I'll Take Biochar Dressing on the Side

In addition to top-dressing, side-dressing with biochar looks like a labor-saving method of application. Not only is it easier, but the resulting black mulch will enhance the appearance of gardens like mine. I've been using free shredded wood mulch on the paths between my garden beds. With cardboard underneath, a thick mulch layer helps keep weeds to a minimum and feeds the underlying soil as it breaks down. The same can be said of biochar, but there are several additional advantages. (1) Biochar will last much longer than decayed wood chips. (2) Walking paths suffer from compaction, making them less hospitable to roots. Walking on the biochar grinds it down. Biochar particles contain pore space that will compensate for compaction, aerating the soil as they are leached in over time. Paths that are less compacted (containing more air) are more inviting to roots and mycelia. If the roots don't reach that far, mycorrhizae can perform their horizontal drilling trick, expanding the resources available to the plants. (3) Charred wood spread all over is more reminiscent of a forest fire, which is a kick-starter for new growth. (4) More carbon sequestration. (5) It looks more attractive and doesn't fade out the way wood chips do. (6) It's a provocative way to make neighboring gardeners interested in biochar.
The beginning of my biochar mulched paths project. 
This method will have me applying biochar to paths at a greater rate than most of my garden beds, but they will eventually catch up, due to repeated dosing with biochar-infused compost. Biochar application rates over 150 t/ha have been shown to be excessive. For 10 cm of soil, that comes out to almost 50% biochar, which I take to be the target for my gardens. Most gardeners and farmers won't shoot that high, because diminishing returns come into play around 10 t/ha, but I should be able to make this much biochar, and diminishing returns or not, I hope to see some marginal improvement for 10 successive years all the way up to 50% concentration by using biochar on both my beds and paths. Once applications are maxed out, the infiltration of biochar on the paths will continue to promise some improvement for years afterward.


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