Lecture 3

Soil Organic and InorganicCARBON• Carbon (C) is present in all soils in the form of soil organic matter;however, soils formed arid regions can contain significant amountsof inorganic C as carbonate minerals.• Soil organic matter contents vary from less than 1% in coarsetexturedsoils and soils of arid regions to nearly 100% in somepoorly drained organic soils. Typical farmland topsoils may containto 10% organic matter.• Organic matter influences soil physical, chemical, and biologicalproperties. Soil structure is often improved with the addition oforganic materials such as animal manures, municipal biosolids,composts, and from crop residues that are returned to the soils.• Soil inorganic carbon includes the solid-phase carbonate mineralsas well as the soluble carbonate species — carbonic acid (H2C03),bicarbonate (HCO3 ), and carbonate (C03 2- ) are important inbuffering calcareous soil systems.