Does biochar really help increase crop yields? The latest scientific research

Are you wondering whether biochar—the "biological charcoal" everyone’s been talking about—really lives up to the hype? Or is it just an expensive fad that offers no real value?

The story of Mr. Nguyen Van Thanh, a farmer in the Mekong Delta, may help you gain a clearer understanding. After two years of using biochar on 3 hectares of rice fields, Mr. Thanh reported a yield increase from 5.2 tons to 6.8 tons per hectare, while reducing chemical fertilizer use by 25%. However, many others have not seen similar results and even feel it’s a “waste of money.”

So what’s the truth? Does biochar really help increase crop yields? In this article, we’ll take a closer look the latest scientific studies from 2020 to 2024...and thereby provide answers based on factual evidence, not on personal feelings or commercial advertising.

Biochar: From Controversy to Scientific Evidence

Why is biochar controversial within the agricultural community?

In recent years, biochar has become a hot topic in Vietnam’s agricultural community. On one side are enthusiastic supporters who believe it is a “miracle solution” for farmland. On the other side are skeptics who argue that biochar is merely a marketing gimmick, no different from ordinary charcoal.

This polarization stems from a variety of causes. First, the market price of biochar is quite high (ranging from 8,000 to 15,000 VND per kilogram), causing many farmers to hesitate. Monday, the quality of biochar varies; while some products are good, others are of poor quality. Tuesday, effectiveness depends on many factors such as soil type, crop type, and application method—something not everyone fully understands.

That is why it is crucial to consult independent, non-commercial scientific studies. This article will summarize and analyze the most reliable scientific evidence to help you make an informed decision.

What Is Biochar and How Does It Affect Farmland?

Definition of biochar and the production process

Biochar is a biochar product produced through the pyrolysis of biomass under oxygen-deprived or oxygen-free conditions at temperatures ranging from 300 to 700°C. Raw materials can include rice straw, eggshells, sawdust, coffee husks, or any agricultural byproducts.

Unlike conventional coal combustion (which involves oxygen), the pyrolysis process helps preserve biochar’s unique porous structure, which has an extremely large surface area—potentially reaching 300–500 m²/gram. It is this structure that gives biochar its superior properties for soil improvement.

The three main mechanisms by which biochar improves soil

1. Improve physical structure:

• Improves soil porosity, promoting better root growth
• Improve drainage in clay soil and water retention in sandy soil
• Reduces soil compaction, creating a favorable environment for microorganisms

2. Improving chemical properties:

• Increase the pH of acidic soil (biochar is slightly alkaline)
• Increases CEC (cation exchange capacity), helping the soil retain nutrients more effectively
• Provides trace elements such as Ca, Mg, and K
• Reducing the toxicity of aluminum and iron in acidic soil

3. Improve biological activity:

• Provide a habitat for beneficial microorganisms
• Increase mycorrhizal activity
• Improving the soil nutrient cycle

The difference between biochar and conventional coal

Many people confuse biochar with charcoal or briquettes. However, there are important differences:

Factors affecting biochar quality

Firing temperature is the most important factor. Biochar produced at 400–500°C typically has a higher pH and is suitable for acidic soils. Biochar produced at 600–700°C has a more stable carbon structure and persists longer in the soil.

Raw materials also determines the quality. Biochar made from hardwood typically has a better porous structure, while biochar made from agricultural byproducts (rice husks, coffee husks) is richer in minerals but may contain more ash.

Overview of the Latest Scientific Research (2020–2024)

A meta-analysis of 127 international studies

A meta-analysis published in the journal Agriculture, Ecosystems & Environment In 2023, data from 127 experiments across 32 countries were analyzed. The results showed:

• Increase average productivity by 10–25% on various crops
• Most effective on acidic soil and nutrient-poor soil (up 20–42%)
• On fertile soil, the yield is slightly lower (5–10%)
• Optimal dosage: 10–20 tons per hectare for first-time use

In particular, this study indicates that cumulative effect over time. In the first year, yields may increase by only 8–12%, but in the second and third years, they may rise to 15–25% thanks to long-term improvements in soil structure.

