Effects on some soil qualities in central Italy following the passage of four wheel drive tractor fitted with single and dual tires

Field tests were carried out using the same four wheel drive tractor (113 kW engine power) fitted with two different tire arrangements: single and dual. Tests were conducted on arable soil previously ploughed and harrowed in order to check the compacting effects resulting from one to four passes of the tractor in the same track, fitted with two different tire configurations. Soil parameters studied were: penetration resistance, bulk density, soil shear strength and their increment ratio, soil macroporosity, pore size distribution and saturated hydraulic conductivity. Multiple passes made by the tractor fitted with the two-tire arrangements caused different effects on the soil with regard to the studied soil parameters. Mean values of penetration resistance (0-0.20 m depth) were 2.02 MPa for the single tires tractor and 1.86 MPa for the dual tires tractor; mean values of penetration resistance (0.21-0.35 m depth) were 2.72 MPa for the single tires tractor and 1.72 MPa for the dual tires tractor. The decrease in macroporosity, in particular that of elongated pores in the soil layers (0-0.10 m and 0.11-0.20 m depth) was greater in treatments involving the single tire arrangement of the tractor (from 25.3 to 1.1% and from 15.9 to 2.0%, respectively) than for the dual tire arrangement (from 25.3 to 2.8% and from 15.9 to 5.2%, respectively, for 0-0.10 m and 0.11-0.20 m depth). Following traffic of the tractor with the different tire arrangements, hydraulic conductivity decreased and the following values were found for the five treatments: control, 15.8 mm h−1; single tires one and four passes, 2.8 and 1.6 mm h−1, respectively; dual tires one and four passes, 5.9 and 5.8 mm h−1, respectively). Highly significant correlations between hydraulic conductivity and elongated pores and total macroporosity were found. Significant relationships between macroporosity and penetration resistance for one and four passes of both tractor tire arrangements were found in the soil layers (0-0.20 m). However, in the soil layer examined, with respect to the higher degree of macroporosity and hydraulic conductivity and the low values of penetration resistance, treatments involving tractor fitted with dual tires (one and four passes) showed a lower degree of soil compaction than was observed after the same passes of the tractor fitted with single tires.