Die gebruikswaarde van besluitnemingsondersteuningsmodelle vir trekkervervanging in die Vrystaat

The replacement of farm tractors and availability of decision support models for assisting farmers in taking replacement decisions were studied. A literature survey, postal survey of farmers and interviews with various persons were used to gain information on the available replacement models, replacement policies, information availability and farmers' decision making processes. This information was used to model the replacement decision and develop different decision support systems. Different replacement optimising techniques were studied. Minimum-cost models are unpractical for modelling replacement decisions. An extended version of the minimum discounted cost model can be used as a decision support model for advising farmers. A simulation model for establishing replacement strategies was also developed and used to determine optimal replacement strategies. Both models indicate an economic life for tractors in excess of 10 years. An increase in the tax rate results in replacement at an earlier life than with lower tax rates.