Using Biochar with Trees


Research into the use of biochar to boost the establishment and survival of saplings and the growth of mature trees has yielded impressive results that have important implications for farmers, nurseries, landscapers, foresters, forest regenerators, and home gardeners alike.

Improved establishment and growth of trees using biochar

Much like the constraints facing the growth of annual crops, the growth of trees is limited by declining soil fertility, poor soil water and nutrient status, and disease and pests. Having deeper roots than most annual crops, trees are resourceful and able to scavenge nutrients and water from the soils either laterally or deep within the profile.

Biochar has been shown to improve soil fertility and tree growth by various mechanisms, including: increasing soil pH (liming effect), increasing nutrient retention and exchange, improving soil structure and porosity, water holding capacity, and boosting the growth of symbiotic plant associates (e.g. fungi, soil microbia and macroinvertebrates).

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 Stimulation of beneficial soil fungi

Makoto et al. (2009) found that biochar stimulated the growth of symbiotic ectomycorrhiza (the fungal hyphae that grow on the surface of plant root cells which help plants access nutrients and water) in potted trials of conifer saplings. The stimulated ectomycorrhiza were linked to higher solubilisation of phosphorous and nitrification in soils which was subsequently absorbed by the trees, leading to marked increases of above ground and below ground biomass. Makoto et al. (2009) found that the incorporation of a layer of biochar into the mid depth of the soil profile at the root zone returned the best results with an average 216% increase in below ground root biomass and a 330% increase in above ground biomass when comparing biochar treatments to controls containing only soil.

The authors concluded from the results of this trial that biochar applied directly to the root zone of conifers increase nutrient retention, encourages root elongation and increases soil surface area for microbial colonisation. The implications of this research may suggest that the establishment and survival of saplings can be greatly improved by the use of biochar.

Alleviating salt stress

Salt stress is a major factor limiting productivity in Australia, particularly on heavily modified agricultural soils or where plants are irrigated with groundwater, or saline surface water. Coastal areas that are prone to deposition of wind or water transported sea salt are also vulnerable to increased incidence of salt induced plant stress.

Biochar has been shown to reduce salt stress in plants by decreasing plant uptake of sodium (Na+) while increasing uptake of potassium (K+) (Ali et al. 2017). This leads to increased water uptake and deeper root exploration from which the trees could access a larger pool of minerals and water. The findings of this study suggest that biochar may be a low impact and long-lasting amendment to target salt stress, particularly in soils that are heavily depleted of soil carbon due to prolonged degradation.

Reducing soil compaction

Trials conducted by the Tasmanian Institute of Agriculture (TIA 2013) applied biochar to the soil of mature apple trees and found a significant increase in fruit weight and trunk girth after four years with a decrease in soil bulk density overall. The study concluded that even in high potential orchards, the benefits of biochar, particularly when used in combination with compost can have marked effects on soil quality. Of particular interest is biochar’s influence on resisting soil compaction which could be of use in farming systems where heavy machinery is used within interrows for harvesting and farm maintenance but where resultant soil compaction degrades soil structure.

Reducing leaching of nutrients

Ventura et al. (2012) found that leaching of nitrate (NO3-) from fertiliser applications was decreased by 75% after two years of biochar treatments compared to non-biochar amended soils. This finding is of critical importance for farmers and land managers hoping to reduce the cost and energy of fertiliser inputs and minimise the environmental impacts that result from fertiliser runoff or leaching, such as the eutrophication of surrounding waterways that can lead to toxic algal blooms and mass fish kills (Smith et al. 1999).

Biochar to assist urban greening and landscaping

A high mortality rate is associated with transplanted trees, particularly where roots are transplanted bare and into poor soils. The hardened landscapes of urban environments mean that trees (and their symbiotic associates) grown on sidewalks, nature strips and parks are subject to suboptimal conditions, including limited soil water, nutrition, oxygen and organic matter. The low survival rate among transplanted trees means that the establishment of trees in urban/suburban greening projects where soil resources are constrained is costly and variable.

Schaffert and Percival (2016) found that the use of biochar in combination with fertiliser significantly increased survival of transplanted bare-root trees and led to an increase in canopy cover and fruit growth compared to trees grown in non-biochar amended soils.

An article in the Biochar Journal by Embrén (2016) highlights the outcomes from trials conducted over 10 years in Stockholm using biochar and structured soils where cherry trees exhibited enhanced growth. In some cases, six year old trees planted with biochar were reportedly five times larger than 30 year old trees. The author noted that the biochar increased surface permeability which could aid storm water filtration and subterranean water storage. An unexpected outcome from the use of biochar and gravel planting beds was the reduction in local noise and vibration, which was attributed to the absorption of sound waves by the voids in the filled trenches that acted as noise and vibration traps.

Follow the link to read about Embrén's work in more detail.

The research above indicates that the benefits to the survival and growth of trees occurs via a number of physical, chemical and biological interactions in soils which are increasingly being utilised to enhance the survival and growth of trees. Given the value of trees, their myriad products and the extensive success to date in the use of biochar to improve tree growth, biochar and trees is likely to emerge as a cost-effective, environmentally sustainable and potent tree management strategy.

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References and further reading:

Ali, S., Rizwan, M., Qayyum, M.F., Ok, Y.S., Ibrahim, M., Riaz, M., Arif, M.S., Hafeez, F., Al-Wabel, M.I. and Shahzad, A.N., 2017. Biochar soil amendment on alleviation of drought and salt stress in plants: a critical review. Environmental Science and Pollution Research, 24(14), pp.12700-12712.

Embrén B: Planting Urban Trees with Biochar, the Biochar Journal (tBJ), 2016, Arbaz, Switzerland. ISSN 2297-1114,, pp 44-47

Lambers, H., 2003. Introduction, dryland salinity: a key environmental issue in southern Australia. Plant and Soil, 257(2), pp.5-7.

Makoto, K., Tamai, Y., Kim, Y.S. and Koike, T., 2010. Buried charcoal layer and ectomycorrhizae cooperatively promote the growth of Larix gmelinii seedlings. Plant and Soil, 327(1-2), pp.143-152

Schaffert, E. and Percival, G., 2016. The Influence of Biochar, Slow-Release Molasses, and an Organic N: P: K Fertilizer on Transplant Survival of Pyrus communis ‘Williams’ Bon Chrétien’. Arboriculture & Urban Forestry, 42(2).

Smith, V.H., Tilman, G.D. and Nekola, J.C., 1999. Eutrophication: impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems. Environmental pollution, 100(1-3), pp.179-196.

Ventura, M., Sorrenti, G., Panzacchi, P., George, E. and Tonon, G., 2013. Biochar reduces short-term nitrate leaching from a horizon in an apple orchard. Journal of environmental quality, 42(1), pp.76-82.

Tasmanian Institute of Agriculture, 2013, Soil amendment with biochar & compost, accessed via:$file/Biochar_Update_July_2013.pdf