Introduction

Soybean (Glycine max) is an important leguminous crop widely cultivated in Nigeria for food, oil, and feed purposes. It is grown due to its inherent ability to improve soil fertility thereby boosting crop production. Soybean is a cheap source of protein eaten to alleviate nutritional problems in Nigeria (Idrisa et al., 2010). Nigerians feed more on starchy staples with resultant malnutrition and a high incidence of chronic illnesses such as diabetes, hence a need to ameliorate the trend with the incorporation of soybean in our meals (Akah et al., 2021). Nigerians suffer from health issues such as heart problems due to the consumption of vegetable oils high in omega-6 fat (Falade et al., 2017). However, soybean oil is known to lower the chances of heart problems because it reduces cholesterol levels in the digestive system through the reduction of cholesterol absorption (Messina et al., 2021).

In Nigeria today, soybean is processed into soy-lafun, soy-gari, dadawa, soymilk, tom brown, and soy-ogi (Osho, 2003). In livestock production, soybean meal is an important ingredient of formulated feed. Soybean cultivation is most times intercropped with other crops such as maize, wheat, and sorghum to increase their yield (Smith, 2006) and manage parasitic weeds such as striga.

The influence of climate change is grievous on agroecology due to its direct impact on soil and water resources. Nigeria’s agriculture is faced with a decline in the productive capacity of its soil resources because of diminishing soil fertility and the high cost of fertilizer due to subsidy removal (Aniekwe and Mbah, 2014). This state of soil fertility depletion and consistent soil degradation resulted in a decline in crop production.

This review article examines existing works of literature on the impact of soil fertility, agronomic practices, pest and disease management approaches, and differences in agroecology on soybean production in Nigeria. This is a broad summary to aid in understanding the level of knowledge on Soybean production in Nigeria. Based on the information provided, suggestions for further studies would be provided.

Soybean Production in Nigeria

The trend in Nigeria’s Soybean Production

In the early 20th century, imported soybean seed was only thriving in the guinea savanna region of Nigeria after several failed attempts to cultivate it in the rainforest region of southern Nigeria (Shurtleff and Aoyagi, 2021). Soybean was introduced to Nigeria in 1908 (Fennel, 1966) but extensive production only began in 1937 using the ‘Malayan variety’ found suitable in Benue State (Root et al., 1987). The great potential of the ‘Malayan’ variety which showed a promising yield potential led to its mass multiplication and supply to farmers in 1946. A total of about 9 tons of soybean were initially exported from Nigeria by 1947 from cultivation in Benue, Zaria, and Katsina (Shurtleff and Aoyagi, 2021). The Tiv Division of Benue Province was the main production area with about 10.5 tons and 700 tons of soybean in 1946 and 1948 respectively. Subsequently, Nigeria’s soybean exportation rose from 9 tons in 1947 to 15,860tons in 1963(Shurtleff and Aoyagi, 2021). To date, the Benue province remains the most important location of soybean production in Nigeria.

After the introduction of the ‘Malayan’ variety for commercial cultivation of soybean in Nigeria, the variety was found to be late-maturing, low yielding, susceptible to bacterial diseases, and pod shattering (Smith et al., 1995). Therefore, studies were conducted to develop early maturing varieties that are high yielding with good agronomic traits and capable of nodulating in association with local rhizobia, (IITA, 1994). Improvement of African soybean lines through the crossing of Tropical Glycine Cross (TGx) lines with other Asian origins by the International Institute of Tropical Agriculture (IITA) has boosted Nigeria’s soybean production since around 1974 to about 758,033 tones (1.0 ton/hectare) from 780,679 hectares in 2018 (Nzossié and Bring, 2020). The study was conducted to provide a solution to the challenges of soybean production using the available cultivars cultivated in Nigeria.

The expansion of soybean production in other states was accredited to its nutritional composition and economic importance (Nater et al., 2021). Nigeria is currently the second-largest African producer of soybean after South Africa (Khojely et al., 2018). It is well-grown in the Northern region of Nigeria within subhumid and semiarid savanna agroecology due to its peculiar soils with low nitrogen and phosphorus (Dugje et al., 2009). The Guinea savanna belt of Nigeria is considered the major production region (Haruna et al., 2015) of the seventeen (17) producing states (Fig. 1). The low amount and duration of rainfall within Sudan and Sahel savanna suggest the use of early maturing soybean varieties. However, late-maturing soybean varieties are known to produce higher grain with more biomass yield when compared to early maturing varieties.

America’s soybean yield of about 3.4 tones/ hectares in 2018 implies a huge yield gap in Nigeria’s production due to several contributing factors. Therefore, studies to understand the limiting factors to optimum soybean production are ongoing as means of attaining yield potential of above 2.5 tones/ha. Smallholder farmers dominate soybean production in Nigeria which is reflected in the use of small farm sizes and no or little farm inputs such as fertilizer and improved varieties. This limits the optimum production of soybean as most farmer rely on the use of local soybean varieties and rainfed situations to cut down on the cost of production.

