Biochar in Farming: Three Real Uses in Vertical Farming

1.1 What is biochar, and how is it made?

Biochar is made by heating plant or animal waste with very little oxygen. The process is called pyrolysis. The waste does not burn to ash. It turns into a black, charcoal-like solid.

Common raw materials, called feedstocks, include sawmill waste, straw, manure and sewage solids. The kind of feedstock and the heat used both change how the biochar behaves.

1.2 What did the UPSC ask in 2020?

UPSC’s 2020 prelims asked whether three specific statements about biochar were correct. All three were.

• What it is. Biochar is a charcoal-like material. It’s made by heating organic matter with little oxygen, a process called pyrolysis.
• In vertical farming. Biochar can be used as part of the growing medium in vertical farming, a stacked, often indoor cultivation method.
• Supporting nitrogen fixers. When biochar is part of the growing medium, it promotes the growth of nitrogen-fixing microorganisms. Studies link the gain to better phosphorus supply and lower soil acidity.
• Retaining water longer. Biochar also lets the growing medium hold water for a longer time. This comes from the same high porosity and surface area.

1.3 Is biochar really used in vertical farming?

Yes, as research material and as one ingredient. A 2024 study built a compostable growing gel for hydroponics and vertical farming. One of its five ingredients was activated charcoal made from biochar.

Vertical farms need a growing medium. The usual choices are rockwool, peat and coconut coir. Each has a drawback. Rockwool is mined and does not rot. Peat is dug from the environment and renews very slowly. Coir can carry pests.

The 2024 gel had five ingredients, so a growing medium is a mix, not one material. The authors report that activated charcoal from biochar was already a known plant growth promoter.

1.4 Does biochar help nitrogen-fixing microbes?

The IPCC lists higher biological nitrogen fixation among biochar’s possible co-benefits. The IPCC lists it as a potential co-benefit.

The reason is more complicated than shelter alone. In one greenhouse study, biochar raised nodule weight in beans by a very large margin. The study linked this to better phosphorus supply and more mycorrhizal fungi. In a field study on acid soil, the gain came from lower acidity and better molybdenum uptake.

So the exam statement is correct. But the cause is not just one thing. Some biochars also carry volatile compounds that can slow rhizobia, the root bacteria that fix nitrogen.

1.5 Does biochar help soil hold water?

Yes. The IPCC says biochar can improve infiltration and the soil’s water-holding capacity. The IPCC also lists resilience to drought among its co-benefits.

The effect is not the same everywhere. It depends on the soil and on the biochar itself.

2.1 Why does one property give three benefits?

• A sponge-like structure. Biochar’s porous structure gives it a huge internal surface area. That helps it hold water and nutrients.
• Useful beyond farming too. The IPCC says biochar can adsorb organic pollutants and heavy metals and cut odour from manure. So its uses go beyond the growing medium.
• Fits vertical farming’s needs. Biochar is being tested as one part of a growing-medium mix for stacked farms.

2.2 What do the IPCC lists say about uses beyond water?

The IPCC names several co-benefits. Biochar can improve nitrogen use efficiency. It can adsorb organic pollutants and heavy metals. It can cut odour from manure.

It can also lower nitrous oxide from soil. In paddy rice, studies show an average fall of 20 to 40 per cent in N2O.

2.3 Is every biochar the same?

No. The IPCC says effects vary with the feedstock and the production conditions. They also vary with the soil where the biochar is applied.

A farmer cannot assume that one batch behaves like another.

3.1 Why does stubble matter so much in India?

India burns a very large amount of crop residue every year. The 2014 National Policy for Management of Crop Residues gives the official estimate. India produced about 501.73 million tonnes of residue. About 140.84 million tonnes was surplus. About 92.81 million tonnes was burned.

Those figures cover all crops. Rice, wheat and sugarcane are the crops most prone to burning. The policy says burning is common in Haryana, Punjab, Uttar Pradesh and West Bengal.

3.2 What does burning cost the farmer?

The same policy gives the loss from burning one tonne of rice straw. It is about 5.5 kg of nitrogen, 2.3 kg of phosphorus, 25 kg of potassium and 1.2 kg of sulphur. Organic carbon is lost too.

Farmers burn because the gap between paddy harvest and wheat sowing is short. Clearing the field by fire is quick and cheap.

3.3 What changes if the stubble becomes biochar?

Plants are about half carbon. When residue is burnt or rots, that carbon returns to the air as CO2. When it is pyrolysed, about half of the plant’s carbon turns into a very stable solid, per the European Biochar Certificate.

So making biochar from that stubble keeps about half of its carbon in the soil. That figure is from the European Biochar Certificate. Burning sends the carbon to the air.

3.4 What do the farm benefits look like?

• Biochar can raise a soil’s water-holding capacity, and the IPCC lists this as a co-benefit.
• In nutrient-poor soil, it can lift crop yields. Reviews report an average gain of about 10 per cent, depending on the soil and the study.
• This turns a disposal problem, and an air-pollution source, into a farming input.

