The Influence of Biochar Soil Amendment on Tree Growth and Soil Quality: A Review for the Arboricultural Industry

Abstract

Studies assessing the effects of biochar used as a soil amendment in agriculture and forestry have indicated variable results, from significant improvements in growth and health to no effect at all. Research into biochar use for trees within the urban landscape is extremely limited. This review is aimed at arboricultural practitioners and professionals involved in urban tree landscape management and provides a critical analysis of the use of biochar to support tree health and establishment. Biochar, specifically wood biomass-based biochar, has the potential to enhance tree establishment and survival. However, considerable variability in the physical and chemical properties of biochar currently limits universal application. Therefore, practitioners should aim to use biochar types suitable for the desired function, such as transplant establishment, remediation of declining mature trees, and pest/disease management. Biochar also represents a promising complementary amendment to more established soil management techniques such as mulching and fertilization, but further long-term studies in a range of conditions typical of urban environments are required to fully understand the effects of specific biochar types on urban trees.

Biochar-biofertilizer combinations enhance growth and nutrient uptake in silver maple grown in an urban soil

“…Biochar amendments were each bulk-mixed by hand at a rate of 40 g of biochar per 2500 ml of soil then added to ~4-L nursery pots, which was equivalent by weight per area to ~20 t/ha. Several prior studies have indicated that 20 t/ha is an appropriate biochar application rate to benefit trees [ 16 , 70 ]. Biofertilizer treatments were mixed using filtered water according to supplier recommendations at a rate of ~0.5% solution for Bv with IY and a ~0.56% solution for just IY, and were both applied one week after planting and then again 1 month later.…”

“…While biochar applications have been studied extensively in an agricultural context, research into the potential use of biochar for urban tree applications is still limited to a few studies (eg. [10,[14][15][16][17][18][19]. With municipal governments increasingly restricting use of fertilizers and inorganic materials in the urban landscape [20], there have been calls for innovations in soil amendments for urban ecosystems [21,22].…”

“…Most high temperature biochars are moderately to strongly basic, and studies have documented a liming effect from the addition of higher pH biochars to soils with low pH [26][27][28]. However, studies examining the impact of biochar on alkaline and human-altered soils common in many urban areas are few [16,29]. Through selection of appropriate feedstock and pyrolysis conditions, it is possible to produce biochars that are near neutral in pH [28,30].…”

The Influence of Soil Decompaction and Amendments on Soil Quality

“…The application of biochar as a soil amendment has been shown to enhance transplant survival of young trees, improve root growth and health of mature established trees, reduce soil compaction, and reduce the severity of root pathogens such as Armillaria and Phytophthora (Scharenbroch et al 2013;Schaffert and Percival 2016;Blanco-Canqui 2017;Yoo et al 2020;Schaffert et al 2022). Results of this study, however, show little improvement in soil quality when biochar was added via vertical mulching.…”

“…Biochar is the solid co-product of biomass pyrolysis: a technique used for carbon-negative production of second-generation biofuels. Biochar can be applied as a soil amendment, where it permanently sequesters carbon from the atmosphere as well as improving soil structure, nutrient retention, and crop productivity (Blackwell et al 2009;Elad et al 2012;Schaffert et al 2022). Indirect evidence exists that biochar will aid in the reduction of soil compaction by altering the physical nature of most soils through increasing the soil surface area and enhancing soil pore space (Blackwell et al 2009).…”