Plant diversity is reported to increase the diversity and activity of belowground organisms. Sowing pigeon pea (Cajanus cajan (CC), Fabaceae), a woody legume, into fallow land invaded by mycotrophic siam weed (Chromolaena odorata (CO), Asteraceae), may thus boost soil biology and fertility. To test this prediction, we assessed in an on-farm survey whether root colonization by arbuscular mycorrhizal fungi (AMF) and P availability were higher in bi-species fallow fields with siam weed and pigeon pea (COCC) than in the two single-species fallow fields, in the second year of fallow. The study was conducted in central Côte d’Ivoire and considered four sites with three types of fallow field, each, namely fallows (i) spontaneously invaded by siam weed (CO), (ii) sown to pigeon pea (CC) and kept free from weeds, and (iii) invaded by siam weed, but additionally sown at a quarter strength to the normal seed density to pigeon pea (COCC). Soil and root samples were collected from 0 to 20 cm soil depth for chemical analyses and determination of root colonization intensity (rCI) and AMF taxon richness in soil by 18S ribosomal DNA metabarcoding. In the bi-species fallow fields, rCI was assessed in both siam weed and pigeon pea to compare the observed and expected rCI in an effort to detect mixture advantages, namely greater than expected rCI. The fallow types COCC and CO both hosted 28 AMF virtual taxa, while the fallow CC hosted 30. The AMF community composition in the bi-species fallow fields was close to that of the CO single-species fallow fields (Complementarity index C: 13.3

Because prescribed mid-dry season burn (MDS) failed in preventing shrub encroachment in wet savannahs of central Cote d'Ivoire, other times of burning are under investigation to identify a successful one. However, the management mainly focuses on vegetation, neglecting soil biodiversity including earthworms despite their critical role in soil functioning. This study explores how earthworms are impacted when shifting savannah burning from MDS to early-dry season (EDS) or late-dry season (LDS). It was carried out at three sites comprised of three plots each, where the fire treatments were respectively and annually applied for eight years. Earthworms were sampled using the Tropical Soil Biology and Fertility (TSBF) 25 cm & times; 25 cm x 30 cm-soil monolith protocol. Relative to MDS (352 ind. m- 2), total earthworm density was lower under the alternative burns particularly LDS (229 ind.m- 2). EDS fire strongly suppressed epigeic earthworms' population while LDS fire reduced endogeic earthworms by 60 % relative to MDS. Consequently, earthworm community composition was markedly altered by EDS, and weakly by LDS (40 % and 18 % of Colwell complementarity, respectively). Importantly, earthworm species richness and Shannon-Weaver index were lower under both alternative burns. Thus, EDS fire was the most detrimental to epigeic earthworms whilst LDS fire, to the entire earthworm community. Although earthworms were influenced by soil attributes, it is likely that their phenology during the dry season critically determined their responses to fires. After eight years of implementation, neither of the alternative burning regimes can be considered a viable substitute for MDS with regard to earthworm diversity conservation. These findings are of vital importance for the development of management strategies aimed at the integrated conservation of biodiversity in wet savannahs, highlighting the need to reconcile MDS burning with other shrubcontrol techniques that are less destructive to soil fauna.

Unsustainable land use practices in Central and West African Ecosystems (CWAEs) have resulted in a substantial decrease in soil organic carbon (SOC) and an increase in soil erosion in these ecosystems, with severe repercussions on climate, biodiversity and food security. However, the potential for SOC accretion as a nature-based solutions (NbS) strategy in CWAEs is scarcely understood. A systematic review of 77 articles published from 1990 to 2024, extracted from three electronic databases, was conducted to fill this knowledge gap while stressing other proven efficient SOC accretion land management strategies. SOC stocks at 0–25 cm depth increased by up to 0.8 Mg C ha−1 yr−1 in monocultures and 1.9 Mg C ha−1 yr−1 in mixed stands of nitrogen-fixing trees (NFTs) and non-NFTs compared to seven-year-old afforested stands of non-NFTs in central Africa. Tree-based plantations (i.e., Faidherbia albida, Piliostigma reticulatum) increased SOC stocks by 1–1.5-fold in Sahelian degraded lands of western Africa. Mixed stands of Cajanus cajan and Chromolaena odorata increased SOC stocks by 17 % at 0–10 cm depth after 2 years in Guinea savanna. SOC accretion was found to depend on tree presence and species, climatic and edaphic conditions, and management practices. In Sahelian ecosystems where tree density is low, tree planting should be recommended. In wetter and more forested zones, herbaceous legume-based fallows and planting mixtures of tree species, including NFS is recommended. Nature-based solutions have great potential for enhancing SOC stocks in the CWAEs. Despite biodiversity and ecological issues associated with afforestation of natural savanna ecosystems, the intervention proved to be an effective means of increasing SOC storage in the poorly structured savanna soils. All these strategies should be further evaluated under more diverse local socioeconomic conditions. The paper also summarizes knowledge gaps and suggests future research and policy actions to enhance the use of NbS in addressing societal challenges.

