Sorghum–legume intercropping for sustainable intensification in Sub-Saharan Africa: a systematic review

1 Introduction

Agriculture faces the dual challenge of increasing food production while reducing environmental degradation and strengthening resilience to climate change (Godfray et al., 2010; Foley et al., 2011; Tilman et al., 2011; Denning, 2025). These challenges are particularly acute in Sub-Saharan Africa (SSA), where rapid population growth, declining soil fertility, climate variability and persistent rural poverty continue to threaten agricultural productivity and food security (Sanchez, 2002; Masso et al., 2017; Vanlauwe et al., 2017; Mawanda, 2025; Olarewaju et al., 2025). Approximately 75% of agricultural land in SSA is affected by soil fertility depletion, with annual nutrient losses estimated at 22 kg N, 2.5 kg P and 15 kg K ha⁻¹ (Sanchez, 2002; Masso et al., 2017; Falconnier et al., 2023). At the same time, climate variability disproportionately affects the predominantly smallholder farming systems that underpin agricultural production across the region (Omotoso et al., 2023). With food demand projected to double by 2050, there is increasing pressure to identify production systems capable of raising productivity while maintaining environmental sustainability (Tilman et al., 2011; Hamad and Tayel, 2026).

Sustainable intensification has emerged as a leading framework for addressing these challenges. It seeks to increase agricultural productivity while maintaining or enhancing environmental quality, ecosystem services and resilience (Firbank et al., 2013; Garnett et al., 2013; Pretty and Bharucha, 2014; Denning, 2025). In smallholder farming systems, however, sustainable intensification extends beyond yield improvement to include economic viability, environmental sustainability and social acceptability (Pretty and Bharucha, 2014; Rockström et al., 2017). Consequently, agricultural technologies are increasingly judged by their ability to improve productivity while simultaneously enhancing resource-use efficiency, profitability and resilience (Firbank et al., 2013; Pretty, 2018).

In smallholder farming systems, cereal–legume intercropping has attracted considerable attention as a sustainable agroecological practice because legumes complement cereals through biological nitrogen fixation, improved nutrient cycling, more efficient resource use and greater crop diversity (Lithourgidis et al., 2011; Brooker et al., 2015; Falconnier et al., 2023; Martin-Guay et al., 2018; Adam et al., 2025; Wang et al., 2026). These ecological interactions promote resource complementarity and niche differentiation, enabling intercrops to achieve greater productivity and resource-use efficiency than sole cropping systems under appropriate management (Martin-Guay et al., 2018; Li et al., 2020; Adam et al., 2025). Consequently, cereal-legume intercropping can reduce dependence on external inputs while improving soil health, suppressing weeds and pests, enhancing resilience to climatic variability and diversifying household food and income sources (Wang et al., 2026).

Among the major cereals cultivated in SSA, sorghum (Sorghum bicolor L. Moench) occupies a particularly important position because of its adaptation to drought-prone and resource-constrained production environments (Hossain et al., 2022; Liaqat et al., 2025). In 2024, sorghum was cultivated on approximately 30.6 million ha and produced 28.4 million t across SSA, with Nigeria, Sudan and Ethiopia contributing 6.5, 5.4 and 4.1 million t, respectively (FAO, 2026). Sorghum remains a critical staple for more than 500 million people, particularly in semi-arid regions where its drought tolerance, heat resistance and adaptation to marginal soils support production under increasing climatic variability (Dube et al., 2023; Hossain et al., 2022; Liaqat et al., 2025). As climate change intensifies, sorghum is expected to play an increasingly important role in sustaining agricultural production across large parts of the continent (Orr et al., 2016). Unlike maize-based systems, which have dominated much of the cereal-legume intercropping literature (Namatsheve et al., 2021; Chikowo et al., 2022), sorghum is predominantly cultivated under low-input, water-limited conditions where crop interactions, nutrient dynamics and management responses differ substantially (Hadebe et al., 2017; Abreha et al., 2021). Thus, findings from broader cereal-legume intercropping syntheses cannot be assumed to apply directly to sorghum-based production systems.

Grain legumes are integral to food and farming systems in sub-Saharan Africa. In 2024, cowpea, groundnut, dry beans, soybean and pigeon pea collectively occupied approximately 44.6 million ha and produced 38.8 million t. Cowpea and groundnut dominated, covering 15.3 and 14.5 million ha and producing 9.6 and 15.0 million t, respectively. Dry beans occupied 9.5 million ha and produced 7.7 million t, while soybean and pigeon pea contributed smaller shares. Production was geographically concentrated, with Nigeria leading cowpea and groundnut production, Tanzania dry beans, South Africa soybean and Malawi pigeon pea (FAO, 2026). Beyond supplying protein-rich food, livestock feed and income, these legumes can contribute biologically fixed nitrogen, improve soil cover and nutrient cycling, and strengthen the productivity and stability of cereal-based systems (Ncube et al., 2009; Barasa, 2022; Abroulaye et al., 2023; Kiita et al., 2025).

