Nitrate was almost absent at the beginning and
started to increase after the thermophilic phase (data
not shown) because of inhibition by an excessive
amount of ammonia and the high temperature of the
growth of nitrifying bacteria (Morisaki et al., 1989).
The control had a higher content of nitrate than its
counterparts with the added ash, which might have
been due to the inhibition by high salinity and
alkalinity of the growth of nitrifiers (Pichtel, 1990).
Soluble organic N increased initially and was either
mineralized into NH4-N which partly evaporated, or
was assimilated into organic-N by microorganisms in
the compost (Morisaki et al., 1989) [Fig. 2(c)]. High
concentrations of soluble organic N in the control
indicated that more organic nitrogen compounds were
synthesized in the control than in treatments with ash
amendment.
The content of total N increased during the
composting process for all treatments due to a net loss
of dry mass (data not shown), which coincided with
those reported by Inoko et al. (1979). Nitrogen-fixing
bacteria may also have contributed to the increase in
total N in the later stage of composting (Bishop &
Godfrey, 1983). Addition of ash did not cause a significant
loss of nitrogen, with only a maximum loss of 6%
that of the control with 35% coal fly ash-amended
compost.