Compost Magazine

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Pile of biochar with a single leaf poking out of the top.

How Biochar Can Help Improve Compost Speed and Quality

Biochar is under-used in compost, but there’s some promising research suggesting that it can help with everything from helping us to create faster, better compost to helping the environment.

In this article, we’ll take a science-backed look at how biochar can help speed up the composting process, and what the benefits and drawbacks of using biochar in compost are.

What is Biochar?

View of the Amazon rainforest from above.
The process of making and using Biochar is thought to have originated in the Amazon rain forest.

Biochar is a type of charcoal that is produced from organic materials, such as wood and other plant matter.

It is created through a process called pyrolysis, which involves burning in a low-oxygen environment. This process produces a stable, carbon-rich material that can be beneficial for soil health. 

It’s not new!

In fact, biochar has been used for centuries in agriculture and soil management.

It’s believed to have originated in the Amazon rainforest as part of a traditional farming practice, which involved adding charcoal to the soil to improve fertility and soil structure. 

Today, it is gaining popularity due to its ability to store carbon and improve crop yield.

Still, it’s worth noting that one meta-analysis found that when using biochar alone there was no increase in crop yield. However, as we’ll explore below, biochar mixed with compost does appear to be superior to pure compost.

Types of biochar

There are many different types of biochar, each with its own unique characteristics. The most common types are wood-based, manure-based, and agricultural waste-based biochar.

Each type has different properties that make it more suitable for a specific application. Wood-based biochar, for example, is often used in horticulture and gardening applications due to its high carbon content and purported ability to improve soil structure

Manure-based biochar can be used to reduce ammonia emissions from livestock farms, while agricultural waste-based biochar is often used to reduce the environmental impact of crop production.

Using biochar to speed up and improve the composting process

Thermometer in pile.
Biochar may the help composting process by trapping air in compost.

Biochar can increase aeration in compost – possibly because it acts as a bulking agent to create free air spaces. This can help create an ideal environment for the microorganisms in compost to thrive, thus speeding up the composting process.

In fact, one study by M. Sánchez-García et al found that adding 3% biochar can improve the speed of creating compost by 20%.

Using biochar in compost has other advantages too. In addition to speeding up the composting process, research by Nguyen et al has shown biochar can reduce odors released from compost and increase the speed at which your compost matures.

Biochar can also reduce nutrient leaking from compost. The surface of biochar is negatively charged, which helps it retain potassium, calcium and magnesium.

Finally, biochar has also been shown to improve the final nutrient value of compost.

One study argued that the main way it achieves this is by increasing the pH of the compost. This also had the additional benefit of reducing the availability of heavy metals. 

How to use biochar in your compost

When using biochar in compost, it is important to ensure that it is added in the correct proportion.

Generally, 2-4% of the compost’s weight should be made up of biochar. This will ensure that the compost doesn’t become too acidic, which could have a detrimental effect on your compost. 

Biochar is high in carbon. However, not all of this carbon is readily usable, and biochar can also absorb nitrogen.

Because of this, it’s important to ensure that your compost has plenty of both high nitrogen (green) materials, and high carbon (brown) materials that can be easily broken down by bacteria.

Learn more about the role of carbon and nitrogen in compost

Inoculated biochar

Scientists have found that biochar inoculated with bacteria can provide even greater benefits than pure biochar. 

One study found that inoculated biochar increased the hot stage of composting, the speed of breakdown of organic material and compost maturity. 

Read more about the study: Scientists Find Biochar Improves Compost Speed and Quality

Benefits of using biochar compost

Wakefield biochar compost

Biochar compost can help to improve soil structure

This in turn helps to increase aeration and drainage, which can be essential for keeping your plants healthy.

Another benefit of using biochar compost is increased nutrient retention. The porous nature of biochar helps to absorb and hold onto nutrients, making them available for your plants to use. 

This means that you can use less fertilizer, as your plants will be able to make better use of the nutrients already in the soil. 

Finally, biochar compost has been found to improve soil water retention. This is especially useful for gardens in dry or arid climates, as it helps to hold onto moisture for longer.

Read more: Potential of Biochar-Compost to Improve Problem Soils Revealed in New Study

Potential drawbacks to using biochar compost

Biochar can increase the alkalinity of your soil. While that should be a positive for acidic soil, you should be careful about adding significant amounts of high-alkaline biochar or biochar compost to alkaline soils. 

Not all biochar is alkaline, though, and an alternative is to use a biochar with neutral pH. 

Wrapping up

In summary, there’s increasing evidence that biochar can help improve both the composting process and the final quality of the compost.

Just remember not to go overboard with it, as that biochar will be in your soil for a lot longer than you will be alive!

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