prediction of combine economic life based on repair and maintenance costs model

farm machinery managers often need to make complex economic decisions on machinery replacement. repair and maintenance costs can have significant impacts on this economic decision. the farm manager must be able to predict farm machinery repair and maintenance costs. this study aimed to identify a regression model that can adequately represent the repair and maintenance costs in terms of machine age in cumulative hours of use. the regression model has the ability to predict the repair and maintenance costs for longer time periods. therefore, it can be used for the estimation of the economic life. the study was conducted using field data collected from 11 john-deer 955 combine harvesters used in several western provinces of iran. it was found that power model has a better performance for the prediction of combine repair and maintenance costs. the results showed that the optimum replacement age of john-deer 955 combine was 54300 cumulative hours.