roots and without them, your plants will starve for lack of nitrogen. Make sure you locate a source of rhizobia inoculum and treat the seed before you plant it. And check your soil pH and make sure it is above 6.0. Rhizobia don’t do well when pH is below 6.Below are some production basics you should consider:

1. Find an adapted variety with good yield potential.
2. Plant good quality seed that is clear and has germination potential over 90%.
3. Plant in loose and crumbly soil that is moist to the touch.
4. Plant at a depth of 3.5 to 4.0 centimeters (1.4 to 1.6 inches) and firmly cover the row. Plant soybeans similar to how you plant corn.
5. Inoculate seed with a rhizobia species so seeds form nodules that fix nitrogen.
6. Plant soybeans in rows using the same machinery you would use for corn. However, if you can plant in narrow rows—30 to 40 cm (12 to 16 inches)—I suggest doing so. The field will canopy over sooner, which improves weed control.
7. Start with a population of 480,000 seeds per hectare (200,000 seeds per acre) till you get some experience and success establishing a good stand; then you can lower the population by 20 to 25%.
8. Soybeans grow best at a soil pH of 6.2 to 6.5. Check your soil pH and add lime to raise the pH.
9. As with any crop, weed control is important. Start with a weed-free seedbed and strive to keep it weed free. Herbicide choices are few on soybeans, so you will probably resort to cultivation and hand-roguing.
10. Start with a good base of fertility, manure or previous cover crop. For soybeans to reach their yield potential they have to have abundant phosphorus and potassium.

Lastly, monitor your crop and watch for signs of seedling, root, stem and foliar diseases; insect pests; and nutrient deficiency symptoms. Use this information to guide how you grow soybeans the following season. Remember, you are just starting out as a soybean producer so you will make mistakes and learn things along the way. Scout the crop and take notes, talk to any local experts, and make a plan to do a better job next season to reach your yield potential. If you have more questions, just send an email.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com.