Scientia Forestalis, volume 45, n. 113
Physic-chemical properties and substrate formulation for Eucalyptus seedlings production
Propriedades físico-quimicas e formulação de substratos para produção de mudas de Eucalyptus
1Professor(a) do Departamento de Ciências Florestais. UFPR - Universidade Federal do Paraná. Av. Prefeito Lothario Meissner - Jardim Botânico - 80210170 - Curitiba, PR, Brasil. E-mail: email@example.com; firstname.lastname@example.org
Recebido em 08/10/2015 - Aceito para publicação em 06/07/2016
Objetivou-se avaliar a viabilidade de uma série de materiais para formulação de substratos, com foco em resíduos agroindustriais, e a influência de suas propriedades físico-químicas na produção de mudas de Eucalyptus benthamii, e verificar a semelhança entre os componentes testados. Foram formulados 100 tratamentos. Realizou-se semeadura direta em tubetes de 55 cm³, acondicionados em bandejas plásticas, alocadas em estufa por 120 dias. Como resultados, em relação às propriedades físicas, formaram-se quatro grupos: Grupo 1- constituído por elementos de alta macroporosidade; Grupo 2- equilíbrio entre macro e microporos, Grupo 3- maior proporção de microporos e Grupo 4- alta densidade associada à alta microporosidade. Quanto às propriedades químicas, formaram 2 grupos: Grupo 2- biossólido e Grupo 1 - demais componentes. Verificou-se maior crescimento nos substratos com maior capacidade de retenção de água e os altos níveis de condutividade elétrica e pH não prejudicaram o crescimento das mudas. A casca de pinus semidecomposta e diferentes granulometrias de moinha de carvão proporcionaram redução no crescimento quando inseridas na formulação dos substratos. O resíduo regional, biossólido, apresentou o menor custo aliado ao bom crescimento das plantas e a utilização da moinha de carvão justifica-se a fim de reduzir os custos de produção.
Based on substrate importance for seedling production, we evaluated the feasibility of using a variety of materials, with a focus on agro-industrial residues, and the influence of their physic-chemical properties on Eucalyptus benthamii seedling production, as well as to check for similarities between the tested components. One hundred treatments were formulated. Direct seeding was performed in plastic tubes of 55 cm³, packed in plastic trays, and placed in a greenhouse for 120 days. According to physical properties, four groups were made: Group 1- elements with high macro-porosity; Group 2 - balance between macro-pores and micro-pores; Group 3 - higher proportion of micro-pores; and Group 4 - high density associated with high micro-porosity. Concerning chemical properties, two groups were formed: Group 2 - sewage sludge and Group 1 - other components. In general, we observed more growth in substrates with greater water-holding capacity. High levels of electric conductivity and pH did not hinder seedlings growth. Almost decomposed pine bark and different fine charcoal grain size provided reduction in growth when inserted in substrate formulation. Regional sewage sludge presented the lowest cost coupled with good plant growth, and the use of fine charcoal is justified in order to reduce production costs.
The area planted with Eucalyptus in Brazil has been growing year after year, due mainly to investments of paper and cellulose companies (IBA, 2014). This reflects on the increased demand for plus trees plantation, which is possible mainly through cloning. However, subtropical species cultivated in Brazil’s southern region, have low levels of adventitious rootings (ASSIS; MAFIA, 2007; XAVIER et al., 2013). According to Brondani et al. (2014), the average percentage of Eucalyptus benthamii rooting is 43.5%, being considered a hard rooting species, thus justifying the production of seedlings by seed, the demand for plants of this species (SCHULTZ et al., 2012; KRATZ et al., 2013a).
Seedlings should have a good quality in order to avoid losses by mortality and low growth after planting, coupled the reduction of crop treatment applied to plantation, due to reduced competition from invasive plants, promoted by greater early growth of the crop (FIGUEIREDO et al., 2011). In this sense, many efforts have been made to improve the quality and reduce production costs. Among the factors of influence is the substrate, which needs to support the seedlings and supply water and nutrients needed for plant growth (HARTMANN et al., 2011). Intrinsic factors of substrates that affect plant growth are: their physicochemical properties, which vary depending on their origin, production method and components proportions (WENDLING et al., 2007; MELO et al., 2014).
The use of substrates with low cost coupled with formation of plants with a superior morphological quality, results in reduction of production cycle and lower economic spending (SIMÕES et al., 2012). Most commercial substrates are available only in specific locations in the country, increasing the costs when transported to more distant regions (KRATZ et al., 2013a). The use of regional waste substantially reduces the cost of substrate, although costs can vary depending on availability of each material (WENDLING et al., 2007; MELO et al., 2014).
