In a ferralytic red soil (Oxisol) representative of the Red Plains to the South of La Habana, partially degraded by soil density and located in the Soils Experimental Station La Renee, a trial was conducted in 1993-1995, to simulate different degrees of soil density obtained by successive passes of tillage. The objective was to determine the relationship between the low fertility of these soils and the man-induced soil density. The indicator crop used was the common bean in succession with maize. The evaluation of soil density was carried out through cartographic profiles, which were used to observe and measure: the degree of penetration; the state of the internal structure, and root colonization. Results indicate a direct correspondence between degradation by soil density and a reduction in structural porosity. Similarly, the thickness of the compacted layer increased depending on the number of passes of tillage, and root colonization that was restricted to the loose surface layer, being least favorable in the treatment of 20 passes, in which its depth was the less. Yields of beans and maize presented a close relationship with soil density, being reduced as density increased. Therefore, the maninduced soil density that results from intensive cultivation of these soils is the cause of low fertility.