Soil microbial communities underpin ecosystem functions critical for sustainable agriculture, yet our understanding of how long-term management of tropical agroecosystems shapes these communities remains limited. This is particularly the case in sub-Saharan Africa where soil health challenges are most acute for food security. Using four long-term (~20 years) experiments across contrasting agroecological zones in Kenya, we studied how organic inputs (farmyard manure, Tithonia diversifolia, Zea mays stover; applied at 4 Mg C ha-1 year-1) and nitrogen fertilizer (±120 kg N ha-1 per season as calcium ammonium nitrate) affect soil microbial communities. We combined amplicon sequencing of prokaryotic (16S rRNA) and fungal (ITS2) communities with quantification of nitrogen-cycling functional genes to examine microbial diversity, community composition, and functional potential. Site-level edaphic properties were the main correlate of community variation, namely 30% and 28% of prokaryotic and fungal β-diversity, respectively. Despite this strong environmental control, farmyard manure created distinguishable community patterns across all sites, significantly affecting 65 prokaryotic genera and achieving 96% reclassification success for fungal communities. Prokaryotic and fungal communities exhibited contrasting response patterns: prokaryotes responded predominantly to farmyard manure through enrichment of copiotrophic Bacillota (formerly Firmicutes), while fungi were sensitive to both farmyard manure and T. diversifolia green manure, recruiting distinct decomposer guilds based on substrate biochemistry. Functional gene responses were amplified at the driest, most nutrient-poor site, where farmyard manure led to a 30-fold increase in the abundance of ammonia-oxidizing bacteria compared to the control treatment. Mineral nitrogen fertilization alone did not produce distinct community composition but modestly reduced specific nitrogen-cycling genes. This demonstrates that organic resource management, not mineral inputs, drives long-term microbial community development. These findings provide decadal-scale evidence that sustained organic amendments can generate predictable microbial responses across environmentally heterogeneous tropical landscapes, informing integrated soil fertility management strategies for sub-Saharan Africa.

Climate change is projected to exacerbate food insecurity in sub-Saharan Africa (SSA) by reducing crop yields and soil fertility. Many climate change impact studies in SSA have overlooked long-term effects of soil fertility on crop yield. We evaluated maize yields under different scenarios of soil fertility (using soil organic carbon as a proxy) and climate change (considering changes in temperature, rainfall, and CO2) at four sites in SSA. Using an ensemble of 15 calibrated soil-crop models, we found a strong consensus that, without fertilization, soil fertility declines over time, impacting maize yields more strongly than changes in temperature, rainfall, or CO2. The model ensemble indicated that when accounting for soil fertility changes, the yield benefits of combined application of organic and mineral inputs increase over time, even under climate change. These findings highlight the importance of considering long-term change in soil fertility when assessing impacts of climate change and integrated nutrient management on crop production in SSA.

Soil degradation severely limits agricultural productivity and food security across sub-Saharan Africa, particularly due to declining soil functions related to nutrient cycling, organic matter turnover, and water retention. Addressing this challenge requires management practices that can regenerate and sustain these functions, as well as sensitive indicators to track progress. In this study, we evaluated the effects of crop diversification, legume integration, manure application, and their impacts on soil health across four sites representing contrasting agroecological settings in Kenya. All sites contained long-term experiments that were recently redesigned from maize monoculture to include more diversified systems, such as maize-legume rotations, maize-fodder relay, and improved intercropping. We assessed soil health indicators linked to carbon (C) cycling (permanganate oxidizable C, POXC; particulate organic matter, POM), nutrient availability (potentially mineralizable nitrogen, PMN, available N and Phosphorus, pH), and substrate-induced respiration (SIR)rates. Within one year of implementation, crop diversification had improved soil health indicators relative to a degraded control soil, although the magnitude of improvement varied by site. Sandy soils exhibited stronger increases in soil health indicators compared to clay soils. Legume integration had a stronger influence on SIR than manure inputs (evenness decreased from similar to 2.0 to similar to 1.3 in legume systems), contributing to more specialized respiration patterns linked to labile C, likely root derived substrates. Manure application generally improved available P and PMN, though effects varied by site and cropping system. Mineral N fertilizer application contributed to soil acidification (pH decreased by 0.3-0.6 units) despite recent liming but had limited effects on other soil health indicators. Microbial activity was driven primarily by cropping treatments rather than site, whereas other soil health parameters were sensitive to both treatment and site differences. Our findings highlight that integrating legumes and applying organic amendments can initiate rapid improvements in key soil properties and functions, but agroecological context and crop type strongly modulate these outcomes.

