How biochar is processed changes green roof water storage
Liao W, Drake JAP, Thomas SC
Soil Health
If you're building a green roof or raised bed with biochar, this shows the size and shape of the biochar chunks matters just as much as the material itself for keeping plants watered and preventing soggy, eroded soil.
Biochar is charcoal-like material added to soil to help it hold water and nutrients better. This study found that grinding biochar into fine pieces creates lots of tiny pores that soak up water, while forming it into granules smooths those pores away and makes the water behavior more uniform no matter the size. For green roofs, medium-sized crushed biochar or granulated biochar struck the best balance, holding enough water for plants while still draining well enough to avoid waterlogging.
Key Findings
Granulated biochar had collapsed pore structure, giving consistent hydrological behavior regardless of particle size, while unprocessed biochar's surface area and pore volume rose sharply as particle size decreased
Granulated biochar amendment improved substrate field capacity, pointing to better stormwater retention potential
Fine (0.5-1 mm) and intermediate (2-2.8 mm) unprocessed biochar increased plant available water, but fine particles also lowered saturated hydraulic conductivity and raised risks of erosion and waterlogging
chevron_right Technical Summary
Scientists found that how biochar is processed, whether crushed into small particles or formed into granules, changes how well it helps green roof soils soak up and hold water. Granulated biochar or medium-sized crushed biochar gave the best balance of water retention and drainage for green roofs.
Abstract Preview
Original paper
Biochar granulation and particle size influence hydrological performance of green roof substrates.
Green roofs are increasingly implemented in cities to improve stormwater management and provide additional ecosystem services. Biochar, a carbon-rich material derived from pyrolyzed biomass, has em...
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