Agriculture Reference
In-Depth Information
Table 9.2
Typical ranges of characters of compost prepared according to the Australian Standard
4454. Composts, soil conditioners and mulches. (Anonymous
2012
)
Variable
Typical range
pH
5-7.5
Electrical conductivity
No limit, although high EC can be detrimental to
crop production
Soluble phosphorus (mg/L)
≤ 5 for phosphorus sensitive plants
Total phosphorus (% dry mass)
≤ 0.1 for phosphorous sensitive plants
Ammonium (mg/L)
< 300
Ammonium + nitrate (mg/L)
≥ 100 if an input to plant nutrition is required
Nitrogen (% dry matter)
≥ 0.8 if an input to plant nutrition is required
Organic matter content (% dry matter)
≥ 25
Boron (mg/kg)
< 200
Sodium (% dry mass)
< 1
Moisture content (%)
25-40 (maximum dependent on % organic matter)
carbonates (Watson
2004
). Compost prepared with animal manure, will lead to a
compost with a higher EC than those prepared with plant materials (Watson
2004
).
9.4.2
Compost Maturity and Microbial Community
The diversity, abundance and activity of microorganisms in compost vary according
to compost source and maturity (Hoitink and Boehm
1999
). Composts produced in
open windrows undergo a predictable series of biological, physical and chemical
processes (Fig.
9.1
), including a microbial community that follows a predictable
successional pattern (Herrmann and Shann
1997
).
The internal windrow temperature of aerobic compost is the primary regulator
of microbial diversity (Ishii et al.
2000
; Peters et al.
2000
; Tiquia
2005
), activ-
ity (Ryckeboer et al.
2003a
) and population structure (Herrmann and Shann
1997
;
Ryckeboer et al.
2003b
). In the first stage of composting, known as the primary
mesophilic stage, the fresh compost contains readily degradable compounds that
can be utilised by mesophilic microorganisms resulting in a rapid increase in tem-
perature from ambient temperature to around 60 °C. As the process continues, tem-
perature stabilises at approximately 55-70 °C, humic substances and thermophilic
bacterial numbers increase, while human, plant and animal pathogens, weed seeds
and other microorganisms are destroyed.
At temperatures between 40 and 50 °C in the early secondary mesophilic phase
of composting, thermophiles and mesophiles co-exist (Ryckeboer et al.
2003b
). The
following conditions are observed in compost at this time: (a) the optimum temper-
ature for thermophilic fungi that moderate levels of nitrogen (Finstein and Morris
1975
) (b) a diverse range of bacteria that use numerous enzymes to degrade organic
material and transfer soluble materials into bacterial cells (Ryckeboer et al.
2003b
),
and (c) a great diversity and abundance of actinobacteria (Amner et al.
1988
; Fin-
stein and Morris
1975
).
