Determination of optimal replacement time for combine harvester John Deere 955 in Fars province

 
The decision to replace an item of farm machinery can be made because of cost minimization, reliability, new technology, need for capacity, obsolescence, wear and tear, and has a vital role in machinery management. In other words, most capital goods have an optimal lifespan and replacing machinery at a more or less than optimal age could significantly affect profitability. Therefore, this study aims to investigate the optimal replacement time under certainty condition using four methods for combine harvester in Fars province. According to the first method, the most appropriate time for combine harvester is the year in which the accumulated annual repairs, depreciation and maintenance cost per working hour is minimum. The second method considers the optimal replacement time for combine to be the year in which the initial value of the machine and accumulated annual repairs and maintenance cost per working hour is minimum. The third method for economic life determination is based on minimizing the accumulated average total cost per working hour and according to the fourth method, the most appropriate time for combine harvester replacement is considered to be the year in which the accumulated net income is maximum. By a stratified random sampling method, 160 John Deere 955 combine which is dominant in Fars province were chosen for interview to collect the technical and economic data and other needed information. The results showed that the optimal replacement time of a John Deere 955 combine under certainty condition were 16, 18, 14 15^th year of its productive life with 18786, 21291, 16076, 17424 working hours respectively based on the results of four relevant methods.