How Human And Animal Waste Could Feed Africa’s Fields
On the edge of Ngundu Growth Point in Zimbabwe’s Masvingo Province, a sour smell hangs over the small stream that snakes past the business centre. It comes from an unlined dumpsite and an overworked sewer pond. Just 10 kilometres away, communal farmers are paying cash for chemical fertiliser to top-dress their maize.
Two different worlds, divided by a short dusty road – and the same missed opportunity.
A new study from Cornell University argues that what we call “waste” could, in fact, replace most synthetic fertilisers used in modern agriculture. While the research focused on the United States, its message resonates strongly from Chiredzi to Chipinge, and from Lagos to Lusaka: the nutrients we flush, pile, and throw away could be feeding our crops.
What Does The Study Actually Say About Fertiliser Waste?
For decades, industrial farming systems worldwide have relied heavily on synthetic fertilisers to keep yields up. Nitrogen, phosphorus, and potassium – NPK – arrive in bright bags, often imported, always expensive. Yet farms themselves already sit inside a natural nutrient cycle, which human systems continue to ignore.
The Cornell team mapped that cycle carefully. They examined how much usable nutrient is locked up in two streams: animal manure and human waste. Their conclusion is startling in its simplicity.
If those nutrients were fully recovered and reused, they could supply all the nitrogen needed for U.S. agriculture and about half of its phosphorus requirements. In economic terms, that translates into fertiliser worth billions of dollars every year [SOURCE REQUIRED: value estimate].
“This is a coordination problem, not a resource problem,” said study co-author Professor Chuan Liao, quoted by Earth.com. “Even considering the real-world constraints, there’s still a substantial amount of nutrients that can be economically redistributed to meet crop needs.”
FFA Explainer:
Synthetic fertilisers are industrially produced products that provide plants with nutrients such as nitrogen and phosphorus. They are highly concentrated and fast-acting, but their manufacture consumes a lot of energy, and excess use can pollute rivers, dams, and groundwater.
The core finding is clear: the planet does not have a nutrient shortage. It has a nutrient management problem.
Where Are The Nutrients, And Where Are The Farms?
The way nutrients move today is deeply uneven. Liao and colleagues show that nutrients tend to concentrate in places with dense human populations and large livestock operations. Think peri-urban settlements, big piggeries, or intensive poultry belts.
Meanwhile, major grain-producing regions are often far away from these nutrient-rich areas. In the U.S., the study highlights the Midwest and parts of the Great Plains as examples: huge maize and soybean belts that still rely heavily on synthetic fertilisers because they lack nearby natural nutrient supplies.
African farmers know this pattern too, even if they don’t use the word “nutrient”. In Harare, Bulawayo, Nairobi, and Accra, sewage ponds and dumpsites struggle with overflows, while rural communities complain of tired soils and the rising price of urea and Compound D.
What the Cornell work adds is a sharper, quantified picture: the nutrients are already there, just not where or how farmers can use them.
Can Waste Be Used Close To Where It Is Produced?
Despite the national-level imbalance, the study finds cause for optimism at local and regional levels. A large share of nutrients can be reused close to where they are generated, especially when farms sit near towns or livestock operations.
The researchers created detailed maps tracking both waste generation and crop demand, across multiple crops and regions. Those maps revealed many opportunities for “short-distance” recycling – moving nutrients within a district or between neighbouring regions, rather than hauling them across an entire country.
The picture will feel familiar to farmers in Mashonaland East, where broiler producers, piggeries, and maize farmers all share the same landscape. Instead of shipping in fertiliser from ports or distant factories, nearby fields could, in principle, be nourished by nearby waste.
It’s a simple idea, but it demands organisation: safe collection, proper treatment, and predictable logistics.
FFA Explainer:
Nutrient recycling means collecting nutrients from waste streams (like manure, crop residues, or sewage), treating them to make them safe and stable, and then applying them back to fields as fertiliser. It closes the loop between cities, livestock, and croplands.
