Agriculture Reference
In-Depth Information
Fig. 9.1
Schematic representation of the temporal variation in compost internal windrow tempera-
ture during aerobic composting. Adapted from Epstein (
1997
) and reproduced from Palmer (
2009
).
In the final stage of composting, known as the secondary mesophilic stage, the
temperature falls gradually from 55-70 °C to ambient temperature and remains at
this temperature for several weeks. Mesophilic microorganisms, which are often
different from the primary mesophilic microorganisms, recolonise the compost in-
cluding those with the potential to suppress plant disease, such as actinobacteria,
and species of
Trichoderma
,
Ulocladium
,
Penicillium
and
Cladosporium
(Rycke-
boer et al.
2003b
). In this late phase, there is a reduction in the amount of degradable
products available and consequently a decline in microbial activity (Hoitink and
Boehm
1999
; Ryckeboer et al.
2003a
; Tuomela et al.
2000
).
Most studies evaluating compost tea have used mature compost. Immature com-
posts have been tested occasionally; for example, Palmer et al. (
2010b
) found that
ACTs produced from open-windrow composts sampled in the early secondary me-
sophilic stage of composting, when the internal compost temperature was ≤ 51 °C,
inhibited colonisation of detached bean leaflets by the fungal pathogen
Botrytis
cinerea
to a greater extent than ACTs produced from compost sampled in the later
mesophilic stages. The diversity of bacteria and fungi in a tea from immature com-
post, determined by culture-independent analysis, was higher 28 days after wind-
row initiation than at later stages of composting, suggesting that microbial diversity
should be explored further as a factor contributing to the suppression of
B. cinerea
(Palmer et al.
2010b
). Analysis of terminal restriction fragments (T-RFs) (Osborn
et al.
2000
) in the same tea revealed 102 bacterial T-RFs and 23 fungal T-RFs when
three restriction enzymes were used for each domain of microorganisms. A single
T-RF can represent several species or taxonomic units. Knowledge of the microbial
community present in immature or mature compost, such as the presence of acti-
nobacteria and fungal genera that have shown potential as single biological control
agents, might provide clues as to what components might be associated with patho-
gen suppression by the resulting compost tea.
