Abstract
During timber exploitation in forest stands harvesting machines pass repeatedly along the same track and can cause soil compaction, which leads to soil erosion and restricted tree root growth. The level of soil compaction depends on the number of passes and weight of the wood load. This paper aimed to evaluate soil compaction and eucalyptus growth as affected by the number of passes and wood load of a forwarder. The study was carried out in Santa Maria de Itabira county, Minas Gerais State - Brazil, on a seven-year-old eucalyptus stand planted on an Oxisol. The trees were felled by chainsaw and manually removed. Plots of 144 m² (four rows 12 m long in a 3 x 2 m spacing) were then marked off for the conduction of two trials. The first tested the traffic intensity of a forwarder which weighed 11,900 kg and carried 12 m³ wood (density of 480 kg m-3) and passed 2, 4, and 8 times along the same track. In the second trial, the forwarder carried loads of 4, 8, and 12 m³ of wood, and the machine was driven four times along the same track. In each plot, the passes affected four rows. Eucalyptus was planted in 30 x 30 x 30 cm holes on the compacted tracks. The soil in the area is clayey (470 clay and 440 g kg-1 sand content) and at depths of 0-5 cm and 5-10 cm, respectively, soil organic carbon was 406 and 272 g kg-1 and the moisture content during the trial 248 and 249 g kg-1. These layers were assessed for soil bulk density and water-stable aggregates. The infiltration rate was measured by a cylinder infiltrometer. After 441 days the measurements were repeated, with additional analyses of: soil organic carbon, total nitrogen, N-NH4+, N-NO3-, porosity, and penetration resistance. Tree height, stem diameter, and stem dry matter were measured. Forwarder traffic increased soil compaction, resistance to penetration and microporosity while it reduced the geometric mean diameter, total porosity, macroporosity and infiltration rate. Stem dry matter yield and tree height were not affected by soil compaction. Two passes of the forwarder were enough to cause the disturbances at the highest levels. The compaction effects were still persistent 441 days after forwarder traffic.
Highlights
The constant and significant weight increase of agricultural and forest vehicles over the last decades in Brazil has caused concern in view of the possible long-term consequences on eucalyptus yield in soils under traffic
This study aimed to evaluate soil compaction and eucalyptus growth as related to the traffic intensity and wood load of a forwarder
There was an increase in the soil bulk density (DS) caused by forwarder traffic (Figures 2a,b)
Summary
The constant and significant weight increase of agricultural and forest vehicles over the last decades in Brazil has caused concern in view of the possible long-term consequences on eucalyptus yield in soils under traffic. Repeated traffic in a same area intensifies the damage done to the soil structure with consequent reductions in crop yields in the first as well as in the following years of production (Håkansson & Reeder, 1994; Lal, 1996; Jorajuria et al, 1997). During the removal of the wood from forest stands the machines drive along one and the same row several times. This can cause soil compaction and, hinder root growth. The degree of compaction is related to the weight of the wood load, leading to soil deformation when the pressure on the soil exceeds the load support capacity (Dias Júnior, 2000; Dias Júnior et al, 2005; Silva et al, 2007a,b)
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