American-Eurasian J. Agric. & Environ. Sci., 4 (1): 81-85, 2008 ISSN 1818-6769 Š IDOSI Publications, 2008 Corresponding Author: M. Karimi, Department of Agricultural Machinery, Faculty of Biosystems Engineering, University of Tehran, Iran 81 Determination of Optimum Life (Economic Life) for Mf285 Tractor: A Case Study in Center Region of Iran G. Khoub Bakht, H. Ahmadi, A. Akram and M. Karimi Department of Agricultural Machinery, Faculty of Biosystems Engineering, University of Tehran, Iran Abstract: Making use of tractor to do agricultural mechanized operations is responsible for a fundamental and important role to mechanize agricultural section. Replacement of farm machinery with a new similar machine is one of the most important objects of farm machinery management. Decision making about replacement of used farm equipment with a new similar one is one of the important items in farm machinery management. Proper performance in this case can lead to timely, high quality farm operations which in turns results in considerable decrease in product expenditures and also more income. Based on that the study in order to determine optimum life or economic life for MF285 in west region of Isfahan province was performed. Listed price of tractor, annual depreciation and Internal Rate of Return (I.R.R) in the study period were calculated. These items accompanied by their repair and maintenance cost were used to determine their economic life. Finally replacement time for the study tractor 18316 hours was predicted. Key word: Economic life Replacement time cost MF285 INTRODUCTION operating of farm machinery represent 35 to 50% of the Today, tractor is one of the most important power [8]. The R&M (repair and maintenance cost) is an sources in agriculture. Effect of tractor power on important item in costs of owning and operation. In agriculture is considerable [1]. The use of modern general, the costs other than those for R&M usually technology during latter decades resulted in…