Method for assessing the carbon efficiency (eC) of soil microbial populations in the presence of subterranean plant biomass and residual inorganic mineral nitrogen (rNm), and for the recommendation of the use of microorganisms reintroduced by inoculation that can utilize these biomasses, by transformation of agronomic and pedological data into an index of the relative carbon efficiency of the bacterial fraction of soil microflora, eC BAC /eC MIC, characterized in that it comprises the following steps; first step, soil sampling to obtain a representative sample of the zone or soil volume in which will be incorporated the said biomasses of plant origin; second step, the determination of the residual mineral nitrogen (rNm) of the sample to determine as a function of rNm the N:C ratio (rb MIC) of the soil microbial; third step, the determination of the carbon / nitrogen ratio of the soil sample (rCN sol) in order to determine as a function of rCN sol the ratio between fungal and bacterial fractions of the soil (rFB); fourth step, the determination of the N:C ratio (rb BAC) of the bacterial fraction of the microbial flora of the soil according to rb MIC once this value rb MIC has been adjusted according to rFB; fifth step, the determination of the carbon efficiency (eC) of the BAC (eC BAC) and MIC (eC MIC) fractions; sixth step, the determination of the relative carbon efficiency index, eC BAC /eC MIC, of the BAC fraction relative to that of MIC; seventh step, the determination of the relative carbon efficiency index, eC BAC /eC MIC, that is, the relationship between the eC of the bacterial and microbial fractions of the soil, and the evaluation of this index relative to a critical threshold within a confidence interval of 0.75 and 1.00, more particularly between the values of 0.92 and 0.98, and preferably about 0.95 indicating a relative efficiency level of 1.0 compared to a non-inoculated control of reintroduced microorganisms via inoculation and utilizing such subterranean plant biomasses. first step, soil sampling to obtain a representative sample of the zone or soil volume in which will be incorporated the said biomasses of plant origin; second step, the determination of the residual mineral nitrogen (rNm) of the sample to determine as a function of rNm the N:C ratio (rb MIC) of the soil microbial; third step, the determination of the carbon / nitrogen ratio of the soil sample (rCN sol) in order to determine as a function of rCN sol the ratio between fungal and bacterial fractions of the soil (rFB); fourth step, the determination of the N:C ratio (rb BAC) of the bacterial fraction of the microbial flora of the soil according to rb MIC once this value rb MIC has been adjusted according to rFB; fifth step, the determination of the carbon efficiency (eC) of the BAC (eC BAC) and MIC (eC MIC) fractions; sixth step, the determination of the relative carbon efficiency index, eC BAC /eC MIC, of the BAC fraction relative to that of MIC; seventh step, the determination of the relative carbon efficiency index, eC BAC /eC MIC, that is, the relationship between the eC of the bacterial and microbial fractions of the soil, and the evaluation of this index relative to a critical threshold within a confidence interval of 0.75 and 1.00, more particularly between the values of 0.92 and 0.98, and preferably about 0.95 indicating a relative efficiency level of 1.0 compared to a non-inoculated control of reintroduced microorganisms via inoculation and utilizing such subterranean plant biomasses.