Bio char Kiln Fabrication and Operation

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2010: $3,893.00
Projected End Date: 12/31/2013
Region: North Central
State: Minnesota
Project Coordinator:

Annual Reports


Not commodity specific


  • Education and Training: on-farm/ranch research
  • Natural Resources/Environment: carbon sequestration, soil stabilization
  • Production Systems: organic agriculture
  • Soil Management: organic matter, composting


    The focus of my grant FNC10-807 was to design, fabricate and develop a process to produce scaled up quantities of bio char. The grant enabled me to fabricate 3 kilns, purchase a chainsaw, and paid for a month’s worth of labor. I utilized downed wood in windbreaks and sawmill scraps; wood that generally was of little use as firewood.

    Some photos have been added to this report, but there are even more photos available online. Copy and paste this link to find more photos from this project.


    I first became interested in bio char application to soils from reading about terra preta, a fertile soil from Brazil which has a large percentage of carbon. Currently there are two reasons for the worldwide interest in bio char. First being the improvement of soils through the addition of bio char. The second is the fact that bio char is a carbon negative phenomenon. The char sequesters carbon for years even decades and could possibly be a candidate for carbon offset credits. Personally I am more interested in the soil improvement aspect because I believe the improvement of soils will be the next Green Revolution and although carbon offset credits will possibly be of some economic benefit, I don’t think they will prove to be especially lucrative. The focus of this study has been the generation of char and its use in soils.

    History of Terra Preta
    Terra preta is a Portugese term meaning dark earth. Terra Preta first interested western science in 1950’s from the work of Wim Sombroek, a Dutch soil scientist. During his work in the Amazon, areas of dark earth were described that had increased fertility from the surrounding soil. It had been generally believed that tropical soils hold little nutrients and decomposing plant material is quickly recycled into living vegetation. However these areas of terra preta had remarkable fertility over many years, even decades. In fact they are still farmed today and are prized. Some of them are even mined for potting soil. They are believed to be man-made and quite ancient, having been formed by adding bone, manure, and charcoal to the native soil. The presence of large amounts of pottery shards also points to their human origin. There is no definitive answer on how they were produced, but it seems there was a long period of formation which ceased at the European conquest or even before. So they have retained remarkable fertility for hundreds of years. A striking difference between the surrounding soils is the large amount of carbon in the soil, up to 70 times more, which gives it a distinctive dark hue, as opposed to the surrounding soils which are much lighter. The patches of terra preta range from small plots to areas of hundreds of acres and can be several feet thick. Whatever process that generated this soil very likely occurred over hundreds or even thousands of years.

    Project objectives:

    Practical kiln design and operation

    I structured this experiment around a large kiln because the limitation of bio char seems to be the manufacturing of enough of it to actually be of use. The kiln is based on a classic and simple design. My kiln is 50 cubic feet or around a third of a cord and will generate 25 cubic feet of bio char on each firing. The cost of the kiln for the metal and fabrication has been around 500 dollars.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.