Container nursery

Gasifier Charcoal as a Substitute for Vermiculite in Container Growing Media
Tom Miles, August 22, 2009
P Pine Seedlings in 25% Biochar
Our second trial of biochar as a substitute for vermiculite in container media for growing tree seedling has proved successful. These tests are by a private nursery to determine if charcoal from a gasifier heating system can be used in container growing media.

Last year weathered charcoal was collected from forest fire burns, milled, and used as a direct substitute for vermiculite in up to 50% of the container mix. Some of those trees have been retained in containers for a second year and still look good. At that time the forest tree nursery concluded that the biochar could be used for up to 50% of the mix with some adjustments to plant nutrition.
http://terrapreta.bioenergylists.org/charcoalmedia

This year the nursery filled a larger sample with media containing 25% biochar from a gasifier.

During gasification the char is made as wood (mixed Pine and Douglas Fir from the California Coast range) is subjected to temperatures of 1000 C (1832 F) in an oxidizing atmosphere and 850C (1562 F) in a reducing environment. Tars are volatilized and combusted to carbon dioxide and water. Tars are completely consumed in the process. The CO2 reacts with the devolatilized charcoal to form a gas rich in carbon monoxide and hydrogen. The gas will be used in place of propane to heat greenhouses.

Water is condensed from the gas. The recovered water (condensate) could probably be used to supplement irrigation. It is clear to light lemon colored and has a faint odor. It has a pH of 7.1 and is highly saline with an electrical conductivity (EC) of 5.1 mS/cm. It will be analyzed for composition.

Less than 5% of the dry fuel is recovered from the gasifier as a charcoal residue. The charcoal residue is still being characterized. It is small in size and puffy with powdery fines that are like a confectioner’s sugar. Due to the conditions of carbonization it is likely that it has very low labile (volatile) carbon, high surface area, high CEC and high pH. (High pH does not appear to have affected nutrient availability in previous trials even up to 50% charcoal in the container mix.) It was tested at the nursery as biochar.

Ponderosa pine seedlings grown in 25% gasifier charcoal since June were identical in root development and plant growth as those grown in the vermiculite mix. Two of each are shown in the attached image.

Future trials will use biochar in media to grow other tree species.
Condensate from Wood Gas

Charcoal in Container Growing Media
Tom Miles, January 11, 2009

P Pine Grown in Vermiculite (Left) and Charcoal (Right) Media

After visiting Richard Haard and Larry Williams in early 2007 I started discussing the use of charcoal with various nursery growers and researchers in the West. A commercial nursery in California became interested in substituting charcoal for vermiculite in a growing media - soilless substrate - for container grown tree seedlings.

There could be both financial and ecological benefits from using charcoal in place of vermiculite. Vermiculite is increasingly expensive, especially in the quantities used by commercial nurseries. Locally made charcoal should be cheaper. Vermiculite has a poor carbon footprint since it is heated to 1000 C (1832 F) in processing and transported long distances, often imported. Charcoal that is made locally as a byproduct of energy production could be used in growing media. Since it would be planted in the forest with the seedling the carbon sequestration would be permanent.

The nursery uses a growing media made of combinations of peat (50%), bark (20%) and vermiculite (30%). Bark is a common material in Northwest nurseries and has been studied extensively. (See Landis, Altland, Buamscha, Scagel). The grower tested seven mixtures substituting charcoal for vermiculite (up to 30% of the mix) and substituting compost for peat, another expensive substrate.

Each blend was placed in two Styrofoam blocks containing 112 plants for a total of 896 plants including the control. Ponderosa pine was grown in all containers.

Charcoal was gathered from mixed conifer burns in a local watershed. It was crushed and screened through a 1/4 inch (6 mm) screen.

The bulk density of the charcoal was 14.6 lbs/ft3 (0.23 g/cm^3 ) compared with vermiculite at 4-10 lb/ft3 (.06-.160 g/cm^3 ); bark at 0.17 to 0.20 g/cm^3 ; and peat at 0.08 g/cm^3. Perlite and pumice are also used in some nursery mixes. They are denser with perlite at 0.32-.4 g/cm^3 and pumice at .38-.66 g/cm^3 .

The density of the 30% charcoal mix 15.4 lb/ft3 (0.25 g/cm3) was similar to the control at 14.6 lb/ft3 (0.23 g/cm3). The other blends were somewhat heavier at 18-29 lb/ft3 (0.29-0.47 g/cm3).

Water availability was similar for the 30% char (67%) to the 30% vermiculite control (68%) and slightly less (48-60%) for the other mixes. 50% is typical. At loading it was noted that the char mix was "very hydrophobic."

Air-filled porosity was similar (14%) for the 30% charcoal to the 30% vermiculite control (16%) and in a similar range (14%-19%) for the other mixes. Typical is 12-15% with a maximum of 25%.

pH was 5.2 in the 30% vermiculite control mix and 6.1 in the 30% charcoal mix. Substitution of compost for peat in the mixes raised the pH to between 7.1 and 7.5.

At the time of my visit last week both plant health and root growth looked the same for the 30% char and 30% vermiculite. Root plugs were firm. The grower is both surprised and satisfied with the success of the charcoal substitution and will be doing further testing after a closer evaluation of the plants.

Tom Miles
www.terrapreta.bioenergylists.org/

Links:

Haard, Richard, FourthCorner Nursery, Washington, http://terrapreta.bioenergylists.org/taxonomy/term/229

Landis, T.,D., 1990. Containers and Growing Media,Vol 2, The Container Tree Nursery Manual, Agricultural Handbook 674, Washington,D. C.: US Department of Agriculture Forest Service 41-5.
http://www.rngr.net/Publications/ctnm/Folder.2003-05-16.0558

Landis, T.D. and Morgan, N. 2008. Growing Media: Overiew and Update Preentation to Western Forest and Conservation Nursery Association, Missoula, MT. (attached)

Altland,J Baumscha G-Nutrient Availability from Douglas Fir Bark in Response to Substrate pH
http://www.ars.usda.gov/research/publications/publications.htm?SEQ_NO_11...

Gabriela Buamscha and James Altland, Pumice and the Oregon Nursery Industry
http://oan.org/displaycommon.cfm?an=1&subarticlenbr=162

Altland, J, Changing Container Substrate pH: What are the affects of peat moss, lime source and lime rate? http://oan.org/displaycommon.cfm?an=1&subarticlenbr=20

Buamscha, G, Container no-brainer, The physical properties of substrates play a big part in crop health and costs, Oregon Associationof Nurseries
http://oan.org/displaycommon.cfm?an=1&subarticlenbr=452
http://www.rngr.net/About/personnel

Scagel, Carolyn, Container Soilless Substrate Component Fertility for the Northwest Nursery Industry http://www.ars.usda.gov/research/projects/projects.htm?accn_no=412543
Publications: http://www.ars.usda.gov/pandp/docs.htm?docid=12357