"Farmers need fertilizer."

It sounds obvious.

Fertilizer adds nutrients to soil and can increase crop yields. In a continent where agricultural productivity remains a major concern, increasing fertilizer use can appear to be a straightforward solution.

But there is a problem with simple solutions.

What if fertilizer doesn't always make economic sense for the farmer?

Researchers Ellen McCullough, Julianne Quinn and Andrew Simons investigated precisely this question across sub-Saharan Africa. Their 2022 study in Nature Food examined how fertilizer profitability varies according to factors including rainfall, temperature, soil conditions and the relationship between fertilizer and maize prices. They used experimental maize data alongside environmental information to model how fertilizer investments could perform across different locations.

The results reveal an important complication.

Fertilizer profitability was robust in some areas, but not in roughly one-quarter of the analysed area under the study's profitability criteria.

Why does this matter?

Imagine being a smallholder farmer with limited capital.

You borrow money or use your savings to purchase fertilizer. You apply it to your field expecting higher yields.

But then rainfall is poor.

Or soil conditions limit the response.

Or fertilizer prices rise.

Or maize prices fall.

You may harvest more—but still fail to earn enough additional income to justify the investment.

This is why agricultural policy cannot simply say:

"Farmers need more fertilizer."

The more useful question is:

"Where, when and under what economic and environmental conditions does fertilizer actually pay?"

That distinction could be critical for African agricultural policy.

Input subsidies, fertilizer distribution programmes and agricultural financing schemes can involve enormous public resources. If they are designed without considering local climate, soil conditions, input prices and crop prices, governments may spend money encouraging farmers to make investments that are not equally profitable everywhere.

This does not mean fertilizer should be abandoned.

Quite the opposite.

It means fertilizer policy needs to become more intelligent and more geographically specific.

Africa is not one farm.

The continent contains enormous differences in soils, rainfall patterns, market access, infrastructure and farming systems.

A national agricultural policy may be politically convenient, but agricultural reality is local.

The research therefore offers a broader lesson:

A productive input is not necessarily a profitable input.

And for a smallholder farmer operating on thin margins, that difference can determine whether an intervention improves a livelihood—or increases financial risk.

Should African governments stop promoting agricultural inputs uniformly and instead tailor fertilizer support to specific soil, climate and market conditions?