Summary The choice of tree species planted with cacao trees is essential for ensuring the efficiency and sustainability of cacao farming systems. This raises the question of the long-term impact of associated tree legumes (ATLs) on cacao bean yields and biomass accumulation. This study was carried out in accordance with four-block randomised experimental design in Divo (Ivory Coast, West Africa). The study involved cacao-Albizia lebbeck (Cacao-Alb) and cacao-Acacia mangium (Cacao-Aca) intercrops and unshaded cacao plots (Control). After 20 years of intercropping, we assessed cacao dendrometry (height, circumference, biomass, and biomass C-stock) and production (number of pods per tree and bean yield at the plot level) as well as soil fertility (soil organic matter (SOM) concentration) at various distances from ATLs (D1:0–1.75 m; D2:3.25–5 m; D3:7–9 m). The distance from the ATLs had no significant effect on the measured cacao dendrometric parameters, except for cacao height. In contrast, the Cacao-Aca association had a negative impact on the SOM concentration (−22%), cacao tree height (−6.15%), and productivity parameters (biomass: −12.4%; bean yield: −43%). However, Cacao-Alb and the Control had no significant differences in terms of SOM, tree biomass, or bean production. Intercropping cacao with the tested tree legumes did not enhance cacao productivity and, in some cases, hindered it, depending on the ATL species. This study highlighted the importance of identifying appropriate shade tree legume species that could be promoted in cacao-based agroforestry systems.

Soil organic carbon (SOC) stock assessment is important regarding soil fertility, crop production, land degradation, and climate change mitigation particularly for Sub Saharan Africa (SSA) region. SSA countries face several methodological and operational challenges for producing SOC stock data. This paper analyzed the methods commonly recommended and used, and the barriers encountered in SOC measurement and monitoring in SSA. A literature review was complemented with a survey within eight research partner laboratories of the CaSA (Soil carbon for sustainable agriculture in Africa) network. Results showed that SOC stock assessment varied according to (i) studied depth (8 identified depths), (ii) SOC content analysis (5 identified methods), (iii) bulk density assessment (6 identified methods), (iv) coarse fragment percentage computation (4 identified methods); but also in monitoring (3 identified approaches). The main barriers in SOC stock studies are the lack of financial and expert human resources. Therefore, SSA laboratories adapt methods according existing equipment for producing SOC stock data. Challenges facing SSA are to raise funding to increase the number of soil analyses and to empower its technical and scientific teams. The challenges are also to be able to establish a common and specific guideline and database for SOC stock studies in SSA.

