The boundary between soil and atmosphere is an important and active place. It controls to a large extent the flux of nutrients, water, gasses, and heat to and from the underlying soil and so it has a direct and dramatic influence on the conditions of the soil below the interface, the microbes, animals, and plants that live in the soil, and the amount of surface runoff generated from excess rainfall. The upper few millimeters of soil is the gateway to the soil below, and thus it has a direct and ...