Agriculture Reference
In-Depth Information
samples is usually very low. For this reason, Hue and Liu (
1995
) suggested using
the Cw:N
org
ratio as a suitable parameter for assessing compost maturity, proposing
a value of < 0.70 as a new index of compost stability. However, Bernal et al. (
1998
)
found that some immature compost reached this value at thermophilic stage, thus
they proposed a limit < 0.55 of Cw:N
org
to describe well matured and stabilized
composts. Raj and Antil (
2011
) also confirmed this value as maturity index of com-
posts prepared from farm and agro-industrial waste materials.
5.3.2.5
Water Soluble Carbon (WSC)
The WSC represents the most easily biodegradable C fraction during the compost-
ing process because it consists of sugars, organic acids, amino acids and phenols,
apart from the soluble fraction of fulvic acids (Garcia et al.
1991
). The concentration
of WSC declined with composting time in all types of composts. The biodegrad-
able C fractions were consumed first by microbes, which leads the decomposition
of complex organic compounds resulting the release of CO
2
at the end and some of
them polymerizes with nitrogenous compound producing humic substances. Eggen
and Vethe (
2001
) and Garcia et al. (
1991
) established the 0.5 % value of WSC as
a maximum content above which compost could be considered as mature. Other
values of this parameter were those suggested by Hue and Liu (
1995
) (WSC < 1 %)
and by Bernal et al. (
1998
) (WSC < 1.7 %).
5.3.2.6
NH
4
+
and NO
3
-N Concentration
Compost maturity can also be defined in terms of nitrification. When the NH
4
+
-N
concentration decreases and NO
3
-N concentration increases in the composting ma-
terial is considered ready to be used as compost (Finstein and Miller
1985
). A high
level of NH
4
+
concentration indicates an un-stabilized material. The absence or de-
crease in NH
4
+
-N is an indication of both good quality and completion of maturation
process (Tiquia et al.
1997
). Zucconi and de Bertoldi (
1987
) suggested the maxi-
mum limit of NH
4
+
-N content to be below 0.04 % for mature compost. However,
Raj and Antil (
2011
,
2012b
) did not found this limit as an indication of maturity of
composts prepared from different organic wastes. They suggested that decrease in
NH
4
+
-N concentration and increase in NO
3
-N concentration indicates the maturity
of compost. Bernal et al. (
1998
) suggested that the ratio of NH
4
+
: NO
3
-N < 0.16 is
an indication of maturity of composts prepared from wide range of organic wastes.
5.3.2.7
CEC (Ash Free Material Basis)
The CEC of the composts increased with the advancement of composting time due
to decomposition of organic matter. The humification process produces functional
groups influenced by the increased oxidation of organic matter, which leads to rise