Arable soils are generally characterised by a low soil organic carbon (SOC) content, with negative consequences for soil health, crop yield and global climate. Thus, over the past decades, there has been a focus on how agricultural management practices, such as organic resource amendments, can increase the amount of SOC. To sustainably increase SOC stocks, a portion of the organic resources added to the soil has to be stabilised in persistent fractions such as mineral-associated organic carbon (MAOC). However, there is a lack of research on the magnitude of changes in MAOC in tropical agroecosystems in response to organic resource amendments. Here, we show for four long-term field trials in Kenya that the addition of large amounts of organic resources (farmyard manure or Tithonia diversifolia biomass at 4 t C ha1 yr-1 for 16 to 19 years) to maize monocropping systems had variable effects on topsoil MAOC stocks (0-15 cm depth), and no significant effect on subsoil MAOC stocks (15-50 cm depth) compared to a control treatment. The addition of mineral N fertiliser did not affect MAOC stocks at any site. Using the distinct stable carbon isotopic signature (delta 13C) of the maize crop (C4) and the Tithonia amendments (C3), we calculated that the portion of topsoil MAOC originating from Tithonia biomass was larger in the sandy (25 %-40 %) compared to the clayey soils (0.5 %-12 %), while the portion of total added Tithonia biomass that was stabilised over a time period of 16-19 years was below 7 % across all sites, or a SOC stabilisation rate of 0.8-27 g C m-2 yr-1. Using these results, we conclude that while in sandy soils the stabilisation of added OC contributed substantially to limiting SOC losses upon cultivation, this was not the case for clayey soils. These differences were due to the much lower SOC stocks in the sandy soils, compared to the clayey soils. Our results underline the challenges associated with improving soil health in sub-Saharan Africa and stress the need for more research to reliably assess if and how organic resource amendments can be stabilised over decadal time scales in highly weathered tropical soils.

Soil health is the capacity to support the production of food, feed, and fiber while delivering other essential ecosystem services. We suggest key soil health indicators and examine the three-way interactions between mineral fertilizer, crop productivity, and soil health. Given the long history of soil nutrient depletion in Sub-Saharan Africa, we conclude that mineral fertilizer use, as a core component of integrated soil fertility management, must increase and be co-applied with organic inputs to increase productivity and fertilizer use efficiency and restore and sustain soil health.

Soil health is critical for sustainable agriculture and climate resilience, yet monitoring approaches remain static and provide limited guidance on how soil conditions evolve in response to management over time. Soil health forecasting, defined here as the forward estimation of soil functions under alternative management scenarios, may have the potential to complement existing assessment approaches by providing dynamic, management-relevant soil health information. This article examines whether advances in process-based and empirical models, and their integration through hybrid approaches, could support the development of predictive soil health information relevant to agronomic decision-making. Particular attention is given to the prerequisites required for operational use, model calibration and validation, uncertainty assessment, and demonstration of decision relevance. Sub-Saharan Africa is used as an illustrative context, where soil health constraints are substantial and digital agronomic advisory systems are expanding. Rather than presenting soil health forecasting as a readily applicable solution, the article proposes a staged research pathway linking modelling advances with empirical validation and progressive integration into digital agronomic advisory systems. It is expected that strengthening these foundations could help determine the extent to which predictive soil health information could enhance soil management decisions and improve soil stewardship, as well as contribute to more sustainable and climate-resilient agricultural systems in Sub-Saharan Africa.

ABSTRACT Modern industrial agriculture is predicated largely on the production and utilization of chemical fertilizers. Although this approach has played an integral role in increasing food security in many parts of the world, the long‐term sustainability of this resource‐intensive approach is questionable. Efforts to quantify the sustainability implications of various fertilizer sources typically focus on individual elements within the larger issue of sustainability. We argue that a more comprehensive framework, one that accounts for the biophysical, socio‐economic, and political implications of fertilizer production and consumption, is necessary to direct agricultural production towards a more environmentally sustainable and socially equitable trajectory. By incorporating criteria associated with equitable access, environmental production impacts, closed loop fulfilment, and agroecosystem performance into a single framework, we hope to stimulate renewed discussion regarding how to comprehensively assess sustainable fertilizer production and use.