Research at Hanoi University of Agriculture

Hanoi University of Agriculture conducted biochar trials on rice and vegetables from 2021 to 2023 in the northern provinces. Notable results:

On rice (variety IR50404):

• Yield increased from 5.8 to 6.9 tons per hectare (a 19% increase)
• A 20% reduction in nitrogen fertilizer use while maintaining yields comparable to the control group
• The percentage of sound kernels increased from 85% to 91%

On the tomato:

• Yield increased by 28% (from 42 tons to 54 tons per hectare)
• Reduced the incidence of bacterial wilt by 15% (compared to 32% in the control group)
• Improved sweetness (Brix increased from 4.2 to 4.8)

Data from IRRI and FAO on Southeast Asia

The International Rice Research Institute (IRRI) conducted biochar trials in the Philippines, Vietnam, and Indonesia from 2020 to 2023. The report shows:

• Above alluvial soil of the Mekong Delta, biochar helps increase rice yields by 12–18%
• Above gray soil of the Central Highlands, with efficiency of up to 25–35% thanks to improved pH and water retention
• Combining biochar with microbial fertilizer yields the best results (an additional 8–10% increase)

The FAO also recommends that biochar is particularly suitable for small-scale farming in less fertile areas, where traditional soil reclamation methods are costly and time-consuming.

Critical studies: When is biochar NOT effective?

Biochar does not always yield positive results. Some studies point to cases where biochar is ineffective or even has a negative impact:

• On fertile soil rich in organic matter: Very low effectiveness (less than 5%) or negligible
• Overdose (over 30 tons per hectare): May cause nutritional imbalances, particularly nitrogen deficiency
• Low-quality biochar: Biochar contains impurities and PAHs (polycyclic aromatic hydrocarbons), which may be toxic
• Do not mix with fertilizer: Biochar alone does not provide enough nutrients for plants

A study conducted in Australia (2022) also found that on certain types of alkaline soils (pH > 7.5), biochar can raise the pH to excessive levels, making it difficult for plants to absorb micronutrients.

Biochar Boosts Yields in Specific Crops

Food crops (rice, corn): Degree of improvement and optimal conditions

Rice:

• Increase in yield: 10–25% depending on soil type
• Best results on acidic soil (pH < 5.5)
• Recommended dosage: 5–10 tons per hectare for the first application
• Application timing: Mix thoroughly before plowing, or apply as a basal fertilizer before transplanting
• Note: Use in combination with nitrogen fertilizer to prevent nitrogen deficiency during the early stages

Corn:

• Increase in yield: 15–30% on sandy and gray soils
• Significantly improves drought tolerance
• Application rate: 8–15 tons per hectare
• Method: Apply a base fertilizer 2–3 weeks before sowing

Vegetables: Field trial results

Tomatoes:

• Increase productivity: 20–35%
• Reduce bacterial and fungal wilt
• Improve fruit quality (sweetness, firmness)
• Application rate: 10–20 tons per hectare

Chili peppers:

• Increase productivity: 18–28%
• Increase the capsaicin content (heat level)
• Reduce flower and young fruit drop
• Application rate: 8–15 tons per hectare

Green leafy vegetables (mustard greens, water spinach):

• Increase productivity: 15–25%
• Reduce nitrate accumulation in vegetables
• Shorten the harvest time by 3–5 days
• Application rate: 5–10 tons per hectare

Fruit trees: Long-term effects spanning multiple growing seasons

Coffee: A study conducted in the Central Highlands (2021–2023) found that:

• First year: 12% increase in productivity
• Second year: 22% increase in productivity
• Third year: 18% increase in productivity
• Improve seed quality (increase the percentage of Grade A seeds)
• Dosage: 3–5 kg per plant (mix into the soil around the base of the plant)

Mango:

• Increase the fruit-setting rate by 15–20%
• Improve fruit size
• Reduce anthracnose
• Dosage: 5–10 kg per plant

Grapefruit:

• Increase productivity by 10–18%
• Reduce premature fruit drop
• Enhance sweetness and reduce acidity
• Dosage: 8–12 kg per plant

Summary Table of Productivity Growth Rates

Factors Determining the Effectiveness of Biochar

Soil type: Where is biochar most effective?

