Fertilization effects on eucalyptus... FERTILIZATION EFFECTS ON EUCALYPTUS PELLITA F. MUELL PRODUCTIVITY IN THE COLOMBIAN ORINOCO REGION

1 Received on 07.02.2018 accepted for publication on 24.08.2018. 2 Universidade Federal de Viçosa, Mestre em Ciência Florestal, Viçosa, MG-Brasil. E-mail: <sandramont2@hotmail.com>. 3 Universidad Distrital Francisco José de Caldas,Ingenieria Forestal,Bogotá-Colômbia . E-mail: <anmaru3189@gmail.com> 4 Universidade Federal de Viçosa, Doutor em Agronomia, Viçosa, MG-Brasil. E-mail: <nairam.filho@thetimbergroup.com>. 5 Embrapa Rondônia, Porto Velho, RO-Brasil. E-mail: <hncipriani@hotmail.com>. *Corresponding author.


1.INTRODUCTION
There are approximately 24.8 Mha suitable for commercial plantations, which is equivalent to 21.8% of the national territory (UPRA, 2014).Nonetheless, although the forest potential is considerably high, the country has not achieved to increase its production capacity.During this last years, furniture and timber sectors are showing negative trade balances with generalized export decrease and import increase trends (Colombia, 2016).
The Colombian Orinoco region is the one with the largest areas for forest development, including Meta and Vichada states, with more than 2.5 Mha suitable for forestry activities each.However, edaphic restrictions like high acidity and low natural fertility rates are common (UPRA, 2014).On top of that, the region is characterized by high rain levels that cause a very active lixiviation process implying nutrients loss and biological activity reduction, limiting forest plantations development and productivity (Zavala et al., 2005).
Eucalyptus pellita F. Muell is native to North of Queensland, Australia and New Guinea, playing an important role in commercial reforestation in countries like Indonesia, Malaysia, the Philippines and Australia, among others.The species has good growth and coppicing properties, resistance to plagues, adaptability to a variety of environmental conditions and multipurpose timber (Clarke et al., 2009).In Colombia, it is one of the most adapted species to tropical rainforest conditions in the northeastern Orinoco region (Giraldo et al., 2014).Nonetheless, plantations with this species have shown low productivity mainly due to the lack of knowledge about the species nutrition requirements.Among the practices to improve forest productivity in acidic soils are: soil preparation, liming and chemical fertilization (Rojas, 2015).Nonetheless, in order to achieve forest plantation sustainability during its development, it is necessary to balance nutrients on the short, long and medium term (Santana et al., 2002) by using the optimum dose adjusted to soil nutrients availability to achieve maximum site productivity (Rodríguez and Álvarez, 2010;Zapata, 2013).Some species of the Eucalyptus genus are pretty tolerant to high aluminum, as well as to low nutrients concentrations (Barros and Novais, 1999).Nonetheless, in order to obtain high productivity rates, using fertilizers is necessary.Liming, is an agricultural practice that has been employed since very remote ages in order to improve acidic soil productivity, given its multiple effects on several soil chemical, physical and microbiological characteristics (Osorno, 2012).
Proper fertilization using phosphorus and potassium is essential for eucalypt plantations full development (Rocha et al., 2008).Usually, eucalypts require much P in planting and K in young and mature stages (Stahl et al., 2013).Bammanahali et al. (2011), for instance, improved young E. pellita productivity by using 100 kg ha -1 of P 2 O 5 and 200 kg ha -1 of K 2 O compared to the control treatment in Karnataka, south of India.
In eucalypt plantations, K and Ca, are among the nutrients with the highest accumulation rate in the trunk: between 312 and 455 kg ha -1 of Ca and between 148 and 192 kg ha -1 of K for 134 to 187 Mg ha -1 of trunk biomass at the age of 6.5 years (Santana et al., 2008).Several studies have demonstrated the high response to K, and this nutrient is one of the best indicators of eucalypt plantation sustainable productivity (Gonçalves et al., 2009).
In accordance with the above, this study had the purpose of assessing the effects of liming, phosphorus and potassium fertilization on 34-month-old E. pellita growth.
The studied areas are approximately 100 to 300 meters above sea level, plain relief, with temperatures of 25.8 to 27.5 ºC; average rainfall of 2,197 to 2,699 mm, yearly average potential evapotranspiration between 1,321 and 1,547 mm and relative humidity rates of 76.7% to 81%.According to the Köppen's classification, the climate is (Am), tropical monsoonal with monomodal rain regime, the rainy season going from April to November and dry season from December to March.Minimum rainfall is recorded in January, where the water-deficit period begins and lasts until the first quarter of the year.
Fertilization effects on eucalyptus...According to IGAC (1995), the area soils are classified as oxisols (in La Primavera and Puerto Lopez) and entisols (in Villanueva).These soils are typical of the region and are chemically characterized by low organic matter and interchangeable base contents, low fertility and sand content greater than 500 g kg -1 (Table 1).

