Biochar of Sawdust Origin in Passion Fruit Seedling Production

Great part of solid waste are deposited inappropriately near cities or in rural areas, contributing to negative environmental impacts. There are numerous forms of waste processing, one of them is pyrolysis to produce biochar and subsequent use in agricultural systems. The objective of this study was to evaluate different substrates with activated biochar (AB) and biochar (B) in substrate and its effect on the growth of passion fruit seedlings. The test was conducted in a nursery, located in Sinop/MT, May to July 2013, designed in four blocks with ten treatments: commercial substrate (CS), composed by pine bark and vermiculite 4:1; nursery substrate (NS) composed by carbonized rice husk and coconut fiber 1:1; and the eigth treatments represented were B and AB additions of 25; 50; 75; and 100% in CS, (B25, B50, B75, B100, AB25, AB50, AB75 and AB100, respectively). After 60 days sowing the stem diameter, plant height, leaf number was evaluated and at the end of the experiment the fresh and dry weight of shoots and roots, and Dickson Quality Index (DQI) were assessed. AB at concentrations of 25, 50 and 75% combined with commercial substrate showed increases in parameters fresh and dry biomass weight, height, stem diameter and number of leaves. The dose of 25% AB is presented as the best dose to be adopted in commercial crops. The sawdust processed into AB is an alternative in the production of passion fruit system and the reintegration of this raw material to the productive sector.


Introduction
The production of organic waste is high and growing in both rural and urban areas.Great part of the solid waste, including sawdust, are deposited inappropriately near cities or in rural areas, resulting in material potentially liable to spontaneous or criminal firel, fact worsened in the dry season.They also imply negative environmental impacts, which range from immobilization of nutrients by microorganisms and even cause serious problems such as contamination of water reserves (Silva, 2008).
There are numerous forms of waste processing aiming its stabilization.Among them stands out the pyrolysis method to obtain biochar and subsequent use in agricultural systems.
Biochar is a carbon-rich product obtained from the thermal decomposition of organic materials with atmosphere in absence or minimal presence of oxygen at temperatures ranging from 350 to 700 °C, used as a soil conditioner (Lehmann, 2009).Almost any source of biomass can be carbonized (Maia & Sohi, 2010).
When added to soil, biochar can improve its physico-chemical and biological characteristics.Effects such as density reduction, porosity increase and water retention in soil, aggregate formation and improvement of the sorption complex are commonly reported.Biochar can also promote absorption of soluble organic compounds due to its polycyclic aromatic structures.Such structures are the core of biochar and explain its stability and chemical activity and when this core brings organic functions as carboxyls and hydroxyls at the border, it can increased exchangeable capacity and agronomic efficiency of fertilization (Benites et al., 2005;Novotny et al., 2009;Atkinson et al., 2010).Besides, biochar provides changes in soil microbial communities, increasing biodiversity and consenquently enhancing agricultural productivity.Some studies also report a suppression or decreasing of methane emissions and nitrous oxides (Novotny et al., 2012).
According to Casselman (2007), as the biochar does not decompose easily, its structure could hold, for thousands of years, all carbon contained in it, instead of releasing it into the atmosphere as CO 2 , the main greenhouse gas.This fact can contribute to increasing agricultural productivity by enhancing the ability to retain nutrients and moisture in addition to sequestering carbon and reduce the greenhouse effect.
Biochar can be described as a porous carbonaceous material, rich in pyrogenic carbon, which structure varies according to the pyrolysis process.The material is usually of high chemical stability, but when submitted to wheater action or to physical/chemical activation processes it presents a high porous density (Hammes & Schmidt, 2009;Downie et al., 2009).
The activation process will act unclogging the surface pores from residual tar, increasing the specific surface and the number and the size of pores in the final material.This feature will also influence the development of possible surface charges originated through chemical reactions during the pyrolysis process or later, once applied in soil.This treatment improves the biochar properties as a soil conditioner and can be obtained by different methods, resulting in a higher adsorption capacity (Zhang et al., 2013).
Activated biochar has properties to be applied to soil or as a component of growing media (substrate or potting soil) to produce seedlings, since it is light and has porous, reactive structure and appropriate physical and hydraulic properties (Verheijen et al., 2010).Growing media for seedlings production must be of low density and exhibit good water retention capacity (Gonçalves et al., 2000).
According to Terra et al. (2011), a good substrate shall provide, aside low density and high capacity of water retention, high cation exchange capacity, good aeration and drainage.When added to a growing media, biochar increases its water retention ability at both low and high pressures, favoring conditions for seedlings development (Zannetti et al., 2003;Souza et al., 2006).However, there are few studies evaluating the direct effect of biochar and their mechanisms of action on soil processes and plant growing media.Furthermore, new growing media constituents for seedling production are highly important for the nursery sector, since the substrate is a key factor for the development of seedlings and the use of materials as peat, the most common used in growing media, are not always environmental friendly.Cavalcante et al. (2012) states that biochar has been well studied as a soil conditioner, but little information is available on biochar as a substrate component for production of fruit seedlings.However, the authors stress the importance of biochar as a substrate component especially for the production of seedlings whose propagation is economically viable, such as the yellow passion fruit.
In this context, the main objective of this study was to evaluate different growing media mixtures, including biochar (B) and activated biochar (AB), at various proportions, and its effects on the growth of passion fruit seedlings.

