Abstract

Africa is the second continent suffering from soil compaction; studies of this phenomenon must be multiplied in order to overcome this problem. Very few studies have been conducted in Tunisia to understand soil compaction, its causes and its effect on soil properties. The research was conducted on experimental field at the Higher Institute of Agronomy of Chott Mariam, Sousse, Tunisia. The main objective of this study was to evaluate the effect of different speed of tractor compaction on soil, that is, no compaction (C0), speed 1 (C2) = 4 km h-1, speed 2 (C3) = 9 km h-1 on the hydraulic and physical properties of a silt loam texture under three natural moisture conditions: H0, H1 (15 days later), and H2 (30 days later). Each test run was limited to one pass. Undisturbed soil cores were collected in the topsoil (0-10 cm), at 10-20 cm and in the subsoil (20-30 cm) below the trace of the wheel at site. Soil compaction level was determined by penetration resistance using a penetrologger. Bulk density was then determined to evaluate the impact of the two tractor frequency passages at the three moisture conditions on soil compaction. For initial soil (C0), bulk density was 1.38 Mg m-3. After the tractor pass, the highest degree of compaction was observed with tractor speed 1 (C1) which signi?cantly changed soil bulk density resulting in values of up to 1.74 Mg m-3 in the topsoil and compacted subsoil under H1, which is significantly above the critical value of 1.6 Mg m-3 for soils with clay content below 17.5%. The high degree of compaction signi?cantly affected penetration resistance of topsoil. The results demonstrate that different degrees of soil compaction under different moisture levels could greatly influence physical properties in different ways. Even under relatively low water contents, that is, below field capacity, substantial top soil compaction was induced after one tractor pass.

Key words: Soil compaction, tractor speed, soil moisture, penetration resistance, bulk density.