Vehicles travelling over a crop field have become a primary source of forces compacting agricultural soils.The type of tires used by those vehicles, their physical dimensions, their displacement speed on the soil, the number of times that their tires pass by the same place, and the load those tires support are some factors which cause higher or lower degree of soil compaction. The objective of this study was to determine, under field condictions, the effect of slip of an agricultural tractor driving wheel upon the compaction of a specific type of soil. A field experiment arranged in a randomized complete block design was carried out to analyse four different levels of slip (0, 10, 20 and 30%) with five replications, in split-plots. The degree of compaction was determined through the cone index of a soil penetrometer. Fifteen samples were taken from points along the center line of the driving wheel track, and another fifteen samples were taken from points along but outside the driving wheel track on soil band not compacted by the tires. Each sample was composed by readings from the penetrometer cone index at six different depths: 25; 50; 75; 100; 125 and 150 mm. It was found that slip had influence on the degree of soil compaction up to 5 cm depth, under the conditions this study was carried out. The 30% level of slip was the one that produced significant differences on soil compaction degree. Although it was observed an increasing compacting effect from 19.2 to 31.9%, no significant differences were observed among the cone index values for the 10 to 20% slip range.
compaction; soil; agricultural tractor; tire; slip