Experiment design
The experiment was designed in randomized blocks with three repetitions and a factorial arrangement of 3x3x3 corresponding to 3 doses of LIME (0, 1 and 3 Mg ha -1 of dolomitic lime); 3 doses of P (30, 75 and 120 kg ha -1 of P 2 O 5 ) and 3 doses of K (60, 120 and 180 kg ha -1 of K 2 O).Triple superphosphate with 43% of P 2 O 5 was used as P source, potassium chloride with 60% of K 2 O as K source and dolomitic lime with 32% of CaO and 17% of MgO as LIME.The sample unit was composed of 20 trees spaced in 3x3 meters, considering utile for assessment the six central trees.

Trial planting
The seedlings were produced at Reforestadora de la Costa's nursery with seed proceeded from Villanueva-Casanare.The seeds were sown on seedbeds and the seedlings transplanted to dibble tubes, being grown for 80 days.LIME was applied to the soil a month before planting and incorporated with a subsoiler.P was applied in a unique dose after planting, in lateral dibble holes 20 cm away from the seedling.K doses were applied in three moments: planting (lateral dibble holes 30 cm away from the seedling), seven months after planting and eight months after planting (in lateral dibble holes under the projection of tree canopy).
A base fertilization was applied to all trees, composed of 50 kg ha -1 of nitrogen and 57 kg ha -1 of sulfur, in the form of ammonium sulphate applied at planting and six months after, under tree canopy projection.Borax (11 kg ha -1 , with 15% of boron) and other micronutrients were also applied.

Statistical Analysis
At 34 months after planting, height (H) and diameter at 1.3 m above ground level (DBH) were measured using a VERTEX IV Haglof and a girth band, respectively.Data related to the six trees located in the center of each plot were used for analysis.The mean volume with bark (Vol) per tree was estimated from the formula adjusted for the species in the studied area (López, 2007): Eq-1 Volume data obtained as a response to fertilization treatments were subjected to the Ryan-Joiner and Bartlett tests, for normality and homoscedasticity check, respectively.These tests showed that data was normal and homoscedastic (p>0.05) in the three locations.Subsequently, the ANOVA was carried out in order to determine treatment effect.The following regression models were assessed: simple linear, square root, exponential, hyperbolic and logarithmic.Analyses were carried out by means of the Sisvar and Minitab 18 statistical software.

La Primavera (Vichada)
There was a significant effect (p<0.01) of LIME and P doses on E. pellita growth.In Table 2, ANOVA related to the volume variable is presented, indicating that there was no interaction between P 2 O 5 and LIME doses used in this experiment.The volume response Table 1 -Chemical and physical properties of the soil at 0 to 20 cm of depth in experimental areas Tabela 1 -Propriedades químicas e físicas do solo a 0-20 cm de profundidade, nas áreas experimentais.
to LIME was better adjusted to the logarithmic model, whereas for P doses the model with the best adjustment was the square-root one (Figure 1).Decreasing increments with LIME were observed, with stability beginning at 1 Mg ha 1 of LIME, approximately.
Eucalyptus pellita trees that received 1 and 3 Mg ha -1 of LIME, had a volume production of 0.046 and 0.049 m 3 respectively, a 34 and 39% increase compared with those that did not receive fertilization and had a mean volume of 0.033 m 3 .The application of 75 and 120 kg ha -1 of P 2 O 5 resulted in volume increase of 20 and 35% respectively, compared with the lowest dose (30 kg ha -1 ) of P 2 O 5. In La Primavera, K doses did not produce significant effects (p>0.05) on E. pellita tree volume.

Villanueva (Casanare)
LIME doses applied on soil before planting of E. pellita trees had a significant effect (p<0.01) on tree volume at 34 months after planting.No significant effect was observed (p>0.05)regarding P and K application and interactions (Table 2).
The mean volume per tree without LIME was 0.058 3 , while a mean of 0.071 and 0.075 m 3 was obtained by applying 1 and 3 Mg ha -1 , a 23 and 27% increase on tree volume (Figure 2).The volume response to LIME adjusted better to the logarithmic model.

Puerto Lopez (Meta)
Variance analysis indicated that a significant effect was produced on 34-month-old E. pellita trees volume due to LIME application before planting (Table 2).Volume as a function of LIME doses followed a simple linear model (Figure 3).Tree volume reached 0.08 and 0.10 m 3 , increasing by 8 and 24%, respectively, compared with those that did not receive LIME (Figure 3).K and P application did not produce significant effects (p>0.05) on E. pellita tree volume in Puerto Lopez.

