Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 124

Fig. 3.3.3. C emissions during days 3-9 of incubation of experimental soils at 20 ° C with
5 mg C g − 1 soil as cellulose in various physical forms.

if we assume the cellulose is 100% RPM, immobilization and mineraliza-
tion are too slow. Dalenbergh and Jager (1989) postulated that cellulose
decomposition may show a lag phase as cellulolytic microorganisms need to
be activated by supply of soluble C. However, this was not expected to be
the case in this work as cellulose decomposers would have the opportunity
to develop in the PMS during storage prior to spreading.
Finally, the initial and potential biological activity of the soil will
influence the kinetics of decomposition. In the laboratory, incubation
decomposition rates for the organic soil were close to or above those
predicted by MOTOR, on the cellulose powder and filter paper square
treatments (Fig. 3.3.3). Counts in field soil sampled in May 1999 showed
that bacterivorous nematode numbers in the Balmalcolm soil (~3 g −1 of
soil) were only 20% of those in the organic soil (Sattar, 1999). The ratio of
bacterial grazer C to bacterial C at the start of a parallel incubation experi-
ment was 1% for the Balmalcolm soil and 11% for the organic soil (Sattar,
1999). Thus initial grazing of bacteria on the Balmalcolm soil would be
slow, extending the period of immobilization. Incubation with cellulose for
4 weeks did not lead to a significant increase in nematode numbers with
Balmalcolm soil, but did in the organic soil (Sattar, 1999). The initial value
of

(the proportion of total biomass that consists of primary and secondary
consumers) on the Balmalcolm soil was only ~2%, compared with a value of
7% used in the parameter estimation work of Whitmore (1996). This could
retard mineralization significantly and make invalid the assumption that
k 2 α

α

) is constant, implicit in the rate constant used for biomass C
decomposition. We have made calculations of the expected steady-state
mineralization rate of Balmalcolm soil using the food web model of de
Ruiter et al . (1993). These show that mineralization during decomposition

(1 −α