Cacao-based agroforestry systems are promoted as adaptation and mitigation solutions for cacao production and carbon sequestration. Based on a 20-year experiment, we assessed the impact of associated shade tree legume (ATL), Albizia lebbeck and Acacia mangium on the total carbon stock (in soil at 60 cm depth + tree biomass + litter) of cacao stands. This study included cacao systems shaded with either A. lebbeck (Cacao-Alb) or A. mangium (Cacao-Aca) and full-sun cacao stands (Control). Soil organic carbon (SOC) contents (up to 60 cm deep) were estimated by a calibrated near-infrared spectroscopy model. Total tree biomasses were estimated using allometric equations. Leaf litter was sampled from 1-m2 quadrats. Compared to Control, Cacao-Aca had a significant negative impact on the carbon stock in the cacao biomass (-47%) as well and in the soil at depths of 10 cm (-23%), 30 cm (-21%) and 60 cm (-12%). In contrast, Cacao-Alb had a nonsignificant effect on carbon storage in the cacao biomass, whereas it generally had a positive influence on the SOC stock regardless of depth, i.e., +6% at the 0-10 cm depth, +7% at 0-30 cm, +20% at 30-60 cm and + 11% at 0-60 cm. Cacao-Aca had a significant positive impact (+71%) on the total carbon stock per hectare. The increase in Cacao-Alb relative to that in the Control reached +38%, but the difference was not significant. These contrasting results between the two tree legume species could be explained by the high-quality litter, reflected by the lower C/N and C/P ratios produced by A. lebbeck, and the greater negative impact of A. mangium on cacao biomass. The main finding of this study is that the impact of intercropping cacao with shade tree legumes on the stand-level total carbon stock depends on the ATL species.

Beneficial effects of organic fertilisers in the management of soil fertility have been proven, but their role on soil functioning in Sub Saharan savanna lowlands remains understudied. This study explores (i) the potential of stockyard litter (SYL) amendment in restoring soil microbial efficiency in a degraded lowland paddy in the short term and (ii) whether SYL amendment benefits soil spatial homogeneity. Three treatments described as no fertilisation (NF), annual mineral fertilisation with NPK + urea for four years (MinF), and annual mineral fertilisation for three years followed by SYL amendment in the fourth year (MinF-SYL) were tested. Soil samples (0–20 cm depth) were collected in the fifth year and analysed for common soil chemical properties and diverse microbial and enzyme attributes in addition to the CNP stoichiometry. Effects on the soil spatial homogeneity was assessed through the coefficient of variation (CV). Annual application of NPK + urea led to significant decreases in the microbial biomass-C (MBC) (-45.4

One option of improving the Chromolaena odorata (Asteraceae) fallow on which subsistence agriculture depends in West Africa could be the integration of ligneous plant species without drastically limiting litter decomposition. This study conducted in Central Côte d’Ivoire aimed to explore the effect of such a mixture (referred to as Mixing effect—ME) on leaf litter decomposition. It included pure fallows of C. odorata (CO) and Cajanus cajan (CC), and a mixed fallow of the two species (COCC) established at four sites. Litter decomposition was studied in litterbags for six months. Observed and expected mass losses were calculated in the litter mixture, which then allowed calculation of the ME. Soil-surface litter mass was highest in CC (9.3 ± 0.3 Mg ha−1), lowest in CO (5.5 ± 0.2 Mg ha−1) and intermediate in COCC (7.9 ± 0.3 Mg ha−1). Initial litter C concentration, and the C:N and C:P ratios were higher in CC than in CO while the opposite was observed for litter Ca2+and Mg2+, reflecting significant dissimilarities in the quality of the litter species. Interestingly, these parameters were those determining the overall litter mass loss. The decomposition coefficient in COCC (k = 0.45 month−1) was lower than that in CO (k = 0.93 month−1) but higher than that in CC (k = 0.21 month−1). The overall ME was found to be non-additive antagonistic (ME = -8.2

Substantial areas of agricultural lands in Sub-Saharan Africa have been invaded by Chromolaena odorata (Asteraceae), but the consequences for arbuscular mycorrhiza fungi (AMF) remains poorly understood. This study explores changes in diverse AMF community attributes and soil available phosphorus following C. odorata invasion in forest and savanna fragments in Côte d’Ivoire (West Africa). Invaded-forest (COF) and savanna (COS) sites were compared to adjacent natural forest (FOR) and savanna (SAV) fragments, respectively. Physico-chemical variables and AMF spore density parameters were determined for soil samples from 0–20 cm depth. An 18S ribosomal RNA metabarcoding analysis of AMF communities was conducted. In addition, cowpea (Vigna unguiculata) was grown on soils collected from these sites under greenhouse conditions for determination of soil mycorrhizal infectivity. Noticeable changes in the composition of AMF communities in C. odorata relative to nearby forest and savanna non-invaded sites were observed. AMF-specific richness in COS (47 species) was lower than that in SAV (57 species) while it was higher in COF (68 species) than in FOR (63 species). COF and COS differed in AMF specific composition (Dissimilarity index = 50.6%). Chromolaena odorata invasions resulted in increased relative abundances of the genera Claroideoglomus and Glomus in COF, a decreased relative abundance of Paraglomus in COS and decreased relative abundances of Ambispora in both COF and COS. Total and healthy spore densities, cowpea root colonization intensity and soil available P were all higher in invaded sites than in natural ecosystems. Remarkably, although these values were different in FOR and SAV, they turned out to be similar in COF and COS (4.6 and 4.2 total spores g−1 soil, 2.3 and 2.0 healthy spores g−1 soil, and 52.6 and 51.6% root colonization, respectively) suggesting a C. odorata-specific effect. These findings indicate that soil mycorrhizal potential and phosphorus availability have improved following C. odorata invasion.