Problem: Low crop yields in sub-Saharan Africa mainly result from low soil fertility and insufficient nutrient inputs. A key component of Integrated Soil Fertility Management (ISFM), namely combining inputs of mineral fertilizers and organic resources, presents an opportunity to boost yields and maintain soil organic carbon (SOC) stocks in the long run. Soil-crop models help to assess the performance of ISFM under contrasting soil, climate, and management combinations. Yet, to date, most soil-crop models have been calibrated and tested in temperate conditions. Objective: Our objective was to evaluate and compare the performance of two different soil-crop models, DayCent and STICS, to represent crop yields and SOC dynamics under contrasting organic resource amendments. Methods: We used a large dataset representing 3384 cropping situations (site x season x treatment) from four long-term experiments in Kenya. Each experiment included the same treatments with the addition of two quantities of low- to high-quality organic resource amendments (high vs low C/N ratio, respectively), with (+N) and without (-N) mineral nitrogen fertilizer. Each treatment included a cropped and uncropped subplot, allowing for a unique stepwise calibration of soil and crop parameters. Results: Both models represented SOC and yield dynamics with similar accuracy across sites and treatments. They reproduced SOC dynamics well (nRMSE below 30 %) in the two clayey soils sites but not in the two sandy soils. Yet, in most sites they reproduced well SOC differences between high (Farmyard manure, Thithonia and Calliandra) and low-quality (maize stover and sawdust) organic resources. Models reproduced the average yield across sites and treatments similarly. They reproduced the positive effects of high-quality organic resources and the addition of mineral N on maize yield well. Models had similar inaccuracy in reproducing yield and yield variability under poor-quality organic resources and -N treatments. Conclusion: The stepwise calibration approach used in this study enabled highlighting the models' strengths and weaknesses in soil and plant simulations. The results suggest that the two models have similar strengths and struggle with the same problems despite having different structures. Collecting detailed plant (leaf area index, plant N uptake) and soil (water, nitrogen dynamics) in-season data from long-term experiments will be critical to exploit the full model complexity and improve their accuracy for tropical conditions.

Context Rice systems across Asia and Africa face persistent production constraints and rising climate-related stresses. Yet adaptation planning remains fragmented, with limited comparability across locations and insufficient integration of stakeholder perspectives. Decision makers increasingly need transparent, data-driven tools capable of identifying locally relevant but cross-comparable adaptation priorities. Objective This study systematically quantified major agronomic and climatic constraints in the Mekong Delta and West African Sahel rice systems and prioritised adaptation options using a structured, participatory, multi-criteria framework. Methods We applied the PAiCE (Prioritising Agronomy in Changing Environments) toolkit through 11 workshops in six countries, engaging 100 experts from 59 organisations. PAiCE integrates system characterisation, estimation of production and climate losses, adaptation longlisting and shortlisting, and multi-criteria evaluation of adoptability, implications, support requirements, economic performance, and uncertainty. In total, 99 adaptation options underwent full assessment across 5.6 million ha of rice production. Results and conclusions In the Mekong Delta, losses were driven by suboptimal planting practices, water deficits, and poor fertility and residue management. Mechanised direct seeding and in field Trichoderma straw management were consistently identified as high priority adaptations. In contrast, the West African Sahel showed highly heterogeneous constraints (e.g. temperature extremes, climate induced biotic stresses, and soil limitations) resulting in location specific adaptation priorities such as varietal change and SRI in Mali and Senegal, residue retention in Burkina Faso, and staggered planting in Nigeria. High ranking adaptations often exhibited trade offs between economic benefit and farmer adoptability or institutional support. Data certainty averaged 38%, underscoring evidence gaps, particularly for climate-related impacts. Significance As the first multi continent, comparable multi-criteria assessment of rice system challenges and adaptations, this work demonstrates the value of structured, participatory processes for identifying high impact, context sensitive adaptation pathways and supporting more effective climate resilient agricultural planning.

