This method is for the determination of water-soluble phosphorus.
Applicable to all fertilisers where water-soluble phosphorus is to be determined.
Extraction in water by shaking under specified conditions.
500 ml graduated flask with a wide neck (eg Stohmann).
Rotary shaker, 35 – 40 turns per minute.
See Method 1.
6.1 Weigh to the nearest 0.001 g, 5 g of the prepared sample and place it in a 500 ml graduated flask (4.1). Add 450 ml of water, the temperature of which must be between 20°C and 25°C. Close the flask and shake on the rotary shaker (4.2) for 30 minutes. Then make up to the mark with water, mix thoroughly and filter through a dry fluted paper into a dry container.
6.2 Determine the phosphorus using Method 10, on an aliquot portion of the clear filtrate.