It must be noted that despite the concentrations of NH4
+
–N and
NO3
–N may significantly vary in different composted materials at
the initial and final phases, both NH4
+
–N and NO3
–N are considered
as important maturity indexes in the composting process, and the
emergence of nitric acid can be regarded as an indicator of maturity (Bertoldi et al., 1987; Finstein and Miller, 1985; Riffeldi et al.,
1986).