The food that makes it to your plate is but a fraction of what actually grew in a field somewhere. Cassava, corn, wheat, rice — all critical crops produce waste biomass that farmers might be burning or throwing into piles to rot, both of which send planet-warming carbon into the atmosphere. Increasingly, though, they are turning all those husks and stalks into biochar that captures carbon and improves yields .

This material is a simple, clever way to catalyze photosynthesis. As plants grow, they suck CO2 out of the air, but that carbon returns to the sky when they die and decompose. Heat those dead plants in a low oxygen environment, though, and they turn to concentrated, crumbly carbon that’s a magnet for nutrients. Workers “charge” this biochar by soaking it in manure or other ferti

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