Bioenergy waste residues as alternatives to conventional inorganic fertilisers for sustainable food production in sub-Saharan Africa

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Soils provide, support and regulate fundamental processes in the environment, including nutrient cycling, plant growth, andhave a strong influence on ensuring purity of the atmosphere, as well as water supply and quality. Through the delivery of these ecosystem services, vital global biodiversity and, ultimately, the sustenance of the human population is maintained. However, exploitation of soils through intensive agricultural practices such as the over application of phosphorus and nitrogen fertilisers, has resulted in their degradation and, as a result, a diminishment of soil fertility, threatening future global food security.Phosphorus is a vital, non-renewable element required for crop growth, upon which agriculture is now almost entirely dependent to maintain current levels of food production. The extraction and processing of phosphorus, is also extremely environmentally damaging, and originates from a non-renewable source for which demand is rapidly increasing with no alternative available in the volume required. The production of nitrogen fertiliser is also a highly energy intensive and unstainable process, is tied strongly to the price and availability of fossil fuels. As the global population is expected to reach 9 billion by 2050, humanity faces an urgent need to balance an ever increasing demand for energy and natural resources, with the sustainable management of ecosystems and the vital services that they provide.A huge amount of waste is generated daily in African countries, much of which is dumped or landfilled. Zoomlion, a major waste management company in West Africa, have reported that there are high levels of organic content of waste generated in most African cities. In Ghana, for example, about 66% of the total waste generated is organic. African countries can transform their energy landscape through waste-to-energy, but there needs to be political and institutional commitment. It is encouraging to note that in recent times a lot of governments in Africa are gradually embracing the Green Growth development pathway, with some having already mainstreamed Green Economy actions in their national development plans. These steps signal great prospects for waste-to-energy development in Africa because Green Growth developmental actions foster economic, social and environmental development. The knock on from this is what to do with the residual waste streams from waste-to-energy processes including anaerobic digestate, organic residues from bioethanol production, ash from burning wood and soots from charcoal. In discussing this with scientists and policy makers from sub-Saharan Africa, it is clear that soils are vulnerable to degradation through environmental conditions (extremes of wetting and drying, leaching, erosion, loss of organic matter) and anthropogenic impacts (fertiliser and pesticide application, land use, deforestation, dumping of wastes and pollution). However, the maintenance of soil health and fertility is crucial to continued sustainable production of food, welfare of families and communities and local and national economies. A shift in emphasis to more sustainable farming systems, utilising recycled and recovered nutrient products, incorporating OM to improve soil structure and biodiversity, and improved crop-soil management for nutrient acquisition are needed. By using these bioenergy residues, soils will become more resilient to environmental impacts and will offer a sustainable alternative to expensive and finite made N and mined P fertilisers.