Efficiency of micronutrients and sodium use of a Eucalyptus clone as a function of planting density in short-rotation cropping

Abstract

ABSTRACT The objective of this study was to assess the effect of planting density on the concentration, amount per hectare and nutrient-use efficiency (NUE) of micronutrients (boron – B, copper – Cu, Fe– iron, manganese – Mn, and zinc – Zn) and sodium (Na) of a Eucalyptus grandis × Eucalyptus urophylla clone planted in a systematic experimental design in the coastal region of the state of Rio Grande do Norte, Brazil. The experimental treatments encompassed ten planting densities from 606 to 2564 trees ha-1, with three replicates per treatment. Thirty-six months after planting, the trees were harvested and the concentration (mg kg-1), amount per hectare (kg ha-1), and NUE of micronutrients and Na were evaluated for each tree component (bark, branches, leaves and wood). Regression models were fitted for bark, branches, leaves and wood as a function of growing space. Linear, quadratic, exponential and logarithmic models were fitted. The increase in planting density brought the following results: increases in the concentration of B in leaves, Mn in bark and Na in leaves and bark; decreases in the concentration of Cu in branches and wood; increases in the export of micronutrients per area; increases in the NUE of B and Cu in branches; and decreases in the NUE of Mn for wood, Zn for bark and Na for leaves and bark. There was no significant effect of planting density on the concentration of Fe and Zn. Initial planting density affected the concentration (except Fe and Zn), amount exported per hectare and NUE (except Fe) of micronutrients and Na, but the degree and trend varied according to plant part (e.g. leaves, branches) and elements under study. The harvest of wood only or wood + bark combined with the reincorporation of leaves and branches in the soil show strong potential for returning the micronutrients to the planting site, especially B and Mn.