Work package numberWP4Lead beneficiaryToulouse III – Paul Sabatier University (UT3)
TitleImpacts in relation to nitrogen uses  
Start month1 (Feb 2020)End month48 (Jan 2024)


Atmospheric emission, deposition and transport of nitrogen compounds are greatly affected by climate and land use variability and change. In turn, atmospheric chemical forms of nitrogen can result in direct and indirect radiative forcing (e.g. N2O, aerosol nitrate) and contribute to photo-oxidant chemistry (via NOx) which further affects concentration of major greenhouse gases, and pollutants such as ozone. Finally ecosystems are impacted by direct nitrogen deposition, rainfall pH and other chemicals controlled by nitrogen concentrations, with possible longer term feedback on climate.

Two approaches are developed in this WP, (i) Earth system modelling to study the impact on atmospheric chemistry and climate, and (ii) the Steady-State Mass Balance model (SSMB) to estimate the N critical load on ecosystems. N budgets calculated in task 1 will give additional information to task 2. The impact on food security, agricultural sustainability and Nitrogen Use Efficiency (NUE) will then be assessed in task 3, by combining knowledge resulting from task 1 and task 2 concerning the impacts on ecosystems. Indeed, Nitrogen, one of the major plant nutrients, is deficient in over 80% of African agricultural soils due to insufficient application of fertilizers and organic manure, whereas it is in excess in forest soils. The current yield gap is partially related to such deficiencies and leads to the chronic food insecurity in sub-Saharan Africa. Poor crop stands result in minimum land cover and consequently soil erosion, particularly under conventional tillage.

Description of work and role of partners

Task 4.1: Interactions with atmospheric chemistry and climate (Lead Toulouse III – Paul Sabatier University (UT3))

Earth system models are developed in order to apprehend the complex interactions and the response of the system to external perturbation such as anthropogenic emissions, climate and land use change. The objective of this task is to develop and use such a system with a special focus on African ecosystems. The main aspects to be studied as part of INSA deal with:

  • Developing and optimizing the nitrogen cycle representation in a system which couples regional climate, atmospheric chemistry and biogeochemical processes (based on the existing regional climate modelling system) using available observation data and outcomes of INSA activities from WP2 and WP3
  • Characterizing the regional N budget and howit is controlled by regional climate and anthropogenic development, depending on emissions. Characterizing theassociated variability and possible trends of this budget over the historical period (typically 1970/2020, and 1990/2020 for emissions),
  • Assessing the impact of nitrogen cycle processes on the regional atmospheric chemistry including N2O, NOx, O3, and aerosol nitrates concentrations. Characterizing these impacts in terms of air quality and radiative forcing,
  • Performing projection of the possible evolution of N cycle and impacts for African ecosystems following CMIP6 climate and land use change scenarios, with associated emissions developed in T3.5. Computing centre in Félix-Houphouët-Boigny University (FHBU) and skills of UT3, and FHBU partners in computing will be reliable inputs. Institut Sénégalais de recherche agricole (ISRA) will bring knowledge onnitrogen emission parameterizations.

Task 4.2: Impacts on natural ecosystems, biodiversity, eutrophication and critical loads (Lead Toulouse III – Paul Sabatier University (UT3))

Modelling of critical loads has been applied mostly on temperate ecosystems by UT3-EcoLab, but far less developed in tropical ecosystems. As mentioned by Bobbink et al (2010) in Africa, “reductions in plant diversity by increased atmospheric N deposition may be more widespread than first thought”. This task will use the results of data synthesis from WP2 and WP3 on N stocks and fluxes. N budget (leaching, N immobilization, drainage, N uptake by vegetation, denitrification, emissions, and atmospheric deposition) will be calculated at study site scale, and extrapolated at the ecosystem scale, by using spatialized ecosystem mapping (soil type, bedrock, vegetation) and considering environmental conditions (drainage, precipitation).

As a first approach, the SSMB will be used to assess critical loads of atmospheric nitrogen. This approach is based on the determination of a critical drainage flux of nitrogen relevant for soil and vegetation; the critical nitrogen concentration will be estimated from the literature data and expertise from the project. This critical load of N will be compared with deposition flux estimates at the site and regional scales with the expertise of FHBU and ISRA. Using this steady-state mass-balance approach a first approximation of nitrogen critical loads, of the excess of N deposition by comparing with current deposition fluxes at various scales in different areas of the African continent, will be addressed. By integrating these data with the various fluxes estimated in WP 2, 3 and 4, the ability of the ecosystems to adapt to nitrogen deposition changes, particularly regarding vegetation cover, will be discussed at the final step of the project.

Task 4.3: Impacts of food security, agricultural sustainability, and nitrogen use efficiency (Lead: Institute of Agricultural Research & Training in Nigeria (IAR&T)

Optimizing the use of improved seeds, fertilizers, organic amendment (e.g. manure), liming material, and water management, and importantly adapting them to local conditions is critical and requires further investigations to develop site specific N fertilizer recommendations taking into consideration local biophysical conditions and crop N requirements. To optimize N use efficiency of applied N, Integrated Soil Fertility Management (ISFM) must address the need of balanced fertilization, improve the physical conditions of the soil including organic matter (recycling of various organic amendments) and microbial activity. Sustainability of the agricultural sector in Africa requires scaling up and adoption of holistic solutions including good agronomic practices and enabling environment (e.g. advisory services, financing mechanisms, policies and markets). INSA will evaluate the current N state in focused studied regions in tasks 4.1 and 4.2, and relate it to the agronomic efficiency of applied N, developed in T3.3 and T3.4, taking into consideration various scenarios of N management. A strong link between this task and task 5.3 on communication with stakeholders and policy makers will be built thanks to the expertise of International Institute of Tropical Agriculture (IITA) and the Kenyan Ministry of Water and Sanitation. INSA shall be the place to reconcile agricultural development (data obtained from University of Ghent and IAR&T works) and wise use of N resources and provision of a platform for sharing experiences with participants from various countries, and build linkages for effective collaborations (IITA and IAR&T expertise) with different institutions for the management of multi-stakeholder N partnerships in Africa.

Description of deliverables

D4.1: Synthesis of existing data on impacts of excess of nitrogen on ecosystems (month 26, March 2022)

D4.2: Quantification and analysis of the impact of interactive nitrogen emissions on atmospheric chemistry and regional radiative (month 30, July 2022)

D4.3: Calculation of critical loads using SSMB, comparison with deposition fluxes at the site scale and assessment of the sites in excess of nitrogen deposition (month 33, October 2022)

D4.4: First tests of a regionalization of the SSMB approach (month 40, May 2023)

D4.5: Projections and analysis of the evolution of the regional N cycle under the effect of climate change, emission change and land use change in RegCM (month 42, July 2023)

D4.6: Synthesis between earth system modelling results and studies on Nitrogen Use Efficiency and agriculture (month 45, October 2023)