2.3.2. Procedure for phosphate in a soil sample [30]
2.5 g of each of the soil sample was weighed and transferred to a
250 ml conical flask. It was shaken with a measured volume, 50 ml,
of sodium bicarbonate solution of pH 8.5 and continued the shaking
for another 30 min. Then it was kept aside for 20–30 min to attain
equilibration and filtered through a Whatmann filter paper. The
clear filtrate was collected in a 50 ml volumetric flask and diluted
the filtrate to the volume with water. A measured volume, 10 ml,
of the filtrate was transferred into a 50 ml beaker. It was acidified
by drop wise addition of about 1 ml of dilute sulfuric acid.
The acidification of the filtrate could be easily noticed by ceasing
of evolving gas bubbles. Then the solution was transferred into a
25 ml volumetric flask and diluted to volume with water. It was
used for the determination of its phosphate content following the
recommended procedure.