From waste to fertiliser: Why biodigesters matter for food systems

Food security starts with healthy, fertile soils, including access to the nutrients required to produce food. Recent disruptions around the Strait of Hormuz have highlighted a structural vulnerability in global agricultural supply chains, resulting in reduced access to fertilisers and higher food prices. Reducing countries’ dependence on imported nutrients and diversifying nutrient sources can make food systems less vulnerable to external shocks. Developing biodigester markets can help farmers make better use of locally available organic resources as a source of soil nutrients.

As recent disruptions in global fertiliser markets have demonstrated, food systems are vulnerable when nutrient supply depends heavily on imports and fragile trade routes. According to IFPRI, urea prices, a key fertiliser, roughly doubled within weeks, approximately 3.9 million tonnes of urea exports from Gulf countries were suspended, and concerns emerged about prolonged shortages.  

Farmers in Africa can face greater difficulty accessing fertilisers when supplies are under pressure and prices rise in local markets. 

 Higher energy prices increase the cost of fertiliser production and raise the cost of transporting inputs to farms and food products to markets. This amplifies price effects across African food systems. Reduced access to fertilisers can affect yields, while lower yields and higher production and transport costs put further pressure on food prices and food security.   

The Strait of Hormuz is the most recent, but certainly not the only example of how African food systems are highly dependent on external factors for fertiliser inputs. COVID-19 and the war in Ukraine are other recent examples.   

Reducing dependence on imported nutrients can make food systems less vulnerable to geopolitical disruption and market volatility. These disruptions also underline the value of diversifying nutrient sources. 

Organic, locally produced fertilisers can simultaneously offer an alternative to mineral fertilisers and reduce the transport of these fertilisers.  

While we should not forget that mineral fertilisers have revolutionised agriculture and that it’s not an option to abandon them, dependence on imported mineral fertilisers can be decreased by recycling locally available nutrients. Diversification reduces vulnerability while maintaining productivity.  

This is where biodigesters enter the story. They are not a complete answer to fertiliser dependency, but they offer a practical, locally available way to make better use of organic resources already present in farming systems.  

Biodigesters process organic materials such as livestock manure and produce two outputs: biogas and bioslurry. Bioslurry contains most of the nutrients originally present in the manure and makes them more readily available for the crops. When applied directly or converted into bioslurry-enriched compost (BEC) through co-composting with crop residues or other organic materials, these nutrients can be returned to agricultural soils. This accelerates nutrient recycling within farming systems and helps increase soil organic matter, an important factor in improving soil structure and water retention. 

Biodigesters can thus turn underutilised organic resources into locally produced soil-fertility inputs, strengthening agricultural productivity, climate resilience, rural enterprise development and food security, while simultaneously providing energy and improving waste management. This aligns with growing interest in circular food systems and climate-resilient agriculture. 

In Food systems thinking, biodigesters contribute to multiple outcomes. They affect not only production inputs, but also environmental sustainability, rural livelihoods and the resilience of food supply systems. 

By supporting soil fertility and improving the efficiency of nutrient use, biodigesters can contribute to more stable crop production. In contexts where fertiliser prices become volatile or imported inputs are delayed, locally available nutrient sources can help buffer productivity shocks and strengthen the resilience of food production systems. 

Biodigester market development creates opportunities not only for farmers, but also for construction companies, masons, compost producers, transporters and advisory service providers. It can reduce expenditure on fertiliser and fuel while strengthening rural enterprise development. 

The Sahel illustrates both the challenge and the opportunity. The region’s soil fertility challenge is not only about limited access to mineral fertilisers, but also about declining soil organic matter. Even if mineral fertilisers were more affordable and readily available, many Sahelian soils would still require higher organic matter content to improve water and nutrient retention, and resilience to drought and climate variability. Biodigester-derived bioslurry and BEC can therefore help restore soil health, improve nutrient recycling and reduce unmanaged organic waste. Experiences from Burkina Faso, Mali and Niger show that biodigester market development can support these broader food-system objectives when linked to farmer organisations, finance and local enterprises. 

SNV’s three decades of biodigester sector development have contributed to the installation of more than one million biodigesters across Africa, Asia and Latin America. This experience shows that biodigesters can be scaled when market systems are developed around quality construction, after-sales services, finance, user training and enabling policies. The next step is to connect these market systems more deliberately to soil fertility, bioslurry use and food-system resilience objectives.  

We started with the argument that resilient food systems should be less dependent on imported nutrients. In the Sahel, where soils need more organic matter and farming systems are exposed to climate shocks, increasing the use of organic soil amendments is necessary for long-term resilience. Biodigester market development can be one practical entry point for addressing these challenges. 

Biodigesters will not replace mineral fertilisers, nor will they solve Africa’s food-security challenges on their own. But they can help reduce dependence on imported nutrients, recycle organic resources and strengthen soil fertility and soil health in ways that are directly relevant to food-system resilience. The challenge for governments, donors and agri-food programmes is therefore not whether biodigesters belong on the food-systems agenda, but how their contribution can be scaled and integrated more effectively. This requires positioning biodigesters within a broader market for diversified agri-input supply, particularly in the Sahel and across Africa more generally.