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Biochar As A Soil Enhancer: The Basics

Bio = From Biology - Life; Living organism

Char = From Charcoal - Produced from the heating of carbonaceous material in an environment free of oxygen. AKA “Pyrolysis”.

This article is a meant as a brief and accessible explanation of some of the main benefits of how using biochar and improve soil fertility in growing systems What Is Biochar? Biochar, generally speaking, is the term given to charcoal that has been produced at temperatures in excess of 350°C and then specifically processed (crushed) for use as a soil enhancer in agricultural and plant growing systems. Different grades are available for different applications

Charcoal is produced from the heating of carbonaceous material in the absence of oxygen, a process known as pyrolysis. Whilst there are numerous applications for this biochar, the main focus of this post is to present the role and function that biochar plays in enhancing soil fertility and the benefits it can provide to soil regeneration, carbon sequestration and food sustainability.

The use of biochar in cultural living systems throughout history is not a new one. Re-popularised and reintroduced into western consciousness in the 20th century largely by the bestselling book ‘1491’ authored by Charles C. Mann. Throughout the Amazon basin pockets of highly productive soils are found. They have been carefully studied and these pockets are believed not to be a wholly natural occurrence. These pockets not only contain a huge amount of charcoal but also contains broken clay pots, animal bones, biomass, food waste and human excrement suggests they were created by a now forgotten civilisation, with proposed dating as far back as 8,000 years. Sources for exact dating are still in conflict as is the exact process behind how these soils came to be.

“Terra preta”, “black soil” or sometimes "black gold" is now being discovered all over the world in ancient agricultural systems from West Africa to Japan. Although the details of how the Amazonian soils were actually made is still open to debate, the fact that these soils were created before recorded history and still provide fertility with no additional inputs, except the organic matter created by the plants that inhabit the areas, is certainly worthy of attention when looking to secure the soils that feed us for future generations

What Does Biochar Do? Let us look at the main functions that biochar plays in soils that make it such an valuable tool to enhance soil fertility. Firstly, a very brief explanation of biochars basic properties -

  1. Biochar is highly absorbent: this means that it is able to soak up water into itself. It has complex internal microstructures that provide habitats for microbes.

  2. Biochar is highly adsorbent: This means that biochar is able to hold nutrients and water on its surface. This is in connection to the following point.

  3. Biochar can improve a soils Cation Exchange Capacity (CEC): With the proper process of co-composting biochar (this simply means incorporating biochar into the compost making process rather than adding it to finished compost) the resulting char’s capacity for holding in place nutrients, moisture and reducing nitrate runoff is greatly improved. Very basically, during the composting process the biochar undergoes something of a secondary phase of structural change. Without getting too technical the chemical processes that happen during the composting process improve the capacity of the biochar to retain positively charged cation nutrients. Each nutrient has a positive charge, neutral charge or a negative charge. The increased CEC in the soil allows for these positively charged ions to bond to the biochar’s surface making them available for use by the plants.

  4. Biochar has a huge surface area - A ground up 2" chunk of charcoal has a surface area the size of a football field and has been measured to hold up to 33 times its weight in water on its surface!

With these points in mind let’s take a closer look into what these properties offer in terms of long environmental regeneration and long term soil fertility.

Key Benefits Of Biochar As A Soil Enhancer

Hazel Coppice Regeneration - As we work towards regenerating the local coppice systems, we are left with a lot of excess material. This is the wood that we turn into biochar. By turning this material into biochar we are opening up larger spaces within the woodlands that will improve and increase the biodiversity of the flora and fauna.

Nutrient Holding - Biochar locks nutrients onto its surface for soil microorganisms to utilise making it available for plants to use. This can result in less fertiliser usage and reduced leaching of nutrients in the winter months. It can also reduce pollutants entering the lower soil levels and water courses.

1000+ Years Life - Biochar is recalcitrant carbon, meaning that it will not degrade in the soil for at least 1000 years.

Soil Aeration - Biochar will improve the aeration and bulk density in soil. Useful for heavy, clay soils.

Water Retention - Biochar has a high water holding capacity which can reduce watering requirements and act as a buffer in drought conditions. Especially useful in light, sandy soils.

Reduced GHG (Green House Gas) - Biochar has been shown to reduce emissions of nitrogen, methane and ammonia gases from the soil. This appears to be achieved in part by biochars improvement of the soils CEC. Research is ongoing.

Microbe “Motel” - The internal microstructure of biochar can be seen as a home for microbes in the soil to reside in, better protecting their function and usefulness in climatic extremes such as periods of drought and heavy rain. Microbes play a huge role in soil health (see The Soil Food Web for more details) and with the infinite array of shapes and sizes of microstructure within the biochar, improvements in microbial diversity are made possible.

