Best tillage practices for eucalyptus growth and productivity: A review on the Brazilian experience

Commercial eucalyptus forestry has significantly increased in the last decades to supply the growing demand for forest goods (pulp, paper, sawmill, by-product industries, and biomass for bioenergy and biofuels). Among factors most influencing forest productivity, the soil physical environment is very important and can be harmful or beneficial to trees. In the effort to increase environmental and economic sustainability of commercial plantations, in this literature review, we summarize relationships between soil type and properties, forest rotation, and forest growth and productivity. Mechanized soil tillage must consider soil type, particularly land slope, soil drainage and depth, along with forest rotation (first or higher-order). Soil surveys, including soil physical properties (e.g., compaction, granulometry including gravel) and morphological attributes (e.g., horizons, solum depth, subsurface drainage impedance), are thus essential for foresters to make knowledgeable decisions on soil tillage, provided tillage is the single most costly practice in eucalyptus forestry. Subsoiling is the most common soil tillage for eucalyptus, but it is best for deep, drained soils. Existing scientific publications show, for clayey cohesive or compacted soils, tillage depth might be of 0.70 m (deep subsoiling) to ameliorate compacted soil of low microporosity and restriction to root growth, but 0.50 m (shallow) subsoiling plus ridding produce similar results. The latter, nonetheless, has a higher operational cost. Downslope subsoiling on sloppy lands increases the risk for soil erosion, which may be reduced by interrupting ripping, mechanized holeor pit-drilling with low operational cost. Chiseling performed for fertilizer application (minimum 0.25 m deep) might be the only tillage required for non-compacted sandy soils. Mechanical or manual pitting could also be an option for second or higher rotations, but results show crop early-growth is restricted, possibly because of root confinement. For second or higher rotations, stumps require cutting to allow cross-slope tractor traffic and tillage. Subsoiling plus ridging or bedding is required in low-drainage or shallow soils to increase the soil volume to be explored by roots. The ridges can be built by grade bedding or terracing plows. In areas with waterlogging, drainage and ridging without subsoiling are necessary. Research opportunities include further studies for slopy lands and low-drainage or compacted soils, tillage affecting soil erosion and eucalyptus productivity, equipment for special tillage, and mapping compaction risk and special tillage needs.