Using isotopes to build resilience to climate change in the Great Lakes Region

It is predicted that climate change will cause an increase in frequency and duration of dry spells in Central Africa, the target region of the Consortium for Improving Agriculture-based Livelihoods in Central Africa (CIALCA). This will lower yields of cassava and banana consumed daily by approximately 6 million people in the highlands of Burundi, the Democratic Republic of Congo (DRC) and Rwanda.

To cope with problems of drought stress in cassava and banana cropping systems, stable isotope techniques based on carbon-13 or 13C (related to water use efficiency) and oxygen-18 or 18O (related to stomatal conductance) are being developed by the Soil and Water Management & Crop Nutrition (SWMCN) Laboratory of the Joint Food and Agriculture Organization of the United Nations/ International Atomic Energy Agency (FAO/IAEA) Division of Nuclear Techniques in Food and Agriculture in Seibersdorf, in close collaboration with the International Institute of Tropical Agriculture (IITA), the University of Leuven (Belgium) and the University of Natural Resources and Life Sciences (Austria).

Once these techniques are established and validated, they will help in decision making processes related to variety selection, choice of planting time and fertilizer application to counteract the effects of drought on cassava and banana productivity.

In 2018, the focus of the research activities coordinated by the Joint FAO/IAEA Division was on how to sample leaves of cassava to assess water use efficiency based on 13C and 18O stable isotopes.

Cassava leaf sampling in the nutrient omission trials (NOT) for carbon-13 and ICP-OES analysis

One year later, in 2019, the emphasis was further laid on the understanding of the drivers of water use efficiency in cassava, with emphasis on soil fertility, in particular potassium availability in the soil. Therefore, a set of experiments focusing on the application of potassium to alleviate drought stress was carried out in the SWMCN greenhouses. Cassava plants, originating from Democratic Republic of Congo, were grown on sand substrates with nutrient solution either high or low in potassium. Water use was monitored every other day by weighing the pots and water content adjusted to field capacity.

In total 121 nutrient omission and planting scheduling trials were implemented to better understand how varieties, planting time and fertilizer management can help make cassava production more climate-resilient. Close to 3000 leaf samples have been taken for stable isotope and ICP-OES analysis, allowing to evaluate also the role of fertilizer application in drought tolerance and water use efficiency.

Cassava storage root, stem and leaf sampling in the NOT trials for oxygen -18 analysis

Further, an IAEA funded regional Technical Cooperation Project on ‘Enhancing productivity and climate-resilience in cassava-based systems through improved nutrient, water and soil management (2020 – 2023)’ was approved and was supposed to start in 2020 but delayed due to COVID 19. About 15 targeted countries from West, Central and East Africa will participate in this project, focusing on capacity building in the use of isotope and related conventional techniques for climate-smart and sustainable cassava production.