Respuesta del Eucaliptus Nitens a la fertilización con dosis crecientes de N-P-K en terrenos graníticos forestales: Penas Agudas

Abstract

Despite its economic importance, there are few studies on the fertilization needs of eucalyptus in Galicia. For this reason, the objective of this work was to determine the effect of increasing amounts of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), boron (B), as well as the absence or presence of other microelements (M0) in the fertilization treatment, on the growth of Eucalyptus nitens over five years, using diameter at breast height and volume as study variables. This research was conducted in a tree plantation in the region of A Mariña (North of the Lugo province). For the field trials, three areas close to each other were selected, in each of which 14 plots were prepared with a sample size of at least 32 plants each. Each plot was exposed to one of the fertilization treatments, which included four doses of N, P and K, two doses of B (addition or no addition), and two doses of micronutrients (addition or no addition). At the beginning of the study, soil and leaf samples were collected to analyze their composition. Plant growth was monitored for 5 years, using a digital caliper to measure diameter at breast height, and a laser hypsometer to measure height. Periodic measurements were made every 6 months during the first year, and annually during the rest of the study period. Plant volume was calculated with a dasometric model using diameter and height as independent variables. The measurements of the diameter and initial volume were subjected to the Shapiro-Wilks Normality Test using the statistical package EPIDAT v 4.0. Student's t-test was applied to compare means, and contrasts were carried out to assess the effect of each treatment against the standard fertilization and a control without fertilization, expressed as differences in initial and final diameters, as well as differences in volumes. A mixed linear model was applied to evaluate the effect of the treatments on the analyzed variables. The significance level for all tests was p<0.05. The soils of the three zones are acidic, with a sandy-loam texture, although with different clay content, organic matter content, and C/N ratio, which could influence nutrient availability in each zone. Statistically significant differences were observed with increasing doses of NPK compared to the fertilization considered standard and to the control (without the addition of fertilizers). In zone 3, this effect was more significantly observed, with an increase in growth when nitrogen and phosphorus doses increased compared to standard fertilization. No general best fertilization treatment could be defined for the three areas. The main conclusions drawn from the results were: 1. In all cases, the treatment without fertilization (TT) showed limited growth compared to any of the other treatments in the three zones, although only in one of them were these differences statistically significant. 2. There was no evidence of a treatment with a stronger response in final diameter and final volume for all zones, but optimal fertilization depended on the zone in which the trial was carried out. 3. In zone 3, the treatments with the highest doses of N and P showed greater growth tan the rest of the applied treatments. 4. A greater response was observed with the standard fertilization treatment in all the zones, expressed in an increase in diameter, although no statistically significant differences were found with all the treatments. 5. The effect of the different fertilization treatments on the volume was not significant, due to the high intra-treatment variability observed for this variable.