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The soil improver: transforming forestry slash with biochar

Kev Dowman tells Paula Sharp why we should be producing biochar on a commercial scale. He says it is an investment for our future, specifically the future of New Zealand’s land quality and how we can contain carbon.
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Globally, there is scientific investment going into producing biochar, an activated type of charcoal, because of its environmental upside. And the upside is potentially massive. Biochar has the ability to hold carbon in the soil for thousands of years and simultaneously increase land fertility. Kevin Dowman is passionate for New Zealand to play a big part in this movement.

Kev is tapping into his experience and knowledge of logging and logging practices (milling wood, farming, and commercial waste products) to create biochar for domestic and commercial use. The process involves wood (or woodchip, garden waste, cardboard, or bones) heated to around 500oC with limited oxygen until it forms a charcoal, then dousing it with liquid, thereby activating the charcoal and creating biochar.

Biochar stabilises carbon (carbon sequestration). It is about 70 percent carbon, the remaining 30 percent is a composite of nitrogen, hydrogen, and oxygen. Biochar is so porous it can interact with its surroundings. Research has proven that using biochar to increase soil carbon also increases soil pH and biodiversity, soil water retention and water quality improve, crop yield doubles, land fertility increases, there is less land erosion, microbials are more active (less disease), livestock health improves (therefore human health improves), and climate mitigation is in play. Biochar is so efficient at storing carbon (in a world where we are looking to cut greenhouse gases (GHG)), that it is being hailed as ‘black gold’ by product developers and innovators around the world.

Why is Kev so keen on biochar?

Kev converted to biochar from the other side. When he was 10 years old, Kev started skipping school to go logging with his father. By 14 he’d all but quit school to be a logger. By 19 he was helping to clear farms of their forestry before joining Kinleith Pulp and Paper Mill in Tokoroa in charge of his own logging gang.

In those days, logging was a hugely lucrative business with whole native forests being cleared and planted in pine, then cleared again. Kev worked the length and breadth of New Zealand, he saw the change from under-scrubbing (slashing the undergrowth) with machetes before felling trees with axes and a (singular) chainsaw, to the use of a version of agent orange (245T) to kill off the scrub before the trees were levelled with machinery. (He has memories of his crew working as the chemical was dropped, their clothes and vehicles covered in its residue. “We were told it was safe, they were using this type of thing in the Vietnam war.”).

Fast forward to 2019, and things ‘weren’t quite right’ with his health. Kev was on his way to the doctor but got delayed by school students protesting against climate change. ‘We have 12 years left’ [to stop climate change] was the message he heard. Kev didn’t know if he had 12 years left. But he wanted a solution for these young people. Kev is a father, a grandfather, a man who has worked (and damaged) the land and a man who deeply loves the land. And he is not one to shy away from a challenge. In that moment he decided; ‘I’ve got to do something to change this. These kids need a future.’

Kev is an intelligent and articulate man who never went to university. His white hair and tanned face speak of decades outside. Self-educated on biochar, today he has a high level of technical knowledge on the subject. To meet him, he is more than ‘a man who can’, he is ‘a man who does.’

Kev’s thought process kept coming back to ‘nature knows how to do this’. His bright blue eyes sparkle as he explains; “Nature, by way of photosynthesis, converts carbon gases into solid carbon (plants and trees). As they grow, they are a natural carbon store. (A tree or plant is considered carbon neutral when it reaches maturity.) The gas converted in this process is now stored within the tree as wood and plant fibre. Carbon remains in this state until it begins to breakdown, by natural or other means. Insects, decay, burning, and weathering, all break down the carbon and release the gases back into the atmosphere.”

Unless it is stabilised. “Over billions of years carbon has been formed into a solid state, then trapped under ground, in the sea, lakes, swamps, bogs, and even in permafrost, in the form of coal, oil, natural gas and peat. In short, nature takes carbon from the air and puts it in the ground.

“It is well known that wood burned in a non-oxygen environment produces charcoal. Once activated, charcoal is very difficult to break down and carbon in this form can be stored for thousands of years.”

