Fertilizer management of eucalypt plantations on sandy soil in Brazil: initial growth and nutrient cycling. (Special Issue: Challenges and opportunities for sustainable management of eucalypt plantations.)

摘要

The sustainability of plantation forests requires the consideration of environmental and economic factors. Fertilization is an important practice in eucalypt plantations that should be adjusted to provide high productivity at the lowest cost without negatively affecting the environment. Eucalypt plantations are expanding worldwide, mainly because of the growing demand for wood and the high potential biomass production. Many field experiments have shown that using large amounts of fertilizer increases tree growth. However, the excessive or inappropriate application of fertilizer can cause nutrient leaching and the loss of the fertilizer. In this study, we evaluated the effect of increasing the fertilizer doses on the early growth and nutrient cycling in eucalypt plantations. Moreover, the amount of N and K leached after the application of split vs. single applications of N and K fertilizers after planting were quantified. A eucalypt plantation with a randomized block design was established in southern Brazil, consisting of six treatments and five blocks. The split application include the following five treatments of N and K fertilizers after planting: T1=control (without fertilizer), T2=40 kg ha-1 N; 16 kg ha-1 P; 53 kg ha-1 K (literature recommendation), T3=twofold the dose in T2 (commercial application used by forest companies), T4=threefold the dose in T2, T5=fourfold the dose in T2 (highest dose), and one treatment (T6) where the N and K fertilizers after planting amount in T3 was with a single application added at age 3 months. At harvest, the export of nutrients was greater than the amounts added by a commercial mineral fertilization only for N. The eucalypt trees responded positively to increasing the fertilization rates, especially during the first year after planting. The highest dose of fertilizer led to the production of 57 Mg ha-1 of biomass (at age 24 months), 48% higher than in the control treatment. However, the effect of the highest dose was more evident the first year after planting. The enhancement in biomass production decreased in the second year. The application of fertilizer also resulted in a large nutrient transfer to the soil through the leaf litter. The eucalypt trees receiving the highest dose of fertilizer transferred 50 kg N, 20 kg K and 80 kg Ca ha-1 to the soil over the second year after planting, whereas only 25 kg N, 6.5 kg K and 47 kg Ca ha-1 was returned to the soil by the control-treated trees in the same period. At age 24 months, there were no significant differences between the T3 and T6 regarding productivity and nutritional status. Splitting the application of the N and K fertilizers after planting reduced the amounts N-NO₃- leached at a depth of 0.9 m by 3.0 kg ha-1 (T3=5.6 kg and T6=8.6 kg) and the amount of K+ by 31.7 kg ha-1 (T3=8.3 kg and T6=40 kg) over the first 2 years after planting. Our results suggest that the number of N and K fertilizer applications can be reduced after planting in commercial plantations established on deep tropical soils without negatively affecting on productivity and limited losses by deep drainage.