The transition from traditional fallow systems to more permanent cultivating has occurred in wide areas of the Southern Highlands of Tanzania. This change in agricultural practice is largely due to three factors: the villagization programme; introduction of hybrid maize along with biochemicals; and the development of animal traction. Social differentiation has been reinforced due to an unequal access to the production factors and thereby hindering the upward social mobility of the poor peasantry. The pressure on land has increased as a consequence of the high population growth rate, concentration of the rural population into villages and the increased use of continuous mono-cropping. Furthermore, the introduction of ox-mechanization has caused a change in the labour bottleneck from land preparation to weeding which, in the end, enforces the social differentiation. -from Author