Identifying and scaling up agricultural practices that promote atmospheric carbon transfer into the soil are keys to tackle climate change. A study was carried out in Central Côte d’Ivoire (West Africa) to assess soil organic carbon (SOC) storage and its edaphic constraints under diverse fallow management options. Trials were conducted at two locations—Ahérémou-II village and near the Lamto reserve. The impact of long-term Chromolaena odorata (Asteraceae) fallow was assessed relative to the native savanna. Those of short-term herbaceous (Mucuna pruriens, Lablab purpureus, Pueraria phaseoloides and a mixture of these three) and shrub (Cajanus cajan) legume (Fabaceae) fallows were assessed relative to the time of sowing (T0) or relative to C. odorata fallow. In Lamto, the legumes were grown simultaneously at two sites side-by-side—a native shrub savanna (“savanna”) and a 17-year C. odorata fallow (“fallow”)—with contrasting soil fertility levels. At both locations, SOC stock was higher in C. odorata than in the natural savanna, the increase being restricted to the 0–0.1-m depth. SOC accumulation rates at 0–0.4 m depth were 0.46% year−1 and 1.87% year−1 in the Lamto 17-year and Ahérémou-II 10-year C. odorata fallows, respectively. In Ahérémou-II, L. purpureus rather than C. cajan significantly increased SOC stock (0–0.1-m depth) relative to C. odorata (2-year fallows). In Lamto, SOC stock significantly increased in all legume plots (0–0.1-m depth) relative to T0, particularly the mixture (14.1% year−1) and L. purpureus (13.7% year−1). SOC storage was not found to be influenced by legume biomass yield nor by legume species x site interaction, although it was greater at the more fertile “fallow” than at the “savanna” sites. That increase was positively linked to the initial SOC, total N, clay + fine silt, Mg2+ and Ca2+ concentrations, with the latter exhibiting the strongest influence. This study highlights the agronomic and climatic benefits C. odorata may provide in savanna environment despite the inimical attributes linked to its invader status. Mixed legume fallowing should be further encouraged in Côte d’Ivoire and other West African coastal countries in the framework of the 4p1000 Initiative.

East Africa remains one of the most severely affected regions impacted by food insecurity with an increasing number of undernourished people (NEPAD 2013). The sustainable management of agricultural land and water resources is recognized as essential to achieve global food security. Almost 70% of the population of East Africa rely on agriculture (NEPAD 2013), and land degradation combined with declines in soil fertility constitutes a major barrier resulting in poverty and decreases in per-capita food production especially in Ethiopia (Zeleke et al. 2010; Agegnehu et al. 2014). Limited irrigation water resources and the deficiency of irrigation infrastructures have also, until now limited yield production, especially in smallholder farming systems experiencing climatic stress (Barron et al. 2015). Therefore, analyzing soil and water conservation issues should be considered and prioritized in the different countries of East Africa.

