ABSTRACT
Soil organic matter (SOM) has long been recognized as an important indicator of soil productivity (Haynes, 2005). Organic matter (OM) refers to the solid, nonmineral portions of the soil, originating from plant and animal residues (Aust and Lea, 1991). According to the Soil Science Society of America (2008), SOM can be dened as the organic fraction of the soil exclusive of undecayed plant and animal residues. Hayes and Swift (1983) dened OM as the term used to refer more specically to the nonliving components, which are a heterogeneous mixture, largely composed of products resulting from microbial and chemical transformations of organic debris. This transformation, collectively known as the humication process, gives rise to humus, a mixture of substances, which has a degree of resistance to further microbial attack. An adequate amount of OM in the soil plays an important role in improving the soil physical, chemical, and biological properties, and consequently improves or maintains the sustainability of cropping systems. In agricultural systems, maintenance of SOM has long been recognized as a strategy to reduce soil degradation (Mikha and Rice, 2004; Baldock and Broos, 2012).
