NOVELTY - The method comprises: performing soil sampling step to obtain a representative sample of the area or volume of soil in which the vegetable biomass is included; determining a ratio of remnants of mineral nitrogen and carbon of microbial flora of the soil; determining the carbon/nitrogen ratio of the soil sample according to the ratio of fungal and bacterial fractions of the soil; determining the ratio of nitrogen and carbon of the bacterial fraction of the microbial flora of soil; and determining the carbon efficiency of the fungal and bacterial fractions.    USE - The method is useful for assessing carbon efficiency of soil microbial populations in the presence of subterranean vegetable biomass and remnants autumn of mineral nitrogen and recommending the use of microorganisms reintroduced by inoculation that enhance the biomass and by transformation of agronomic and pedological index (claimed).    ADVANTAGE - The method is capable of efficiently assessing the carbon efficiency of soil microbial populations in an environmentally friendly manner.    DETAILED DESCRIPTION - The method comprises: performing soil sampling step to obtain a representative sample of the area or volume of soil in which the vegetable biomass is included; determining a ratio of remnants of mineral nitrogen and carbon of microbial flora of the soil; determining the carbon/nitrogen ratio of the soil sample according to the ratio of fungal and bacterial fractions of the soil; determining the ratio of nitrogen and carbon of the bacterial fraction of the microbial flora of soil; determining the carbon efficiency of the fungal and bacterial fractions; determining the index of the relative carbon efficiency from bacterial fraction with respect to microbial flora; and determining the index of efficiency of carbon. A ratio between bacterial and microbial fractions with respect to a critical threshold is 0.95. The vegetable biomass is residues of cellulosic culture, preferably strawy. The microorganisms are bacteria, preferably azotobacteria. The step of determining the carbon/nitrogen ratio of the soil sample is carried out using a function of rb(MIC) = a(rNm)(b), where the rb(MIC) is carbon/nitrogen ratio of the soil sample, the rNm is remnants of mineral nitrogen and the value of a and b is 0.0068 plus minus 5-7% and 0.7336 plus minus 4-6%. The step of determining fungal and bacterial fractions of the soil is carried out using a function of rFB (mass) = a(exp(b(rCNsol))), where the rFB is fungal and bacterial fractions, the rCNsol is ratio of carbon/nitrogen of soil sample and the value of a and b is 0.008 plus minus 5-7% and 0.11 plus minus 4-6%. The step of determining carbon efficiency of fungal and bacterial fractions of the soil is carried out using a function of eC = a(rf/rb)(b), where the eC is carbon efficiency, the rf is fungal ratio, the rb is bacterial ratio and the value of a and b is 0.54 plus minus 5-7% and 0.65 plus minus 4-6%. The critical threshold is calculated using a function as given in the specification.