CO2 is captured in the soil organic material as carbon. Plants capture CO2 from the air through photosynthesis into organic matter, therefore, leaves, wood and roots form an endless storage vessel for CO2. Micro-organisms are also a major source of soil organic material, however, soil life (fungi, bacteria, small insects etc.) also breaks down organic material. This causes CO2 to be released again and this is known as the carbon cycle.
CO2 capture in organic matter therefore depends on the type of organic matter: stable organic matter contains more carbon than fresh organic matter. The activity of the soil life is important for the degree of degradation. Carbon Check provides insight into the amount of carbon captured.
At the COP21 (Paris) a 4 per 1000 increase was anticipated; so an annual increase of 0.4% per year. On average an increase of 2 ton CO2 can be expected (depending on among others weather conditions and management).