Context: To avoid soil fertility decline and increased greenhouse gas (GHG) emissions, it has been recommended to improve maize yields in sub-Saharan Africa with sustainable practices such as Integrated Soil Fertility Management (ISFM), instead of relying solely on mineral fertilizer. However, the yield responses and environmental trade-offs of ISFM likely depend on soil and climatic conditions. Objective: To explore this, we used the DayCent model to simulate 30-year average yields of maize monoculture across Kenya under 17 different ISFM scenarios, co-created with Kenyan smallholder farmers. We compared yields, changes in SOC stocks and N2O emissions against current baseline conditions (monocropping with minimal nutrient inputs). Methods: The scenario that best represented a 'feasible-input' level consisted of 2 t C ha-1 yr-1 of farmyard manure and 60 kg N ha-1 season-1 of mineral fertilizer. Other scenarios included different amounts (0, 1, and 2 t C ha-1 yr-1) and types of organic inputs in combination with four rates of mineral N fertilizer (0, 30, 60, and 90 kg N ha-1 season-1). The uncertainty of model predictions was quantified through Monte Carlo simulations. Results and Conclusions: The model results indicate a significant potential for yield improvements in the humid regions of western Kenya (from 3.7 to 8.1 t ha-1 yr-1) with the 'feasible-input' compared to the baseline scenario; GHG emissions per kg of yield were generally lower (the median value reduced from 0.9 to 0.5 kg CO2-eq kg-1 yield). However, in the semi-arid regions of eastern Kenya, maximum yields under any scenario were 1.1 t ha-1 yr-1, reached at inputs of 1 t C farmyard manure ha-1 yr-1 or 60 kg mineral N ha-1 season-1. The uncertainty analysis showed a high confidence in the 'feasible-input' scenario's ability to increase yields and reduce SOC losses compared to the baseline, but a high uncertainty regarding its impact on GHG emissions. Specifically, the 95% credibility intervals for the combined CO2 and N2O emissions ranged from reductions of up to 1000 kg CO2-eq ha-1 yr-1 to increases of up to 200 kg CO2-eq ha-1 yr-1. Significance: These results strongly support the use of ISFM practices to enhance maize yields and mitigate soil fertility losses, particularly in areas with sufficient rainfall. However, due to the high uncertainty surrounding simulated N2O emissions, we cannot establish with certainty whether ISFM reduces GHG emissions on a per hectare basis or increases them.

To ensure the sustainable management of tropical cropping systems, tracking changes in soil fertility and distinguishing long-term crop yield trends from season-to-season fluctuations are essential. However, a scarcity of long-term datasets for tropical systems has left a gap in understanding how soil organic carbon (SOC, used as a proxy for soil fertility) and yield co-evolve in these systems. Here, we present a unique analysis of maize yield and SOC trends in four long-term experiments in Kenya, conducted under contrasting pedo-climatic conditions. Experimental treatments consisted of yearly applications of organic resources with different C:N ratios (12 to 200) at two quantities (1.2 and 4 t C ha-1 yr-1), with and without mineral nitrogen fertilizer (240 kg ha-1 yr-1). At sites with adequate rainfall (475-600 mm in-season rainfall), long-term Maintenance of Maize yields and SOC were strongly correlated. Specifically, 74% of the variation in long-term yield trends across sites was explained by the interaction between site and the trend in SOC, increasing to 84% when adding the interaction with the mineral nitrogen fertilizer treatment. In contrast, no significant correlation between yield and SOC trends existed at the driest site (300 mm in-season rainfall). Differences in the strength of the SOC-yield relationships between treatments with and without mineral N fertilizer were significant at only one of the four sites. In addition, seasonal maize yield variability at three of the four sites was strongly influenced by seasonal mean temperature and total rainfall, overriding the effect of site fertility and SOC in any given season. However, the strength of climate effects varied between sites. We conclude that maintaining SOC is important for sustaining maize yields, but this potential can only be fully realized under favorable climatic conditions, particularly sufficient rainfall.