The integration of legumes into sorghum-based production systems has long been practiced by smallholder farmers across sub-Saharan Africa as a strategy for improving food security, soil fertility and production stability (Traore et al., 2023; Kiita et al., 2025). Common intercrop species include cowpea (Vigna unguiculata), groundnut (Arachis hypogaea), soybean (Glycine max), common bean (Phaseolus vulgaris), mung bean (Vigna radiata), pigeon pea (Cajanus cajan) and bambara groundnut (Vigna subterranea) (Barasa, 2022; Kiita et al., 2025). In addition to providing grain and fodder, these legumes contribute to nitrogen fixation, improve soil cover and increase system diversity (Ncube et al., 2009; Abroulaye et al., 2023). Both theoretical and empirical evidence suggest that sorghum–legume intercropping can improve land-use efficiency, increase total system productivity and strengthen resilience relative to sole cropping systems (Lithourgidis et al., 2011; Brooker et al., 2015; Martin-Guay et al., 2018; Assefa et al., 2025). These potential benefits have stimulated increasing research interest in sorghum–legume intercropping as a sustainable intensification strategy for smallholder farming systems in sub-Saharan Africa.

Despite growing interest in sorghum–legume intercropping, the available evidence remains fragmented across diverse agroecological zones, crop combinations and management practices. Previous reviews have synthesized cereal-legume intercropping more broadly for example (Matusso et al., 2014; Kiwia et al., 2019) or have focused primarily on productivity outcomes, particularly land equivalent ratio (LER), transgressive overyielding index (TOI) and yield advantages (Adam et al., 2025). However, none has systematically synthesized evidence specifically on sorghum–legume intercropping across sub-Saharan Africa while simultaneously evaluating agronomic, environmental, economic and social outcomes within a sustainable intensification framework. This limits our understanding of the overall contribution of sorghum–legume intercropping to resilient and sustainable smallholder farming systems and constrains the development of evidence-based management recommendations and policy interventions.

A comprehensive assessment of these multiple dimensions is needed because sustainable intensification cannot be evaluated on productivity alone (Firbank et al., 2013; Pretty, 2018). Technologies that increase yields but fail to improve profitability, maintain environmental sustainability or fit within the socio-economic realities of smallholder farmers are unlikely to achieve widespread adoption or long-term impact (Andersson and D’Souza, 2014; Giller et al., 2021). Understanding the extent to which sorghum–legume intercropping contributes simultaneously to productivity, environmental sustainability, economic performance and farmer livelihoods is therefore essential for guiding future research, development investments and policy interventions.

The review addressed the following question: Among sorghum-based production systems in Sub-Saharan Africa, how does sorghum–legume intercropping, compared with sole cropping or alternative intercropping management practices, influence productivity, environmental sustainability, economic performance and social outcomes? The review considered evidence from field experiments, on-farm trials, observational studies and socio-economic investigations reporting original empirical data.

To the best of our knowledge, no previous systematic review has synthesized evidence on sorghum–legume intercropping across sub-Saharan Africa from a sustainable intensification perspective. Specifically, the review aims to (i) characterize the intercropping systems and management practices reported in the literature; (ii) evaluate their productivity, environmental, economic and social outcomes; and (iii) identify knowledge gaps and research priorities for advancing sustainable intensification. By integrating these complementary dimensions, the review provides an evidence base to inform future research, policy and management decisions for resilient sorghum-based production systems in sub-Saharan Africa.

2 Methods

2.1 Review design and protocol

This study was conducted as a systematic review to synthesize evidence on sorghum–legume intercropping and its contribution to sustainable intensification in Sub-Saharan Africa. The review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines (Page et al., 2021) for planning, conducting and reporting systematic reviews. The review protocol was not prospectively registered; however, predefined eligibility criteria, search procedures, study-selection methods and data-extraction requirements were established before screening commenced. Owing to substantial methodological heterogeneity among the included studies, a narrative synthesis approach was adopted rather than quantitative meta-analysis.

2.2 Eligibility criteria

The review addressed the following research question: How does sorghum–legume intercropping influence productivity, environmental sustainability, economic performance and social outcomes in Sub-Saharan Africa compared with sole cropping systems or alternative intercropping management practices? The question was formulated using the Population, Intervention, Comparator, Outcomes and Study design (PICOS) framework to define the study eligibility criteria. The population comprised sorghum-based production systems in Sub-Saharan Africa, while the intervention was sorghum intercropped with one or more legume species. Comparators included sole sorghum, sole legumes and alternative intercropping management practices. Outcomes of interest included productivity, environmental sustainability, economic performance and social outcomes, while eligible study designs comprised field experiments, on-farm trials, observational studies and socio-economic investigations reporting original empirical data.

Studies were eligible if they were conducted in Sub-Saharan Africa, evaluated sorghum–legume intercropping under field conditions and reported at least one productivity, environmental, economic or social outcome. Studies investigating agronomic management practices, including legume species selection, planting arrangement, planting density, fertilizer management and related production practices within sorghum–legume intercropping systems, were also included. Only original research articles published in peer-reviewed journals between January 2000 and December 2025 and written in English were considered.

Productivity outcomes included grain yield, biomass production and land-use efficiency metrics such as land equivalent ratio (LER). Environmental outcomes included soil fertility indicators, biological nitrogen fixation, soil moisture, weed suppression and Striga management. Economic outcomes included profitability, gross margins and benefit–cost ratios, while social outcomes included farmer perceptions, labor requirements, adoption constraints and related socio-economic factors.

Studies were excluded if they were conducted outside Sub-Saharan Africa, evaluated sole cropping systems without an intercropping comparison, were conducted exclusively under greenhouse, pot or laboratory conditions, or did not report original empirical data. Reviews, conference papers, book chapters, editorials and studies with insufficient methodological or outcome information were also excluded.

