Soil compaction distribution under land clearing in calden (Prosopis Caldenia Burkart) forest in Argentinean pampas

Abstract

Although the virgin soil has a high organic matter content that reduces the soil's susceptibility to compaction, the high weight of the tractors used for land clearing cause a high degree of soil compaction. This study was performed in the Calden (Prosopis Caldenia Burkart) forest at La Pampa State, in West Argentina. The object of this study was to assess the soil compaction during mechanical land clearing with heavy machinery. Variables measured were (CI) cone index, (BD) dry bulk density, tractor rut depth (TRD) and Proctor test. The land clearing was performed with a Caterpillar tractor D6, with 0.7×2.3m metallic tracks. The engine power was 300kW and the weight was 18 Mg. The relevant results were as follows: in topsoil (0-0.2m) 1 and 2 passes of a tractor caused mean CI values of 1833 and 2437kPa, respectively. Dry bulk density mean values had a similar behaviour to those of CI, measuring 1.75 and 1.85Mgm -3 for 1 and 2 passes, respectively. In the subsoil (0.2-0.9m), two tractor passes caused higher CI and BD values than one tractor pass: CI mean values were between 1991 and 2439kPa for one and two tractor passes, respectively. Dry bulk density mean values were between 1.81 and 1.89Mgm -3 for 1 and 2 passes, respectively. Significant differences were found in TRD when the tractor passed one or two times, measuring 0.092m TRD for one tractor pass and 0.111m for two tractor passes. The main conclusions of this study are as follow: the level of soil compactability increases as the maximum BD attains a higher level and at a lower water content level. When soil with a moisture content level over the critical water content is compressed (for example, by one tractor pass with 18 Mg total load) it reaches saturation, and the compaction stress travels deeper in the soil than when the soil is drier. Then if the use of heavy machinery cannot be avoided, special attention should be given to traffic at a water content which the soil do not attain saturation by compression. Compared with most agricultural practices the high weight of the land clearing machinery generate greater compaction stresses in the soil, raising the maximum BD that develops at lower water content and subsequently reducing the work opportunities.