One of the important factors that can control and decrease soil compaction is incorporation farmyard manure to the soil. It increases soil elasticity and soil tolerance to the imported load. To evaluate the farmyard manure effect on the soil compaction, it was incorporated in the clay soil at different rates of 0, 45, 60, and 90 Mg ha-1. Tests were conducted at different tire passes of 1, 6, 11 and 16 on the same track at three soil moisture contents of 8%, 11% and 14% (dry base); soil bulk density was measured at depths of 10, 20, and 30 cm. To evaluate soil compaction, cylindrical cores were employed to measure the soil bulk density. To assess soil behavior during the soil compaction process, three displacement transducers were placed in the soil in three coordinate directions of x, y and z. The soil volumetric change was measured using the transducers and soil sinkage was also measured. A single-wheel tester was used in a soil bin with a Barez 8.25-16 (8) P.R HLF agricultural tractor tire operated at a forward velocity of 0.8 m s-1 under a vertical load of 4 kN and an inflation pressure of 300 kPa. Incorporating the farmyard manure noticeably decreased the final vertical and longitudinal displacement below the tire track, while the lateral displacement increased. Bulk density decrements of 14.7%, 9.7% and 6.3% were occurred via farmyard manure application rates of 90, 60 and 45 Mg ha-1, respectively. Maximum soil sinkage occurred at 14% moisture, 16 passes of tire and with no manure condition.