2.3 Literature search strategy

Literature was searched in Web of Science Core Collection, Scopus and Google Scholar for studies published between January 2000 and December 2025, with the final search completed in March 2026. The search strategy combined keywords and synonyms linked with Boolean operators, truncation, and phrase searching. Searches were performed using combinations of keywords in the title, abstract and keyword fields where database functionality permitted. The sorghum component included the terms sorghum and Sorghum bicolor. The intercropping component included terms such as intercrop, intercropping, mixed cropping, mixed culture, relay cropping, strip cropping, association cropping, crop mixture, companion cropping, interplanting, and crop diversification. The legume component included both general and species-specific terms, including legume, pulse, cowpea, groundnut, peanut, pigeonpea, soybean, common bean, haricot bean, mung bean, green gram, bambara groundnut, lablab, mucuna, chickpea, and faba bean. The geographic component included the term Sub-Saharan Africa, regional identifiers such as Sahel and Southern Africa, and the names of individual countries within the region to capture studies that did not explicitly use the broader regional descriptor. Backward and forward citation searches were undertaken to identify additional eligible studies.

2.4 Study selection process

All retrieved records were imported into Covidence, where duplicate records were removed prior to screening. Titles and abstracts were screened against predefined eligibility criteria, followed by full-text assessment of potentially relevant articles. Study selection and data extraction were undertaken by a single reviewer using the predefined protocol. To enhance consistency, the extracted information and synthesis were reviewed and discussed by all authors before finalization. Full-text articles were assessed manually using predefined eligibility criteria. SciSpace was used as a supplementary tool to assist in interrogating full-text articles and verifying study characteristics; however, all inclusion decisions and data extraction were undertaken by the reviewer. The study-selection process is summarized in a PRISMA 2020 flow diagram (Figure 1).

2.5 Data extraction and synthesis

Data were extracted from all eligible studies using a standardized data extraction form developed specifically for this review. Extracted information included publication details (authors and year), country, agroecological region, experimental setting, sorghum and legume species, experimental design, management practices, comparator treatments and reported outcomes.

Management variables extracted included legume species, planting arrangement, row ratio, planting density, fertilizer and soil fertility management, cultivar selection and other agronomic interventions. Outcome variables included crop yield, biomass production, land equivalent ratio (LER), partial land equivalent ratio (PLER), resource-use efficiency, soil fertility indicators, biological nitrogen fixation, soil organic carbon, available phosphorus, soil moisture, pest and weed suppression, profitability, benefit-cost ratio, adoption indicators and other reported socio-economic outcomes.

2.6 Quality assessment

The methodological quality of included studies was assessed to evaluate the reliability and robustness of the evidence. Each study was assessed for clarity of objectives, appropriateness of experimental design, adequacy of methodological description, reporting of statistical analyses and completeness of outcome reporting. Studies were not excluded based on quality assessment; rather, the assessment was used to support interpretation of the strength and consistency of the available evidence. Each criterion was assessed as adequately reported, partially reported or not reported. The assessment was used to evaluate the overall quality of the evidence and was not applied as an exclusion criterion.

2.7 Data synthesis

Given the considerable heterogeneity in study objectives, experimental designs, measured variables and reporting approaches, a quantitative meta-analysis was not considered appropriate. Instead, findings were synthesized narratively. Studies were grouped according to thematic outcomes, including productivity, environmental sustainability, economic performance and social outcomes. Evidence was further synthesized according to agronomic management practices such as legume species, planting arrangement, planting density and fertilizer management. Descriptive statistics were used to summarize study characteristics, while evidence maps, summary tables and graphical visualizations were developed to illustrate research trends, geographical distribution and reported outcomes across Sub-Saharan Africa. Descriptive analyses were performed and graphical summaries were prepared using R (version 4.5.1) and Microsoft Excel.

3 Findings of the review and synthesis

3.1 Study selection

The literature search identified 562 records, comprising 213 from Web of Science, 180 from Scopus and 169 from Google Scholar. Following the removal of 240 duplicate records, 322 unique articles remained for title and abstract screening. Of these, 220 records were excluded for failing to meet the eligibility criteria, leaving 102 articles for full-text assessment. A further 29 studies were excluded because they were conducted outside Sub-Saharan Africa, did not evaluate sorghum–legume intercropping, lacked primary empirical data, reported outcomes outside the scope of this review, or represented duplicate datasets. Consequently, 73 studies met the inclusion criteria and were included in the qualitative synthesis (Figure 1). The references of the included studies are provided in the Supplementary Material.

The included studies represented a broad range of agroecological conditions, cropping systems and experimental approaches across Sub-Saharan Africa, providing a comprehensive evidence base for evaluating the agronomic, environmental, economic and social dimensions of sorghum–legume intercropping. However, substantial variation in study objectives, management practices, outcome measures and reporting methods precluded quantitative synthesis through meta-analysis. Furthermore, the evidence base was dominated by short-term field experiments, while relatively few studies evaluated long-term environmental impacts, economic performance or farmer adoption.

3.2 Characteristics of included studies

3.2.1 Geographical distribution of research

The 73 studies included in the review were conducted across 12 countries in Sub-Saharan Africa, although their distribution was highly uneven (Figure 2). Ethiopia accounted for the largest share of studies (38.4%), followed by Nigeria (20.5%), Mali and Kenya contributed 8.2% each while Burkina Faso contributed 6.8%. South Africa and Zimbabwe each represented 4.1% of the evidence base, Botswana and Sudan contributed 2.7% each, and Ghana, Malawi and Tanzania were represented by a single study (1.4%). At the regional level, Eastern Africa accounted for 50.7% of all studies, followed by Western Africa (37%) and Southern Africa (12.3%). No eligible studies were identified from Central Africa.

