1. ISO: 1994. Soil quality. Determination of pH. ISO 10390:1994
2. ISO: 1998. Soil quality. Determination of organic carbon by sulfochromic oxidation. ISO 14235:1998.
3. Response of soybeans to potassium fertilization on high potassium fixing soil;Kovacevic V.;Rostlinna vyroba,1995
4. The potassium requirements of maize and soyabeans on a high K-fixing soil;Kovacevic V.;South African J. of Plant and Soil,1992