Otimização da produtividade de Eucalyptus spp. a partir da suplementação luminosa em minijardim clonal

Abstract

Species of the Eucalyptus genus are on the list of the most planted in the world, occupying around 7,6 million hectares in Brazil, which includes different genetic materials cultivated mainly in the Southeast, South and Central-West regions. Recently, with the use of mini greenhouses on mini clonal gardens (MJCs), greater control of temperature, relative air humidity and CO₂ concentration was obtained under the mini stumps, promoting an improvement in the quality of the material to be propagated. However, in subtropical regions during autumn and winter, productivity is limited by reduced sprouting of ministumps in response to reduced photoperiod and temperature. In view of the above, the objective was to evaluate the effect of light supplementation in addition to the mini-greenhouse on the productivity of mini-strains of E. saligna and E. urophylla x E. globulus during the winter season. The research was carried out in the South of Brazil, a region with seasonality and winter, which results in low plant productivity. The experimental design used was randomized blocks, consisting of three MJC managements (T1- SME: MJC without mini-greenhouse, only with natural light, considered as control; T2 - CME: MJC covered with mini-greenhouse; T3 - ME+L: MJC with mini-greenhouse associated with white LED light in a 24-hour photoperiod) containing four replications of 24 mini-stumps. The physiological attributes and productivity of the mini-stumps, as well as the rooting of the mini-cuttings, quality of the seedlings produced and environmental factors were evaluated in the three MJCs. Minicuttings were collected weekly, obtaining monthly productivity per ministump, while survival and rooting assessments were carried out at 45 and 90 days after cutting. The morphological attributes of the seedlings were also evaluated 120 days after staking. The mini-greenhouse associated with light supplementation promoted an increase in temperature, relative humidity and CO2. The ministumps of the E. saligna and E. urophylla x E. globulus clones, when grown in an environment with light supplementation (ME+L), showed a 23% increase in productivity (number of minicuttings/strain/month), in relation to the SME and CME. However, the minicuttings obtained from ME+L expressed greater nutritional demand for N, showing symptoms due to leaf spots, due to the greater nutritional demand in response to the high production of shoots. Despite this, the rooting of the minicuttings was not significantly affected by management in the MJC. The E. urophylla x E. globulus hybrid seedlings produced from the ME+L environment showed greater morphological quality when considering height and diameter. Conclusively, the use of the mini-greenhouse associated with light supplementation effectively contributes to increasing the productivity of minicuttings in the winter season, allowing a reduction in the MJC area used to meet the demand for seedlings in subtropical regions.