October 31, 2022

Exploring the Potential and Pitfalls of Biochar for Soil Amendment

30 minutes

This episode of "The Poor Proles Almanac" centers on biochar, a soil amendment with purported benefits but also potential risks. Hosts Elliot and Andy, along with guest host Matt, discuss what biochar is, how it differs from charcoal, its potential applications, and the complexities of using it effectively.

What is Biochar and How is it Made?

Biochar is a type of charcoal produced by heating biomass in the absence of oxygen to high temperatures (600-950°F). This process, known as pyrolysis, breaks the bonds in the biomass and creates a porous material with a high surface area.

While regular charcoal is produced at lower temperatures, biochar's higher production temperature results in greater purity and a reduction of hydrocarbons.

This high-temperature pyrolysis creates unique "chemisorption" properties in biochar, allowing it to attract and hold substances on its surface at a molecular level.

Biochar can be made using a variety of methods, ranging from simple DIY setups using metal containers in a wood stove to more sophisticated designs like the Annela stove, which utilizes a secondary burn of the off-gases to reach higher temperatures.

Biochar as a Soil Amendment: Benefits and Challenges

Biochar is commonly touted as a soil amendment that raises pH, acts as a carbon sink, and improves soil health.

One of its key benefits is its ability to increase water retention, particularly in sandy soils, which are known for poor water retention. Studies have shown that biochar can increase water retention by up to 20% in sandy soils.

Biochar's "chemisorption" properties enable it to absorb and hold nutrients, potentially improving soil fertility. However, freshly produced biochar has a low cation exchange capacity (CEC), which limits its ability to immediately release those nutrients to plants.

The CEC of biochar increases over time through oxidation in the soil. This means that the benefits of biochar are not always immediate and can vary depending on factors like the soil type and the biochar's feedstock (the material it's made from).

The Complicated Nature of Biochar: A "Yes and No" Story

Throughout the episode, the hosts emphasize the complexity of biochar and the lack of definitive answers regarding its use. They often use the phrase "yes and no" to highlight this uncertainty.

While biochar can be beneficial, there are also instances where it has had negative effects on soil health. For example, the pH change caused by biochar can suppress beneficial microbial communities, and freshly produced biochar can temporarily absorb nutrients, leading to deficiencies.

Some studies have shown that biochar's benefits may only last a few years, and in some cases, it has even suppressed plant growth. There are also concerns about biochar potentially accumulating pollutants and heavy metals, drawing them closer to plant roots.

In some cases, the effects of biochar have been negligible, with no observable changes in soil health or plant growth.

The hosts underscore that more research is needed to fully understand biochar's interactions with soil and its long-term effects.

Charging Biochar and Practical Considerations

The hosts discuss the concept of "charging" biochar to enhance its nutrient content. Soaking biochar in nutrient-rich liquids like urine, compost tea, or fish emulsion can increase its CEC and nutrient availability.

The episode also touches on the importance of choosing the right feedstock for biochar based on the intended use and location. Hardwood biochar is generally considered better for forest soils, while corn stover or similar materials might be more suitable for pastures or prairies.

While there are no hard and fast rules for biochar application rates, a general guideline is around 20 pounds per acre, incorporated into the soil at a depth of 5-10 inches.

Conclusion: Proceed with Caution and Observation

The episode concludes by emphasizing the need for caution and careful observation when using biochar. It's not a magic fix for all soil problems, and in some cases, it may even be detrimental. However, biochar holds potential for improving soil health, particularly in certain contexts like sandy soils and areas with low pH. The hosts encourage listeners to experiment with biochar, but to do so responsibly and with an awareness of its complexities.

For sources, transcripts, and to read more about this subject, visit: www.agroecologies.org

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By The Poor Prole’s Alamanac, Bleav

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