Growth Response to Weed Control and Fertilisation in Mid-Rotation Plantations of Eucalyptus pellita in South Sumatra, Indonesia

Abstract

We report on a study of mid-rotation weed control and nutrient management in Eucalyptus pellita plantations in South Sumatra. The study was established at two contrasting sites (representing high and low productivity for the region) that had previously carried three rotations of Acacia mangium. A combination of weed control, nitrogen (N), and phosphorus (P) fertiliser were applied at 1 and 2 years after establishment. We found that the addition of up to 250 kg N ha−1 applied either at 1 year or 2 years after planting did not improve growth. The application of P (30 kg P ha−1) at age 1 year (in addition to 12 kg P ha−1 applied at planting) did not enhance tree growth either. Keeping the plantation free from weed competition throughout rotation (full weed control) enhanced wood volume up to age 4 years at the high-productivity site, while it improved wood volume up to the end of rotation at age 6 years at the low-productivity site. An additional experiment assessing the effect of weed control in the early phase of plantation establishment revealed that weed competition reduced young tree growth of E. pellita substantially. The results of the studies support the current practice of plantation management of E. pellita in the region that applied only P fertiliser at planting time and that kept trees free from weed competition before canopy closure. Full weed control throughout rotation is worth practicing at lower-productivity sites to achieve maximum productivity.

How Weed Control Affects Eucalyptus globulus Labill. Productivity: Results from Two Long-Term Trials

“…Both trials presented a positive growth response to the herbicide treatment in terms of H, DHB, and VOL, as reported by other authors [13][14][15]18,29,31]. A possible explanation may be the increment in the leaf area index and the photosynthetic rate of trees with less competition from understory vegetation, as reported by other authors [18,32].…”

“…A possible explanation may be the increment in the leaf area index and the photosynthetic rate of trees with less competition from understory vegetation, as reported by other authors [18,32]. The results from the experiment demonstrated that at both sites, the understory vegetation development and E. globulus growth responded to weed control differently, possibly due to climate conditions, the timing of weed control operations, and understory vegetation composition [13,17,30,31]. Differences between treatments were evident from the start of the trial in Soure, being only perceived in Torres Vedras at a later stage of the experiment.…”

“…No phytotoxic impacts related to herbicide applications were observed in E. globulus trees in either trial. Weed competition substantially reduced the growth of Eucalyptus pellita, particularly in low-productivity sites, but this effect was less evident in high to medium-productivity sites [31]. Our results suggested that, although there were differences in site productivity between the two trials, productivity gains during the first five years of E. globulus growth, before canopy closure, were apparently more dependent on the timing of weed control operations (defined by weed cover) than on the number of operations per se, as differences in the height increment between treatments at Soure were significantly different between 1.6 and 1.9 years.…”

“…Weed competition impacted E. globulus productivity mainly during the early phase of plantation establishment [5,14,15], but our results demonstrated that later weeding operations also contributed to growth increment at the end of the plantation cycle. Inail et al [31] found significant differences between the DHB and VOL of E. globulus pellita from plots treated with herbicide during the first year and plots treated with herbicide after initial tree establishment, with the last presenting larger mean diameters. Nevertheless, the maintenance of such differences in stand productivity at the end of the rotation was dependent on the site productivity potential [31].…”

“…Inail et al [31] found significant differences between the DHB and VOL of E. globulus pellita from plots treated with herbicide during the first year and plots treated with herbicide after initial tree establishment, with the last presenting larger mean diameters. Nevertheless, the maintenance of such differences in stand productivity at the end of the rotation was dependent on the site productivity potential [31]. During tree establishment, competition for light, water, and nutrients is limiting for young E. globulus trees [14].…”