Agriculture Reference
In-Depth Information
compost because the GI values reported by previous researchers were not a suitable
threshold value for determining the maturity of composted animal manure. How-
ever, the results obtained using GI should be interpreted with caution, because the
GI was affected by the type of seed used and applied extraction rates (Bernal et al.
1998
; Wu et al.
2000
; Tang et al.
2006
).
5.3.3.2
Oxygen and CO
2
Respirometry
The aerobic respiration rate was selected as the most suitable parameters to assess
the aerobic biological activity and hence stability. The respiration can be measured
in several ways: carbon dioxide evolution, oxygen consumption and self-heating,
which are indicative of the amount of degradable OM still present and which are
related inversely to stabilization (Zucconi and de Bertoldi
1987
). Immature com-
post has a strong demand for oxygen and high CO
2
production rates, due to high
microbial activity as a consequence of the abundance of easily biodegradable com-
pounds in the raw material. For this reason, O
2
consumption and CO
2
production
are indicative of compost stability and maturity (Iannotti et al.
1994
; Hue and Liu
1995
; Barrena-Gómez et al.
2006
). Hue and Liu (
1995
) set the limit of the CO
2
production rate for compost maturity at < 120 mg CO
2
kg
−1
h
−1
. Wang et al. (
2004
)
used a respiration rate of < 1 mg CO
2
-C g
−1
dwd
−1
to define a highly stabilized
compost. Cooperband et al. (
2003
) suggested a NO
3
-N/CO
2
-C g
−1
ratio > 8 per day
as an index for compost maturity. The relationship between CO
2
respiration and
phytotoxicity of immature compost was studied by García-Gómez et al. (
2003
) and
found that the CO
2
-C evolved correlated with plant growth and immature compost
caused N-immobilisation in the soil, leading to plant N-deficiency.
5.3.3.3
Microbial Population/Count
The decomposition of organic matter is a microbial process and directly related
with total microbial count and their activity during composting of organic wastes
(Morel et al.
1985
). This method is based on the initial hypothesis that the microbial
population stabilized on the maturity of compost. Some important studies in the
evolution and quantification of different group of microorganisms involved in the
process of composting have been carried (Albonetti and Massari
1979
; De Bertoldi
and Zucconi
1980
). The microbial population increased at thermophilic stage and
then decreased at maturation phase and become constant at the end of compost-
ing indicating the stable nature of composting material (Petkova and Kostov
1996
;
Tiquia et al.
1996
). A decrease in bacterial and fungal counts, and increase in acti-
nomycetes counts and stable at the end of composting appear as useful indicator for
establishing biological stabilization and optimum degree of compost maturity (An-
til and Raj
2012
). A gummy whitish appearance in composting materials indicates
the presence of actinomycetes. For compost hygenization, the average number of
total coliform, faecal coliforms and faecal enterococci densities should be less than
< 500 MPN/g (Vuorinen and Saharinen
1997
; Dahshan et al.
2013
).
