1. This method is for the determination of water-soluble phosphorus.
2. All fertilisers, including compound fertilisers, where water-soluble phosphorus is to be determined.
3. Extraction in water by shaking under specific conditions.
4.—4.1 500 ml graduated flask (for example Stohmann).
4.2 Rotary shaker, 35-40 turns per minute.
5. See Method 1.
6.—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 to the flask 450 ml of water, the temperature of which must be between 20° and 25°C. Shake on the rotary shaker (4.2) for 30 minutes. Then make up to the mark with water, mix thoroughly by shaking the filter through a dry fluted filter, into a dry container.
6.2 Determine the phosphorus according to Method 10, on an aliquot part of the clear filtrate.