Why "Just Add Fertilizer" Isn't Enough to Raise African Yields

“Fertilizer answers one question. Most African soil is asking three or four.”

It's an easy sell. A bag with a number on it, a promise that better inputs mean better harvests. That story has driven summits, subsidy budgets, and donor programs across the continent for two decades. It isn't wrong. It's just not the whole picture, and treating it like the whole picture has cost farmers real seasons and money they didn't have to spend.

The Numbers That Look Too Good to Be True

Back in 2006, African Union member states signed the Abuja Declaration, pledging to raise average fertilizer use from about 8 to 50 kilograms per hectare by 2015. The logic was sound: no region has industrialized its farming without using more fertilizer. Nearly two decades later, the AU's own 2024 assessment put the continental average at about 18 kilograms per hectare, still less than half that target and a fraction of the global average of around 135. South Sudan, Uganda, and the Comoros are still in single digits; Egypt, at the other end, is above 500.

On paper, closing that gap should be the entire fix. Ghana tested it directly. Per the country's Ministry of Food and Agriculture, its subsidy program lifted fertilizer use from 7.4 to nearly 21 kilograms per hectare between 2009 and 2016. Yields moved, but a study in the journal Food Security found the gains fell well short of what fertilizer alone should have produced and that subsidies weren't enough on their own to close the gap. It points to something the bag itself never mentions: fertilizer is a delivery system for nutrients, not a fix for what's wrong with the soil underneath it.

The Ground Was Never a Blank Slate

Here's the part that tends to get left out of the pitch. Kenya's Ministry of Agriculture and KALRO put roughly 63 percent of the country's arable land, about 7.5 million hectares, as acidic, concentrated largely in the western, Rift Valley, and central regions. Zimbabwe puts its figure closer to 70 percent. The African Union describes decades of intensive farming without adequate replenishment as leaving soils across the continent widely depleted of nutrients, organic matter, and biological life.

Acidic, degraded soil doesn't just cap plant growth; it actively fights the fertilizer sitting on top of it. Acidity locks phosphorus into forms roots struggle to reach, strips out the calcium and magnesium a plant needs to use nitrogen, and breaks down the structure that lets water and roots move through the ground. Pour a standard NPK blend onto ground that's acidic enough, and you're applying nutrients to a system that may not use them efficiently, with phosphorus fixation and similar lockup effects limiting how much the crop actually gets. Acidity itself isn't something fertilizer fixes; that takes lime or another amendment, guided by a real soil test.

There's a nastier twist too. In some systems, continued fertilizer use without addressing soil constraints produces diminishing returns, and where nothing organic goes back into the soil, it may compound the acidity problem rather than solve it: the soil degrades a little more, the response to each application shrinks a little more, and adding still more fertilizer doesn't necessarily fix what's actually wrong.

Malawi Already Ran the Experiment

Malawi's Farm Input Subsidy Program is about the closest thing Africa has to a live test of the fertilizer-first theory, and for a while it looked like proof the theory was right. After the program launched in 2005, national maize production climbed from about 1.2 million metric tons to well over 3 million within a few years.

Then, per a 2017 re-evaluation of the program by researchers Messina, Peter, and Snapp, growth leveled off: yields settled around 2 tons per hectare from 2009 onward even as fertilizer distribution kept expanding. Analysts pointed to familiar culprits: soil nutrient loss, fertilizer not reversing on its own, limited uptake of improved seed, and diminishing returns from soil that had received little besides synthetic fertilizer for years running. None of that erases what the program accomplished; it's widely credited with real food security gains. But it's a documented example of a single input hitting a ceiling that had nothing to do with the input itself.

One Blend Doesn't Fit Every Field

Underneath the acidity issue is a quieter one: most fertilizer reaching smallholders comes as a generic blend, not matched to what a field is actually short on. Soil varies even within one country: a recent mapping study across Kenya's counties found lime requirements ranging from roughly half a ton per hectare in some counties to more than one and a half tons in others. Handing out the same NPK recommendation everywhere is very likely the wrong call for much of the ground it lands on. Some fields are short on phosphorus but fine on potassium; others are missing zinc or sulfur, which a standard bag doesn't contain. Without a soil test, buying “the fertilizer” is really just an expensive guess.

And It Still Needs Everything Else to Cooperate

Even on soil that can make good use of it, fertilizer rarely works alone. It needs water to carry it to the roots, and with roughly 96 percent of sub-Saharan African cropland still rainfed rather than irrigated, an application ahead of a late or failed rainy season can accomplish close to nothing. It requires correct timing and placement relative to the seed, a skill built over seasons rather than printed on a bag.

Furthermore, it also requires soil with enough organic matter to use it: a study of 260 farms in western Kenya by Cornell and University of Nairobi researchers found fertilizer's effect on yields was far larger on soils with higher organic carbon. On roughly a third of the degraded plots studied, fertilizer wasn't even profitable at prevailing prices. And it has to actually be what the label claims: in 2024, the Associated Press reported thousands of Kenyan farmers had unknowingly bought quarry dust bagged up as fertilizer through the country's subsidy program, a case President Ruto acknowledged and pledged to remedy.

Line it all up: acidic ground, a one-size blend, unpredictable rain, thin agronomy support, and a supply chain that isn't always reliable. Fertilizer starts looking less like a fix and more like one piece asked to cover for several problems it wasn't designed to solve.

What Actually Moves the Needle

None of this is a case against fertilizer. Soils showing zero response to it are genuinely rare, and underuse remains a real constraint across the continent. It's a case against fertilizer alone, sold as the whole answer. The programs that produce lasting, compounding gains tend to stack numerous things together: a soil test before recommending a blend, lime or organic matter where acidity is the real limiting factor, and crop residue and manure going back into degraded ground. They also provide real agronomy support so farmers know not just what to buy but when and how to put it down.

It's the same lesson we bring to every engagement, whether the question is fertilizer policy in Ghana, seed and credit access in Kenya, or irrigation timing wherever rain is the bottleneck: there's seldom a single input that solves a yield problem alone. The work is diagnosing which constraints are actually binding on a given field and building the plan around what that field actually needs.