Simultaneous decomposition processes in soils.

Abstract

IT has been found1 that following the moistening of a dry soil two independent decomposition processes occur, namely, (1) decomposition of soluble organic material without nitrification and (2) decomposition of non-soluble organic material with nitrification. Both rates of decomposition fall off rapidly, with (1) as the soluble substrate is exhausted and with (2) as physical changes, among others, occur at the surface. These changes appear to involve organic gels the surface area of which is increased by drying, possibly as a result of fragmentation or increased porosity. On first moistening, a greater surface area is exposed to solution processes (followed by (1)), and to decomposition (2) than later when, under continued moist conditions, reversible changes occur in the colloids leading to reduced surface area. Prolongation of the dry state, without the soil necessarily becoming drier, increases the magnitude of (1) and (2), which indicates that ageing, a typical colloidal phenomenon, is involved. Moreover, since the behaviour described under (1) and (2) is repetitive with successive dryings and rewettings the changes in the colloids must be reversible, indicating that elastic gels are involved.