Wood chips in the Garden?! Do they EVER break down? (yep!)


A comment:

Wood chips are fantastic, but with come some caveats like mentioned. A high C:N in any mulch actually has a negative priming effect on soil carbon, and soil carbon is needed to build microbial communities that fix nitrogen, adding these mulches to low carbon soils can initially slow the process, this is the reason some wood chip or even straw mulch soils can take a while to become productive soils, especially in drier climates where they take longer to biodegrade. It’s only when the C:N of the material biodegrades to about 50:1 that positive priming of soil carbon occurs. In low carbon soils you’re better off putting down compost first before a mulch.
When put on too thick the existing soil can also become deprived of air or saturated with moisture which slows the microbes that perform the nitrification process which happens for the most part in the top 10-15cm of soil. 10 cm of mulch is enough to keep moisture levels high, more doesn’t seem to help much there. Some mulches are also allelopathic and impede microbial communities and plant growth. Allelopathy can often be broken down by composting first, like in those piles the road crew made.
The priming process can be sped up by adding a carbon source like glucose that plants normally feed microbes, or with nitrogen for example from chicken manure. I’d rather add a liquid carbon that microbes can use to replicate themselves immediately rather than nitrogen, as carbon-13 labelling studies have shown that adding nitrogen can mean plants allocate less below-ground carbon for the soil microbes that fix nitrogen. I read one study that showed soil carbon was correlated with 86% of all soil nitrogen in forest ecosystems. You eventually get lots of useful soil carbon and other goodies from wood chips! Eventually…


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