International Center for Tropical Agriculture

Abstract Soil nitrogen (N) fertility in sub‐Saharan Africa is limited by a range of environmental and edaphic factors. Some tropical perennial forage grasses, such as Brachiaria sp., conserve soil mineral nitrate (NO 3 − ) through biological nitrification inhibition. However, there is limited evidence for the field‐scale relevance of this approach under typical smallholder management regimes. We evaluated N cycling dynamics under four forage crops that included a locally scalable Brachiaria hybrid (CIAT 36087) and two farmer‐preferred fodder sources, Cenchrus purpureus (Napier grass) and Zea mays (maize). We also evaluated whether a perennial legume intercrop contributed to soil fertility or altered N cycling. We collected samples from 1 year‐old forage plantings at two locations in Rwanda across a 6‐month period that captured the transition between the rainy and dry seasons. We analyzed multiple fractions of mineral and organic nitrogen, potential nitrogen cycling activity, and organic carbon, and quantified 20 N cycle microbial functional genes. We found that annual maize, not Brachiaria , exhibited the lowest overall potential nitrification activity when averaged across timepoints, which was associated with reduced nitrifier gene abundance in one location. However, maize plots exhibited the greatest seasonal increases in potential nitrification activity and the largest declines in NO 3 − ‐N between the dry and rainy seasons. While Brachiaria did not exhibit strong field‐scale evidence for BNI, forage planting treatment was predictive of potential nitrification activity. We conclude that perennial forages present an opportunity to enhance soil N retention during seasonal variations in soil moisture in rainfed tropical smallholder systems.

Agricultural standards are increasingly vital for global trade, yet they present a complex paradox as both trade enablers and significant barriers for developing countries. This study examines the food safety and quality regulatory frameworks in Tanzania, focusing on the horticultural sector’s engagement with intra-African and European Union (EU) markets. Despite horticulture being Tanzania’s fastest-growing agricultural sub-sector, accessing export markets remains a challenge, with only 0.3% of the produce reaching international markets. Findings reveal critical gaps in national standards. For instance, while the Tanzania Bureau of Standards (TBS) has developed over 3,000 standards, those relating to fruits and vegetables often lack specific safety limits for different hazards. This regulatory void leaves domestic consumers vulnerable to food safety hazards while forcing exporters to adhere to costly private standards like GlobalGAP for EU market access. The results highlight a heavy reliance on traditional, reactive food inspections rather than more effective risk-based approaches, with inspection efforts disproportionately focused on export produce while neglecting local markets. Furthermore, regional harmonization of standards remains fragmented. While the East African Community and the African Continental Free Trade Area have made progress in aligning regional standards, Tanzania’s inconsistent implementation creates regional trade hurdles and increases compliance costs. To overcome these barriers and boost trade, Tanzania must establish robust, transparent, and harmonized food safety standards. Further improving quality infrastructure, domestic surveillance, and resource-sharing through bodies such as the African Organization for Standardization is essential to enhance Tanzania’s competitiveness in international export markets.

Rangelands are pivotal for global carbon cycling, climate regulation, and rural livelihoods, yet they are increasingly threatened by overgrazing, land-use conversion, and climate variability. Carbon storage serves as a key ecological indicator, reflecting both ecosystem health and the capacity of rangelands to contribute to climate mitigation. This study assessed carbon storage and its economic value in the Borana rangelands of southern Ethiopia between 2010 and 2024. Four major carbon pools, aboveground biomass, belowground biomass, soil organic carbon, and dead organic matter, were assessed and mapped using the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model. Results showed a total-carbon storage decline from 505.18 Mt C in 2010 to 503.93 Mt C in 2024, a net loss of 1.25 Mt C (0.25% of baseline stock). Spatial analysis revealed heterogeneous change patterns: intact bushlands and woodland retained the highest carbon densities, while heavily grazed and cultivated areas experienced substantial depletion. The associated economic valuation showed a Net Present Value loss of US$ 108.16 million over the 14-year period, with per-hectare economic value of carbon loss ranging between US$ 9,174 and 18,952. Although the magnitude of losses is relatively small compared to the total stock, the trend indicates a net release of carbon to the atmosphere, reducing the rangelands' potential to function as a carbon sink. From an ecological and management perspective, these losses serve as an early-warning signal of rangeland degradation. Continued depletion will compromise forage availability, livestock productivity, and ecosystem resilience. Implementing sustainable grazing management and integrating carbon finance and restoration initiatives could enhance local resilience, improve carbon retention, and support pastoral livelihoods, enabling Borana to transition toward a climate-resilient carbon sink, delivering ecological, economic, and social co-benefits while contributing to national and global climate objectives.

Climate change is projected to reduce land suitable for common bean cultivation in Sub-Saharan Africa. This poses serious risks to food security and livelihoods, especially as most farmers continue to grow older varieties under changing conditions. This study evaluated current and future suitability of common bean varieties in Tanzania by comparing older (>10 years) and newly released, market-preferred cultivars under a CMIP6 climate scenario. Suitability was analyzed for near-current (1970–2000) and future (2021–2040) periods using the Targeting Tool Kit and land suitability models in R. Model outputs were validated with 98.7% accuracy. By 2040, highly suitable areas are projected to decline by 4.9%, while low-suitability areas may expand by 31.2%. Older varieties (JESCA, UYOLE 03) experience the greatest reductions (–5.7%, –5.0%), whereas newer varieties show greater resilience. TARIBEAN7 shows no clear spatial advantage over Lyamungu 90. Although JESCA may decline under future climates, its strong environmental predictability makes it a valuable reference variety for breeding. Altitude, rainfall, and soil properties remain dominant factors shaping suitability. Findings highlight the need for climate-smart and area -targeted breeding, broader seed dissemination, and improved soil management to sustain production and resilience.

Nature-based solutions (NbS) are increasingly promoted as sustainable approaches for reducing drought impacts, yet evidence of their effectiveness under both current and future climate conditions remains limited. This study assessed the effectiveness of bush encroachment control in mitigating agricultural and hydrological drought severity under historical and future climate conditions (1982–2100) in the Ganale Dawa River Basin, Ethiopia. Remote sensing data, bias-corrected CMIP6 climate projections, and a Random Forest modelling framework were integrated to simulate soil moisture and runoff under SSP2-4.5 and SSP5-8.5 scenarios. Three bush encroachment management scenarios: (i) severe bush encroachment (SBE), (ii) moderate bush clearing (MBC), and (iii) intensive bush clearing (IBC) was compared with a baseline condition to evaluate their effects on drought severity. Results showed that unmanaged bush encroachment increased drought severity, whereas bush clearing interventions reduced drought severity across all climate periods. The magnitude of the response depended on management intensity and climate pathway. SBE increased agricultural drought severity by up to 21