How Biochar Actually Works

Biochar is sold with a lot of big promises. The honest place to start is with what the research has actually established, because the evidence is clearer — and more useful — than the marketing.

Here is the headline most biochar advertising leaves out. When researchers pool together the hundreds of trials run on biochar around the world, the average crop yield response is small — on the order of a few percent — and a large share of individual trials show no significant yield gain at all. Read quickly, that sounds like a problem.

It is not. It is the single most important thing to understand about biochar: it does not do a little good everywhere. It does a lot of good in specific conditions and very little in the wrong ones. Average those two outcomes together and you get a small, misleading number. The science is really about knowing which situation you are in.

What biochar actually does in the soil

Before the yield numbers, it helps to know the mechanisms — and these are well established. Biochar is not a fertiliser. It is a stable, porous carbon structure that changes how soil behaves in four main ways:

It raises pH on acidic soils. Most biochar is alkaline. Worked into acidic soil, it neutralises acidity, frees up phosphorus that acidic ground normally locks away, and reduces the aluminium toxicity that stunts roots. This "liming effect" is one of the most consistently measured benefits in the literature.

It holds onto nutrients. Biochar's enormous internal surface area gives it a high capacity to grab and store nutrients (a property soil scientists call cation exchange capacity), so they stay in the root zone instead of leaching away with the rain.

It holds onto water. That same sponge-like porosity lets sandy, free-draining soils retain more moisture between rains.

It shelters soil life. The pore network is a physical habitat for the microbes and fungi that healthy soil depends on.

Biochar is not plant food. It is the structure that makes the soil — and the nutrients you add — work harder.

Where the evidence is strongest

Because those mechanisms fix specific problems, the largest and most reliable yield gains in the research show up exactly where those problems exist:

Acidic, weathered tropical soils. This is biochar's home ground — the same kind of soil that built terra preta. Meta-analyses report average yield gains of around 25%, and up to roughly 40% or more, on low-nutrient acidic tropical soils. Much of West Africa's farmland fits this description precisely.

Sandy, leached soils. Where soil cannot hold water or nutrients, biochar's structure does measurable work retaining both.

Contaminated soils. Biochar reliably binds heavy metals such as cadmium and nickel, holding them out of crops — an effect that strengthens as the char ages in the ground.

The pattern is consistent across the literature: the worse the starting soil, the more biochar helps.

Where the science says it disappoints

The same research is just as clear about where biochar underperforms — and being honest about this is what separates a real soil tool from a miracle cure.

Already-healthy or alkaline soils. If soil is rich and near-neutral, biochar has little to fix; above about pH 7.5 its alkalinity can even push micronutrients out of reach.

Application rates that are too low. The research-backed rates run from roughly 5 to 50 tonnes per hectare. Products promising big results from a few pounds per acre are operating hundreds of times below any dose the science supports.

Biochar applied alone, without nutrients. This is the most important caveat for any first-time user. Fresh biochar is a holding structure, not a nutrient source. Added on its own to soil that is already nutrient-poor, it can spend its first season absorbing what little is there — and yields can dip before they recover. The literature is consistent on this: biochar's biggest, most dependable gains come when it is paired with fertiliser or compost, not used as a substitute for them. The char makes the nutrients go further.

A small trial of our own

The global research is the real evidence base. But to see the fertiliser-pairing effect on a crop our region actually grows, we ran one small field trial on waterleaf (Talinum triangulare) in Ugep, Cross River, on acidic sandy soil over a single five-week cycle.

The pattern is the same one the literature predicts: biochar on its own held the crop back in its first season, a low dose of fertiliser alone barely moved the needle, but the two together did far more than either could alone — the porous char holding the nutrients in the root zone instead of letting them wash through the sandy soil. One small trial cannot prove that. The hundreds of trials behind it are what make it believable.

What this means for West Africa

Put the evidence together and the practical guidance is simple. On the acidic tropical soils common across West Africa, biochar is one of the better-supported soil amendments there is — provided it is applied at a real rate and paired with nutrients rather than used in their place. Judge it over seasons, not on its first few weeks.

There is a second story underneath the first. The biochar in that trial was made from agricultural residues — palm kernel shells, cashew shells, sawdust — the same waste streams mills across the region burn or dump today. Turned into biochar, that residue does two proven jobs at once: it improves local soil, and it locks away carbon that earns verified carbon revenue on international markets.

That is the model BIG is built on — and it is the same lesson the Amazon taught two thousand years ago, now backed by modern science: the right char, on the right soil, paired with the right nutrients. For the full backstory, read "The 2,000-Year History of Biochar."