Quantifying the Effects of Implement Type, Field Condition, and Gear Stage on Tractor Traction Performance Under Representative Field Operating Conditions

The aim of this study was to quantify the effects of implement type, field condition, and gear stage on tractor traction performance under representative field operating conditions using full-scale field-measured data. Field experiments were conducted in five fields using a 78-kW agricultural tractor equipped with a moldboard plow, chisel plow, and subsoiler, and traction performance was evaluated based on the tractive coefficient (TC) and tractive efficiency (TE), both computed from directly measured drawbar pull and axle power. An effect size (η2) analysis revealed a clear and consistent hierarchy among the three factors: field condition was dominant (η2 = 91.6% for TC and 88.2% for TE), followed by implement type (67.8% for TC but only 11.3% for TE), whereas gear stage was minor (≤5.9%). TC and TE were highest in the firm loam field and lowest in the wet loamy sand field, with clearly separated, non-overlapping distributions across fields. The pronounced TC–TE asymmetry of implement type shows that the two indicators capture complementary aspects of traction and must be evaluated jointly. Measured TC distributions were broadly consistent with soil texture and moisture-based net TC reference bands, and the measured TE values deviated from the ASAE D497.4 reference values depending on the soil texture and moisture content, demonstrating that traction performance can vary substantially even within the same soil texture class. These results indicate that soil texture, moisture content, and cone index must be considered jointly when evaluating tractor traction performance, and are expected to contribute to tractor design optimization and the establishment of field condition-based work management standards.