The strong representation of Ethiopia and other East African countries reflects the importance of sorghum in drought-prone production systems, where intercropping has received considerable research attention as a strategy for improving productivity, soil fertility and resilience. Similarly, the substantial contribution from Western Africa highlights the importance of sorghum–legume systems in the Sudanian and Sahelian zones, where low soil fertility, rainfall variability and Striga infestation remain major production constraints. By contrast, Southern Africa was comparatively underrepresented despite the strategic importance of sorghum in climate adaptation and food security.

The absence of eligible studies from Central Africa should be interpreted with caution. The region accounts for approximately 6.4% of the sorghum area and 7.0% of production in 2024, with production concentrated in Chad and Cameroon (FAO, 2026). Thus, the absence of eligible studies does not indicate that sorghum–legume intercropping is absent from Central African farming systems. Publication and language biases may also have limited the retrieval of relevant research, particularly studies published in French. Nevertheless, the available evidence indicates that research on sorghum–legume intercropping remains concentrated in Eastern and Western Africa, highlighting the need for greater investment in underrepresented regions to improve the geographical relevance and transferability of research findings across SSA.

3.2.2 Agroecological representation of the evidence base

The reviewed studies spanned a range of agroecological environments across SSA, although research was concentrated in semi-arid and sub-humid regions. Semi-arid environments accounted for 50.0% of the studies, followed by sub-humid environments (32.9%), while humid and arid environments represented 8.6% and 7.1%, respectively. Only one study (1.4%) was conducted across multiple agroecological zones. Overall, more than 80% of the available evidence originated from semi-arid and sub-humid production systems.

This distribution is consistent with the agroecological adaptation of sorghum, which is predominantly cultivated in the semi-arid and sub-humid regions of SSA where it serves as a major food security crop. Consequently, the current evidence base is well aligned with the environments in which sorghum–legume intercropping is most relevant. Nevertheless, relatively few studies have evaluated these systems in humid or arid environments, limiting understanding of their performance across the full range of agroecological conditions in which sorghum is grown.

3.3 Management practices in sorghum–legume intercropping systems

Intercrop performance was influenced by a combination of management practices that determined the extent of complementarity and competition between sorghum and the companion legume. Across the reviewed studies, researchers investigated legume species, spatial arrangement, plant population, planting time and fertility management either individually or in combination to optimize resource use. Collectively, the evidence indicates that successful intercropping depends not only on the choice of component crops but also on how the system is configured and managed.

3.3.1 Legume species

A wide range of legumes has been evaluated in sorghum-based intercropping systems across sub-Saharan Africa, although research has concentrated on relatively few species. Cowpea (Vigna unguiculata) was the most extensively investigated intercrop species, occurring in 45 of the 73 studies (61.6%). Soybean (Glycine max) was evaluated in 17 studies (23.3%), common bean (Phaseolus vulgaris) in 13 (17.8%) and groundnut (Arachis hypogaea) in 11 (15.1%). Pigeon pea (Cajanus cajan) was evaluated in seven studies (9.6%), mung bean (Vigna radiata) in six (8.2%) and Bambara groundnut (Vigna subterranea) in five (6.8%). Chickpea (Cicer arietinum) and lablab (Lablab purpureus) were each evaluated in two studies (2.7%), while Piliostigma reticulatum and vetch (Vicia spp.) were each evaluated in one study (1.4%).

The predominance of cowpea reflects its broad adaptation to semi-arid environments, compatibility with sorghum production systems and multiple functions as a grain, fodder and nitrogen-fixing crop, making it particularly attractive for smallholder farming systems (Ajeigbe et al., 2006; Mohammed et al., 2008; Falconnier et al., 2016). Soybean, common bean and groundnut have also received considerable attention because of their economic value, nutritional importance and contribution to biological nitrogen fixation (Langat et al., 2006; Egbe, 2010; Dembele, 2022). In contrast, species such as Bambara groundnut, pigeon pea, lablab and chickpea remain relatively underrepresented despite evidence that they can improve system resilience, diversify production and contribute to soil fertility under specific agroecological conditions.

3.3.2 Spatial arrangements and planting configurations

The available evidence demonstrates a strong preference for row intercropping as the dominant planting strategy in sorghum–legume systems, with comparatively little research devoted to mixed or relay intercropping (Ayisi et al., 2001; Mohammed et al., 2008). Within row-intercropping systems, experimentation has focused predominantly on a small number of planting geometries, particularly the 1:1 (41 studies), 2:1 (18 studies), 1:2 (17 studies) and 2:2 (10 studies) row ratios, while more complex configurations were evaluated in only one to four studies (Table 1). This concentration suggests that research has prioritized practical planting arrangements that are readily implemented under smallholder farming conditions but has explored only a narrow range of possible spatial configurations.

Table 1. Frequency of evaluation and recommendation of sorghum-to-legume row ratios in the reviewed studies.

