Different perspectives, related to different hierarchical levels of analysis, should be used when discussing technological changes in agriculture. In fact, technological choices are affected by: (i) the characteristics of the socioeconomic system to which the farming system belongs; (ii) the characteristics of the ecosystem managed for agricultural production; and (iii) the farmers' feelings and aspirations. This paper presents a model of biophysical analysis that can be used to establish bridges among different perspectives. The agricultural throughput per hour of labor and per hectare obtained at farm level is evaluated against two sets of indicators characterizing the constraints coming from societal and ecological sides. Economic growth pushes for increases in the intensity of the throughput 'per hour of labor' and 'per hectare' at the farm level (two indicators, namely socioeconomic and demographic pressure, are proposed to assess this effect). The need of maintaining ecological compatibility generates a contrasting pressure pushing for keeping as low as possible the intensity of throughput in the agroecosystem. A family of indicators (the ratios of 'current environmental loading (EL)'/'critical environmental loading (GEL)') is proposed to assess such a pressure. Feelings and aspirations of farmers determine the acceptability of compromises, at the moment of technological choices, after considering the severity of these two pressures. A plan 'productivity per hour' and 'productivity per hectare' can be used to study technological changes on two hierarchical levels (societal level and farming system level). A third axis can be added to this plane to include assessments of EL, Numerical examples are given for a sample of more than 60 world countries. (C) 1997 Elsevier Science B.V.