Kev’s solution

Was simple, if we take it out, we help put it back. Five years on and many proto-types of biochar furnaces (the Tin Man, the Jolly Rodger, the Kon-Tiki, and the Retort Kiln), Kev has built his own energy and time-efficient kiln in order to make biochar for domestic use (copyright pending). With investment, it is something that could also be upscaled for commercial use. Kev uses a variety of techniques for different materials in order to create biochar, but at the moment, he recommends the bucket style Kon-Tiki for domestic use. His advice to the home gardener is; “No matter what system; Retort, Kon-Tiki, Pit, or other, the drier the material, the better – under 20 percent moisture content is ideal. This means less energy is wasted driving out moisture, allowing for higher temperatures to be reached in the process, resulting in better char. All systems used should have a double burning ability of gases, at higher temperatures to keep down GHG.”

He knows New Zealand is an ideal country to utilise this on a large scale. There is simply a lot of waste wood (and other materials). He is not alone in this; Professor Jim Jones and his team at Massey University see the value of using slash to create biochar on a commercial scale.

As a nation we produce a lot of slash which enter the water ways – damaging bridges, making rivers dangerous, damming small water reservoirs and washing up in large quantities on our beaches as logs or smaller driftwood. Recent weather events have seen huge amounts of damage caused by slash. Moreover, vast quantities of noncommercial grade logs are left in our remote forests, out of (public) sight, out of (the industry’s) mind. This wood currently has no commercial value, but could be a resource for biochar.

Future potential

Kev sees a future where slash or logging refuse is used as fuel for biochar, to harness CO2 as a resource for land quality. Low-grade waste logs could be made into biochar on location to replenish the soil, creating forest fertility.

Globally, historic over-farming, monoculture, and chemical use, has meant our soil is lacking in available micro- and macronutrients. Kev and other experts know biochar, mixed with organic matter, can alter this. Instead of nitrogen leaching below the plant root zone, biochar holds nitrate/nitrogen in place. Biochar increases the cations (positively charged ions within the soil) and anions (negatively charged ions). Higher levels of cations provide potassium, ammonium, magnesium, calcium, zinc, manganese, iron and copper to the plant. Anions allow for higher amounts of nitrate, phosphate, sulphate, borate, and molybdate. When biochar is present, plants perform and absorb to a higher standard.

Biochar in our waterways could act as natural carbon filters, key to New Zealand being able to clean up its lakes, rivers and streams.

Research is also proving biochar as a feed additive could reduce methane production in the cow’s rumen. This benefit to our meat and dairy industry could be vast. In 2025, He Waka Eke Noa, the Primary Sector Climate Action Partnership plans to implement taxes on farmed animal’s methane and CO2 emissions. This tax will be the farmer’s responsibility (and therefore passed onto the consumer). Instead of taxing emissions in this way, perhaps He Waka Eke Noa, could support farmers to change their methane and CO2 levels at ‘grass roots’? Independently, and as a collective, farmers given this information and access to biochar or biochar furnaces could be incentivised to change their farming practices, producing fewer animal gases. Australian farmer, Doug Pow, found (and published) that by adding biochar to feed, livestock showed improved nutritional intake therefore increased milk production, and less odour and gas. As an aside, Kevin also questions whether our bee population is being ‘carbon starved’, that by introducing biochar into our pastures our bees would thrive at a higher level.

Biochar is not new to the world. Evidence of its use has been found in the Amazon between 500-9000 years BP (before present) to make arid soil fertile. In 2010, scientists James Hansen and James Lovelock started working with biochar for carbon dioxide removal. Many countries are exploring ways of eliminating or storing carbon. In New Zealand, Manaaki Whenua – Landcare Research, has benchmarked and monitored soil carbon in 275 of its 500 on-farm sites (to June 2022). They are well aware of our carbon resources.

Is biochar part of the answer?

In 2023, the Wall Street Journal writes that large companies around the world are offsetting their carbon emissions with carbon credits and by buying into biochar and biochar products. In 2018, Fonterra Nelson transitioned from using coal to burning wood in a process called ‘co-firing’ to power its premises. Kev suggests it would be a small step to create biochar in the process. Fonterra, will you lead the way?

Should New Zealand be refocusing its CO2 gaze on options like biochar in order to validate its green credentials? Kev Dowman certainly thinks so.

