Dissolved organic matter (DOM) is one of the most active and mobile carbon pools and has an important role in global carbon cycling. In addition, dissolved organic carbon (DOC) affects the soil negative electrical charges denitrification process, acid-base reactions in the soil solution, retention and translocation of nutrients (cations), and immobilization of heavy metals and xenobiotics. Soil DOM can be derived from different sources (inputs), such as atmospheric carbon dissolved in rainfall, litter and crop residues, manure, root exudates, and decomposition of soil organic matter (SOM). In the soil, DOM availability depends on its interactions with mineral components (e.g., clays, Fe and Al oxides) modulated by adsorption and desorption processes. It also depends on SOM fractions (e.g., stabilized organic molecules and microbial biomass) by mineralization and immobilization processes. In addition, the intensity of these interactions changes according to soil inherent properties, land use, and crop management.
During the decomposition of organic material, most carbon is lost as CO to the atmosphere by microbial oxidation. Soil type and landscape slope, leaching, and runoff are also important processes associated to DOM losses in the soil. In well-drained soils, leached DOC can reach the water table and release nutrients and pollutants that can contaminate groundwater, whereas runoff transports DOM and xenobiotics to other areas, rivers, and lakes.