Extraction and composition analysis of humic
substances
Humic and fulvic acids from compost samples
were extracted with 0.1 N NaOH by using the method
of Schnitzer and Skinner (1968). The alkali extraction
was repeated thrice for complete extraction of hum ic
acid. The pooled alkali extract (soluble humic
substances) was acidified to pH 2.0 with 2N Hel,
stirred well and allowed to stand at room temperature
for 24 hours. The precipitated humic acid fraction was
separated by centrifugation. Precipitation and
centrifugation were repeated to attain partial
purification of hum ic acid fraction as described by
Stevenson (1981). The fractions were further purified
by treating with HCI-HF mixture (5ml of each HCI and
HF acids were dissolved in 990 ml of double distilled
water) for 24 hours and this acid mixture was separated
by centrifugation. The residue so obtained was
thoroughly washed with distilled water, freeze dried.
weighed, and expressed as a percentage of dry weight.
The soluble fulvic acid from coagulate ",as
separated by centrifugation and purified by t:le
modified procedure as given by Wander and Traina
(1996). The aqueous solution obtained after centrifugation
was passed through exchange resin (Sera lite
SRC-120) in the H" form. For this, adsorption columns
of 20 cm length with a porcelain perforated bed were