Comparison of Soybean production in Nigeria and Korea

Soybean production in Nigeria, one of the major producers in Africa was compared with Korea, one of the East Asian Countries considered to be countries of origin of soybean (Larson et al., 2014). It is observed that more area of land is cultivated with an increase in soybean yield annually and per hectare, in Nigeria (Fig. 2). But in Korea, there is a decline in the available area of land for soybean production and yet a constant increase in yield per hectare although a decline in annual production since the 1980s (Fig. 2). This establishes that soybean varieties cultivated in Korea are efficient in attaining their yield potential, that is lower yield gap when compared to Nigeria with a high yield gap. In the last five years, Korean soybean yield per hectare is double the Nigerian soybean yield per hectare (Fig. 2c) despite the decline in the available land in Korea.

Agronomic Practice

The soil suitable for soybean cultivation is moderately fertile well-drained sandy or medium loam soil with a pH of 4.5 – 8.5 (Solomon et al., 2012). Due to the difference in precipitation volume in the savanna region of Nigeria, there is a recommended sowing period of early June and the second week of July (Dugje et al., 2009). Studies on the effect of row spacing on soybean yield establish that the shorter the row spacing the better the yield for some selected soybean varieties (Nater et al., 2021). A spacing of 50 cm x 10cm was recommended against the commonly used spacing of 75 cm x 10 cm. In boosting soybean production, it is recommended that triple super phosphate and single super phosphate fertilizer be supplied to the soybean field at moderate rates of about 75 and 150 kg/ha respectively. Control of weeds is crucial in optimum soybean production.

Cultivar selection

The current shift in the agroecological zones of Nigeria which are impacts of climate change creates a challenge to previously surviving soybean varieties. This necessitates the selection of soybean varieties that can thrive under harsh environmental conditions and can tolerate or resist pests and pathogens. IITA in conjunction with other institutes such as the National cereal research institute (NCRI) worked on improving soybean variety to boost the yield and impute resistance to rust, blight, and leaf spot (Table 2). They focused on three agroecological zones (Derived, Guinea, and Sudan savanna) considered suitable for soybean production. The improved varieties produced from the breeding programs were classified into three based on the maturity group; early (91-100 days), medium (100-110 days), and late (>110 days) maturing soybean varieties (Tefera et al., 2009). The outcome of this soybean improvement program was a boost in yield from 0.5 tons/ ha to above 1 ton/ha and the availability of soybean varieties suitable for each agroecology in the savanna zone of Nigeria (Table 1). Nevertheless, there is a clear gap between the yield of soybean obtain in research stations during field trials of improved varieties (above 1.5 t/ha) and on farmer’s fields (below 1.5 t/ha).

Soybean cultivar TGX 1485-1D has high yield potential in the southwestern region of Nigeria although susceptible to rust (Adeniyan and Ayoola, 2006) while TGX1951-3F performed better in all the savanna agroecology of Nigeria (Bebeley et al., 2022). Soybean cultivars TGX 1448-2E, TGX 1987-10F, and TGX 1835-10E thrive well with higher yield in Guinea savanna agroecology (Aduloju et al., 2009;Pajo et al., 2018)

Factors affecting Soybean Production in Nigeria

Abiotic Stress

Climate change is a major threat to soybean and other food crop production in Nigeria. Nigeria farmers are solely dependent on rainfed agriculture which makes the effects of climate change such as rise in temperature, flooding or shortage of water, the emergence of new pests and diseases, and so on devastating (Tologbonse et al., 2010). Evidence of climate change in Nigeria includes flooding on coastlines, reduced harmattan season duration in some locations from five months (November to March) to two months (December to January), and low crop yield (Sambo, 2010). Summarily, climate change is responsible for the shift in agroecological zones of Nigeria (Audu et al., 2013).

The duration and volume of rainfall reduce as we move northward in the production region (Bebeley et al., 2022). Guinea savannah agroecology of Nigeria is characterized by high sunshine during crop maturity with harmattan wind which aids pod-shattering causing about 80% of losses that affect soybean production (Tefera et al., 2009).