Ready-to-use substrates may be found on the agricultural market; the main products being based on pine bark and peat moss. However, currently there is a low offer of pine bark for substrate manufacturing due to its increased use as an energy source for forestry industry boilers, as well as due to the reduction in the area planted with Pinus in Brazil (IBA, 2014). In the case of peat moss, its main disadvantage is the environmental impact, since it is a non-renewable material (CALDEIRA et al., 2011), together with temporary prohibition of its importation from Canada, the main supplier of the raw material (BRASIL, 2013).
Other wastes are already being used as substrate components, such as coconut fiber and carbonized rice husks; however, these are not found in all regions of the country, raising the cost of acquisition at sites distant from the production source. In contrast, there are residues found in all locations, such as sewage sludge, being technically feasible for seedling production (TRIGUEIRO; GUERRINI, 2004; GOMES et al, 2013; CALDEIRA et al., 2014), but not commonly used for this.
Considering the importance of using organic waste and the need to present new options of substrates, this study assessed the feasibility of using a range of materials, focusing on agro-industrial waste, and the influence of their physic-chemical properties E. benthamii seedling production, as well as checking the similarity between the tested components through cluster analysis.
MATERIAL AND METHODS
Preparation of substrates
The experiment began in December 2013, in the Laboratory of Forest Species Propagation, from Embrapa Florestas, located in Colombo, Paraná, Brazil (25°19’17” S and 49°09’39” W). The climate, according to Köppen, is Cfb (subtropical humid climate).
Two commercial substrates were used (based on peat moss and almost decomposed pine bark) and mixtures of different components (carbonized rice husk, fine charcoal, coconut fiber, almost decomposed pine bark, fine vermiculite, sewage sludge and peat moss) for formulation of 100 substrates (Table 1).
Tabela 1. Materials used (%) for substrate formulation (volume/volume).
Charcoal from wood of Pinus and Eucalyptus was used to obtain two different grain sizes (3-5 mm and 1-3 mm). For this, three sieves with meshes of 5, 3 and 1 mm were used. Carbonized rice husk and sewage sludge were prepared according to the methodology described by Kratz et al. (2013a), and fine vermiculite (grain size around 0.71 to 2 mm), coconut fiber (grain size around 0.25 to 2 mm), Brazilian black peat moss, almost decomposed pine bark and commercial substrates were acquired from a substrates factory.
Materials were mixed manually along with basic fertilization (0.6 kg m³ ammonium sulfate [20% of N], 4 kg m³ simple superphosphate [20% of P2O5 and 14% of SO4], 0.2 kg m³ potassium chloride [58% of K2O] and 1.5 kg m³ FTE BR 12 [9% of Zn, 3% of Fe, 2% of Mn, 0.1% of Mo, 1.8% of B, 0.8% of Cu]).
Physical and chemical characterization of substrates was performed in the Watershed Management Laboratory, from Federal University of Paraná and Soil Chemistry Laboratory, Embrapa Florestas, respectively, according to the methodology described in the instruction No. 17 of Ministério da Agricultura, Pecuária e Abastecimento (BRASIL, 2007). Through this normative instruction the values of apparent density (Ad), water-holding capacity on a 10 cm tension (WHC 10) or micro-porosity (micro), potential of hydrogen (pH) and electrical conductivity (EC) were obtained. From these results, total porosity (Tp) and macro-porosity (Macro) were obtained. Tp corresponds to the volume of water retained in substrate at 0 hPa tension (fully saturated), while macro-porosity consists of difference between Pt and the volume of water held up at 10 hPa (WHC 10 or micro-porosity) (DE BOODT; VERDONCK, 1972).
Mineral nutrients phosphorus, potassium, calcium and magnesium were determined in their available form (NOGUEIRA; SOUZA, 2005), while carbon, nitrogen and sulfur in their total form were obtained using the CHNS Elemental Analyzer.
Direct seeding was performed in plastic tubes of 55 cm³ (packed in metal trays and separated at a spacing of cell tray) with Eucalyptus benthamii seeds from a Seed Production Area, located in Guarapuava, Paraná, Brazil. Manual seeder was used, in which every container received around 4 seeds, covered with a layer of 0.5 cm of fine vermiculite. After sowing, trays were placed in a greenhouse (4 daily irrigations of 10 min with flow rate of 144 L hour-1) with monitored temperature (Table 2), where they remained for 120 days. Thirty days after sowing, thinning was done, leaving only one plant per tube.
Tabela 2. Minimal (T min.), maximal (T max.) and medium (T med.) air temperature inside greenhouse during the E. benthamii seedlings production period.
