Too many people focus on surface soils, and they're missing out on most of the (soil carbon) action when they do. Here we show that ecosystems favoring forests (wetter, more iron and aluminum) release more CO2 compared to grassland-like ecosystems (dryer, more calcium and magnesium). As our earth warms, we need to consider not only how surface soils will change due to management, but how subsurface soils (where most of the carbon is) will respond due to climate change.