Weeding is a common farming practice for optimal emergence, growth and maturity of crops. Smallholders in Central Africa use a traditional hoe for weed control. This is a hard and time-consuming activity. To address this bottleneck, a study was conducted at three sites, namely Walungu, Uvira, and Mulungu in South-Kivu in the Democratic Republic of the Congo (DRC), over two growing seasons (September 2020 and February 2021). The purpose was to minimize the workload involved in weed control and boosting cassava yields via time-, labour, and energy-saving through adjusted weeding. Experiments were carried out as a split-plot design with three randomized blocks at multiple locations. Weed control was assessed for hand hoe, herbicide, and single-wheeled hoe (a weeding tool that combines manpower with improved weeding precision) in a cassava-legume intercropping system. Results show that the use of herbicide translated into about 6 times less energy use than a hand hoe, accounting for a ca. 4 times reduced weeding workload, and a reduction in weeding time up to 84%. The single-wheeled hoe use accounted for almost 61% reduction in weeding energy consumed, a reduction of 40% of the weeding time, and for about 38% of the weeding load saving. Although the three weeding methods gave statistically similar yields, it nevertheless turned out that herbicide treatment achieved the lowest cost-benefit ratio (CBR) (0.2), evoking its superiority in terms of profitability over both the hand hoe and the single-wheeled hoe. The study asserted that weed control is ‘moderately heavy’ and ‘light’ when involving the single-wheeled hoe and herbicide, respectively.

This study aimed to examine the factors driving the adoption of improved cassava seeds and fertilizers among smallholder farmers in South Kivu and Tanganyika provinces, Eastern Democratic Republic of the Congo (DRC), using data from 1317 farming households. Data were analyzed using principal component analysis (PCA) and cluster analysis by classifying farmers based on their cassava agricultural practices while capturing their preferences, attitudes, and socioeconomic characteristics. Logistic regression was then applied to evaluate the adoption of improved cassava seeds and fertilizers across different farmer-type groups. Therefore, farmers were classified into five distinct groups in both provinces. In general, for cassava-improved seed, farming experience increases its adoption by 15.1% per year in Cluster 5. At the same time, primary education boosts adoption in Cluster 1 by 17.4%, and university education raises it by 20.1% in Cluster 5. Larger land areas significantly enhance adoption by 46.9% in Cluster 4 and 79.6% in Cluster 1, reflecting the benefits of larger farms. Livestock ownership raises adoption by 26.8% in Cluster 1, highlighting the value of assets in agricultural investment. Agriculture training and income are highly effective, improving adoption by 18.2% in Cluster 5 and 8% overall. Specifically, in South Kivu, gender influences fertilizer adoption by 18.0% (Cluster 1) and 14.9% (Cluster 5) while marital status enhances fertilizer adoption and with being married raising the probability by 0.52% (Cluster 4). These findings emphasize the importance of education, gender, income resource access, and targeted interventions to improve agricultural technology adoption. Furthermore, promoting farmer engagement in agricultural activities is recommended through enhanced extension services and cooperative memberships.

Africa’s vast arable land offers immense agricultural potential, yet productivity remains constrained by climate change, soil degradation, limited technology adoption, and socio-economic barriers. This has created the need for transformative change in the agricultural sector, with soil health playing a key role in this transition. Soil health is essential for agricultural productivity, economic viability, and ecosystem resilience, while also advancing sustainability and inclusivity. Achieving these outcomes depends on effective soil management, but slow growth in fertilizer use and limited understanding of its efficiency by farmers pose significant challenges. The Africa Fertilizer and Soil Health Summit (Nairobi, May 2024) underscored the urgency of these challenges, endorsing the African Fertilizer and Soil Health Action Plan. This commentary outlines key considerations for successful implementation of the plan, highlighting enabling conditions and strategic approaches: (1) trusted multi-sectoral partnerships fostering collaboration among farmers, governments, private companies, non-governmental organisations, and donors, (2) demand-driven research and development with strong focus on measurable development outcomes, (3) targeted investments and finance effectively expanding the role of the private sector, (4) effective policy mandates relying on comprehensive policy mixes, and (5) inclusive capacity-building using gender-transformative approaches. These strategic contributions are essential to achieving sustainable, equitable agricultural transformation in Africa. The transformation will demand innovation, long-term commitment, and coordinated action across sectors to ensure impact beyond the timeframe of the African Fertilizer and Soil Health Action Plan.

