Soil Physical Chemistry, Second Edition

Abstract

Soil organic matter (SOM) is one of the most important natural resources and the basis of soil fertility. The term SOM generally refers to the total organic carbon (C)-containing substances in soil. The total mass of organic C in soils has been estimated at 22 × 10 14 kg, similar to the total of all other C reservoirs on the earth’s surface (21 × 10 14 kg). 1 SOM contents range from less than 1% in sandy and desert soils to 1%-5% (w/w) in the surface horizons (top 15 cm) of typical mineral and agricultural soils, to almost 100% in organic soils. 2 Even at the lowest levels, the role of SOM in all processes occurring in soil is ascertained to be highly relevant.