On the 30th day, growth fertilization began (4 g L-1 of urea, 3 g L-1 of simple superphosphate, 0.25 g L-1 of FTE BR 10 (7% Zn, 4 % Fe, 4 % Mn, 0.1% Mo, 2.5 % B, 0.8% Cu) and 3 g L-1 of potassium chloride), applied every seven days until the 90th day. After this, rustication fertilization was performed (4 g L-1 of ammonium sulfate, 10 g L-1 of simple superphosphate, 4 g L-1 of potassium chloride, 1 g L-1 of FTE BR 10), which was also given every seven days until the 120th day. For fertilization preparation, the fertilizers were mixed with water and the resulting solution was applied to the seedlings with use of manual watering cans, applying approximately 5 ml per plant.
For the evaluation of seedling quality, the height of the aerial part was measured (ruler graduated in mm) and stem diameter (digital caliper) on the 90th and 120th days. On the 120th day, an evaluation of aerial and root part dry biomass (48 hours in oven at 65° C and weighing in a precision analytical balance of 0.001 g) of 100 seedlings of different height classes was made, in order to fit an equation to estimate the dry biomass of all seedlings.
Experimental design and statistical analysis
The applied experimental design was completely randomized with five replications of 10 plants and 100 treatments. In order to observe the influence of each component addition in different combinations, a regression analysis was performed. To verify which components used in the substrates formulation presented greater similarity concerning physic-chemical properties, a cluster analysis was performed by the nearest neighbor method. To determine groups, a 50% cut in the Euclidean distance was adopted (Albuquerque et al., 2006).
For evaluation of commercial components costs, the values of purchase were considered. Costs of fine charcoal and sewage sludge were obtained by summing the costs of transportation and of labor to prepare it, on the basis of a worker’s wage employed in Farming, Forestry and Fishing Activities (PARANÁ, 2014).
RESULTS AND DISCUSSION
Cluster components analysis concerning physical properties, formed four substrates groups (G) in a 50% reduction of Euclidian distance: G1 - carbonized rice husk, G2- two grain sizes of charcoal, G3 - coconut fiber, fine vermiculite, peat moss and pine bark, and G4 - sewage sludge, being G1 and G4 the groups with greater differences regarding others (Figure 1A). From cluster analysis we found that G1 group had high macro-porosity, G2 had components that presented greater balance between macro and micro-porosity, G3 was formed by elements with higher proportion of micro-pores, and G4 had high density associated with high micro-porosity (Figures 1A and 2).
Among physical properties, total porosity and micro-porosity presented greater similarity, followed by apparent density and macro-porosity, similar in cluster analysis result of components, in which carbonized rice husk, followed by sewage sludge, were the substances with higher difference compared to the others (Figure 1 C and A). In spite of presenting similarities with charcoal-based components, carbonized rice husk differentiates itself due to its high macro-porosity, a feature specific to this component (Figure 2 D), and sewage sludge due to its high micro-porosity and apparent density (Figure 2 A).
The addition of G1 (carbonized rice husk) to G3 (coconut fiber, fine vermiculite, peat moss and pine bark) and G4 (sewage sludge) groups resulted in a decrease of apparent density and micro-porosity and increase of porosity and macro-porosity values. On the other hand, G2 (different grain size of charcoal) when combined with fine vermiculite (G3) led to an increased density and reduction of total porosity and micro-porosity. When combined with peat moss and pine bark (G3) or sewage sludge (G4), it provided a reduction in density, porosity and micro-porosity (Table 3).
Tabela 3. Physic-chemical analysis results. Apparent density (AD), total porosity (TP), micro-porosity (Micro), macro-porosity (Macro), potential of hydrogen (pH), electric conductivity (EC), magnesium (Mg), potassium (K), phosphorus (P), calcium (Ca), nitrogen (N), carbon (C) and sulfur (S).
Results from cluster analysis show that carbonized rice husk and sewage sludge cannot be replaced by any of studied elements, due to high macro-porosity of carbonized rice husk (56.9%) and high micro-porosity associated with apparent density of sewage sludge (56.3%; 583.3 Kg m-3). Results indicate that it is necessary to combine elements of G1 and G2 to G3 and G4, to improve its physical characteristics, obtaining as a result substrates with greater balance between macro- and micro-pores. Despite not being in the same group, charcoal based components should not be combined with carbonized rice husk, because all components feature low water retention capacity and micro-porosity (Figure 2 C).
