Mauritia vinifera Mart Substrates and Nitrogen Doses in Acacia mangium Willd Growth

The objective of this study was to evaluate the effect of the combination of a substrate formulated with decomposed buriti stem ( Mauritia vinifera Mart.) and nitrogen doses in the production of Acácia mangium Willd seedlings. A completely randomized design was used in a 3 × 5 factorial scheme, being the factors constituted of substrates formulated from decomposed buriti stem (DBS) mixed with dystrophic yellow oxisol in three proportions (0; 25 and 50%) and nitrogen doses (0; 100; 200; 300 and 400 mg dm -3 ) applied in cover. After 60 days from the emergency, it was made the following evaluations: Plant Height (PH), stem diameter (SD), internodes number (IN), dry mass of the shoot part (DMA), length and dry mass of the roots, robustness quotient through stem height/diameter relation, roots/dry mass relation and Dickson Quality Index (DQI). The multivariate analysis of variance showed a significant difference ( p < 0.01) among averages vectors of treatments. The grouping analysis for the evaluated treatments allowed the division into four distinct groups. In the bi-dimensional plane formed by the first two canonical variables (Can.1 and Can.2) that withheld 99,47% of the total variance contained in the nine original variables, it is observed that the group II of treatments, composed of substrates formulated with 50% of soil + 50% of DBS supplemented with the doses of 200, 300 and 400 mg dm -3 of nitrogen, has provided a greater initial growth of A. mangium plants, as stated by the highest averages in all evaluated variables.

It is known that the success of forest planting, among other factors, depends on the production of quality seedlings (Araújo et al., 2018). The substrates are widely used in this phase, and a lot of times, the mineral supplementation. Among the essential elements required by the plants, stands out the nitrogen, macronutrient required in larger quantities by plants, constituent of various compounds and physiological processes (nucleic acids, enzymatic cofactors, proteins, photosynthesis, respiration, and others) (Shiri-Janagard et al., 2012;Egamberdieva et al., 2018).
However, the commercial organic substrates and the mineral fertilization are, most times, expensive (Chae et al., 2018), thus becoming inaccessible to small and medium producers, but they are still essential to the production of more vigorous seedlings, which increases the chances of field survival. The organic substrates improve the chemical, physical and biological characteristics of the soil, hence providing suitable conditions for the good development of the seedlings (Cavalcante et al., 2019;Oliveira et al., 2019).
In this way, it has resorted to the search for alternative substrates that present good availability, aiming to reduce the production costs and also ensure a better destiny for sediments found and/or produced in the rural properties (Costa Júnior et al., 2018;Sousa et al., 2019). The decomposed buriti stem (Mauritia vinifera Mart.) has been showing promising results in some studies and it is a species of wide distribution, mainly in the cerrado regions, reaching up to 30 meters in height (Horn et al., 2012;Araújo et al., 2018;Oliveira et al., 2018;Fonseca et al., 2019). Buriti is the most abundant palm in the Brazilian territory and occurs in almost homogeneous groups called buritizais (Lorenzi et al., 2004). It is a full sun palm, adapted to permanently flooded soils, with a simple trunk (Santelli et al., 2009). Therefore, the decomposed buriti stem supplemented with nitrogen may become an alternative source of substrate for the production of A. mangium Willd seedlings, hence decreasing the production cost. Thereby, the objective was the evaluation of the initial development of the A. mangium Willd seedlings in the substrate of the decomposed stem of M. vinifera Mart under doses of nitrogen.

Study Site Description
The experiment was conducted in a greenhouse at the Agronomic Experimental Station of the Federal University of Piauí (UFPI), in Bom Jesus, Piauí State, Brazil (09°04′28″ S, 44°21′31″ W, and altitude of 277 m), from October to November 2015. The regional climate, according to the Köppen classification, is Aw, characterized as tropical, with hot summers and a tendency toward high rainfall levels between October and April, and dry winters, with a dry season between May and September. The mean annual temperature is 26.5 ºC, with a mean annual rainfall of 900 to 1,200 mm (Viana et al., 2002).
The substrates were packed in plastic bags (commercial dimensions 12.5 × 10 cm) in which it was made the manual seeding of five seeds of A. mangium seeded ±2 cm deep. Ten days after the emergency of seedlings, was realized the thinning, leaving only one plant composing the experimental unity. The substrate's water content was kept close to the capacity of water retention with daily irrigations.

