Effects of B fertilization on biomass production and wood quality of young Corymbia citriodora subsp. variegata plantations

Boron (B) is a micronutrient closely linked to tree productivity and stem quality in eucalyptus, with important implications for industrial wood utilization. However, the field response of Corymbia citriodora subsp. variegata (CCV) to B fertilization remains poorly understood. This study aimed to evaluate the effects of B application rates on wood volume, aboveground biomass, nutritional status, nutrient use efficiency, stem morphology, specific leaf area (SLA), leaf area index (LAI), stem architectural defects, wood basic density, and chemical composition in a young CCV plantation. The trial was established in São Paulo State, Brazil, using a randomized complete block design with four replicates and four B rates: 0, 3, 6, and 9 kg ha⁻¹ , applied as boric acid. Evaluated parameters included wood volume yield, aboveground biomass partitioning, nutrient stocks and use efficiency, SLA, LAI, stem architectural defects, wood basic density, and chemical composition. Only total N and Ca stocks in the biomass responded significantly to B rates. At three years of age, wood mean annual increment (MAI) was 24 m³ ha⁻¹ year⁻¹ (total volume of approximately 71 m³ ha⁻¹), while total aboveground biomass ranged from 34.6 to 35.3 t ha⁻¹ and was not affected by B rates. Stem morphology was the most responsive attribute to B fertilization: the highest incidence of apical leader breakage (20%) occurred in the unfertilized control (0 kg ha⁻¹ B), whereas stem bifurcations below breast height were highest at the extreme rates (52% and 64% at 0 and 9 kg ha⁻¹ B, respectively). Wood basic density, holocellulose, and extractive contents were not affected by B rates. In conclusion, CCV showed limited responses to B fertilization in terms of wood volume yield and wood technological properties; however, to optimize stem straightness and mitigate leader breakage and bifurcation, an operational B fertilization rate of 3–6 kg ha⁻¹ is recommended under similar site conditions.