1. Agro-Technology and Plant Protection "Nikola Pushkarov", Agricultural Academy Sofia,Institute of Soil Science,Department of Agricultural Mechanization and Hydromelorative Systems,Bulgaria
2. Russian State Agrarian University – Moscow Timiryazev Agricultural Academy,Department of Agricultural and Biological Chemistry, Radiology and Vital Activity Security,Moscow,Russia
3. University of Forestry,Department Technologies and Mechanization in Forestry,Sofia,Bulgaria