Tiie ineffectiveness of agricultural extension services in South Africa is characterised by two (//stinct paradigms i.e. the technical-educative and that of agricultural economics. This situation gives· rise to the problem of scientists not being able to present a holistic solution to management problems to farm managers and on agriculture policy to policy makers. As a 1•osult the full consequences of management problems or agricultural policies are seldom Indicated. The reason is that scientists have failed to solve the problems within the systems framework. In spite of attempts to integrate the two paradigms there is, however, no user/ riendly planning model available with a holistic approach (system orientated), that Integrates the technical-biological with the economical aspects. The OPTIMA model has been developed and continuously tested against the original aims that were set. The final result complies, more or less, with all these aims. Even if a model f"nctions mathematically correctly it must be proven valid in practice. Although the validation of a model is subjective, some applications were done to validate the model. The study has indicated that the model can be successfully used on an individual farm level as well as on the impact of agricultural policy on a micro-level.