Despite this emphasis, the evidence provides no support for a universally superior row ratio. Although the 1:1 configuration emerged as the most frequently recommended, it was identified as optimal in only 26 of the 41 studies (63.4%) in which it was evaluated. Likewise, the 1:2 configuration was recommended in 6 of 17 studies (35.3%), whereas the widely investigated 2:1 configuration was identified as optimal in only 1 of 18 studies (5.6%). Conversely, several less frequently studied row ratios performed well within individual experiments, but the limited number of evaluations prevents broad agronomic recommendations (Ajeigbe et al., 2006; Langat et al., 2006; EL Naim et al., 2013; Hailu, 2021; Assefa et al., 2025). Collectively, these findings indicate that intercrop performance is determined less by row ratio itself than by its interaction with legume species, plant population, intercropping design and environmental conditions. Consequently, planting geometry should be considered a context-specific management component rather than a universally transferable recommendation.

3.3.3 Plant population and planting time

The reviewed studies consistently identified plant population as a key determinant of resource partitioning and competitive interactions in sorghum–legume intercrops. Sorghum populations generally ranged from approximately 40,000 to 133,000 plants ha⁻¹, although most studies maintained populations between 55,000 and 90,000 plants ha⁻¹. In contrast, legume populations were manipulated over a wider range, either by varying plant density or by establishing crops at 25–100% of their recommended sole-crop populations (Langat et al., 2006; Mohammed et al., 2008; Sibhatu et al., 2015; Hailu, 2021; Assefa et al., 2025). This reflects the common strategy of regulating legume density to optimize complementarity while maintaining sorghum productivity.

Where explicitly reported, both additive and substitutive (replacement) intercropping designs were employed to regulate crop competition. Additive designs generally maintained sorghum at or close to its recommended sole-crop population while varying legume density, whereas substitutive designs altered the populations of one or both component crops to maintain a fixed overall plant density (Akunda, 2001; Langat et al., 2006; Oseni and Aliyu, 2010; Falconnier et al., 2016). However, many studies described only row ratios, spacing or plant populations without explicitly defining the intercropping design, making direct comparisons among studies difficult and highlighting the need for more consistent reporting of planting configurations.

Planting time was also used to regulate competition between component crops. Although simultaneous planting predominated, several studies evaluated delayed or staggered legume establishment to improve temporal complementarity and reduce early competition for light, water and nutrients (Yusuf et al., 2004, Yusuf et al., 2016; Tarekegn and Shimelash, 2024). Overall, the evidence suggests that intercrop performance is influenced by the combined effects of plant population, intercropping design, planting geometry and sowing time, with optimum management varying according to legume species and local growing conditions rather than a single universally applicable planting strategy.

3.3.4 Fertility management

Fertility management was evaluated in a relatively small subset of the reviewed studies, primarily through mineral nitrogen rate experiments, followed by evaluations of blended fertilizers (NPS), organic nutrient amendments, integrated soil fertility management (ISFM) and biological inoculation. Collectively, these studies demonstrate that nutrient management was used not only to improve sorghum productivity but also to optimize the complementary interactions between sorghum and the associated legume (Table 2). Fertility interventions frequently interacted with plant population, row arrangement and legume density, indicating that nutrient management should be considered within the broader context of intercrop design rather than as an independent management practice (Sibhatu et al., 2015; Falconnier et al., 2016; Degebasa et al., 2025).

Table 2. Fertility management interventions evaluated in sorghum-legume intercropping studies and their principal outcomes.

Across studies, moderate fertilizer inputs generally produced the greatest benefits. Intermediate nitrogen rates frequently improved sorghum productivity while maintaining legume performance, resulting in greater land-use efficiency and economic returns than unfertilized systems or excessive fertilizer application (Sibhatu et al., 2015; Traoré et al., 2022). Similarly, blended fertilizers and organic amendments, including NPS fertilizer and vermicompost, substantially increased intercrop productivity, with Degebasa et al. (2025) reporting a land equivalent ratio of 3.18 and (Ebbisa et al., 2024) achieving sorghum yields exceeding 5.8 t ha⁻¹ under the highest vermicompost rate. Long-term studies further demonstrated that repeated manure application and integrated soil fertility management enhanced both crop productivity and soil quality, although responses remained strongly influenced by soil type and environmental conditions (Kihanda et al., 2005; Falconnier et al., 2016).

Overall, the evidence indicates that the benefits of fertility management arise not from maximizing fertilizer inputs but from optimizing nutrient supply to complement biological nitrogen fixation and intercrop resource use. Consequently, fertility management should be integrated with planting geometry, plant population and species selection to maximize intercrop productivity and sustainability rather than being considered as an isolated management intervention.

3.4 Sustainable intensification outcomes

The reviewed studies evaluated sustainable intensification outcomes across four interrelated dimensions: productivity, environmental sustainability, economic performance and social outcomes (Table 3). However, the strength of evidence differed considerably among these dimensions. Productivity and land-use efficiency were assessed most frequently, whereas environmental, economic and social outcomes received comparatively less attention. Nevertheless, the available evidence indicates that sorghum–legume intercropping contributes positively to several complementary dimensions of sustainable intensification, extending beyond crop productivity alone.

Table 3. Summary of sustainable intensification outcomes reported in sorghum-legume intercropping studies across Sub-Saharan Africa.

