Changes in soil physical parameters of a virgin soil due to compaction by commercial sugarcane haulage vehicles

Soil compaction is often studied by comparing virgin field sites with commercial fields that have experienced long-term cultivation histories. Implementation of a new experiment farm in a virgin area of Mpumalanga Province, South Africa, provided the opportunity to repeatedly induce compaction over a period of three years to quantify the buffer capacity of a virgin soil against degradation. The soil of the trial site was a shallow (0.4 m) Cambisol with 38 to 44% clay, and 3.6 to 4.0% organic matter in the A-horizon, overlying weathered basalt. Following clearing of native bush from the virgin site, sugarcane was planted (2002) at 1.8-m row spacing which perfectly aligned with wheel spacing of the haulage vehicles, which were the only vehicles allowed in the field throughout this 4-year study. Three compaction treatments were imposed, including no vehicular traffic (control) and two compaction treatments consisting of pressure applied once per annum with commercial 30-tonne capacity loaded haulage vehicles fitted with either radial tyres or high flotation tyres. Compaction effects on soil properties and sugarcane yield were assessed on both dry soils and wet soils during the latter half of the 4-year study. Results show reduced water infiltration rates, increased soil bulk density, increased penetration resistance, and reduced root distribution in all the compaction treatments. Soils with higher water contents were more susceptible to degradation. It is concluded that even a virgin soil in very good condition will be degraded over a period of a few years to the physical threshold limits. (Résumé d'auteur