What claims are made about biochar?
Biochar incorporation into soil is an important route for CO2 removal from the atmosphere by terrestrial carbon sequestration (Intergovernmental Panel on Climate Change; 2018). Our understanding of biochar and its properties has developed much over recent years, and considerable scientific research is still underway – including trials at RHS Garden Wisley.
Biochar as a soil additive
The application of biochar to soil is known to have various effects;
Positive effects reported include improving plant health through neutralising acidity, providing improved water and nutrient retention (especially in sandy soils) and improved drainage and aeration. Each fragment can also provide a habitat for beneficial soil microbes.
Negative effects are primarily due to the use of biochars with a high pH (a pH more than 7, or ‘alkaline’) in situations where a rise in soil pH is not desirable, e.g. where pH is already ideal, or where ericaceous plants are grown. However, it is important to note that not all biochars are alkaline, with many having a pH around 7 or lower (acid). There are also concerns related to quality of material purchased. It is a good idea to ensure the origins of your biochar are traceable (e.g. FSC certified). For this reason, at the RHS we use only biochar that is sustainably sourced.
Research at Wisley
Experiments are underway at Wisley to determine 1) If nutrient-use efficiency of plants on Wisley’s sandy soils can be improved through woody biochar, and 2) Any associated effects on plant health/growth.