Plant invasion may have significant ecological and socio-economic impacts across agroecologies. Chromolaena odorata (Asteraceae) is one of the world's most invasive plants albeit it is considered a suitable fallow plant in West Africa. However, its impacts on soil biological processes are poorly understood. This study was conducted in intermingled forest and savanna sites invaded by C. odorata in Central Cote d'Ivoire (West Africa) to bridge this knowledge gap. Invaded forest sites (COFOR) were compared to adjacent natural forest fragments (FOR) while invaded savanna sites (COSAV) were compared to adjacent natural savanna fragments (SAV). Soil (0-10 cm depth) physico-chemical variables, including soil organic C (SOC), total soil N and available N and P concentrations were measured. Additionally, soil microbial biomass (MBC), carbon mineralization (C-min), acid phosphatase, beta-glucosidase, and fluorescein diacetate were measured. Further, the MBC/SOC ratio and the metabolic quotient (qCO(2)) were calculated. An index of invasion effect (IE) computed as the cumulative percent change in the microbial and enzyme activities was determined for each ecosystem context. Results showed that soil MBC and MBC/SOC ratio declined in COFOR relative to FOR. In general, Cmin, enzymatic activities, qCO(2) and available N and P significantly increased in the C. odorata sites relative to the respective reference ecosystems, particularly savanna, potentially due to a larger gap in the litters' quality. As a result, the invasion effect was twice as high in savanna (IE = 292.8%) as in forest (IE = 147.5%). However, a Principal Component Analysis showed that the COSAV were close to COFOR stands without mixing, probably due to contrasting initial soil organic matter and clay contents. These results improved our knowledge on the changes in soil microbial attributes and the mechanisms of soil fertility restoration or improvement in response to C. odorata invasion in natural forests and savannas of West Africa.

Conversion of natural forest to anthropogenic land use systems (LUS) often leads to considerable loss of carbon, however, proper management of these LUS may reverse the trend. A study was conducted in a semi-deciduous forest zone of Côte d'Ivoire to assess soil microbial functioning and soil organic carbon (SOC) stocks in varying tree stands, and to determine whether complex tree stands can mimic the natural forest in terms of these soil attributes. Tree plantations studied were monocultures of teak (Tectona grandis) and full-sun cocoa (Theobroma cacao L.), and a mixture of four tree species (MTS) with Tectona grandis, Gmelina arborea, Terminalia ivoriensis and Terminalia superba. An adjacent natural forest was considered as the reference. Each of these LUS had five replicate stands where soil (0-10 cm depth) samples were taken for physico-chemical parameters and microbial biomass-C (MBC), microbial activities, MBC/SOC ratio and metabolic quotient (qCO2). SOC and total N stocks were also calculated. The C mineralization rate (mg C-CO2 kg-1) and mineral N concentration (mg kg-1) drastically declined in the monocultures of cocoa (154.9 ± 29.3 and 49.8 ± 9.8, respectively) and teak (179.6 ± 27.1 and 54.1 ± 7.3) compared to the natural forest (258.4 ± 21.9 and 108.7 ± 12). However, values in MTS (194.7 ± 24.6 and 105.4 ± 7.4) were not significantly different from those in the natural forest. Similarly, SOC stocks in MTS (28.8 ± 1.9 Mg ha-1) were not significantly different from those recorded in the natural forest (32.9 ± 1.7 Mg ha-1) whereas teak (25.4 ± 1.7 Mg ha-1) and cocoa (23.1 ± 3.4 Mg ha-1) exhibited significantly lower values. Despite the acidic soil and recalcitrant litter conditions, increased MBC/SOC ratio and decreased qCO2 were recorded in the monocrops, suggesting a probable increase in the fungi/bacteria ratio. The complex MTS stand was found to mimic the natural forest in terms of soil microbial activity and organic status, due to the provision of a diversity of litter quality, which may serve as a basis for developing a climate smart timber system in West and Central Africa.