Problem: Although cassava exports large nutrient amount from the soils, there is mixed evidence on its response to fertilizer. Objective: This paper aimed at better understanding variable cassava responses to nutrient application and associated soil causes. Methodology: A network of multi-location two-year on-farm trials, evaluating in contrasting DRC agroecological zones (Tshopo and Kongo Central (KC)) and in Burundi, cassava response to macronutrients (DRC and Burundi) and micronutrients (Burundi), was conducted. Two stochastic frontier models were fitted per DRC agroecological zone and per experiment in Burundi (macronutrient or micronutrient), with observation number ranging between 290 and 490 per scenario of model fitting. The best fitted model was used to estimate soil parameters' contribution to yield response and to calculate the soil-efficient yield gap (YSEG). For nutrient combination "k" and in farm "i", YSEG was calculated as ratio of yield obtained in farm "i" with "k" to the highest yield (derived from the best fitted model) attained from "k" in farms with similar soil fertility as farm "i". Results: In Tshopo, only NK-combination yielded more than no-fertilizer, while all macronutrient combinations, except PK, did in KC and Burundi. Yield response to micronutrient was remarkably poor. YSEG averaged 70%, 63 % and 54% in Tshopo, Burundi and KC, respectively, indicating that, if nutrient use had been efficient, cassava yield should have been 30-50 % higher without increasing nutrient input. Soil fertility significantly determined yield in all zones, but soil parameters effects and the way in which their effect occurred were agroecology specific. In Tshopo and for micronutrients in Burundi (i.e., low yield response), there were complex interactions of soil parameters with the applied nutrients. For instance, soil N, exchangeable K and Mg significantly interacted with applied N in Tshopo, indicating that the farms might have simultaneously optimal levels of these three soil parameters to respond to the applied N. For most of the applied macronutrients in KC and Burundi, only one soil parameter had significant interaction, indicating that farms with optimal level of that soil parameter responded to the applied nutrient irrespective of the other soil parameters' levels. In Burundi, YSEG was lower with no-fertilizer than with fertilizer application, indicating a lesser effectiveness of the native soil nutrients. Conclusion: We conclude that soil fertility management (SFM) should be at the latest stage of prioritization in Tshopo. In Burundi and KC, SFM should be key priority, with focus on improving uptake of native soil nutrients in Burundi.

In arable soils, a substantial portion of soil organic carbon (SOC) is stored below the plough layer. To develop sustainable soil management strategies, it is important to assess how they affect the quantity of SOC stored in the subsoil. Therefore, we investigated the impact of organic and inorganic nutrient inputs on SOC stocks down to 70 cm depth in a long-term field trial in Embu, Kenya. There were three organic input treatments (manure, Tithonia diversifolia residues, and maize stover) and a control treatment, each with and without the application of mineral nitrogen. These different treatments were applied to a maize monoculture over 38 growing seasons (19 years). Our results show that manure application had the largest positive impact on SOC stocks compared to the control; this effect was observed down to 60 cm depth. In contrast, Tithonia diversifolia and maize stover application led to significantly larger SOC stocks compared to the control, although this was only within the top 20 cm and 40 cm, respectively. Among the three organic residue treatments, only the application of manure had a significant effect on the SOC stock of the subsoil (i.e. the 30–70 cm depth layer). However, when considering the whole measured profile (i.e. 0–70 cm), all treatments led to significantly higher SOC stocks compared to the 91 ± 12 t C ha−1 of the control: manure had the highest stocks (120 ± 24 t C ha−1), followed by maize stover (112 ± 17 t C ha−1) and Tithonia diversifolia (105 ± 11 t C ha−1). Mineral nitrogen application did not have a significant impact on SOC stocks down to 70 cm depth. Our findings demonstrate that SOC in the subsoil comprised 48.5 % ± 1.7 % of the total SOC stocks across the 0–70 cm soil profile; however, only manure application affected subsoil OC levels, whereas other organic amendments solely increased SOC in the surface layer. Our results imply that gathering knowledge on the soil below the typically studied 0–30 cm depth layer will improve the overall assessment of agroecosystem properties, which is necessary to optimize soil system resilience, limit organic matter losses, and improve crop productivity.