4.DISCUSSION
Productivity increases obtained by lime application have been observed in different eucalypt species (E.pellita included), in acidic soils with low base content, especially Ca and Mg.Giraldo and Parra (2012), evaluated the response of E. pellita with 14 months to the application of calcium and magnesium fertilizers in Villanueva -Casanare, evidencing a positive response to doses between 2 and 4 Mg ha -1 , in pH 4 soils with Ca levels of approximately 0.2 cmol c dm -3 .In that case, height and DBH increases were between 76 and 160%, respectively, compared with trees that did not receive any fertilizer.Rodríguez et al. (2016), obtained significant volume increases by applying dolomitic lime in E. grandis plantations on a dystrophic Red-Yellow Latosol soil of medium texture, with a pH between 4.06 and 4.88 at 10 to 20-cm depth, and Ca and Mg levels lower than 0.01 cmol c dm -3 , in the Cerrado region, Minas Gerais State, Brazil, increasing productivity by 58% 18 months after planting, compared with tress that received no fertilizer.
On the other hand, the lack of response of E. pellita to P and K doses in Puerto Lopez and Villanueva can be partly associated to a better assimilation of these nutrients due to LIME effects on soil.According to Rocha et al. (2008), increasing Ca supply from lime application increases soil pH, effective cationic exchange capacity, base saturation and interchangeable Ca and Mg, as well as P, K and S availability, allowing significant diameter and height increases.) at 34 months, as a response to K (kg ha -1 of K 2 O); LIME (Dolomitic Lime in Mg ha -1 ) and P (kg ha -1 of P 2 O 5 ) application.Significant** ( = 0.01).Tabela 2 -Analises de variancia para o volume (m 3 ) de E. pellita aos 34 meses de idade como resposta à aplicação de K (kg ha -1 de K 2 O); CAL (Calcário dolomítico em Mg ha -1 ) e P (kg ha -1 de P 2 O 5 ).Significativo** ( = 0.01).
After 34 months of growth, phosphate fertilization response on tree volume was observed only in La Primavera, where P soil levels were the lowest of the three testing sites: 1.14 mg kg -1 , compared with 2.17 and 3 mg kg -1 in Puerto López and Villanueva, respectively (Table 1).Soils with P levels between 0 and 2 mg kg - 1 show high responses to phosphate application (Gonçalves, 2016).AMEZQUITA SPM et al.
Results with similar doses to those used in this study were obtained by Fernandez et al. (2000), who reported increase of 73% at 9.5 years with 112 kg ha -1 of P 2 O 5, compared with trees that did not receive P in E. camandulensis clonal plantations located in Viçosa, Minas Gerais, Brazil.Likewise, Xu et al. (2005), using superphosphate as base fertilizer, significantly increased E. urophylla productivity at 54 months, in ultisols located in the south of China with P contents of 1.53 mg kg.The application of 20 kg ha -1 of P 2 O 5 increased productivity to 21 m 3 ha -1 per year, while 29.7 m 3 ha -1 per year were obtained with 200 kg ha -1 of P 2 O 5.
Potassium is one of the most absorbed elements by the majority of forest species, nonetheless, only a small quantity is available in soils, resulting in high demands of this nutrient to satisfy tree nutrition requirements (Alvarado and Raigosa, 2007).Likewise, K is one of the most demanded nutrients by eucalypts, which usually respond to K fertilization and grow poorly when this element is lacking (Teixeira et al., 2006).However, in this study, no effect of K application was observed in E. pellita tree volume, regardless of the location, which can be attributed to the fact that the lowest dose (60 kg ha -1 de K 2 O) used in this experiment was calculated to supply the species demand.Different studies report positive responses to K in soils with low K levels, similar to those of this study (0.02 to 0.04 cmol c dm -3 ).Gazola (2014), for instance, obtained the maximum diameter of E. urophylla clones at 18 and 24 months after planting by employing 86 and 129 kg ha -1 of K 2 O, respectively.The nutrient source employed that study was also KCl and the soil showed K level of 0.02 cmol c dm -3 .Melo et. al (2016), obtained 130% increase in tree volume by using 125 kg ha -1 of K 2 O compared with trees that did not receive K, in soils with K level of 0.03 cmol dm -3 .

5.CONCLUSIONS
The results obtained indicate the positive effect on E. pellita growth in the areas of study by using doses of approximately 1 Mg ha -1 of lime, in soils with Ca lower levels than 0.3 cmol c dm -3 .In La Primavera, which had 1.14 mg kg -1 of available P in the soil, more than 120 kg ha -1 of P 2 O 5 might be required to achieve maximum productivity, and 30 kg ha -1 of P 2 O 5 can be considered satisfactory for E. pellita in Puerto López and Villanueva.

Table 2 -
Analysis of variance of E. pellita volume (m 3