نبذة مختصرة : The efficiency with which a soil can transmit energy from a traction device on a tractor to the drawbar has been called the tractive efficiency of soil. Experiments were conducted for disc ridging operations in a loamy sand soil, at tillage speeds of 1.94m/s, 2.22m/s and 2.5m/s, using trace tractor techniques. Tractive force models at different tillage speeds were developed using dimensional analysis, describing the tractors tyre- soil interaction. The measured independent variables such as drawbar pull force, rolling (motion) resistance, wheel slip, moisture content, cone index, wheel numeric, contact pressure, speed, width of ridge and height of ridge were used in the developed models. Values of the measured dependent variable (Tractive force) were compared with computed values. High coefficients of determination R 2 = 0.996, 0.996 and 0.986, percentage (%) errors of-0.122620038 and 0.11606597,-0.126307491 and 0.215127604,-0.603425382 and 0.372951166 at minimum and maximum values, for disc ridging at tillage speeds of 1.94m/s, 2.22m/s and 2.5m/s were obtained respectively. Analysis of variance between measured and predicted tractive force values indicated standard errors of 11.15346, 10.15346 and 8.24219, while correlation coefficients of R 2 = 0.996, 0.768 and 0.9674 were obtained for disc ridging at tillage speeds of 1.94m/s, 2.22m/s, and 2.5m/s respectively. These results are clear evidence of the test of goodness of fit of the models between the measured and predicted tractive forces for disc ridging at the various tillage speeds. Disc ridging speed of 2.5m/s illustrated the lowest coefficient of determination R 2 = 0.986. The developed models were validated by comparing the predicted with the measured tractive forces, and shown to closely followed the experimental results.
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