How Is Pollution Linked To Social Inequality?
The Cornell study goes further than agronomy. It points to a powerful connection between where nutrients pile up and who bears the cost.
Areas with excess waste – often low-income neighbourhoods or marginalised rural communities near industrial livestock – are more exposed to pollution as nutrients leak into rivers, lakes, and groundwater. Overloaded sewer ponds contribute to algal blooms and fish kills. Unmanaged manure heaps attract flies and smell, affecting health and dignity.
By contrast, regions that lack natural nutrient supply depend heavily on synthetic fertilisers. These chemicals, if overused or misapplied, can degrade soils, acidify fields, and wash into water bodies. Again, it is often poorer farmers who pay twice: once for the fertiliser, and again for the damaged environment.
“The nutrient inequality seems to mirror social inequality in a large sense,” Liao said. “So potentially fixing the nutrient flow can promote environmental justice.”
For African governments working towards AU Agenda 2063 and the UN Sustainable Development Goals, the implication is sharp: how we move fertiliser is also about who breathes clean air, who drinks clean water, and whose children grow up healthy.
How Would A Local Waste-To-Fertiliser System Work?
Instead of imagining one giant national network moving sludge across thousands of kilometres, the Cornell team argues for smaller, decentralised systems.
Processing waste near its source – in or close to the town, farm, or settlement where it is produced – and then applying it to nearby fields can keep costs down and nutrients cycling efficiently.
A simple example is a livestock farm surrounded by cropland. With the right infrastructure, manure from cattle, pigs, or chickens can be collected, processed, and spread back onto the fields as organic fertiliser. No cross-country trucking. No imported nitrogen.
This is already happening, in small ways, across Zimbabwe. Near Banket, mixed farmers commonly use cattle kraal manure on maize and groundnuts. In Domboshava, vegetable growers line up for chicken litter from nearby poultry units. The difference – as the Cornell study suggests – is scale, safety, and coordination.
FFA Explainer:
Decentralised waste systems are small to medium facilities that handle waste locally instead of sending everything to one big central plant. They’re often better suited for rural districts, growth points, and small towns, where transport distances are short and farmers are close by.
What Kind Of Coordination Is Needed?
“We’re advocating for a decentralised system, so that waste can be processed locally,” Liao said. “But in order to do this, we need to coordinate across different sectors such as agriculture, waste and energy. The technology is there, but we need governance and infrastructure to scale up to the entire U.S.”
Replace “U.S.” with “Zimbabwe” or “Africa”, and the message still holds.
To turn human and animal waste into safe, reliable fertiliser, several players must move together:
- Local authorities manage sewage ponds, landfills, and by-laws.
- Water and sanitation utilities handle treatment technologies.
- Farmers define when, how, and in what form they need nutrients.
- Energy agencies can tap biogas from waste, improving economics.
- Private companies and co-operatives can run processing and distribution.
For governments pursuing Zimbabwe’s National Development Strategy 1 (NDS1), this kind of coordination could support several objectives at once: food security, climate resilience, rural jobs for youth, and cleaner towns.
An example of such cross-sector work is emerging in parts of East Africa, where utilities and municipalities are exploring treatment of faecal sludge into pellets or compost that can be marketed to farmers [SOURCE REQUIRED: regional case study]. Zimbabwean municipalities, working with the Ministry of Lands, Agriculture, Fisheries, Water and Rural Development, could follow similar paths.
Can Waste Really Reduce Reliance On Chemical Fertilisers?
The Cornell study appears at a moment when global fertiliser markets are volatile and costly. Energy prices, geopolitical tensions, and shipping disruptions have all pushed up the cost of urea and phosphates in recent years. Liao warns that supply-chain shocks – he references conflict in Iran – can quickly translate into food insecurity.