3.4.1 Productivity outcomes

Productivity was the most extensively investigated outcome of sorghum–legume intercropping. Although responses of sorghum grain yield varied among studies, increases in total system productivity were generally demonstrated through land equivalent ratio (LER). Among the 37 studies reporting LER, values ranged from 0.37 to 3.18, and 34 studies (91.9%) recorded values greater than one, indicating that intercropping generally produced more combined output per unit land area than sole cropping. Thirteen studies reported LER values between 1.50 and 1.99, eight between 1.25 and 1.49, eight between 1.00 and 1.24, and five reported values of at least 2.00. Sub-unity LER values occurred in three studies. Akunda (2001) reported LER values of 0.37–0.608 for a 1:1 sorghum–soybean intercrop established at different plant densities in Kenya. In Nigeria, a 2:4 sorghum–cowpea row arrangement evaluated by Ajeigbe et al. (2006) produced an LER of 0.96. Gebremichael et al. (2019) reported an LER of 0.90 for a 1:1 sorghum–pigeon pea intercrop in Ethiopia.

Variation in LER reflected differences in the response of the component crops. Sorghum grain yield was frequently maintained and, in some cases, exceeded that of sole sorghum, with reported increases ranging from 7.6% to 159% depending on the legume species and management practices (Debela, 2017; Dembele, 2022; Degebasa et al., 2025). Where sorghum yield declined, reductions generally ranged from 1.3% to 66.8% and were often associated with increased competition under particular intercrop arrangements (Ajeigbe et al., 2006; Oseni and Aliyu, 2010). Nevertheless, these reductions were typically compensated by legume production, resulting in higher overall system productivity and land-use efficiency.

Positive LER values were reported across a wide range of legume species, with the largest evidence base available for cowpea (20 studies), followed by soybean (8), groundnut (6), mung bean (5), common bean (2), pigeon pea (2), Bambara groundnut (2) and lablab (2) (Figure 3). Mean LER values exceeded unity for all species for which estimates were available, ranging from 1.30 in pigeon pea to 1.92 in common bean. Groundnut (mean LER = 1.74), lablab (1.79), Bambara groundnut (1.70) and soybean (1.55) also consistently produced land-use advantages, although the supporting evidence was based on fewer studies than cowpea.

Where partial land equivalent ratios (PLERs) were reported, sorghum PLER values were frequently close to one, indicating that intercrop productivity was achieved with little reduction in sorghum yield. For example, sorghum PLER values of 1.08, 1.08 and 1.00 were reported by Debela (2017); Naim et al. (2013) and Assefa et al. (2025), respectively, while corresponding legume PLER values reflected complementary production rather than replacement of sorghum yield. Similar responses were reported for lablab (Kahsay et al., 2021), mung bean (Dinkale et al., 2022; Assefa et al., 2025) and soybean (Egbe, 2010), indicating efficient sharing of available resources between component crops.

Although sorghum grain yield was frequently lower under intercropping than sole cropping, reductions in the cereal component were generally compensated by legume production, resulting in greater combined system productivity. Studies reporting both components yields consistently concluded that productivity gains depended on complementary resource use rather than increased yield of either crop alone. Higher LER values were commonly associated with appropriate species selection, additive or optimized row arrangements, and suitable fertility management, highlighting the importance of crop complementarity in determining intercrop performance.

3.4.2 Environmental outcomes

Sorghum–legume intercropping improved nutrient regulation, soil condition and biological regulation, although responses varied among indicators (Figure 4). The clearest gains were associated with soil nitrogen, soil organic carbon and suppression of Striga hermonthica.

Total soil nitrogen generally increased under intercropping, although three studies reported no significant difference from sole sorghum (Reda et al., 2005; Egbe, 2007; Guébré et al., 2024). Positive responses were reported across cowpea-, soybean-, pigeon pea-, haricot bean- and mung bean-based systems (Silim et al., 2005; Singh and Ajeigbe, 2007; Udom et al., 2007; Naim et al., 2013; Sibhatu et al., 2015; Falconnier et al., 2016; Jorgi et al., 2020; Hailu, 2021; Akinola et al., 2024). Soil organic carbon and available phosphorus also increased in most studies that reported treatment responses, indicating that legume integration can improve nutrient retention and availability beyond the immediate cropping season (Singh and Ajeigbe, 2007; Falconnier et al., 2016; Jorgi et al., 2020; Hailu, 2021; Akinola et al., 2024; Guébré et al., 2024). Biological nitrogen fixation contributed between 37.5 and 164.8 kg N ha⁻¹ in pigeon pea and 82.5 kg N ha⁻¹ in cowpea, demonstrating the potential contribution of legumes to system nitrogen supply (Egbe, 2007; Udom et al., 2007).

Intercropping also improved indicators of soil physical functioning. Higher soil moisture was reported under cowpea- and mixed-legume systems, while improvements in soil pH, bulk density, hydraulic conductivity, water sorptivity and hydrophobicity were recorded in the Nigerian studies of Akinola et al., 2023, Akinola et al., 2024). These responses suggest that the contribution of intercropping extends beyond nutrient addition to improved water entry, water retention and soil structural condition, particularly where legume biomass and residues are retained in the system.

Biological regulation was most evident in the suppression of Striga hermonthica. Reductions ranged from 32.6% to 99.7%, with strong responses reported in cowpea-, groundnut-, soybean- and desmodium-based systems (Aliyu and Emechebe, 2006; Khan et al., 2007a; Udom et al., 2007; Dereje et al., 2016; Degebasa et al., 2025). Lower pest incidence was also reported in a number of intercrop systems, showing that legume integration can strengthen biological regulation while reducing dependence on external control measures.

