Effects of repeated passages of a wheeled tractor on some physical properties of clayey loam soil

The objective of the study was to quantify the differences in soil physical indicators between inter-track (uncompacted) zone and track (compacted) zone created by four passages of a wheeled tractor (Landini Globus 70/DBKL Techno). Field studies were carried out on plots of the Vicarello experimental station, Tuscany (43° 27‘ N, 11° 30‘ E). A local average annual precipitation is 678 mm and average annual air temperature is 12.7 °C with absolute extreme values -10 °C and 40 °C. Bulk density, moisture content, water-stable aggregation, and penetration resistance were determined by conventional methods in the 0–0.40 m soil layers. The results showed that the 0.05–0.10 m soil layer, compared to the 0.20–0.25 m and 0.35–0.40 m soil layers, showed a higher degree of compaction by tractor wheels. In this soil layer, significant (at P <0.05 and <0.01) differences between the inter-track and track zone were observed for bulk density (1.18 ±0.10 g.cm⁻³ and 1.35 ±0.10 g.cm-3) and moisture content (24.9 ±2.3% and 27.9 ±2.3% of volume). Passages of tractor even resulted in an insignificant increase of total amounts (from 66.2 ±4.7% to 68.6 ±2.7%) and mean weight-diameters (from 2.29 ±0.30 mm to 2.40 ±0.04 mm) of water-stable aggregates. There were no significant differences in average penetration resistance of the uppermost 0–0.10 m soil layers between the inter-track (0.77 ±0.26 MPa) and track zone (0.64 ±0.12 MPa). Average soil penetration resistance was significantly (P <0.001) higher in the 0–0.40 m layer of the track zone (1.07 ±0.23 MPa) than in that of the inter-track zone (0.76 ±0.11 MPa).