Materials with low density raise the mixture’s macro-porosity and reduce water retention capacity of substrates (CALDEIRA et al., 2014), as was verified with increased proportion of carbonized rice husk and different charcoal grain sizes. On the other hand, the lightweight materials such as coconut fiber and fine vermiculite caused an increase in water holding capacity, due to presence of internal pores (SIMÕES et al., 2012; KRATZ et al., 2013a). Different water retention results indicate the need for water management for each substrate composition (SIMÕES et al., 2012). In seedlings of E. grandis produced in two commercial substrates subjected to different irrigation regimes, growth is associated with substrate and irrigation scheme applied by it, as noted by Lopes et al. (2007).
For chemical properties, the components were separated into 2 groups, at distance of 50%: G1 - carbonized rice husk, two different charcoal grain sizes, coconut fiber, fine vermiculite, pine bark and peat moss; and G2 - sewage sludge, in ascending order of fertility (Figure 1B). Concerning chemical properties, groups were formed from a distance of 80%: G1 - carbon, G2 - phosphorus and potassium, G3 - potential of hydrogen - pH, G4 - calcium and nitrogen, G5 - electrical conductivity, magnesium and sulfur (Figure 1 D).
Among evaluated components, coconut fiber was the most inert, with low concentration of all macronutrients examined, together with a pH within appropriate range and low electrical conductivity. Incinerated materials presented greater contents of carbon, phosphorus and potassium, associated with high pH and low values of nitrogen, sulfur, calcium, magnesium and electrical conductivity; and sewage sludge, with higher concentrations of magnesium, sulfur and high values of pH and electrical conductivity; peat moss with higher levels of nitrogen and calcium; and pine bark of phosphorus and calcium (Figure 2).
As for chemical properties, the division of substrates in just two groups is justified by the fact that sewage sludge presented major dissimilarity in a greater number of chemical properties, compared to other components, resulting in high values of magnesium, sulfur and electric conductivity (Figure 3). According to Caldeira et al. (2014), the high electrical conductivity of sewage sludge is linked to its high salt concentration, corroborating Guerrini and Trigueiro (2004) and Kratz et al. (2013b).
Substrates properties and growth
The use of peat moss, sewage sludge and coconut fiber as pure substrates provided greater growth, when compared with its use as mixtures component. On the other hand, carbonized rice bark, fine vermiculite, two different grain sizes of charcoal and pine bark presented the need to be combined with other elements in order to obtain a greater increase in growth (Figures 3 and 4).
A trend in seedlings growth was observed with the increase in proportion of one component in relation to other, however, only 7 of 18 combinations evaluated presented significant value (α<0.05): PB/PM, PB/SS, PB/CF, CRH/PM, CRH/CF, C1/PM and C2/FV (Figure 3).
Among the significant results, linear growth of plants was observed with increasing proportion of coconut fiber and peat moss as opposed to carbonized rice husk. Similar results were verified by adding coconut fiber, sewage sludge and peat moss to pine bark; peat moss to charcoal with grain sizes between 1-3 mm and fine vermiculite to charcoal with grain sizes between 3-5 mm. In general, it was observed among the evaluated components; that the addition of pine bark and charcoal to other components provided a reduction in plant growth. When combined with each other, there was no significant difference in growth (Figure 3).
It is possible to check that addition of peat moss, coconut fiber and sewage sludge to carbonized rice husk provided increased seedling growth, while pine bark had the opposite effect; doses above 70% made growth unsatisfactory (below 25 cm on the 120th day). As for coconut fiber, the use up to 70% is recommended, combined with carbonized rice husk (Figure 3 B).
For commercial substrates, there has been more growth in E. benthamii seedlings using substrates based on peat moss. Similarly to pine bark, commercial substrate based on this substance alone provided less plant growth (23.8 cm), when compared with commercial substrate based on peat moss (31.8 cm) (Figure 3 A).
Similarity between physical properties correlated with results observed in seedling growth. Apart from pine bark, substrates with greater water retention capacity presented more seedling growth, denoting water requirement of the species, which can be justified by high temperatures observed in the production period, associated with the water irrigation program (Table 1). Results indicate that pine bark, when used in high proportions, is not suitable for E. benthamii seedling production, due to the lower growth observed with the use of commercial substrate based on this element (23.8 cm), when compared to commercial substrate based on peat moss (31.8 cm). These results agree with other research work with Eucalyptus (KRATZ et al., 2013b; KRATZ; WENDLING, 2013).
The use of residual charcoal proved to be inadequate as a component of substrates, regardless of associated element, due to reduction in seedlings growth when substrate was added (Figure 3 C and D). This result can be due to its low water retention capacity associated with high pH (Figure 2).