Nutrient cycling has been widely studied in tree plantations. However, studies on the observed negative changes relative to natural vegetations and how these could be capitalized toward setting up ecofriendly agroecosystems are rare. This study was conducted in Central-West Côte d’Ivoire to establish the changes in carbon and macronutrient cycling occurring in full-sun cocoa (Theobroma cacao L.) and Teak (Tectona grandis) relative to primary forest and subsequently make cocoa agroforestry-based recommendations. Leaf litterfall and associated carbon and macronutrient inputs, rates of leaf litter decomposition, and macronutrient release were assessed. In addition, soil (0–10 cm depth) chemical and microbial parameters were evaluated. Litterfall yields were 10.6 ± 2.0, 9.3 ± 0.8, and 10.1 ± 0.4 Mg dry mass ha−1 year−1 in forest, cocoa, and teak, respectively. Compared to the forest, the cocoa plantation supplied lower inputs of C (−736 kg ha−1 year−1 or −15.5%) and N (−75 kg ha−1 year−1 or −27%), similar P, but greater K. Similar quantities of C and N were recorded in the teak plantations and the forest. However, the teak plantation supplied lower K but higher P inputs than the forest. Cocoa leaf litters decomposed at the same rate as those of the forest (k = 0.3 month−1) but faster than the teak’s, the initial leaf litter N:P ratio being the most influencing factor. Except for P, the macronutrient release from cocoa and forest litters exhibited similar patterns and rates, which were significantly different from those observed in the teak leaf litter. Soil C mineralization rate and mineral N concentration drastically declined in both tree plantations, the greatest gap occurring in cocoa (Cmin: −40%, mineral N: –54.2%) due to lower litter Ca input and soil acidity. Teak appears to be a good candidate for shade as it may compensate for the deficit in litter C (and N, to a lesser extent) supply exhibited by cocoa relative to the forest. The trends in microbial activity underscore the need to grow cocoa in association with trees that provide quality litter materials, for improved cocoa nutrient availability and faster C storage in soil. In line with this, some suggestions were made and discussed. This study can be used in support of developing an efficient cocoa agroforestry system in West Africa.

Earthworms are an important soil taxon as ecosystem engineers, providing a variety of crucial ecosystem functions and services. Little is known about their diversity and distribution at large spatial scales, despite the availability of considerable amounts of local-scale data. Earthworm diversity data, obtained from the primary literature or provided directly by authors, were collated with information on site locations, including coordinates, habitat cover, and soil properties. Datasets were required, at a minimum, to include abundance or biomass of earthworms at a site. Where possible, site-level species lists were included, as well as the abundance and biomass of individual species and ecological groups. This global dataset contains 10,840 sites, with 184 species, from 60 countries and all continents except Antarctica. The data were obtained from 182 published articles, published between 1973 and 2017, and 17 unpublished datasets. Amalgamating data into a single global database will assist researchers in investigating and answering a wide variety of pressing questions, for example, jointly assessing aboveground and belowground biodiversity distributions and drivers of biodiversity change.

Integrated soil fertility management options are being promoted as ways of adapting agricultural systems to sustain yields on highly degraded and poor soils encountered throughout West Africa. The efficiency of these practices may be affected by high variability and uncertainty associated with seasonal rainfall, especially for areas such as Côte d’Ivoire, where intra-seasonal rainfall has been observed to change from 1 year to another. The DSSAT crop simulation model was used in this study as a tool to evaluate the impacts of soil improvement options including inorganic fertilizer and conservation agriculture generating higher carbon sequestration and crop yield in maize agro-ecosystems. The model was calibrated using agronomic data for three cropping seasons from 2009 to 2010 in Goulikao (Center-West Côte d’Ivoire) and Ahérémou 2 (Central Côte d’Ivoire), respectively and validated against independent datasets of yield of 2003–2004 seasons in the buffer zone of the Lamto Natural Reserve, Central Côte d’Ivoire. The model predicted average maize yields of 1454 kg ha−1 across the sites versus an observed average value of 1736 kg ha−1, R2 of 0.72, and RMSE of 597 kg ha−1 after the default values for stable soil organic matter fraction used in the model were substituted by the estimated one. For the validation, the predicted higher maize yield was consistently related to fallow biomass inputs and different rates of fertilizer, thus generating a RMSE of total aboveground biomass and grain yield of 606 kg ha−1 and 350 kg ha−1, respectively. The impact of fallow residues and cropping sequence on subsequent maize yield was simulated and compared with conventional fertilizer and control data using 12 years historic climate time series. We conclude that soil fertility improvements through conservation agriculture can sustain grain yield at the same level as conventional inputs of urea against larger climate variability. However, this system may be substituted by conventional agriculture when climate forecast reveals a dry cropping season year.