The authors define fertility as "The fundamental characteristic of the soil, which is a result of the vital activity of the micropopulation, of the plants roots, of the accumulated enzymes and from the chemical processes which generate biomass, humus, mineral salts and biological active substances. The level of fertility is connected to the potential level of the bioaccumulation and mineralization processes, these depending on the program and the conditions of evolution of the ecological sub-system and on the influences of man activity".
Following some researches made between 1982 and 1995, a technology allowing the quantification of the fertility of soils where tobacco is grown was developed. Thus, the biological potential level of the soil is determined by biotic and enzymatic tests, in any period of the year, with the condition of a certain previous preparation of the soil samples.
The main agrobiological indices used by the authors to express the fertility state of the soils where tobacco is grown, are: a) The Index of the Potential of the Vital Activity (IPVA) ; b) The Index of the Potential of the Enzymatic Activity (IPEA); c) The Synthetic Index of The Soil Fertility (SISF), which is an arithmetic average between IPVA and IPEA.
Depending on the quantification of the fertility of the soil where tobacco is grown, there were settled areas of favourability, with a straight answer on yield and the quality of the oriental and Virginia tobacco types. The paper presents the methodology of work and the main results obtained during the time of researches.