Back­ground

In the Cana­di­an province of Quebec, plant coal has been used as a sub­sti­tute for peat and perlite in refor­esta­tion projects for the rearing of tree seedlings for some time. There are two reasons for this. On the one hand, prices for con­ven­tion­al plant­i­ng sub­strates have risen, and on the other hand the forestry indus­try is also striv­ing for more envi­ron­men­tal­ly friend­ly rearing process­es. In the study (see below for details) the use of biochar in the cul­ti­va­tion of white spruce seedlings was inves­ti­gat­ed for over a year.
The authors con­clud­ed that the perlite content can be com­plete­ly replaced with biochar and up to 25% of the peat volume. The growth of the seedlings was not accel­er­at­ed by the use of biochar. However, the eco­nom­ic analy­sis pro­duced a cost advan­tage of 25 percent, which, accord­ing to the authors, is likely to increase further due to further falling prices for biochar on the market, lower trans­port costs and lower main­te­nance costs. The authors also iden­ti­fied an eco­log­i­cal advan­tage: If the entire perlite used in Quebec for gar­den­ing and land­scap­ing were replaced by biochar, this would lead to a CO2 saving of up to 4000 t/a.

Problem with con­ven­tion­al growing sub­strates

The seedlings of white spruce are extreme­ly sen­si­tive to exter­nal envi­ron­men­tal influ­ences such as the correct pH value and sta­bil­i­ty of the plant sub­strate as well as water avail­abil­i­ty. Most nurs­eries in Quebec there­fore use peat-based sub­strates con­tain­ing perlite or ver­mi­culite to main­tain the desired aer­a­tion, bulk density, water avail­abil­i­ty and sta­bil­i­ty. Prices for perlite, ver­mi­culite and peat have risen sig­nif­i­cant­ly and are expect­ed to con­tin­ue to rise. In addi­tion, perlite is usually import­ed and is con­sid­ered a finite resource. Peat is pro­duced in Quebec in large quan­ti­ties and is there­fore afford­able. However, costs have also risen, and peat is con­sid­ered a finite resource like perlite. In addi­tion, peat cutting is accom­pa­nied by the destruc­tion of impor­tant wet­lands and high CO2 emis­sions into the atmos­phere.

Effect of biochar on forestry

The use of biochar in forestry would there­fore have several pos­i­tive effects. On the one hand, the forestry indus­try pro­duces mil­lions of tons of branch­es, bark, sawdust and other forest residues annu­al­ly, from which the required biochar can be pro­duced locally by envi­ron­men­tal­ly friend­ly pyrol­y­sis. On the other hand, biochar has impor­tant prop­er­ties which may vary depend­ing on the pro­duc­tion process and input mate­r­i­al, but which have in prin­ci­ple been proven to be ben­e­fi­cial for tree growth in various studies: Biochar improves root aer­a­tion, increas­es the pH value and thus pre­vents root dis­eases. It reg­u­lates the water content and sup­ports the micro­bial life in the soil, which leads to increased plant pro­duc­tiv­i­ty. What’s more, biochar offers high water storage capac­i­ty and acts as a struc­tur­ing com­po­nent in soils and sub­strates. Fur­ther­more, there is no addi­tion­al effort for the use of biochar, neither for tree nursery pro­duc­ers nor for refor­esta­tion, as the use of biochar requires the same tech­ni­cal equip­ment as for the pro­cess­ing of peat.

3 dif­fer­ent plant carbons in com­par­i­son

In the study 3 dif­fer­ent plant carbons were tested: Firstly, plant carbons were obtained by pyrol­y­sis (15 minutes at 475 °C) of soft­wood bark residues/ soft­wood bark residues (BC1). For the second variant (BC2) spruce sawdust was pyrol­ysed for a few seconds at 454 °C (BC2), for the third variant hard char­coal residues (> 75% sugar maple) were charred at 500 °C for 24–48 hours (BC3). In the respec­tive test sub­strates, the biochar replaced either peat or perlite or both. In addi­tion, the pro­por­tion of biochar in the total volume varied between 6, 12 and 25 percent by volume. The desired growth effects of perlite and peat could be observed with all biochar vari­ants. Dif­fer­ences to the control group result­ed only from greater pH fluc­tu­a­tions in the plant coal sub­strate vari­ants, but accord­ing to the authors this could be avoided by more precise settings/controls.

Orig­i­nal article: Sub­strates con­tain­ing biochar for white spruce pro­duc­tion in nursery: Plant growth, eco­nom­ics and carbon seques­tra­tion
Author: Sébastien F. Lange, Suzanne E. Allaire
Pub­lished in: Centre de Recherche sur les Matéri­aux Renou­ve­lables, Uni­ver­sité Laval and GECA Envi­ron­ment, Quebec, Canada, 2018