Soil Carbon Controversies in the Classroom

I gave the lecture in our Soil Ecology course today: Soils, Carbon, and Climate Change. It was really fun! I’ve been giving that lecture for a couple of years now, and each year I change the presentation. This year, I introduced “Soil Carbon Controversies” – controversial statements to incite and ignite any cocktail party. Hot topics this year: (1) humic/fulvic acids don’t really exist, (2) soil carbon stocks will decrease under climate change, and (3) biochar is carbon negative. I’m pretty sure the undergraduate parties this weekend are going to get crazy.

We also did an activity where students worked in groups to arrange cut-out global C stocks and fluxes to replicate the global carbon cycle. It’s a great activity, because they need to debate the relative sizes of each pool, whether the fluxes are in balance, and how anthropogenic emissions compare to “natural” stocks and flows. People are often surprised to learn how large soil C stocks are relative to the atmospheric stocks (more than twice as large), and that, compared to gross primary productivity, anthropogenic emissions are relatively small – it’s the fact that they are slightly out of balance with net carbon fixation/respiration and oceanic fluxes that creates this huge problem.

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