Not all types of soil respond well to biochar. Based on research, the best results are seen in:

Acidic soil (pH < 5.5):

• Biochar helps raise pH levels and reduce aluminum toxicity
• Improve phosphorus absorption
• Increase microbial activity
• Effectiveness: Very high (20–40% increase in productivity)

Sandy soil:

• Improve water retention and nutrient uptake
• Improve soil structure
• Reduce fertilizer leaching
• Effectiveness: High (15–30% increase in productivity)

Nutrient-poor soil:

• Provide a habitat for microorganisms
• Increase CEC, maintain better nutrient retention
• Effectiveness: High (18–35% increase in productivity)

Fertile alluvial soil:

• Lower effectiveness (5–12%)
• Primarily improves physical structure
• It may not be necessary if the soil is already good

Dosage: How much is enough?

This is the most important question for farmers. Using too little is ineffective, while using too much wastes money and can be harmful.

General recommendations:

• First application: 10–20 tons per hectare (1–2 kg per square meter)
• In subsequent years: 3–5 tons per hectare for maintenance
• Short-season crops: 5–10 tons per hectare
• Perennials: 3–5 kg per plant

Optimal threshold: Studies show that yields increase linearly up to 15–20 tons per hectare, after which the rate of increase slows down. Above 30 tons per hectare, yields do not increase significantly further, and there is a risk of:

• Nitrogen immobilization
• Nutritional imbalance
• Excessive increase in pH

Fertilization Methods: How to Do It Right?

Mix thoroughly with soil (highly recommended):

• Spread the biochar evenly over the field
• Plow and mix thoroughly into the topsoil (15–20 cm)
• Timing: 2–3 weeks before planting
• Advantages: Even distribution, highest efficiency

Basal fertilization:

• Apply to planting rows or holes before sowing or planting
• Suitable for row crops (corn, coffee)
• Save more biochar
• Advantages: Targets the root zone

Top-dressing (not recommended):

• Spread it on the ground after the plants have been planted
• Low effectiveness because it does not come into contact with the roots
• Use only when pre-application is not possible

Combined with fertilizer: An effective formula

Biochar NOT is a complete fertilizer. It needs to be combined with other types of fertilizer:

Basic formula (for 1,000 m²):

• Biochar: 100–200 kg
• Organic fertilizer: 300–500 kg
• NPK Fertilizer: 20–30% less than usual
• Biofertilizer: 5–10 kg (optional)

Important note:

• Increase nitrogen fertilizer by 10–15% in the first year to compensate for nitrogen fixation
• When combined with microbial fertilizer, it increases efficiency by an additional 8–12%
• Apply biochar first, then organic fertilizer, and finally inorganic fertilizer

Benefits Beyond Increased Productivity

Improve water retention

One of the greatest benefits of biochar is its excellent water-holding capacity. The porous structure of biochar can absorb water equivalent to 3–5 times its own weight.

Practical benefits:

• Reduce irrigation needs by 20–30%
• The plant is more drought-tolerant during the dry season
• Reducing flooding during the rainy season (improving drainage)
• Save on water pumping electricity costs

A study in Ninh Thuận (an arid region) found that soil treated with biochar retained moisture 35% better than the control soil after 7 days without irrigation.

Improve fertilizer efficiency

Biochar has the ability to adsorb and retain nutrient ions, thereby reducing leaching:

• Reduction in nitrogen (N) leaching: 15–25%
• Reduction in phosphorus (P) leaching: 20–30%
• Reduction in potassium (K) leaching: 10–20%

Economic significance: Given current fertilizer prices, reducing leaching by 20–25% translates to savings of 500,000–1,000,000 VND per hectare per year.

Carbon sequestration and sustainable agriculture

Biochar can remain in the soil for hundreds to thousands of years, helping to sequester carbon for the long term:

• 1 ton of biochar sequesters approximately 3 tons of CO2
• Contributing to the reduction of greenhouse gas emissions
• Eligible to participate in the carbon market (carbon credits)

Some countries have implemented programs that pay farmers to use biochar as a means of reducing emissions. Vietnam is currently exploring similar policies.

Reducing greenhouse gas emissions from the soil

Biochar also helps reduce N2O emissions (a greenhouse gas 300 times more potent than CO2) from agricultural land:

• Reduce N2O emissions by 30–50%
• Reduce CH4 emissions from paddy fields by 20–40%
• Improving nitrogen use efficiency

This is a significant environmental benefit, particularly important in the context of climate change.

