[[1] Dobrovolskiy G. V. Nikitin E. D., Conservation of soil as a building component of biosphere: functional-ecological approach. M.: Nauka, 2000. 185 p.]Search in Google Scholar
[[2] Terekhova V.A., Soil Bioassay: Problems and Approaches. Eurasian Soil Science, 2011, Vol. 44, No. 2, pp. 173-179.10.1134/S1064229311020141]Search in Google Scholar
[[3] Dobrovolskiy G. V. Nikitin E. D., Function of soil in biosphere and ecosystems. M.: Nauka, 1990. 251 p.]Search in Google Scholar
[[4]. Velev, S., Geography of Bulgaria. Physical and socio-economic geography, Geographical Institute of BAS. ForKom, Sofia, 2002, 760 p.]Search in Google Scholar
[[5] Hristov B., M. Teoharov,, Genetic-diagnostic properties of soils defined as highly eroded chernozems. Soil studies, agrochemistry and ecology, № 2, Sofia., 2008, 37-44.]Search in Google Scholar
[[6] Hristov B., Z. Petkova, M. Teoharov., General chemical and agrochemical characteristics of Regosoli i the hilly area of the Danube plane. Soil studies, agrochemistry and ecology № 1, Sofia, 2009, 62-69]Search in Google Scholar
[[7] Radojevic M., V. Bashkin, Practical Environmental Analysis, RSC, 2006, 480 p. ISBN-10: 0854046799.10.1039/9781847552662]Search in Google Scholar
[[8] Dean J., Analytical chemistry hadbook, McGraw-Hill, 1995, 1280 p., ISBN-10: 0071410600]Search in Google Scholar