On the other hand, the use of organic substrates was shown to be feasible, which in accordance to Guerrini and Trigueiro (2004), is related to increased water and nutrient retention capacity. This is confirmed by results observed with use of sewage sludge on E. grandis and E. benthamii (TRIGUEIRO; GUERRINI, 2004; KRATZ et al., 2013 b), with organic compounds of agro-industrial residues in E. grandis seedlings (SILVA et al., 2014) and with substrates containing matured cattle manure, in seedlings of E. grandis with carbonized rice husk, coconut fiber and vermiculite (MELO et al., 2014).
Electrical conductivity of substrate shall not exceed the limit of 1.0 mS.cm-1 (GONÇALVES et al., 2000), with just sewage sludge being non-standard (Figure 2 F). However, among evaluated components, it takes second position concerning growth (Figure 3), indicating that E. benthamii tolerates high levels of salinity, as verified by Kratz et al. (2013 b), in which substrates with EC ranging from 0.1 to 2.6 mS/cm provided adequate plant growth. Similarly, as verified by Mendonça et al. (2010), E. camaldulensis, E. tereticornis and E. robusta seedlings showed to be resistant to salinity until electrical conductivity of 8.33 dS m-1, and it was noticeable that it did not cause reduction in chlorophyll content, which is a major factor in plants sensitive to salinity.
The pH showed a negative correlation with growth (R = -0.48**), confirming the lower growth observed in substrates based on fine charcoal (pH = 9.7; 8.9) and carbonized rice husk (pH = 7.4). However, sewage sludge with alkaline pH (9.1) provided adequate growth of plants, which means that it is not possible to infer plant growth based on only this property. In general, substrates with pH below 5.0 can cause deficiency of nitrogen, potassium, calcium, magnesium and boron to plants, while in pH above 6.5 deficiencies of phosphorus, iron, manganese, zinc and copper are expected (VALERI; CORRADINI, 2000). However, species from the Eucalyptus genus showed variable tolerance to this factor, as seen in seedlings of E. benthamii (KRATZ et al., 2013 b) and E. urophylla (OLIVEIRA JUNIOR et al., 2011), produced in substrates with different pH values, providing adequate growth.
The regional waste, charcoal chaff and sewage sludge, presented lowest cost, given that they were donated by producing companies. The shipping and preparation cost were responsibilities of the grower. Coconut fiber and pine bark, which in the past were considered as wastes, are currently marketed, due to their technical feasibility, combined with use of bark for energy generation. Fine vermiculite presented higher production cost, followed by commercial substrates (Table 4).
Tabela 4. Purchase price, transport, preparation and total cost of components used for substrate formulation for E. benthamii seedlings production in metropolitan region of Curitiba, in 2014.
Higher cost of commercial substrates in relation to components leads to the possibility of formulating substrates in nurseries to reduce costs, albeit with the need to carry out trials aimed at adapting formulation of different species and growing conditions. The use of substrates with low cost combined with formation of seedling with better morphological quality results in reduction of production cycle and a lower cost (SIMÕES et al., 2012). It is worth noting that the use of regional waste substantially reduces substrate cost (MELO et al., 2014; WENDLING et al., 2007), although the costs can vary depending on the availability of each material (WENDLING et al., 2007).
Among combinations that showed no significant influence (α>0.05) it is appropriate to use charcoal-based components for substrates formulation to reduce costs, especially when combined with vermiculite and peat moss. In spite of showing lower growth, plants reached the minimum height indicated for planting (15 cm) (WENDLING; DUTRA, 2010). However, higher seedlings result in a higher field initial start-up, reducing competition with invasive plants, also promoting a cost reduction (FIGUEIREDO et al., 2011).
The substrates were grouped into four groups by chemical properties: G1 - elements of high macro-porosity (carbonized rice husk); G2 - balance between macro-pores and micro-pores (two different grain sizes of charcoal); G3 - higher proportion of micro-pores (coconut fiber, fine vermiculite, peat moss and pine bark); and G4 - high density associated with high micro-porosity (sewage sludge).
The substrates were grouped into two groups by chemical properties: G1 - lower fertility (carbonized rice husk, two different grain sizes of charcoal, coconut fiber, fine vermiculite, pine bark and peat moss) and G2 - greater fertility (sewage sludge).
Different materials and formulations of substrates can be adopted for E. benthamii seedlings production; better are those with greater water retention capacity, peat moss, sewage sludge and coconut fiber.
Sewage sludge waste presented the lowest cost coupled with good plant growth and the use of fine charcoal is justified to reduce production costs.
Almost decomposed pine bark and different grain sizes of chaff charcoal provided a reduction in growth when inserted into the substrate formulation.
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