Read these gains with care. One large review found an average gain of 10 per cent. The averages for different groups of studies ranged from a fall of 28 per cent to a rise of 39 per cent. Another found that biochar with fertiliser raised yields 15 per cent above fertiliser alone. Biochar alone did not raise yields.

The IPCC adds that gains are most likely in sandy and acidic soils with low nutrient-holding power.

3.5 Is biochar the only alternative to burning?

No. The crop residue policy lists many options. They include mixing residue into soil, mulching, baling for fuel, feeding it to animals, and direct seeding with a Happy Seeder. Charcoal and gasification are on the list too.

Biochar is one choice among several.

4.1 Why does biochar count as climate action?

Biochar resists decomposition. Adding it to soil can lock carbon away for decades to thousands of years, a side benefit beyond its farming use.

The IPCC gives a range for how long. In soil, biochar is estimated to last from decades to thousands of years. The range depends on the feedstock and the production conditions. A conservative certification rule assumes 74 per cent of the carbon is still stored after 100 years.

4.2 What do the IPCC and the numbers say?

• The IPCC recognises biochar as a genuine carbon dioxide removal (CDR) method, not just a soil amendment.
• Each tonne of carbon in biochar equals 3.67 tonnes of CO2 (44 divided by 12), before production emissions are subtracted.
• Used at scale with sustainable feedstock, biochar could remove or avoid up to 1.8 billion tonnes of CO2-equivalent a year. That is the IPCC estimate at costs below 100 US dollars a tonne.

That 1.8 figure is the top of the IPCC range for biochar at costs below 100 US dollars a tonne of CO2. The range is 0.3 to 1.8 billion tonnes of CO2-equivalent a year. The wider technical range for 2050 is 0.2 to 6.6 billion tonnes. It covers removal plus avoided emissions. Land, water and money limit the real figure.

The per-tonne figure comes from simple arithmetic. Take the carbon share of the biochar. Multiply by 44 divided by 12 to convert carbon to CO2. Then subtract the emissions from making it. The European Biochar Certificate uses this method.

4.3 Is there a market for it?

Yes. Buyers pay for each tonne of CO2 that biochar removes. In February 2025, Quantum assessed Latin American spot prices for biochar credits at 130 to 160 US dollars a tonne. Separate data show credits from tree planting, which averaged about 20 dollars a tonne in 2025 (a separate dataset, Ecosystem Marketplace, all transactions).

One producer’s chief executive said in that report that such prices barely cover the cost of making biochar.

4.4 How is this different from burying CO2 deep underground?

Biochar stores carbon in soil as a solid. Carbon capture and storage works differently. It captures CO2 as a gas and injects it into porous rock deep underground.

At depths below about 800 to 1,000 metres, the pressure and heat turn CO2 into a supercritical fluid. It behaves like a dense liquid, so a lot of CO2 fits in the rock pores. This is the state in which CO2 is typically injected for storage. It is not plasma, an ordinary gas or solid dry ice.

The IPCC says it is likely that 99 per cent or more of injected CO2 stays put for 1,000 years at well-chosen sites. Biochar and deep storage are two different tools. Both aim to keep carbon out of the air.

5.1 What is Terra Preta?

Amazonian communities built Terra Preta long before the word biochar existed. The name means dark earth. They added charcoal to poor tropical soil. Pot sherds were found on some sites.

A 2021 study in Rondonia, citing Mangrich and colleagues (2011), gives ages of 500 to 8,000 years BP for Amazonian dark earths.

5.2 Why are these soils still fertile?

The soils hold far more black carbon than the soils around them. Black carbon is charcoal and similar material from incomplete burning. A classic 2001 study found up to 70 times more black carbon in places. The average was about four times more.

Black carbon is stable and lasts a very long time. Over time it also gains chemical groups that help it hold nutrients. That keeps the soil fertile after years of farming.

5.3 Is biochar a silver bullet?

The IPCC says the same. Biochar can improve many soil properties, but effects vary with the biochar and the soil.

6.1 What happens to the carbon in each case?

This table compares what happens to crop residue under two different choices. It is a simple model, not a field measurement.

Burning and rotting both send the plant’s carbon back to the air as CO2. Pyrolysis keeps about half of it in a stable solid, per the European Biochar Certificate. That stable half is the biochar.

The soil benefit of biochar is not guaranteed. It depends on the soil, the feedstock and whether the biochar is used with fertiliser.

7.1 What pattern do examiners keep using?

This topic gets tested by listing several claims about one material, then asking whether all of them hold up.

• UPSC CSP 2020, Q80 Biochar as a vertical-farming medium, a support for nitrogen-fixing microorganisms, and a water-retention aid — are all three correct?

The safe answer is simple. All three statements are correct. If one option says only two are correct, it is wrong.

7.2 What else could be asked?

• How is biochar produced, and with how much oxygen?
• Why does biochar help soil hold water?
• Is biochar recognised as a carbon dioxide removal method?
• How does storing carbon in soil differ from injecting CO2 underground?
• Why is turning stubble into biochar better than burning it?

7.3 Quick Q&A