Also read Tom Philpott's story on no-till, cover-crop farming evangelist David Brandt.
1. After the harvest, the farmer plants a cover crop, which sucks CO2 out of the atmosphere. (Some—like legumes—also enrich the soil with nitrogen.)
2. The cover crop dies, leaving behind organic matter that makes soil more fertile, keeps weeds from growing, and moderates soil temperature.
3. The soil is not tilled before planting cash crops like corn or soybeans so that buried organic matter won't oxidize CO2, and soil-enriching microbes and worms are preserved.
4. Over time, cover crops create a layer of carbon-rich topsoil (humus) resistant to both drought and erosion.