ABSTRACT
This study aimed to evaluate the effect of substrates in the emergence and early development of Baru seedlings. The experiment was performed in a greenhouse in a completely randomized design with five treatments (substrates) and four replications. The substrates were: S1) Oxisol; S2) Oxisol + washed sand (1: 1 v: v); S3) washed sand; S4) Oxisol + washed sand + manure (1: 1: 1 v: v: v); S5) Oxisol + sand washed + poultry litter (1: 1: 1 v: v: v). The emergence, emergence speed index, seedling height (SH), stem diameter (SD), root length, shoot dry mass (SDM), root dry mass (RDM), SH/SD and SDM/RDM ratios and the Dickson quality index were evaluated. The emergence and early development of seedlings were influenced by the type of substrate. The Oxisol substrate is the most efficient for the early development of Baru seedlings.
Key words: Dipteryx alata Vog, emergence, germination, reforestation.
Baru (Dipteryx alata Vog., Fabaceae) is a native forest species in Brazil that is preferably propagated via seeds. The species is important for reforestation, wood production and human consumption (Sano et al., 2006). Baru nuts have a high nutritional value, being a source of minerals such as iron, zinc, calcium, protein, unsaturated fatty acids and tannins (Takemoto et al., 2001; Marin et al., 2009) and the seeds are commercialized. Baru fruits and seeds show great variations (Corrêa et al., 2000; Corrêa et al., 2008; Zuffo et al. 2014a).
Due to the great importance of Baru in food and for being a reforestation species, the recovery of areas with this species becomes timely, being important to produce seedlings with high quality and low cost (Zuffo et al., 2014b), so that the production of seedlings becomes feasible. In the production of seedlings, the substrate to be used is one of the most important factors because it provides ideal conditions for the seedling germination and the root system development (Negreiro et al., 2004; Ajalla et al., 2012). There are several types of substrates, such as subsoil, organic compound, vermiculite, sand, animal manure, sawdust and decomposed trees bark (Wendling et al., 2006).
According to Silva et al. (2011) substrates should have good structure, aeration, water retention capacity and low degree of contamination by pathogens, and these characteristics vary according to the material used in the substrate composition and may affect the germination and establishment of seedling, demonstrating the importance of choosing the ideal substrate composition.
Regarding the production of forest seedlings, each species has a suitable substrate for the formation of seedlings. For example, Albuquerque et al. (2013) observed that the growth of seedlings of sucupira (Bowdichia virgilioides Kunth) is favored with the use of a substrate made of Cerrado soil and vermiculite + black soil + carbonized rice husk in a proportion of 1: 1: 1. However, to Cavalcante et al. (2011), the most suitable substrate for the production of Gurguéia nut seedlings (Dypteryx lacunifera Ducke) is the washed sand.
Therefore it is demonstrated that there are different responses in the production of forest seedlings depending on the substrate type. Thus, this study aimed to evaluate the effect of substrates on the emergence and early development of Baru seedlings.
The experiment was performed at União farm, municipality of Nova Xavantina-MT (14°50'41"S, 52°22' 49''W, with average altitude of 290 m) during the period of 08/24/2013 to 09/21/2013 in a protected environment at 50% of brightness. The region climate is Aw according to the Koppen global climate classification, with two well defined seasons, a dry season that lasts from May to September and a rainy one that lasts from October to April. The climatic data were collected at the meteorological station of the National Institute of Meteorology - INMET and are shown on Figure 1.
The seeds for the experiment were collected from fruits coming from native trees in the municipality of Nova Xavantina-MT. After harvest, the fruits were taken to the laboratory for selection and standardization, and it was promoted the fruit cut and the seeds were taken for sowing. The experiment was performed in a completely randomized design, with five treatments (substrates) and four replications, each plot consisted of 20 seeds. The evaluated substrates were: S1) Oxisol; S2) Oxisol + washed sand (1: 1 v: v); S3) washed sand; S4) Oxisol + washed sand + manure (1: 1: 1 v: v: v); S5) Oxisol + sand washed + poultry litter (1: 1: 1 v: v: v).
The homogenization of the substrate mixture was performed manually and then placed in perforated plastic trays with 7 L capacity (46 cm x 29 cm x 6.5 cm). The Oxisol was removed from a layer of 0 to 20 cm deep in a Cerrado area and the following physical characteristics were found in the soil analysis: 500, 100 and 400 g kg-1 of sand, silt and clay, respectively. Each replication was consisted of a tray. For the sowing, the seeds were placed in the 'hilum down' position, according to the recommendation of Zuffo et al. (2014b).
At 15 days after sowing, a daily assessment of the number of emerged seedlings up to 28 days started, the percentage of emergence and emergence speed index (ESI) of each treatment were determined. To calculate the ESI, the formula of Maguire (1962): ESI=[N1/1+(N2-N1)/2+(N3-N2)/3+....(Nn-Nn-1)/n], where N1, N2, N3...Nn was adopted, which corresponds to the number of emerged plantlets and 1, 2, 3...n, being the number of days after sowing (DAS).
