Tractive efficiency and fuel consumption of Massey Ferguson (MF399) and John Deere (JD 4230) tractors during plowing with moldboard plow were evaluated and compared. The tests were conducted at the Experimental Station, College of Agriculture, Shiraz University, in a field with sandy clay soil at average moisture content of 18% d. b. from zero to 30 cm depth. A randomized complete block design with a 4 3 factorial was used in three replications. The treatments consisted of two types of tractors, MF399 and JD 4230, each at two levels of axle load (standard and liquid ballasted) and three levels of plowing depth, shallow (15-20 cm), medium (20-25 cm) and deep (25-30 cm) using a semi-mounted 4-bottom moldboard plow. In all treatments, the tractor engine speed was set at rated rpm (2000 and 2200 for MF399 and JD 4230, respectively) and forward speed was kept constant at about 4.5±5 km/hr. The measured and calculated parameters included: drawbar pull, rolling resistance, wheel slip, tractive efficiency and fuel consumption. The results indicated that tractive efficiency of MF 399 in deep plowing increased from 36.5% to 53% with ballasting the drive wheels, even though the improved traction was not comparable to that of JD 4230 (64%) at the same plowing depth. However, at ballasted condition it is comparable to JD 4230 at shallow and medium depth plowing due to its lower fuel consumption. Using ballasted JD 4230 for shallow depth plowing is not economically justified due to the excessive fuel consumption and may cause soil compaction due to the lower than optimum wheel slippage. Generally, using MF399 is recommended for lower draft and JD 4230 for higher draft tillage operations. Otherwise, MF399 will encounter severe reduction in tractive efficiency and excessive increase in fuel consumption and JD 4230 will cause soil compaction.

Keywords: Tractor, Tractive efficiency, Rolling resistance, Fuel consumption, Wheel slip, Moldboard plow.

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