Challenges and Limitations in the Use of Biochar

Initial investment costs

This is the biggest obstacle for many farmers. Let’s analyze the costs and benefits:

Cost:

• High-quality biochar: 8,000–15,000 VND/kg
• Recommended application rate: 1–2 tons per 1,000 square meters (first application)
• Total cost: 8–30 million VND per 1,000 m² (initial installation)
• Subsequent years: 3–5 million per 1,000 square meters per year

Benefits (e.g., for rice):

• 15% increase in productivity = 0.75–1 ton per 1,000 square meters
• Added value: 6–8 million VND
• Save 20% on fertilizer: 1–2 million VND
• Save 25% on water: 0.5–1 million VND
• Total annual benefits: 7.5–11 million VND

Payback period: 2–3 crops (10–18 months)

However, for small-scale farmers, the initial costs remain a major challenge.

The quality of biochar is inconsistent

The biochar market in Vietnam lacks strict standards, leading to:

• Many "fake biochar" products (ordinary charcoal)
• Low-quality biochar with high impurity content
• Unknown origin of raw materials
• Significant price differences

How to identify high-quality biochar:

• Lightweight, porous structure that floats on water
• No burning smell or chemical odor
• When it crumbles easily into a fine powder
• To prevent oil from floating on the water
• Certificate of Analysis

Time to see results

Biochar is not a "miracle cure" that delivers immediate results:

Short-term (first term):

• Modest effectiveness (5–12% increase in productivity)
• A protein deficiency may occur if no additional fertilizer is applied
• Some farmers are disappointed and have given up

Long-term (starting from the second crop):

• Gradual increase in effectiveness (15–25%)
• Significant improvement in soil structure
• Gradual reduction in the demand for chemical fertilizers

Recommendation: It takes at least 2–3 growing seasons to properly assess the effectiveness.

Situations in which biochar should NOT be used

1. The soil is fertile and rich in organic matter (>3%): Low effectiveness, unnecessary

2. Alkaline soil (pH > 7.5): Biochar can cause the pH to rise excessively

3. Limited budget: You should prioritize investing in organic fertilizer and basic soil improvement first

4. Short-season crops with low value: Difficulty in recovering the investment

5. There is no reliable source of high-quality biochar: Avoid buying low-quality products

6. Heavily saline soil: Salinity must be addressed first; biochar alone is not enough to solve the problem

Conclusion: Is Biochar Worth the Investment?

Summary of the scientific evidence

After analyzing hundreds of scientific studies, the answer is: Yes, biochar DOES increase crop yields, BUT under certain conditions.

Biochar isn’t a magic bullet for every situation, but when used correctly and under the right conditions, it truly delivers significant benefits:

✅ Increase yields by 10–35% depending on soil type and crop

✅ Reduce fertilizer and irrigation costs by 20–30%

✅ Improve product quality

✅ Long-term environmental benefits

✅ Payback in 2–3 growing seasons

5-Question Checklist Before Making a Decision

Before investing in biochar, ask yourself:

1. Is my soil type suitable?

• ✅ Acidic soil, sandy soil, poor soil → Highly suitable
• ❌ Fertile soil, alkaline soil → Not necessary

2. Do I have enough money for the initial investment?

• 8–30 million VND per 1,000 square meters for the first time
• You can start with a small area to test it out

3. Do I have a reliable source of high-quality biochar?

• Verify the certificate
• Conduct a small-scale trial first

4. Do I need to wait 2–3 harvests to see the full results?

• The first case may not yet be clear
• Cumulative effectiveness over time

5. Do I know how to use it correctly?

• Application rate and method
• Combine with other fertilizers

Recommendation: Start with a small test

Instead of investing in the entire space, try:

1. Select 200–500 square meters for testing
2. Comparison with the control group (without biochar)
3. Take careful notes: Productivity, costs, observations
4. Evaluation after 2–3 harvests and then expand
5. Consult an expert if necessary

Find a source of high-quality biochar

Here are some tips for finding reliable biochar:

• Contact agricultural universities: Many schools are conducting experimental biochar production
• Cooperative, cooperative group: Buy in bulk to get a better price
• Certified business: Verify licenses and quality certifications
• In-house production: If there is a source of scrap material and a suitable kiln

Final tip: Biochar is a useful tool in the modern farmer’s “toolkit,” but it is not the only solution. Combining biochar with other good agricultural practices (crop rotation, organic fertilizer, and beneficial microorganisms) will yield the greatest overall benefits.

Approach biochar with a scientific mindset, careful experimentation, and patience. When used correctly, biochar can truly help you increase yields, reduce costs, and farm more sustainably.