Abstract:
Sequential fractionation of metal cations in various compost types
was carried out to determine the availability of these cations for plant intake.
The selected compost types were domestic, market available, municipal
waste, industrial sludge, weed mulch, vermicompost, fruit waste compost
and cow dung. The metal cations in each compost types were fractionized in
to exchangeable, water soluble, organically bound, carbonate precipitate and
residual fractions by extracting with 0.5M KNO3
for 16 hours, then with de ionized water for 16 hours, then 0.5M NaOH for 16 hours, then 0.05M
Na2EDTA for 16 hours and finally with 4M HNO3
for 16 hours respectively.
Water soluble, exchangeable and organically bound fractions are considered
as mobile fractions and cations in these fractions are available for plant
intake, carbonate precipitate and residual fractions are considered as
residual fractions and are not available for plant intake because they are
tightly bound to respective matrices. The selected micronutrient metals are
zinc (Zn), manganese (Mn), iron (Fe) and copper (Cu). All the metal ions in
each fraction are analyzed by flame atomic absorption spectrometry. This
study found that vermicompost contains the highest level of mobile Cu, fruit
waste compost contains the highest level of mobile Zn and domestic
compost contains the highest level of mobile Mn. All these three types of
compost contain fairly high levels of mobile Fe. Based on this study
vermicompost, fruit waste compost and domestic compost can be considered
as composts with fairly high levels of available (mobile) micronutrients
levels. Among analyzed compost fertilizer sources, vermicompost contains
the highest total (residual + mobile) copper and manganese levels. Industrial
sludge compost contains the highest total zinc level and municipal waste
compost contains the highest total iron level. Because of the non
homogeneous nature of the compost sources, statistical variation of
micronutrient levels in each fractions that are sequenced from various
compost sources are fairly high
