Eucalyptus trees and soil quality
There are frequent questions about the impact of eucalyptus trees on the soil — whether they exhaust soil fertility or cause erosion or compaction. The answer is that, with today’s knowledge, environmental care and procedures, this does not occur in the forestry sector. In Brazil, the current model for planting eucalyptus calls for “minimum impact soil preparation.” The equipment used for this does not expose deeper soil layers to the surface, which avoids an inversion of the upper soil layers. It also keeps the soil protected from rain and sunlight by leaving a vegetable blanket formed by the leaves, branches, roots, and bark residue from harvested trees.
To evaluate the impact of this practice on soil losses caused by erosion from rainfall, Aracruz conducted tests from 1996- 2002 in its experimental watershed in Espírito Santo in partnership with the Federal University of Lavras (Ufla).
Monitoring showed that soil losses in eucalyptus plantations varied between 0.6- 1.0 t of soil/ha/year. These values were much below the estimated tolerance limits for the region (between 10-13 t/ha/year). They were also smaller than the losses for some of the main agricultural crops planted in the area. (Table 4)
Another concern is the compaction of the soil caused by machines and equipment used in eucalyptus cultivation and harvesting. To identify and quantify the effects of this machinery on the soil, Aracruz carried out another study in partnership with Ufla.
The study showed that, managed correctly, the soils are very resilient to compaction. There is a natural reversing of the initial compaction when cutting and transporting logs. After three consecutive cycles of eucalyptus planting, no indication of irreversible alterations to the soil structure was found.
Soil fertility is another key issue that has been getting attention from the technicians involved with eucalyptus plantations in tropical areas. The low natural reserve of nutrients in the soils, the fast growth of the trees, and high productivity with evershorter cycles justify this interest. Aracruz invested in detailed soil examinations and surveys — mapping the physical and chemical characteristics of the soil in relation to the different eucalyptus clones used in the company.
