Nutrient use efficiency in commercial eucalypt plantations in different soils under temperate climate

Abstract

The sustainability of forest production is based on an adequate balance between soil nutrient supply and its demand by forest plantations, which may vary depending on the species and the site. In Uruguay, the low to medium fertility of the soils under forest production makes this aspect relevant. The objectives of the study were: (a) to quantify the concentration and distribution of nutrients in the harvested biomass of Eucalyptus dunnii, Eucalyptus grandis and Eucalyptus globulus in the predominant soils of the zones of greater forestry aptitude of Uruguay; and (b) to compare the nutrient use efficiencies of the three mentioned species in different soil types, as a criterion to evaluate the sustainability of the productive system in the long term. In 29 sites located in the three main forest areas of the country, nine trees with average diameter at breast height (DBH) and height were harvested at eight to eleven years of age. The aerial biomass and nutrient uptake (nitrogen, phosphorus, potassium, calcium and magnesium) in commercial wood, bark, leaves and branches were quantified, and two nutrient use efficiency indexes (nutrient use efficiency and biological utilisation coefficient) were calculated. Although the zones offered different conditions for growth and nutrient uptake, E. dunnii presented the highest extraction of nutrients in commercial wood, considering all sites, these indexes being lower for E. dunnii. Therefore, when planting E. dunnii, its greater use of the soil’s resources must be considered, particularly in soils that are naturally less fertile. Likewise, E. grandis presented a greater extraction of cations than E. globulus because of more extensive growth.