BS EN 13651:2001 – Soil improvers and growing media — Extraction of calcium chloride/DTPA (CAT) soluble nutrients

8 Procedure
8.1 Extraction
8.1.1 Test samples passing through a 20 mm sieve Take a weight equivalent to 60 ml of the sample volume (EN 13040:1999, clause 8.5) to the nearest 1 g and transfer to the container (6.2). Add 300 ml of extracting solution (5.5), secure the cap and shake for 1 h on the shaking machine (6.3) at 22 C 3 C. 8.1.2 Test samples passing through a 40 mm sieve Take a weight equivalent to 250 ml of the sample volume (EN 13040:1999, clause 8.3) to the nearest 1 g and transfer to the container (6.2). Add 1250 ml of extracting solution (5.5), secure the cap and shake for 1 h on the shaking machine (6.3) at 22 C 3 C.
8.1.3 Filtration
Filter through filter paper (6.4) discarding at least the first 10 ml. In some cases paper filtration is too slow or even impossible. In such cases alternative procedures for obtaining a clear supernatant are acceptable and the technique used shall be reported. The filtered extract is stable for three days in a hermetically closed polyethylene bottle if stored in a refrigerator at 0 C to 5 C.
The filtrate can be stored for longer periods in a deep freezer at about 18 C. NOTE Before using a solution that has been frozen, the thawed solution shall be thoroughly mixed to eliminate gradient separation that occurs on freezing and subsequent thawing.
8.2 Blank The reagent blank test shall be carried out in parallel with the determination, by the same procedure as outlined in 8.1.1 or 8.1.2 and 8.1.3, using the same quantities of all the reagents as in the determination but omitting the test portion. NOTE The measurement of a blank is introduced to determine the contribution of the extracting solution, glassware and filter paper used.
9 Determination of the extracted nutrients and elements See annex B.
10 Expression of results Subtract the values determined for the reagent blank from those obtained for the samples. All results shall be calculated using the determined compacted laboratory bulk density and expressed in mg/l substrate as received basis.
11 Precision The repeatability and reproducibility of the calcium chloride DTPA soluble nutrient content in separately prepared samples should be in accordance with Tables A.1 to A.6. A summary of the results of an interlaboratory trial to determine the precision of the method, in accordance with ISO 5725 [2], is given in annex A.
NOTE The values derived from this interlaboratory trial may not be applicable to concentrations and matrices other than those tested.
BS EN 13651:2001 – Soil improvers and growing media — Extraction of calcium chloride/DTPA (CAT) soluble nutrients