3.4.3 Economic outcomes

Economic performance was evaluated less frequently than productivity but generally favored sorghum–legume intercropping. Where directly comparable estimates were available, with studies reporting gains between 39.1% and 264.4% (Figure 5). These findings indicate that improvements in biological productivity were generally translated into higher economic returns.

Additional economic indicators supported the profitability of intercropping. Labor return ratios exceeded 2.2 in profitable intercrop systems but were below 0.8 in less profitable systems (Khan et al., 2007b). A marginal rate of return of 576% was reported by Degebasa et al. (2025), while Dembele (2022) reported a benefit–cost ratio of 12.8, indicating that the additional investment in intercropping generated substantial economic returns. These findings demonstrate that the economic advantages of sorghum–legume intercropping were evident across multiple profitability indicators despite differences in the metrics used.

The magnitude of the economic response varied among studies, reflecting differences in legume species, management practices, environmental conditions and the economic indicators used. Nevertheless, studies consistently attributed improved profitability to the combined value of sorghum and legume production rather than increased sorghum yield alone, reinforcing the close relationship between improved land-use efficiency and farm profitability.

3.4.4 Social outcomes

Social outcomes were reported in relatively few of the reviewed studies, indicating that the evidence base remains heavily weighted towards agronomic, environmental and economic performance. Where social outcomes were evaluated, they centered primarily on dual-purpose production, yield stability, livestock feed provision, farmer participation and existing farming practices, rather than formal assessments of technology adoption or household livelihoods (Table 4). Farmer-managed and participatory on-farm evaluations were also used in several studies to assess the practical performance of sorghum–legume intercrops under smallholder conditions (Khan et al., 2007b; Falconnier et al., 2016; Nyagumbo et al., 2025).

Table 4. Social outcomes reported in sorghum-legume intercropping studies.

Dual-purpose production emerged as the most consistent social benefit. Intercropping legumes such as cowpea, pigeon pea, lablab and vetch enabled simultaneous production of grain for household consumption and fodder for livestock, thereby increasing the diversity of outputs obtained from the same land area (Ajeigbe et al., 2006; Karikari, 2007; Udom et al., 2007). Several studies also reported improved production stability and reduced risk, highlighting the capacity of intercrops to buffer against seasonal variability and minimize the likelihood of complete crop failure compared with sole cropping (Ajeigbe et al., 2006; Karikari, 2007; Udom et al., 2007).

Evidence relating to farmer engagement was limited but demonstrated the practical relevance of intercropping under smallholder conditions. Participatory and farmer-managed evaluations showed that intercrop performance was strongly influenced by local production environments and management practices, reinforcing the importance of evaluating technologies under farmer conditions before wider dissemination (Khan et al., 2007b; Falconnier et al., 2016; Nyagumbo et al., 2025). Survey evidence further indicated that sorghum–legume intercropping was already a familiar practice in some farming systems, with approximately 67% of surveyed farmers in Botswana practicing sorghum–Bambara groundnut intercropping (Karikari, 2007). Overall, the available evidence suggests that the key social benefits of sorghum–legume intercropping arise from diversified farm outputs, enhanced production stability and compatibility with existing smallholder farming systems, although relatively few studies have explicitly quantified broader social or adoption outcomes.

4 Research priorities for sustainable intensification

4.1 Rebalancing sustainable intensification research

One of the clearest findings emerging from this review is that research on sorghum–legume intercropping has been heavily dominated by agronomic productivity, particularly grain yield, biomass production and land equivalent ratio (LER), whereas environmental, economic and social dimensions have received comparatively limited attention. Although productivity remains fundamental to improving food security in smallholder farming systems, sustainable intensification requires agricultural systems that simultaneously enhance environmental quality, economic viability and social well-being rather than increasing production alone (Firbank et al., 2013; Garnett et al., 2013; Pretty, 2018). This broader interpretation of sustainable intensification has become increasingly recognized within agricultural research, where technologies are expected to deliver multiple ecosystem services while strengthening resilience and supporting rural livelihoods (Rockström et al., 2017; Pretty, 2018; Denning, 2025).

The imbalance observed in the present review therefore reflects a wider historical emphasis on production-oriented research rather than integrated evaluation of agricultural systems. While productivity gains provide essential evidence of agronomic potential, they offer only a partial assessment of the contribution of sorghum–legume intercropping to sustainable intensification. For example, only a relatively small proportion of the reviewed studies quantified changes in soil quality, profitability or farmer-centered outcomes despite these factors ultimately determining the long-term sustainability and adoption of agricultural technologies (Falconnier et al., 2016; Hailu, 2021; Dembele, 2022). Similar concerns have been raised in broader assessments of sustainable intensification, which advocate multidisciplinary evaluation frameworks capable of simultaneously capturing production, environmental and socio-economic performance (Firbank et al., 2013; Pretty, 2018).

Future research should therefore adopt integrated assessment frameworks that evaluate productivity, environmental sustainability, economic performance and social outcomes within the same experiments. Such approaches would provide a more comprehensive understanding of the synergies and trade-offs associated with sorghum–legume intercropping while generating stronger evidence for designing management recommendations that are agronomically effective, environmentally sustainable, economically attractive and socially relevant across diverse smallholder farming systems in sub-Saharan Africa.

