Problems Related to the Humification Processes in Soils of Temperate Climates

Soil organic matter has been extensively examined because of its importance for soil fertility and productivity, and as a critical component in agricultural production systems. Furthermore, its importance for establishing favorable physical conditions and architecture in soil has been emphasized. Because biological, chemical, and physical processes are involved in the balance between concurrent mineralization and immobilization of organic residues and nutrients, soils must always be considered in connection with their microflora and microfauna. The biodegradation of lignin is less well understood than that of cellulose. This is partly the result of the complicated structure of lignin, in which phenylpropanoid units- the lignin alcohols- are connected irregularly by C-O-C and C-C linkages. Proteins, amino acids, amino sugars, and nucleic acids, either in plant residues or in dead microbial cells, are generally readily degraded or transformed in soil.