Soybean has been the fastest growing broad land crop for the last 20 years as farmers attempt to meet the rising demand for a variety of feed, food, and industrial products. However, soybean is a new crop for much of the developing world. The total production of soybean in Africa in 2017 was 3.13 million tons, which represents a 5.8-fold increase over the last 30 years compared to a 3.8-fold increase for world production during the same time period. Still, soybean production in Africa represents about one percent of the global production in 2017 (FAOSTAT, 2019), leaving significant room for advancement.
Understanding and adapting to soil context, while finding the right combination of inputs such as phosphorus, inoculum, and lime that target soil-related constraints, can maximize the yield potential of soybean. Phosphorus is a critical macronutrient for supporting soybean growth and yield. Inoculation, bundled with Phosphorus, can enhance soil biological fertility in Sub-Saharan Africa and maximize soybean production. Low pH levels in the soil can cause aluminum toxicity to soybean roots, but lime applications when bundled with Phosphorus and inoculum, can increase pH levels to remedy acidic soils.
To effectively communicate the idea of a bundled input approach, while recognizing that not all producers can procure all the necessary inputs at once, the Feed the Future Soybean Innovation Lab (SIL) recommends a step-wise input bundle approach for producers. A green bundle that couples inputs like certified seed, inoculum, lime, and phosphorous fertilizer, and appropriate crop management practices, will result in the highest soybean yield. However, producers can step up to the Green bundle by starting with the Red bundle, containing only certified seed and good management practices, then moving to the Yellow bundle, which adds inoculum, and the Blue Bundle, which adds phosphorus, before advancing to the Green bundle.
Fig 1. SIL recommends a step-wise input bundle approach for African soybean producers. The green bundle, which includes the necessary soybean inputs and appropriate crop management practices, will result in the highest soybean yield and associated profitability.
As soybean production across Africa is expected to increase, this will likely lead to an increase in soybean pests and disease. Pests can be introduced through trade, the exchange of breeding materials, and naturally through water and wind. Common soybean pests that have been identified in Africa include pod borers, soybean stem flies and stink bugs. The southern green stink bug, native to Ethiopia, injects toxins into pods and seeds leading to necrosis. Leaving the affected pods shriveled and the seeds discolored, an infestation of stink bugs can result in low seed oil content.
Fig 2. The southern green stink bug feeds on pods and seeds, affecting seed germination and quality, and may lead to pod distortion.
As the demand for soybean production increases, so does the interest in breeding for resistance to common soybean diseases, and in management practices that can help producers identify, diagnose and respond to disease and pest pressures and threats. Soybean diseases of particular interest in Africa include frogeye leaf spot, red leaf blotch, rust, and sudden death syndrome. Much like soybean pests, diseases may be introduced to the crop through human activity, seeds, vectors, or water and wind. In other cases, such as with the fungus that causes red leaf blotch, the pathogen may jump from another host to soybean when introduced. Finding disease resistant genes to develop commercial cultivars that can prevent yield loss due to soybean diseases like red leaf blotch is an effective way to increase production and stabilize crops across Sub-Saharan Africa.
SIL developed the first diagnostic guide for the identification of soybean diseases and pests specifically designed for use in Africa. The guide is currently available in English, French, Portuguese, and Amharic. This guide helps agronomic researchers design better disease prevention strategies and provides farmers with another resource to increase their soybean yields. SIL also developed both a basic, in-person pesticide training program, as well as a free, open-access, online course in integrated pest management and pesticide safety. This free, open-access online course covers issues related to when pesticides should be used, common toxins found in pesticides, different types of pesticides available, how to apply, store, and dispose of pesticides safely, and the use of personal protective equipment for pesticide safety, as well as pest management practices that include crop diversification and planting time. The majority of the over 500 students that have taken the course since its launch in August of 2019 are based in Western and Eastern Africa.
Fig 3. SIL’s diagnostic field guide describes the symptoms of red leaf blotch and also provides photos for easier identification in the field.
This blog piece is a summarization of four separate articles (Soils by Andrew Margenot, Agronomy in African Smallholder Systems by Nicole Lee, Soybean Diseases: Unique Situations in Africa by G. L. Hartman and H. M. Murithi, and Soybean Pests by H. M. Murithi, E. N. Wosula, D. M. Lagos-Kutz, and G. L. Hartman) that were previously published as part of a 12-part series entitled The State of Soybean in Africa.