4.2 Optimizing intercrop design for context-specific performance

A second major finding emerging from this review is that no single sorghum–legume intercropping configuration consistently maximized system performance across all production environments. Although cowpea was the most extensively evaluated intercrop species and the 1:1 row arrangement was the most frequently investigated planting configuration, neither consistently produced the highest productivity or land-use efficiency. Likewise, responses to plant population, planting time and fertility management varied considerably among studies, reflecting differences in agroecological conditions, resource availability and management practices. This was evident across studies by Ajeigbe et al. (2006); Langat et al. (2006); Falconnier et al. (2016); Hailu (2021); Assefa et al. (2025), which identified different optimum management combinations depending on crop species, fertility management and local growing conditions.

This conclusion is consistent with ecological theories of intercropping, which attribute productivity gains to complementarity in resource acquisition, temporal niche differentiation and reduced interspecific competition rather than to specific crop combinations or planting arrangements alone (Lithourgidis et al., 2011; Brooker et al., 2015). More recent syntheses further demonstrate that intercrop performance is inherently context dependent because biological interactions are strongly influenced by climate, soil properties and management intensity (Martin-Guay et al., 2018; Li et al., 2020; Adam et al., 2025). The present review extends these broader observations by demonstrating that similar context dependency characterizes sorghum-based intercropping systems across sub-Saharan Africa.

The findings suggest that future research should move beyond evaluating isolated management components toward integrated optimization of complete intercropping systems. Multifactorial experiments that simultaneously investigate legume species, planting geometry, plant population and fertility management across contrasting agroecological environments would provide stronger evidence for identifying robust management packages capable of maximizing productivity, resource-use efficiency and resilience under diverse smallholder farming conditions.

4.3 Broadening environmental assessment towards long-term system resilience

The environmental evidence synthesized in this review demonstrates that sorghum–legume intercropping can enhance nutrient regulation, improve selected soil physical properties and strengthen biological regulation through processes such as biological nitrogen fixation, increased soil organic carbon accumulation and suppression of Striga hermonthica. Positive environmental responses were reported by Hailu (2021); Akinola et al. (2024); Guébré et al. (2024). However, environmental assessments were largely restricted to a relatively narrow set of indicators and were predominantly based on short-term field experiments. Comparatively few studies evaluated broader ecosystem functions, including soil biological activity, biodiversity, greenhouse gas emissions, water-use dynamics or long-term changes in soil quality despite their importance for determining the sustainability of agricultural production systems.

This imbalance contrasts with contemporary sustainable intensification frameworks, which emphasize that agricultural technologies should be evaluated according to their capacity to maintain ecosystem functions while increasing productivity (Firbank et al., 2013; Rockström et al., 2017; Pretty, 2018). As climate variability continues to intensify across sub-Saharan Africa, resilience is increasingly recognized as a fundamental component of sustainable intensification rather than a secondary outcome (Rosenzweig et al., 2017; Denning, 2025). Consequently, understanding how sorghum–legume intercropping influences ecosystem processes over time will be as important as quantifying its immediate effects on crop production.

Addressing these knowledge gaps will require a shift towards longer-term and systems-oriented research. Long-term field experiments should be complemented by crop simulation modelling to evaluate intercrop performance under a wider range of climatic, edaphic and management scenarios than can realistically be tested experimentally. Such integrated approaches would enable researchers to assess not only the persistence of productivity gains but also the long-term consequences of sorghum–legume intercropping for soil health, resource-use efficiency, climate resilience and the sustainability of smallholder farming systems.

4.4 Accelerating adoption and scaling of sorghum–legume intercropping

Although this review demonstrates that sorghum–legume intercropping can improve productivity, environmental performance and farm profitability, relatively few studies explicitly examined the factors influencing adoption and large-scale implementation. Evidence from participatory and farmer-managed studies (Khan et al., 2007b; Falconnier et al., 2016; Nyagumbo et al., 2025) suggests that successful implementation depends not only on biological performance but also on access to quality seed, extension services, production inputs and locally appropriate management knowledge. These studies also demonstrated that intercrop performance varied considerably across production environments, reinforcing the importance of evaluating technologies under realistic smallholder farming conditions before wider dissemination.

Because social, adoption and livelihood outcomes were evaluated in only a minority of the reviewed studies, future research should integrate agronomic experimentation with socio-economic, market and policy analyses. Greater emphasis should also be placed on participatory research and farmer-managed evaluation to determine whether promising intercrop configurations are technically feasible, economically attractive and compatible with farmers’ production objectives and resource constraints.

5 Conclusions

This review provides the first systematic synthesis of sorghum–legume intercropping from a sustainable intensification perspective in sub-Saharan Africa. The available evidence demonstrates that intercropping generally improves land-use efficiency while contributing to enhanced environmental performance and farm profitability. However, these benefits are strongly influenced by legume species, planting configuration, fertility management and local agroecological conditions, indicating that no single management strategy is universally applicable across the region.

Despite the demonstrated potential of sorghum–legume intercropping, important knowledge gaps remain, particularly regarding the integrated assessment of environmental, economic and social outcomes. Future research should adopt multidisciplinary, long-term approaches that combine field experimentation with crop simulation modelling to develop context-specific, climate-resilient management strategies. By synthesizing current evidence and identifying key research priorities, this review provides a foundation for future research, policy and extension aimed at promoting sustainable sorghum production in sub-Saharan Africa.

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fagro.2026.1949974/full#supplementary-material

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Footnotes

Edited by: Desouza Blaise, Central Institute for Cotton Research (ICAR), India

Reviewed by: Amit Anil Shahane, Central Agricultural University, India

Micah Dettweiler, University of Florida, United States