The overarching goal of PASUSI is to improve productivity, livelihoods, nutrition and household wellbeing in Ghana and Uganda, while counteracting environmental degradation and mineral depletion caused by monocultures. A major contribution of PASUSI should be to promote sustainable production of local legume crops and to increase their fraction of the daily diet. The work packages in which NMBU was particularly involved aimed at identifying nitrogen fixing bacterial strains, so-called rhizobia, suitable as inoculants for locally grown legumes to improve their yield and protein content.
Smallholder farming systems in most African countries rely on plant-based proteins for nutrition security and income. Rapidly growing populations require increased plant production, but possibilities to expand cropland are limited and there is a need for intensification of agriculture. Poor soil fertility is an increasing problem, and many areas suffer from severe soil acidification due to excessive use of urea-based fertilizers. Legumes offer solutions to these problems. They have high protein content and general nutritional value and increase soil fertility by providing nitrogen to the soil, which reduces the need for synthetic fertilizers.
Legumes fix nitrogen in symbiosis with root-nodulating rhizobia, and this nitrogen is transformed into forms into forms that the plant can use to make proteins. All combinations of rhizobia and plant type do not, however, lead to efficient nitrogen fixation and soils often compatible bacteria, especially when introducing new plant species. To ensure efficient symbiosis it is therefore becoming increasingly common to inoculate legume seeds with the "right" rhizobia before sowing. There are at present only a limited number of inoculant types on the global market, and there is need for development of new and more efficient varieties that are adapted to local agricultural conditions and plant varieties.
A dual benefit: Our recent results obtained by the PASUSI and other projects show that many rhizobia can also act as efficient consumers of the greenhouse gas N2O, which is produced in agricultural fields, especially from acidic soils. This is the third most severe greenhouse gas and the main destructor of the ozone layer. Our PASUSI partners have isolated rhizobia from relevant legumes in Ghana and Uganda and classified them taxonomically. Work is ongoing to test them for their efficiency to fix nitrogen. Our focus is on rhizobia (genus Bradyrhizobium) that nodulate soybean and Bambara ground nut, since these often can reduce N2O. Surprisingly, and contrary to other collections, almost all of them turned out to lack the gene for N2O reduction. We therefore initiated, together with our partner in Tamale, Ghana, an investigation of acidic soil from northern Ghana to try to isolate bacteria able to reduce N2O. We incubated soil slurries anoxically at an acidity that always was below pH6 and provided N2O as sole electron acceptor and managed to enrich bacteria able to grow under such conditions. The identity of these bacteria is currently being investigated both by metagenomics and by plate isolation. We foresee that this approach will provide us with interesting candidate bacteria for the development of novel types of inoculants with two beneficial roles: efficient N2-fixation and efficient N2O reduction. The long-term goal of this part of PASUSI is to initiate local production of high-quality and climate smart inoculants, adapted for different varieties of selected legumes and able to thrive in acidified soil.
Main results (NMBU partner):
- Revealed the cellular mechanism that makes bradyrhizobia with a complete denitrification machinery strong sinks for the greenhouse gas N2O
- Determined that only a few percent of bradyrhizobia from Ghanaian soils had this capacity, which highlights the importance of choosing inoculants that are not only efficient N2-fixers but also N2O reducers
- Showed that bacteria capable of N2O reduction under low pH conditions can be enriched in Ghanaian acidic soil
Feeding the world’s population in an environmentally and socially sustainable way is a major challenge for the future. Farmland should be used productively without compromising the environment. Sustainable intensification can contribute to this goal by mitigating climate change, creating better soil fertility and health and improving resilience, while providing nutritious food to humans and feed to cattle. Legumes have the capacity to fix nitrogen, when inoculated with rhizobia which can be used as biofertilizers. PASUSI will develop ways to integrate this technology in local farming systems,
evaluate the economically viability and risks connected with these crops, and support local biofertilizer production. The target crops are cowpea, soybean, groundnut and Bambara groundnut which form an important dietary basis in Ghana and Uganda, and are commonly grown by women. For a lasting impact, farmers need to be actively involved in developing sustainable intensification models. Therefore, we take a participatory approach, involving both farmers and other relevant stakeholders through establishing Innovation Platforms. We aim at a holistic approach to find integrated, lasting solutions for both production, environment and for the rural community. Producing high quality biofertilizers requires knowledge and skills about rhizobium bacteria isolation and characterization, carrier material, quality control, proper storage and distribution. Current rhizobia inoculant production chains in Ghana and Uganda will be developed in collaboration with a skilled Finnish inoculant producer and scientific partners in Norway and Finland. The laboratories in Ghana and Uganda will be equipped for the purposes and scientists trained. The expected impact is improved food security, livelihoods and economic improved income generation for small-scale farmers, increased capacity of scientific and technical staff as well as positive environmental effects and improvements in community resilience.