The drawbar pull tests of the farm tractors were carried out on the soft paddy field. Six tractors and various running elements such as pneumatic tires, half tracks, strake type wheels, girdles and dual tires were used.
Field conditions were (1), stubble land of rice plants, humid, clay soil, internal friction angle of soil were 23-24 degree, (2), the field after harvesting the Chinese milk vetch, loamy clay soil, internal friction angle 13°-14°, (3), submerged field after rotary tilling, (4), fallowing land, after harvesting the rice plants, loamy clay soil, internal friction angle 34°-36° at a-d section, 23°-25° at e-f section and 14° at h section.
1. The drawbar pull were dropped as the broken lines in figures 2-9 and having the peak values at 30-40 percent slippage of the running elements when the fibers of the withered weed or hay stuck to the surface of the tires or shoes of the half tracks with the sticky soil.
Maximum drawbar pull increased as the continuous lines in the same figures by removing of the sticked soil and weed fibers. The mean values of the ratios of dropping were 20.6 percent at the tire and 28.2 percent on half tracks for the maximum drawbar pull. The largest decrease was seen in the case of the tire as 40 percent. On the strake type wheel used at subsurface crossing in Bekker's discussion, these phenomenonons were not caused. To give the trong tension to the half tracks had an effect to eliminate these stick ed soil from the tracks.
2. Drawbar pull was increased by attaching the half track or the strake type wheel to the tire. In the test field (2) the increases was 1.98-2.1 times for half tracks and 1.7-1.9 times for the strake wheels. In the test field (4) 1.4-1.7 for half tracks, 1.37 for girdles and 1.3-1.7 for dual tires.
3. On the submerged field after rotary tilling, the drawbar pull we resmaller than that of non-submerged field and the ratios of decrease in the strake type wheels were smaller than that of half tracks, that is, the drawbar pull of the strake type wheel on this field kept the 81 percent of the drawbar pull in the test field (2) while that of the half tracks decreased to 54 percent.
Under these soil conditions, the strake type wheels and lug wheels used usually in Japanese small power tillers, though they belong to the subsurface crossing methods in Bekker's discussion, displayed the splended performances, while the drawbar pull of the half tracks or tracks, which belong to the surface crossing, were very poor.