A Note On Carbon Sequestration

This is a brief summary of how biochar can be used to sequester carbon in the ground. It appears that this is achieved in a twofold manner -

  1. The pyrolysis process turns the carbon present in the feedstock (biomass intended to become biochar) into a recalcitrant form of carbon, that will remain stable in the ground for many years. This means that during the heating process the carbon is not burnt and releasing carbon dioxide into the atmosphere. The feedstock we use is obtained from a fully regenerating source that actually enhances the local ecology and habitats when harvested.

  2. When biochar has been made fit for purpose (please see section below) to be incorporated into a growing system, then the plants in that soil will generally exhibit increased plant growth both below and above the surface. The increased root growth is a result of the plants increased ability to draw more carbon dioxide from the atmosphere and lock it in the ground in the form of organic carbon (roots).

With all of the benefits listed above and many more that are beyond the scope of this article, biochar has the potential to assist as a powerful tool in the remediation of our damaged eco-systems and support the long term health of our soils and agricultural systems.

How To Prepare Biochar For Use As A Soil Enhancer

There are numerous methods with how to treat biochar before it is incorporated as a soil enhancer. The term soil enhancer is slightly misleading. Adding biochar to soil without proper prior treatment will likely have a negative effect on the soil until the biochar has reached its full capacity. This can be over 2 years. During this period, it will deprive plants of water and nutrients and will result in poor plant health and growth. Cover cropping with mycorrhizal fungi producing crops and use of compost teas can help to remediate raw biochar inadvertently put in the soil. The following methods are for general purpose gardening applications. Larger scale operations may (or may not) need to adapt these methods to suit their needs

Method 1 – Co-Composting The simplest way to prepare your biochar for use and arguably the most effective method is to add it to your composting process. A couple of handfuls every so often will reduce the smell and retain the nutrient and microbe (leachate) runoff created by the composting process and lock it away inside and on the surface of the biochar. If doing a batch of compost in one go, incorporate the biochar throughout the pile. A ratio of 3:1 by volume of compost to biochar is recommended. It will allow important aeration and retain moisture and runoff from the pile. Please note that biochar although carbon, is considered “black” carbon and is NOT a substitute for “brown” carbon in your compost making process.

Method 2 – Adding to Finished Compost

  1. Re-hydrate - Firstly you will want to moisten your biochar with rain water or un-chlorinated water. If using tap water let it sit for at least 24 hours in an open container to allow chlorine to evaporate. The chlorine in the water can have a negative impact on the microbes that will be added. The biochar wants to be moist enough that when you squeeze it a little water drips out. The longer you can leave it in the wate rthe better. 2 weeks is ideal but 24 hours will work.

  2. Charge - Next you want to charge the biochar with nutrients and microbes. Using a well-made compost with a biodiverse range of microbes (bacteria, worms, fungi and nematodes) and nutrients is best. Having a high diversity of these microbes in your compost will provide your plants and soil with enhanced health and vitality. If available, add worm castings to improve the microbe and nutrient profile. A ratio of 3:1 by volume, compost to biochar is recommended. Mix the compost and biochar together well. At this stage you can add any specific nutrients, minerals microbes that you require for your growing purpose. If required add more water to reach the squeeze test moisture level as described previously. Transfer the compost/biochar mix into a container or bag that will allow the air flow through the mix. This will allow the microbes to proliferate and prevent the buildup of unwanted anaerobic bacteria and pathogens. Leave the mixture in a shaded, warm place (approx. 12-24°C) to allow the biochar to condition for at least 3 weeks.

  3. Apply - When the mixture is ready, you can apply the biochar by mixing it in to the top few inches of soil at a rate of 1:10 biochar to soil (Please note, a 3:1 mixture contains only 1 part biochar).

Final Thoughts

Biochar and its many uses is receiving a lot of attention from gardeners to conservationists, ecologists and permaculturists alike. Currently vast amounts of research on biochar is being carried out in the areas of regenerative agriculture (from small to large scale), forestry, power production, waste biomass carbon cycling to name a few. The applications and full-cycle potential that the production and use of biochar can provide is staggering. We are excited to be involved with this emerging environmental solution.

As the world awakens to the importance that healthy soils play in supporting healthy societies, it is our current belief at the Whittlewood Concept that biochar, used as a soil enhancer has a very real role to play in mitigating some of the negative impact of our intensive human activity on the environment and resources of planet Earth.

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