Agriculture Reference
In-Depth Information
5.3.2.1
pH
The pH is a good indication showing the development in different stages of com-
posting. The pH dropped slightly at the beginning of the composting process due to
production of organic acids. Soon after, on utilization of these acids as substrates by
other aerobic microbes, the pH increased, during the cooling and maturation stages,
following lowering in pH and reached a value close to neutral (Satisha and Devara-
jan
2007
; Ko et al.
2008
). This trend of pH could be used to monitor the stabilization
and maturation of compost (Gray et al.
1971
; Wu et al.
2000
; Raj and Antil
2012b
).
5.3.2.2
EC
The EC is a measure of dissolved salts in the compost. This measure is significant
because it reflects the salinity of the compost, and overly saline compost is likely
harmful to plants. The sum of soluble salts in the water extracts is increased with the
maturation of compost because of release of organic acids and soluble salts during
organic matter decomposition indicating the stability of compost (Avnimelech et al.
1996
; Wu et al.
2000
).
5.3.2.3
C:N Ratio (Solid Phase)
This is the criteria traditionally used to determine maturity of compost. The rel-
evance of C:N ratio relies on the fact that a decrease in ratio implies in the degree
of humification of organic matter. As the decomposition progressed due to losses
of carbon mainly as carbon dioxide, the carbon content of the compostable mate-
rial decreased with time and N content per unit material increased which resulted
in the decrease of C:N ratio. The researchers reported that a C:N ratio below 20
was assumed to be indicative of maturity compost (Golueke
1981
), a ratio of 15 or
less is preferable (Morel et al.
1985
; Bernal et al.
2009
). On the other hand, some
researchers (Chen and Inber
1993
; Sellami et al.
2008
) reported that C:N ratio alone
is not a sufficient criteria to determine the compost maturity and it is very neces-
sary to associate it with some other chemical and microbial parameters to establish
compost maturity (Goyal et al.
2005
).
5.3.2.4
C:N Ratio (Water Extract)
Composting is a biochemical transformation of organic matter by microorganisms
whose metabolism occurs in water soluble phase. Therefore, a study of the changes
occurring in the soluble organic matter can be useful for the assessing maturity of
compost. A C
w
:N
org
ratio of 5-6 was established by Chanyasak and Kubota (
1981
)
as an essential indicator of compost maturity. However, this ratio is sometimes dif-
ficult to evaluate since the concentration of organic-N in water extract of mature