Further information

Garden Biochar Production

Making biochar, by Living Web Farms.
A six-part series recommended by Kev Dowman.
youtube.com/watch?v=svNg5w7WY0k How to make a Retort Kiln youtube.com/watch?v=PxrsBQDBQOk

How to make a Kon-Tiki Kiln

New Zealand Biochar Research Centre
massey.ac.nz/about/colleges-schools-and-institutes/ college-of-sciences/our-research/research-projectsand-groups/new-zealand-biochar-research-centre/

Paula Sharp is a Nutritional Therapist based in the Bay of Plenty. She is interested in organic food production and how quality food creates quality health. She recently attended a biochar workshop hosted by Kev Dowman and was inspired by his findings on natural soil enhancement.


Submitted by Dylan Graves with permission from BNNZ.

What is biochar?

Biochar is produced by heating biomass in an oxygen-free or air-limited environment, called pyrolysis. If used as a soil amendment it will have biology added to it before application. Yes, it is similar to charcoal, but not the same.

Biochar’s key attributes and benefits

  • Biochar is a stable form of carbon derived from biomass. The chemical carbon bonds are very resistant to breakdown through biological processes.
  • It’s very long lived: Pyrogenic carbon in fertile grassland soils has been dated to over 7,000 years in the US Midwest, and 12-14,000 years in Russia.
  • It has a microscopic pore structure which provides immense internal surface area and optimum habitat for soil microbiota. This porosity makes biochar an ideal amendment for increasing aeration and water retention of soils.
  • Biochar has a high cation exchange capacity, which gives it superior adsorption qualities and provides the ability to bind and retain dissolved nutrients. The soil microbiota can use them and make them available to plant roots.

How is biochar produced?

Traditional charcoal production methods, such as smouldering in earth mounds or beehive kilns, are typically slow, polluting, and inefficient. Because of the lower temperatures in these processes, the charcoal produced has a high level of hydrocarbons remaining and is less suitable for many of the applications appropriate to biochar. It is also less long-lived and will degrade or decompose in soil.

An internet search will generate multiple methods for creating biochar at whichever scale suits you. Purposed incinerators, open air-drums, or small-scale kilns are available for household or farm-scale biochar production.

Commercial reactors produce syngas, industrial heat/ power, biochar; and potentially a range of condensates (pyroligneous acids, oils, and tars).

Things we could be doing with biochar in NZ:

  • Turn virtually any organic material ‘waste’ into a useful product.
  • Improve the fertility, aeration and water retention of our pasture and arable soils.
  • Reduce the emissions of CO2, N2O, NH4+ and CH4 from agricultural soils.
  • Reduce nutrient leaching into our waterways. Biochar can be used in soil or to filter water.
  • After it is saturated with nutrients it can then be used as a soil amendment – the burden becomes a benefit.
  • Carbon sequestration – short rotation crops could be converted to stable carbon.
  • Other applications include animal feed supplements, bedding, manure management, effluent treatment, building materials, and more.

Standards and carbon sequestration eligibility

One of the primary drivers for economic production of biochar is likely to be the price of carbon credits, either through a government-operated cap and trade system like the NZ Emissions Trading Scheme, or via a voluntary market such as Puro.earth. In order for this value to be properly attributed, quantification of the carbon stored in biochar needs to be robust and verifiable and must take into account the complete lifecycle analysis (LCA) of production and application, along with reliable models of its longevity in the environment.

Modern pyrolysis plants as well as certain types of farm-scale methods such as flame cap pyrolysis systems can produce biochar in an energy efficient way.

European Biochar Certificate

The European Biochar Certificate (european-biochar.org) is a voluntary industry standard in Europe. In Switzerland, however, it is obligatory for all biochar sold for use in agriculture.

IBI Standards

The IBI Biochar Certification Program is a voluntary scheme administered by the International Biochar Initiative (IBI) to provide certification of biochar products (biochar-international.org)

The Biochar Network New Zealand Inc. (BNNZ)

Biochar Network of New Zealand (BNNZ) is an incorporated society constituted in 2019 with a mission to promote widespread acceptance of biochar. BNNZ has members with a high degree of practical knowledge who are passionate about biochar and its benefits. Join BNNZ at biochar.net.nz.

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