Material and Methods
Characterization of the study area: the trial was conducted at nursery Flora Sinop, from May to July 2013.The nursery is located in Sinop, Mato Grosso, 500 km far from the state capital Cuiabá, with 384 m above sea level and geographic location of 11°52′23″ South, 55°29′54″ West.The annual average temperature is 24 °C, annual rainfall of 1.900 mm and relative humidity ranging between 80 and 35% during the year (Souza et al., 2012).
Height was measured with a millimetric ruler, the stem diameter was measured with a precision digital caliper (0.01mm).After 60 days, the seedlings were taken for determination of fresh and dry weight of shoot and root.Fonseca et al. (2002) describes the DQI as a good indicator of seedlings quality, because it considers robustness and biomass equilibrium distribution in the plant.We calculated the Dickson Quality Index (DQI) (Dickson et al., 1960) according to the following equation: Where, DQI: Dickson Quality Index; TDM: Total Dry Biomass (g); SDM: Shoot Dry Mass (g); RDM: Root Dry Mass (g); height (cm) stem diameter (mm).
All data were submitted to the average test Scott-Knott at 5% probability by statistical program SISVAR (Ferreira, 2011).

Results and Discussion
Growing media containing 25, 50 and 75% of AB produced the higher increases in fresh and dry total biomass, fresh biomass of root and aerial biomass and dry biomass of root and stem.The increases in total fresh biomasses in treatments containing 25, 50 and 75% of AB when compared to the NS were 24; 23 and 25% and to CS were 31; 30 and 32%, respectively.For total dry weight, increments were 20, 14 and 15% in relation to NS and 17, 11 and 13% in relation to CS (Table 2).Leaves dry weight had no significant difference.Note.FB -fresh biomass, DB -dry biomass, NS -nursery substrate, CS -comercial substrate, AB -activated biochar, B -biochar.
* Means followed by the same letter do not differ by the Scott-Knott test (p < 0.05).
Plant height and stem diameter showed significantly increases for treatments AB25, AB50 and AB75 (Figures 2B and 2C).For number of leaves in passion fruit seedlings, all doses with activated biochar were higher than other treatments (Figure 2A).These results are consistent with those presented by Mendonça et al. (2003), who used charcoal combined with cattle manure + soil and sand in the ratio 1: 2: 1: 1 v/v in the production of papaya seedlings, and obtained around 34% in average higher total fresh and dry weight than the control.Mendonça et al. (2003), andSouza et al. (2006) studies, showed height gain when added charcoal in the composition of the substrate.
The results of this study also corroborate with Gaskin et al. (2010), Junior Marimon et al. (2012) and Petter et al. (2012) confirming the benefic effects in the combination of biochar and chemical fertilizers, superior then fertilizers alone, in plant growth and crop productivity.
The activation of biochar positively influenced the formation of yellow passion fruit seedlings.In this study, lower doses of biochar, both activated and non-activated, positively influenced the quality of seedlings.Therefore, further studies with different forms of biochar activation and/or combinations are particularly recommended in the production of fruit seedlings.
When considering the adoption of the technique by nurseries and fruit production sector, the results achieved here showed the most recommended dose would be the addition of 25% activated biochar.

Conclusions
The studied variables were significantly influenced by the application of activated biochar when added to commercial substrate Mec plant®.Biochar activated at concentrations 25, 50 and 75% combined with Mec plant® showed increases in parameters total fresh and dry biomass, height, stem diameter and number of leaves.
The dose of 25% activated biochar showed the best results when added to commercial substrate.
Sawdust processed into activated biochar is an alternative to improve passion productivity and to recycle this raw material into the production sector.
The study of economic feasibility should be carried out throughout the production system for recommending the use of biochar in passion fruit culture.

Table 2 .
Fresh and dry root biomass, stem and leaves; total fresh biomass and total dry biomass of passion fruit seedlings in relation to substrates