Efficiency of nutrient use for biomass production of a <i>Eucalyptus</i> clone as a function of planting density in short-rotation cropping

The objective of this study was to assess the effects of planting density on nutrient use efficiency (NUE) in the production of biomass of a hybrid of <i>Eucalyptus urophylla</i> × <i>Eucalyptus grandis</i>. Twelve planting densities were evaluated at 36 months of age, ranging from 498 to 2564 plants ha⁻¹. Three trees were harvested in each treatment to determine biomass production and allocation (per plant and per area), concentration (g kg⁻¹), amount (kg ha⁻¹), and NUE of N, P, K, Ca, Mg and S in the biomass of leaves, branches, bark and wood. In summary, the increase in planting density resulted in: higher biomass production per area; a reduction in biomass production per plant; a reduction in homogeneity; an increase in the concentration of N, P and K in leaves, of N, Ca, Mg and S in bark, and of N, P and K in wood; a higher amount of nutrients exported by harvesting; and a higher NUE for wood production. The increase in NUE indicates a possible nutritional deficit in trees at higher stocking rates at the age of three years. The higher the planting density, the sooner the site will require re-fertilisation.