Evaluations in the Trials
At 60 days after the emergency, it was evaluated: plant height (PH)-determined from the soil surface to the insertion of the last leaf with the assistance of a millimeter ruler; stem diameter (SD)-measured at the plant height using a digital caliper (Clarke-150 Where, TDM is the total dry mass (g); PH is the height of the shoot part (cm); SD is the diameter of the stem (mm); DMAP is the dry mass of the shoot part (g), and DMR is the dry mass of the roots (g).

Statistical Analysis
The data were submitted for analysis of multivariate normality through the Doornik-Hansen test (2008)  Hotelling-Lawley Trace, and Roy's Maximum Root at the levels of 5% of significance. Sequentially, the grouping of treatments was realized using Ward's method (formation of hegemonic groups by the smallest minimum internal variance), being used as reference Euclidean distance and Pearson coefficient.
To discriminate the groups of treatment in function of the agronomic variables of A. mangium, it was realized canonical discriminant analysis, which was represented in a biplot graphic built for the first two canonical variables. Ellipses of 95% trustworthiness were built to detect statistical differences (p < 0.05) among treatment groups. All the analyses were realized using the software R version 3.6.1 (R CORE TEAM, 2019). The canonical discriminant analysis was made with the assistance of the candisc package (FRIENDLYE FOX, 2015).

Results
According to the summary of the multivariate analysis of variance, there was a significant difference (p < 0.01) between the averages vectors of treatments in the multivariate tests of Wilk's Lambda, Pillai's Trace, Hotelling-Lawley's Trace, and Roy's Maximum Root (Table 3). Note. 1 num Df: numerator degrees of freedom; 2 denDf: denominator degrees of freedom.

Discussion
According to the results presented in this study, it was observed that the substrate formulated with decomposed buriti stem (DBS) and nitrogen doses provides improvement in the growth of A. mangium plants. The group II of treatments (T13, T14, and T15), composed of the substrates formulated with 50% of soil + 50% of DBS supplemented with the doses of 200, 300, and 400 mg dm -3 of nitrogen, has contributed positively to the shoot and root development of A. mangium, when measured by the variables plants height, stem diameter, internodes number, dry mass of the shoot part, roots length, dry mass of root, dry mass of shoot part/roots relation, robustness quotient and Dickson Quality Index.
Thus, the substrates with the highest doses of decomposed buriti stem (50%) associated with the highest doses of nitrogen (200, 300, and 400 mg dm -3 ) resulted in greater development of Acacia mangium Willd seedlings. This fact is related to the chemical characteristics of the buriti stem and the benefits of nitrogen fertilization, for example, the increase in the number of chlorophylls in the leaves and, consequently, the increase in the photosynthetic production of photoassimilates.
The DBS is a substrate that presents favorable physical-chemicals characteristics to development of plants, such as: pH (6.8), electrical conductivity ( Therefore, the combination of the chemical characteristics of the substrate with doses of nitrogen contributed to a greater growth of plants in this study, hence being a viable alternative in the production of A. mangium seedlings. The results of this study corroborate the combination of DBS with nitrogen doses also evaluated by Oliveira et al. (2018) and Fonseca et al. (2019) with satisfactory results in the development of umburana seedlings (Amburana cearensis) and cagaiteira (Eugenia dysenterica), respectively.

Conclusions
The substrate formulated with Dystrophic Yellow Oxisol + decomposed buriti stem, 1:1 proportion, supplemented with nitrogen fertilization in doses varying from 200 to 400 mg dm -3 is recommended in the production of A. mangium seedlings, with positive effects on the growth and development of plants.