Enriched Biochar is beneficial for trees in the urban environment

What is biochar?

Biochar is the international name for a charcoal-like substance that is created by heating organic material in a low (or no) oxygen environment, whereby the material is heated at a ‘low’ temperature between 400^° and 800^° Celsius. This process is called pyrolysis. As a result, the material does not burn to ash, but a charcoal-like structure remains, which could be used for barbecues. Compared with charcoal, which is formed at a much lower temperatures and requires the presence of oxygen, the structure of the wood and the majority of the carbon is largely preserved during the biochar production process. Thanks to this structure, biochar has many benefits for soil and soil life.

The people who live in the Amazon region have known for a long time that biochar has a positive effect on plant growth. Thousands of years ago the people who live there started to mix the soil with burnt wood residues created during low-oxygen combustion. This process formed terra-preta, a very fertile type of soil. Today many different organic materials can be used to create biochar, from tyres to sewage sludge. The only difference is that the material obtained will be used as a soil improver and not as fuel. The biochar that Terra Nostra has researched, uses wood as the raw material for the pyrolysis process.

The characteristics of biochar

Biochar is unique because it is very stable. Many organic substances decompose very quickly, especially when mixed with soils. Think of the type of compost that is available free of charge at the recycling centre: it has a black colour and it often smells like a poorly functioning sewer! This type of material will be almost completely decomposed within one year. These properties are not a good basis for the type of stable organic matter that our soil really needs. In the Amazon region, on the other hand, researchers have found biochar that is hundreds of years old remains. It is not true that biochar doesn’t decompose, but it certainly is a very stable material with a decomposition rate that is not perceivable by us. Depending on the pyrolysis process, it is known that 50% of the material still exists after 100-600 years.

Another advantage is that it has an amazing internal surface. The structure created by the pyrolysis forms a very large surface area. The internal surface of one teaspoon of biochar corresponds to the surface area of about two tennis courts. This internal surface area is so interesting, because it exponentially increases its moisture and nutrient buffering capacity. The structure itself becomes the living environment for soil life, such as fungi, bacteria and other organisms. This means that biochar is not a nutrient, but rather a storage shed that maintains and increases soil fertility over time.

Biochar research findings

You may start to feel suspicious when you hear me talk so positively about a product - it reeks of advertising! Time to look at some facts. Terra Nostra’s scientific research department has been researching the application for biochar for four years. My colleague, scientist Wendy Batenburg, has tested three different batches for a period of two years. These batches were based on ‘Amsterdam’ structural sandy soil, a coarse sand with a uniform grain size of >400 microns. One batch consisted of the regular ‘Amsterdam’ structural soil, which served as reference. In addition, two other mixtures were tested with biochar and enriched biochar with mycorrhiza fungi and various other natural mineral components. For the test, a sample of 10 x 1 m³ of each batch was placed into a big bag, into which a two-year-old small-leaved lime tree (Tilia cordata) was planted. In total 30 lime trees were tested over two years, of which 10 were reference trees. Above the ground, stress levels and the vitality of the lime trees were measured with a chlorophyll fluorescence meter. The degree of degradation, shoot length and leaf density were also measured. Below the ground the nutritional value (CEC value) of the soil was determined, the size of the roots was measured as well as the growth of mycorrhiza fungi.

The results were highly variable. Compared to the reference trees, the enriched biochar mixture showed by far the best results. More growth and, from the first year, less stress and more leaf vitality. Furthermore, the trees in this mixture turned out to be less sensitive to the larvae of the lime leaf wasp, which were able to develop extremely well on some of the other trees. Below the ground the results were also encouraging. The soil nutrient value of this mixture had decreased 11% after two years, compared with the reference mixture, which showed a decrease of 40%. The strength of the enriched mixture was also preserved, which is an important criterion for planting sand.

At the end of the two year trial the final destructive part of the research project was the measurement of the size of the shoots and roots. When you see these results, you can imagine how happy we are with the help we received from interns and trainee researchers! After two years the 30 lime trees were uprooted, which entailed removing the lime tree from the bulk bags with all roots intact. Then the shoots and roots were sorted into four diameter sizes: smaller than 2 mm, 2-5 mm, 5-10 mm and bigger than 10 mm. The data was totalled for each tree and for each batch.

The enriched mixture yielded more and longer shoots with a lower stress level and a better vitality. The root development in 1 m³ of the mixture was impressive. The ‘bare’ ‘Amsterdam’ structural soil reference mixture contained 706 metres of roots per lime tree. The enriched biochar mixture contained 1,028 metres (!) per lime tree. For the most part (98%), these were very fine roots with a diameter of less than 2 mm.

Conclusions:

• Better growth from year one.
• Less stress and more leaf vitality.
• The trees are less susceptible to diseases and decomposition.
• Efficient use of nutrients.
• Better root development.
• Positive effect on soil life.

Is biochar a miracle material?

I have mainly focused on the application in a public space. Not only for this type of use it is important to conduct further research into the following:

• There must be sufficient certainty that any large-scale use of biochar in the soil will not have any as yet unknown side effects.
• Lifechar which has been used for new plantings and for bare root transplantation of four Carbon Gold biochar Sweden has now its own installation that uses residual flows to satisfy its own biochar demand. However, the production of biochar is more than just blackening wood and selling it. The temperature and oxygen content must be monitored carefully in order to generate the desired end product. It is possible to have the end product certified by the International Biochar Initiative and this is recommended for quality control purposes. Particularly high temperatures render biochar useless for trees because it results in charcoal for the barbeque. Importing biochar from outside Europe, where the trees have possibly been felled without any supervision in order to produce biochar, should be avoided. The use of residual flows that are currently sent to biomass power stations is a much better alternative.

   

  CO₂ targets

  There is an urgent need to sequester CO₂ in order to meet our CO₂ targets. When organic material, such as wood, is heated through pyrolysis, the carbon in the resulting biochar is much more difficult to break down than the original carbon of the untreated wood. The wooden trusses in the half-timbered houses in Germany that are many hundreds of years old, are a good example of the proper way to make wood more sustainable through combustion. Organic matter in the soil breaks down within a few years, decades at most.

  When biochar is used in the soil, it will be retained for centuries, if not millennia. Furthermore it is possible to use the energy released during the production of biochar for other purposes. This way biochar not only benefits trees in urban environments, but it also helps to combat climate change. Are you brave enough to start a new biochar project?

Biochar

Suistainable wooden trusses of German half-timbered houses through combustion

Result 3 different mixes after second growing season

Great root development in bulk bag enriched biochar

Result year 1 transplanted 80 year old elm The Hague

Application of biochar with Stockholm method to improve growth place Utrecht