3.1.3. Germination index
A large amount of metabolic compounds are released during
composting process (Zucconi et al., 1981), which are harmful to
plants. In order to evaluate the effect, GI was used to assess the
phytotoxicity of the compost.
Fig. 3 shows GI changes during composting. Compost with GI of
P80% is considered phytotoxic free and adequately matured
(Nakhshiniev et al., 2014). GI percentage was low in the first 16 h
in DHAF, the reason is various intermediate compounds including
a large amount of organic acids which are harmful to plants generated
due to aerobic composting in this stage, the result is also
reflected in Fig. 1 where EC and pH values were changed due to
generation of phytotoxic intermediate compounds. The GI
increased rapidly after16 h of fermentation, in this stage, phytotoxic
intermediate compounds was degraded gradually. Finally,
the GI percentage reached to 88% which showed good maturity.
In contrast, a similar trend GI percentage was observed in TSC.
The GI percentage was around 20% in the first 8 days, and then
increased to 82% which is lower than the value obtained in DHAF,
the reason is organic fertilizer obtained in DHAF is more mature
than in TSC.