Food insecurity in sub-Saharan Africa is partly due to low staple crop yields, resulting from poor soil fertility and low nutrient inputs. Integrated soil fertility management (ISFM), which includes the combined use of mineral and organic fertilizers, can contribute to increasing yields and sustaining soil organic carbon (SOC) in the long term. Soil-crop simulation models can help assess the performance and trade-offs of a range of crop management practices including ISFM, under current and future climate. Yet, uncertainty in model simulations can be high, resulting from poor model calibration and/or inadequate model structure. Multi-model simulations have been shown to be more robust than those with single models and help understand and reduce modelling uncertainty. In this study, we aim to perform the first multi-model comparison for long-term simulations of crop yield and SOC and their feedbacks in SSA. We evaluated the performance of 16 soil-crop models using data from four long-term maize experiments at sites in SSA with contrasting climates and soils. Each experiment had four treatments: i) no exogenous inputs, ii) addition of mineral nitrogen (N) fertilizer, iii) use of organic amendments, and iv) combined use of mineral and organic inputs. We assessed model performance in two steps: through blind calibration involving a minimum level of experimental data provided to the modeling teams, and subsequently through full calibration, which included a more extensive set of observational data. Model ensemble accuracy was greater with full calibration than blind calibration. Improvement in model accuracy was larger for maize yields (nRMSE 48 vs 18%) than for topsoil SOC (nRMSE 22 vs 14%). Model ensemble uncertainty (defined as the coefficient of variation across the 16 models) increased over the duration of the long-term experiments. Uncertainty of SOC simulations increased when organic amendments were used, whilst uncertainty of yield predictions was largest when no inputs were applied. Our study revealed large discrepancies among the models in simulating i) crop-to-soil feedbacks due to uncertainties in simulated carbon coming from roots, and ii) soil-to-crop feedbacks due to large uncertainties in simulated crop N supply from soil organic matter decomposition. These discrepancies were largest when organic amendments were applied. The results highlight the need for long-term experiments in which root and soil N dynamics are monitored. This will provide the corresponding data to improve and calibrate soil-crop models, which will lead to more robust and reliable simulations of SOC and crop productivity, and their interactions.

The Lake Victoria Basin (LVB) is located in the upper reaches of the Nile River Basin and is shared by five East-African countries. The population in the catchment is growing rapidly and the lake is facing several environmental problems. During the past few decades, numerous efforts have been made across the five countries, with the coordination of the Lake Victoria Basin Commission (LVBC) to reduce the loading of reactive nitrogen (Nr) into the lake and Lake Watershed. However, most of the measures envisaged to ensure long-term sustainable N management are not as easily adopted as planned. This paper reports on a review study on N flows and obstacles in achieving sustainable N management in the LVB, with the objectives of improving the understanding of the N cycle and examining the N management practices and policies that can help reduce the loss of Nr in the region. The scientific literature related to a range of N flows, N management obstacles, and options to overcome obstacles has been analyzed using N prospects developed at the global level for their potential applicability across the LVB. The study showed that an unbalanced use of N input is a serious threat to agricultural productivity leading to extreme soil N mining and degradation, with the majority of LVB farms operating within negative N balances and above the safe operating boundary for N in production systems. From the projections in N input as recommended by various stakeholders, there would likely be changes in both current yield and N use efficiency (NUE) values; however, most small-scale farmers will continue to experience low yields, which remains a challenge for food security in the area. These results suggest that scientists as well as those involved in decision-making and policymaking processes should formulate new targets for fertilizer increment to reduce the yield gap for sustainability, focusing on more integrated soil fertility as a package for nutrient management in cropping systems.

Achieving the United Nation’s 2030 agenda which aims, among other goals, to ensure sustainable consumption and production patterns, requires a sustainable resource use model deployed at scale across global food systems. A circular bioeconomy (CBE) model of resource use has been proposed to reuse of organic waste in agricultural production to enhance food security. However, despite several initiatives recently introduced towards establishing a CBE in sub-Saharan Africa (SSA), minimal scientific efforts have been dedicated to understanding the association of CBE practices and food security. This study use data from 777 smallholder farm households from DRC, Ethiopia, Rwanda, and South Africa, to examine associations between three CBE practices (use of organic waste as compost, as livestock feed, and sorting waste) and household food security. Using different regression and propensity score matching models (PSM). Result reveal that using CBE practices more likely adds a 0.203 score of food insecurity access prevalence (HFIAP), 1.283 food insecurity access scale (HFIAS-score) and 0.277 for household dietary diversity score (HDDS) among households using CBE practiced groups. Associations regarding using organic waste as compost are generally positive but insignificant, while those with sorting waste are significantly and consistently negative. Thus, CBE innovations aiming to enhance household food security could prioritize organic waste valorization into livestock feed consider socio economic aspects such as access to land, access to market, education level, using mobile phone, income and city regions where interventions took place. However, prior sorting of waste is necessary to enable effective waste valorization.