The activity of some metabolical groups of microbes has been studied in three depths of a ñadi soil.
Under natural conditions, the organic carbon and nitrogen mineralize at a reduced rate which allows for accumulation of organic matter.
In the laboratory, these processes are accelerated by an increase in temperature and by furnishing energetical substrates; high figures of CO2 evolution and a marked accumulation of mineral nitrogen are obtained, which implies the presence of a potentially very active population.
A similar effect is obtained, from a given level on, with phosphorous, which liberates a great amount of easily assimilable carbon and ammonia.
Nitrogen by itself would not be a limitant factor in the formation of nitrates, but as the ammonia-producing microorganisms are heterotrophs, they need energetical substrates; in the last end, it is the carbon cycle which holds backs the nitrogen cycle.
The lacking of a source of available energy is postulated to be a limitant factor of the process of mineralization, as the carbon would be partially immobilized, be it biologically or held by the mineral colloid.

1 Ing. Agr. Línea Suelos, Estación Experimental La Platina. Instituto de Investigación Agropecuarias, Casilla 5427, Santiago, Chile.
2 Ing. Agr. Proyecto de Estudios y Reconocimiento de Suelos Chilenos FAO/UNDP/SF - Depto. Agrología, DICORA - Servicio Agrícola y Ganadero.
3 Dr. en Ciencias, Experoto FAO - Naciones Unidas, Laboratorio de Ecología Vegetal, Facultad de Ciencias, Universidad de París, Francia