1. Alt D and Peters I 1992. Die CaCl2/DTPA-Methode zur Untersuchung Gärtnerischer Erden auf Mengen- und Spurenelemente. Agribiol. Res. 45, 204–214.
2. Carpena O Guillén M G Fernandez F G and Caro M 1968. Saline soil classification using the 1:5 aqueous extract. 9th International Congress of Soil Science, Transactions vol. 1, 483–490.
3. CEN 1999a. European Committee for Standardisation CEN/TC 223. Soil improvers and growing media – Sampling. EN 12579, 11 pp.
4. CEN 1999b. European Committee for Standardisation CEN/TC 223. Soil improvers and growing media – Determination of pH. EN 13037, 9 pp.
5. CEN 2001a. European Committee for Standardisation CEN/TC 223. Soil improvers and growing media – Extraction of water soluble nutrients. EN 13652, 15 pp.