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Abstract

The main aims of this study were to examine the optimal
conditions for composting and factors influencing microbiological
changes during the Composting of Eucalyptus bark in the production
of a plant growth medium.
A bench-scale composter was designed to provide strict
control over air composition, moisture content, temperature and
mixing. The composter consisted of six 4-L capacity gas-tight
units of PVC plastic, each of which was provided with a mixing
paddle coupled to a common drive. A natural temperature rise was
simulated by having the units immersed in a water bath, with the
temperature increased at rates consistent with those observed in
large-scale compost heaps. This provided a companitively
inexpensive versatile system, with rates of CO 2 and CH4
production and 02 consumption automatically monitored by gas
chromatography. Levels of volatilized NH3 and nitrogen
oxides (NO.) were manually monitored from acid traps. The
reproducibility of the system was as good as the best reported.
Optimal conditions for the bench-scale composting of eucalypt
bark were considered to be a temperature of 55 0 , on aeration rate
of at least 20 mL min -1and an initial C:N ratio of 25-30,
depending on the availability of nitrogen. Nitrogen, in
decreasing order of availability, was provided in the form of
urea, isobutylidene diurea (IBDU), fish wastes or sewage cake.
Both respiratory activity and nitrogen loss data were considered
to be of value in determining the economic as well as the
microbiological optimal C:N ratio of bark compost. No further
amendment other than water (giving an initial moisture content of
1147. d.w. basis) was found to be necessary.
Ammonification and NH3 volatilization occurred during
the first sixteen days of composting while volatilization of
NO was substantial during times of undesirable nitrogen
availability. Delaying ammonification in the urea amended composts (by either the addition of quinone or urea's replacement
with IBDU) increased ammonia volatilization. Net nitrification
followed peak net ammonification, but nitrate appeared to be
produced largely chemically rather than biologically.
Volatilization of NO. was greatest from compost prepared
using sewage cake.
Up to five peaks of CO 2 output were observed over a 30
day run, three occurring during the transition to thermophilic
conditions and one or two peaks occurring during a plateau
temperature of 55 0 . The predominant flora comprised Bacillus spp.
during the mesophilic and early thermophilic phases (B.brevis and
B.sphaericus followed by B.circulans and B.brevis then
B.circulans, B.sphaericus or B.stearothersophilus). Bacillus spp.
continued to predominate throughout the composting of sewage-bark
and most of the fish-bark composts. However, actinomycetes
(Streptomyces spp. and Thernomonospora spp.) and coryneforms
predominated at latter stages of urea-bark composts. Strictly
anaerobic bacteria appeared to be unimportant during the
composting of bark. The predominant flora isolated during the
mesophilic phase were not inhibited by compost components of any
age, while members of the climax flora were inhibited by fresh
compost components. Cellulase activity was not correlated with
peaks in CO2 output, but showed a slow increase or decrease,
depending on the initial C:N ratio, over 30 days composting.
However, lipase activity correlated with the peak in CO 2
output at about day sixteen in a fish-bark compost.
The identification of thermophilic Bacillus spp. was aided
by a study of their esterase mobilities and the use of numerical
taxonomy. Phenolic compounds present after 30 days composting were
phytotoxic. However, levels of residual ammonium could largely
account for the phytotoxicity exhibited by water extracts from
most of these composts. Eucalypt bark composts had a higher
density than pine-bark composts or peat moss, but were as good as
or better than the latter materials with regard to their water
characteristics and particle-size distribution.

Item Type:	Thesis - PhD
Authors/Creators:	Ashbolt, NJ
Keywords:	Compost, Eucalyptus bark
Copyright Holders:	The Author
Copyright Information:	Copyright 1984 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 1985. Bibliography: leaves 166-216
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