“Excessive use of synthetic fertilisers leads to water pollution, and the production itself generates more emissions – it’s a very intensive process,” he said.
By contrast, reusing existing nutrients offers a more stable, potentially cleaner path. The waste will keep coming, whether or not global trade routes are open. Every human settlement and every herd produces it daily.
Of course, the shift cannot happen overnight. It requires investment in:
- Safe treatment technologies for human waste and sludge.
- Storage and spreading equipment that smallholders can afford.
- Standards, to assure farmers that the product is safe and consistent.
- Training, especially for women and youth farmers, on how to integrate organic inputs into their fertiliser plans.
Yet the core advantage remains: instead of importing nutrients locked up in gas-based fertilisers, countries can harvest nutrients they already have at home.
What Does This Mean For Smallholders In Zimbabwe And Beyond?
On a small wheat plot in Nyanga, or a groundnut field in Gokwe, the idea of “human waste as fertiliser” might feel distant, even risky. Concerns about smell, disease, and social acceptability are real. Any system using human excreta must meet strict health safeguards.
But smallholders are already experts at recycling nutrients. They compost crop residues, recycle cattle manure, and even rotate livestock through fields to drop dung directly onto the soil. The Cornell study essentially says: with proper treatment and coordination, cities can join that cycle.
Organic fertiliser use is already rising, driven by cost and climate pressures. If municipalities and utilities can safely convert sewage sludge and organic solid waste into certified fertiliser, farmers could gain a cheaper, locally produced option to blend with mineral inputs.
This matters for yields and for resilience. Blending organic and synthetic fertilisers can improve soil structure, water holding capacity, and long-term fertility, especially in sandy soils common in southern Africa.
FFA Explainer:
Properly treated human waste (sometimes called biosolids) can be transformed into pellets or compost that are safe for agriculture. Heat, time, and biological processes kill pathogens and stabilise the material. Strong regulations and independent testing are essential before field application.
Where Does Policy Fit Into This Picture?
For policy-makers, Cornell’s findings offer both a warning and an opportunity.
The warning: if nutrient flows continue unmanaged, pollution and inequality will deepen. Poor communities will keep living with waste, while poor farmers keep paying for imported fertiliser.
The opportunity: integrated nutrient management can link urban sanitation, climate goals, and agricultural productivity. Aligning environmental regulations, urban planning, and agricultural policy could unlock new value from what is currently treated as a burden.
Zimbabwe’s NDS1, which emphasises value addition, environmental protection, and food security, is a natural home for such thinking. So is AU Agenda 2063’s focus on modern, productive agriculture and healthy environments. Properly designed, waste-to-fertiliser systems can also support SDG 6 (Clean Water and Sanitation) and SDG 13 (Climate Action).
Practical steps could include:
- Piloting district-level projects that turn sewage and manure into safe compost for local farmers.
- Including nutrient recycling in municipal and agricultural budgets, not just waste budgets.
- Supporting youth-led enterprises that collect, treat, and market organic fertiliser products.
- Building data systems to map where nutrients are produced and where they are needed, as the Cornell team has done for the U.S.
Climate-smart agriculture conversations often focus on drought-tolerant seeds and drip irrigation. This research reminds us that smart nutrient cycles are just as important.
The Nutrients Are Already Here
The Cornell study, published in the journal Nature Sustainability, doesn’t pretend the transition will be simple. It calls for planning, infrastructure, and cooperation across sectors – agriculture, waste, and energy.
Yet its central message is disarmingly straightforward: we already have the nutrients we need.
Back in Ngundu, as the stream carries the town’s lost fertility downstream, farmers in nearby Chilonga worry about the price of top-dressing their winter maize. Between them lies a challenge – and an opportunity – that stretches from the U.S. Midwest to the sugarcane estates of the Lowveld.
If Zimbabwe’s councils, ministries, and farmers can learn to move nutrients differently, that sour smell by the stream might one day mean something else entirely: not waste, but potential.
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