Biotic Stress

Insect pests found predominant in soybean farms of Guinea savanna Nigeria include Aphis glycines (Hemiptera), beetles (Coleoptera), and more insects belonging to the order Hymenoptera and Orthoptera (Asala et al., 2016). Foliage feeding insect pests such as aphids, bugs, and beetle inflict serious damage on soybean plants. They physiologically stress soybean through the sucking of saps and transmission of plant viruses. Common insect pests of the Sudan savanna are Nezara viridula (Hemiptera) a podsucking bug; defoliating beetles Coleoptera such as Siderodactylus sagitarius Meigen, and Egadroma discriminatum Basi (Sastawa et al. 2004). The pod-sucking bugs are attracted to the flowering stage of soybean with an effect of seed quality reduction. In the month of July, the insect pest population is greatest (Asala et al., 2016). The activities and population of insect pests on soybean fields are dependent on the prevailing weather, variety of soybean cultivated, and population of natural enemies. To date, information on the impact of this pest on soybean production in Nigeria is lacking. This information on estimated crop losses due to insect pest damage is crucial to justify an appropriate management strategy (Sastawa et al., 2004).

In most Nigerian soybean fields, the observed premature defoliation is caused by bacterial pustule (Akeem, 1996). Frogeye leaf spot is another important disease of soybean foliage in Nigeria which can also infect the seeds, pods, and stems (Akeem, 1996). Soybean rust is a foliar disease caused by the fungus Phakopsora pachyrhizi responsible for 40-80% yield loss in Nigeria and other African soybean- producing countries hence, a threat to soybean production (Tefera et al., 2009). In Oniyo, Oyo state Nigeria was soybean rust first identified in 1999 during the core soybean growing season (Akinsanmi et al., 2001). Soybean rust is predominant in derived savanna and southern Guinea savanna zones of Nigeria due to high rainfall and humidity (Dugje et al., 2009). It causes a change in immature soybean leaf color to brown followed by a fall off. Root-knot nematode in soybean growing regions of Nigeria affects production (Iheukwuemere, 1996).

Weeds around soybean fields are reservoirs of plant viruses affecting soybean production (Ahmed et al., 2019). Soybean mosaic virus and Blackeye cowpea mosaic virus are important viruses that affect production in soybean growing regions of Nigeria (Iheukwuemere, 1996;Adama et al., 2015).

Impact of Soybean Production

The Northern region of Nigeria has experienced an increase in the number of industries especially oil mills, livestock feed mills, and cereal processing industries due to the availability of soybean produced in that region. Nigerian farmers cultivating soybean, especially in the middle belt zone of Nigeria are now aware of its potential as cash or food crops hence increasing their production to improve income through domestic and export markets. Farmers are encouraged by the current selling price of soybean with the consideration of little fertilizer requirement. The relative availability of soybean meal in Nigeria has helped in the rapid growth of Nigeria’s poultry industry (Dugje et al., 2009). More than 25% of soybean produced in Nigeria is directly consumed within the rural area of production. Soybean production is helping to attain food security, reduce poverty among farmers and improve the nutritional status of Nigerians.

Future directions and Conclusion

Nigeria’s soybean production is challenged by the impact of climate change which creates a productivity yield gap. Hence, a need for further studies in developing more excellent soybean varieties with superior performance through molecular techniques and subjecting to regional adaptation tests. Nigeria can have a collaborative research study with soybean origin countries such as Korea based on their variety yield efficiency. The selection of soybean varieties most suitable to agroecology is important to achieve higher yield and food security in Nigeria. Farmers should be encouraged to cultivate improved varieties. Also, studies on the impact of pests, and diseases on soybean production in Nigeria are needed to guide in the choice of the best management strategy. It is important to consider an economically feasible and ecologically sustainable approach. Hence, heavy reliance by Nigerian farmers on insecticides should be discouraged. Cultural practices found to greatly hinder insect pest build-up and improve soybean performance includes staggered sowing and intercropping (Odo and Futuless, 2000).

Improvement of agronomic management practices which involves the use of fertilizer, narrow spacing to increase plant density, and reduction of weed density would help boost production. The negative nutrient balance and incessant nutrient depletion in the savanna region of Nigeria limit soybean production (Cobo et al., 2010). Government support is needed to make farm inputs such as improved soybean cultivar seeds and fertilizers available and affordable to Nigeria’s smallholder farmers. These efforts will help close soybean yield gaps with the achievement of food security in Nigeria.

Nigerian farmers mostly adopt the use of TGx 1448-2E variety. Improvement of soybean variety will help unlock the economic and nutritional benefits for Nigerians. Soybean production in Nigeria is still below the potential of the crop, therefore more effort is required.

적 요

나이지리아에서 콩은 북부 지역을 중심으로 인간과 동물의 단백질 공급원으로 지난 80년간 상업적으로 재배되고 있는 중 요한 작물이다. 현재 나이지리아에서 국민의 식생활에서의 영 양 불균형 문제를 해결하기 위해 영양가 높고 값싼 식품 원료 도입이 필요성이 제기되면서 콩 및 콩의 가공식품에 대한 수 요 및 재배지역이 증가하고 있는 실정이다. 본 논문에서는 나 이지리아에서 콩의 수요량 증가에 비해 생산성이 향상되지 못 하는 원인을 구명하고 생산성 증대를 위한 방안을 제시하고자 한다.