This researoh project analized the quantitative microbiological differences between a natural vegetation soil and a cultivated soil. Both belonged to the Lo Vásquez Soil Series (Province of Valparaiso), described undet land Capability Class VII.
Two profile levels(0-5 cm. and 5-17 cm.) were studied, and representative samples were taken from each one. Fungi, bacteria and actinomycete were analized by Method of Dilution and Culture in Petri Plates.
Analysis of the soil samples permitted three major observations. First, total microorganism population was higher in the uncultivated soil in relation to the cultivated soil. Second, between the uncultivated and cultivated soil, there was a negative relationship in the location of the high population of microorganisms. Third, uncultivated soil showed the highest microorganism population at the 0-5 cm. level while cultivated soil had the highest total number of microorganism, at the 5-17 cm. level. In both soil areas, the total number of microorganism, through the soil profile was directly related to the organic matter and humidity content.
It is concluded that the fallowing practice and annual cultivation commonly applied to this type of soils of the Cordillera de la Costa, produces an injurious effect on the biotic properties of the soil.

1 Ingeniero Agrónomo, Proyecto Estudios y Reconocimiento de Suelos Chilenos (Ministerio de Agricultura-Organización de las Naciones Unidas) y profesora auxiliar de la Cátedra de Suelos, Facultad de Agronomía, Universidad de Chile