At 28 days after sowing: seedling height (cm) - determined from the soil surface to the insertion of the last leave with the aid of a millimeter ruler; stem diameter (cm) - measured at the height of the surface stem plant by reading in Clarke® digital caliper; root length (cm) - taproot, with the aid of a millimeter ruler were evaluated. Seedlings were separated into shoot and root system, placed in paper bags and taken into a forced air circulation oven for 72 h at 60°C until constant weight, in order to determine the shoot and root dry mass (g).
From these evaluations, the total dry mass (TDM) were determined, and the morphological indices were calculated: height ratio (cm) / stem diameter (mm) (SH/SD); shoot dry mass /root dry mass (SDM / RDM) and Dickson quality index (DQI) (Dickson et al., 1960), by the equation:
DQI = total dry mass/(height/diameter) + (shoot dry mass/root dry mass).
The obtained values were submitted to analysis of variance, and, when significant, the means were grouped by Scott-Knott criteria at 5% of significance using the statistical program SISVAR® (Ferreira, 2011).
All the parameters were significantly influenced by the type of substrate, except the stem diameter and the SDM/RDM ratio (Table 2). The S1 substrate (Oxisol) provided highest values of emergence and emergence speed index (81.25% and 1.78, respectively); which is statistically different from the others (Table 3).
These results are similar to those obtained by Rosa et al. (2006), which also found a higher emergence speed index in baru seedlings using only the soil as substrate. It is important to emphasize that the seedlings that emerge first, tend to grow more and produce more biomass due to the photosynthesis in the early stages of growth, except in stressful conditions. The S1 substrate (Oxisol) has lower sand content in its composition. According to Silva et al. (2011), this component has a high drainage capacity, and does not hold the required amount of water that would start the germination process, which may have adversely affected the emergence and emergence speed index.
There was no significant statistical difference between the substrates for the stem diameter (Table 3). The absence of significant effect of substrates in stem diameter was verified by Cavalcante et al. (2011), studying the Gurguéia nut (Dypterix lacunifera Ducke), species of the same family of baru. By analyzing the height of seedlings, the S1 substrates (oxisol), S2 (oxisol + washed sand) and S3 (washed sand) have provided higher means, being statistically different from the others (Table 3). These results are partially similar to those obtained by Sobrinho et al. (2010) that evaluated different substrates for the production of baru seedlings. The authors found that the substrates that contained only soil (Alfissol eutrophic), or soil + cattle manure or soil + carbonized rice husk showed greater plant height.
The S1 substrate (oxisol) also promoted the root growth and root dry mass (Table 3). Such findings corroborate to those observed by Sobrinho et al. (2010), in which the authors also obtained better root growth and root dry mass with the exclusive use of soil. Probably, with a larger root growth and root dry mass, seedlings tend to absorb a greater amount of water and nutrients by the roots, which may promote a better seedlings growth. Moreover, the substrate has smaller sand content mixed to its composition, presenting no water loss due to the drainage. Regarding the shoot dry mass, it was verified that the S1 substrate (oxisol) and S2 (oxisol + washed sand) had higher means. Similar results were obtained by Rosa et al. (2006) for this parameter.
For the SH/SD ratio, it is observed that the substrates S1 (oxisol), S2 (oxisol + washed sand) and S3 (washed sand) had higher means, being statistically different from the others (Table 3). For the SDM/RDM ratio, no statistical difference between the substrates was verified. However, for the Dickson quality index, the S1 substrate (oxisol) obtained the greater mean, differing statiscally from the others. It should be noted that this index is a good indicator of seedlings quality (Fonseca et al., 2002), however, to obtain this index, the destruction of the seedlings is required (Andrade et al., 2012).
Overall, it was observed that the substrate S1 (oxisol) was superior to the others, because it provides suitable conditions of moisture and aeration, favoring the emergence and early seedling growth (Table 3). Additionally, Neto et al. (2000) reported that species with larger seed size and weight, have greater availability of stocks in order to ensure the initial growth. Therefore, asbaru has large cotyledons, it probably have been responsible for the supply of nutrients for the seedling.
Moreover, Sousa et al. (2015) evaluated nitrogen and potassium in baru seedlings and concluded that this species is undemanding to those macronutrients. Besides the low demand in the early stage and the contents in the S1 substrate (oxisol) may be sufficient for the baru seedlings.
The highest values of emergence, emergence speed index, root length, shoot dry mass, root dry mass, SH/SD ratio and the Dickson quality index showed by the use of S1 (oxisol), may indicate that the baru species, as a native species from naturally poor and acid pH soils, shows adaptability to this type of soil conditions, and therefore, does not respond well to the increase of organic matter and fertility, caused by the substrate that had the addition of manure and poultry litter (S4 and S5).
In Table 1, it is verified that the S1 (oxisol) has the lowest pH and low fertility. For Melo et al. (1998) the native species of the Cerrado, which has low fertility, do not respond to fertility improvement of the substrate, and this increase in fertility, and can even harm the seedlings development. Moreover, as native species and due to their evolutionary characteristics such as hardiness, it is well suited to harsh conditions (Zuffo et al., 2014c). Those authors also verified such hardiness in cajuí (Anacardium microcarpum Ducke).
The S1 substrate (oxisol) is the most efficient for early growth of baru seedlings for providing better emergence, emergence speed index, seedling height, root length, shoot dry mass, root dry mass, SH/SD ratio and Dickson quality.
The authors have not declared any conflict of interests.
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