How Does Biochar Improve Soil Quality?

Soil, as an essential component of the ecosystem, greatly influences human life through its environmental quality. Soil pollution not only poses a serious threat to farmland and the quality of agricultural products but also directly impacts human health. Common soil pollutants include inorganic substances like acids, alkalis, heavy metals, as well as organic pollutants such as organic pesticides, cyanides, and phenols. Biochar is an emerging eco-friendly soil improvement material that effectively absorbs organic and heavy metal pollutants in the soil, offering a promising market outlook.

Biochar is a highly aromatic and refractory solid produced through pyrolysis carbonization of plant biomass under complete or partial anaerobic conditions. Research has shown that biochar can increase crop yield by raising the pH of acidic soil, increasing soil organic carbon, and enhancing soil porosity.

How Does Biochar Lower Greenhouse Gas Emissions of Soil?

When biochar is applied to farmland, it not only aids in carbon sequestration but also suppresses the emission of greenhouse gases NOx and CH4 from soil by altering the activity of soil nitrogen-fixing and nitrifying microorganisms. Our experiments on low-organic carbon content, lime-rich soils have demonstrated a significant reduction in greenhouse gas emissions after biochar application. The total emissions of CH4 and N2O were reduced by 24% and 48%, respectively. Research on aerobic cultivation of two typical rice soils for 60 days revealed that the addition of rice husk biochar (50 t hm-2) significantly reduced N2O emissions, with a reduction rate of up to 94%.

biochar made from agricultural wastes

Carbon elements in biochar are highly stable, making it difficult for them to enter the atmosphere in the form of carbon dioxide (CO2). Experimental evidence shows that biochar made from rice husks, when added to four different field soils, resulted in only 4.4% and 8.5% of the carbon being mineralized to CO2 after three years under aerobic and anaerobic conditions, respectively. In contrast, when non-charred rice husks were added to the soil, the carbon from the rice husks was 100% mineralized. Therefore, the thermal conversion of agricultural and forestry waste into biochar is a highly effective method for carbon sequestration.

How Does Biochar Influence The Physical and Chemical Properties of Soil?

The application of biochar can improve the physical and chemical properties of soil. Experiments have shown that when biochar is applied to acidic soil, it can raise the soil’s pH from 5.2 to 6.7. In addition to pH, biochar can also increase cation exchange capacity, reduce soil bulk density, increase total nitrogen content in the soil, enhance field water-holding capacity, and raise soil phosphorus levels.

Due to the improvement in the physical and chemical properties of soil, crop yields on the land also increase accordingly through biochar application. Biochar itself contains many essential nutrients for plants, further promoting plant growth. In a three-year field experiment conducted in a maize field, the results showed that the application of biochar significantly increased maize yield, with an increase of approximately 15%. In the second year after biochar application, the nitrogen content in the aboveground parts of the crops noticeably increased, and in the third year, the aboveground biomass of the crops significantly increased. Furthermore, the application of biochar also enhances soil respiration and the growth rates of fungi and bacteria.

biochar improves soil quality
Soil improved by biochar

How Does Biochar Lower Organic Pollutants in Soil?

The addition of biochar can influence the migration and transformation of organic pollutants in the soil environment, reducing the bioavailability of these pollutants. Studies have shown that in-field soils with added biochar have increased adsorption capacity for pesticides by 5 to 125 times, and after 56 days, the desorption rate of pesticides decreases by 96%.

Biochar has a significant surface area and abundant polar functional groups, allowing it to adsorb organic pollutants through electrostatic and chemical adsorption. The main factors affecting the effectiveness of biochar adsorption include surface electronegativity, acidity, and aromaticity. Biochar produced through high-temperature pyrolysis primarily relies on surface adsorption for absorbing organic pollutants, with partitioning and pore entrapment as secondary mechanisms. Biochar produced through low-temperature pyrolysis generally has a lower surface area and weaker aromaticity, and its adsorption of non-polar or weakly polar organic substances primarily relies on partitioning.

How Does Biochar Absorb Heavy Metals in Soil?

Biochar has the ability to influence the form of heavy metals in soil, effectively reducing the bioavailability and ecological toxicity of these metals. Scientific studies have shown that biochar adsorption of lead (Pb) in water conforms to a dual Langmuir model and is seven times more effective than activated carbon adsorption. Soil contaminated with lead and subjected to biochar remediation exhibits reductions in the labile, reducible, and oxidizable forms of lead, with a significant increase in residual lead content. In addition to lead, biochar also has a strong adsorption capacity for other heavy metals such as copper (Cu), zinc (Zn), and cadmium (Cd) in soil.

How does biochar absorb heavy metal ions

The mechanisms by which biochar affects heavy metal ions in soil primarily include:

  1. Increasing soil pH, enhances the negative charge on soil particle surfaces, leading to enhanced electrostatic adsorption of heavy metal ions. The rise in soil pH can also precipitate free metal ions such as hydroxides, carbonates, and phosphates.
  2. Increasing soil organic matter content, influences the form and transformation of heavy metals in soil, converting heavy metal ions into more stable states.
  3. It has a large surface area and a developed pore structure that allows biochar to effectively adsorb heavy metal ions.
  4. Possessing a surface with a high negative charge, enabling electrostatic interactions with metal ions in the soil.
  5. Containing surface functional groups capable of adsorbing heavy metals or forming specific metal complexes.

About GEMCO Energy

As biochar production technology matures and costs decrease, more countries are adopting biochar to enhance soil, combat pollution, and mitigate carbon emissions. GEMCO Energy specializes in biomass pyrolysis equipment R&D and production, offering advanced biochar production solutions to global clients. Contact us for detailed equipment information and quotes.

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