An agricultural soil is the result of the interaction of physical, chemical and biological weapons; where microorganisms are essential for fertility, due to mineralization and humification of organic waste, nitrogen fixation, degradation of cellulose, solubilization of phosphorus, redox of sulfates and functional active metabolite production, improving the ion-holding capacity. This study evaluated the populations of microorganisms from an agricultural soil after adding organic fertilizer fermented mineral (aof), whose chemical characteristics are:% H 17 p / w, pH 8.1, C / N 20 / 1, COO 15% CIC 25meq/100g soil, CE 27dS / m, Nt 0.94% P2O5 4.31% 6.27% K2O, MgO 0.87% CaO and 12.42%. Product that complies with technical standards and Colombia 5167. Also reported populations of nitrogen fixing bacteria-free life (BFNVL) 63.9X105 CFU / g, sulfate-Microorganisms (MS) 100UFC / g, phosphorus solubilizing bacteria (BSF) 3X103 CFU / g Cellulose Decomposers (DC) 43X104 CFU / g on average. Samples were taken in 4 lots of 2000 m2 each, T1, incorporation of organic fertilizer for two years (2006 - 2008) in a ratio of five Kg/m2 every three months, growing vegetables, T2, kikuyu pasture ( Penisetum clandestinum) and clover (Trifolium repens), without management or fertilization during eight years (2000-2008), T3, aof addition of eight years six months, at a rate of five kg / m2 in legume crops, grasses and vegetables (2000-2008) and T4, potato (Solanum tuberosum L.) with conventional agriculture management (2000-2008). Samples were taken between 0 and 20 cm, following the protocol for sampling for soil testing conventional transporting to the laboratory without disturbing soil bulk density mea-surements, these samples were processed 24 hours after collection. The variables studied were (BFNVL), (MS), (BSF) and (DC).Laboratory tests show that aof not add nitrogen, but nitrogen-fixing populations reach up to 38 X 105 CFU / g which are incorporated into the soil, making its density increases to the extent that there oxidizable organic carbon released by cellulolytic bacteria.