The Cell Viability on Kelp and Fir Biochar and the Effect on the Field Cultivation of Corn

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    Field cultivation of corn and microbial cell viability tests using Pseudomonas putida K-5 were performed to assess the toxic effect of kelp seaweed biochar (KBC) and fir wood biochar (FBC) produced by pyrolysis. After 63 days growth, FBC increased corn growth by 4.9% without fertilizer and by 7.6% with fertilizer, while KBC decreased it by 20.2% without fertilizer and by 27.9% with fertilizer. Physico-chemical characterization of the biochars such as ICP, CHON, and proximate analyses showed that KBC contained large amount of metals and ashes which could be responsible for its inhibition to corn growth. Upon exposure of K-5 cells for 1 h to biochar extracts, the cell viability in KBC extracts was 48.2% and quite lower than that (78.6%) in FBC. Washed KBC biochar with water at 1:10 w/v % increased the cell viability to 54.0%. The results indicated that seaweed biochar may be careful to be used for plant growing additives due to its high concentrations of metals and ashes. This toxic effect could be reduced by proper washing method with water.


    Biochar , Corn , Fertilizer , Pyrolysis , Toxicity

  • 1. Introduction

    Biochar is a carbon-rich material obtained after the thermo-chemical pyrolysis of organic matter which has wide application as; soil management, mitigation of climate changes, waste management and energy production [1, 2]. Scientific and technological information on biochar has been increasing over the past decades since the discovery that it is the key reason for the sustainable and highly fertile dark earths in the Amazon Basin, Terra Preta de Indio [3]. Increased porosity and surface area are among the characteristics of biochar that results in high yield of crops cultivated in biochar rich soils. Biochar addition to soils has also been found to be a suitable niche for microorganisms [1] and the fauna in soils. Microbial activities in soil conserve soil quality and integrity of soil subsystem.

    While most of cases using biochar for crop growth have resulted in the increase of root mass, stem height, and fruit productivity, a few cases have shown negative effects on crop growth [2]. Even though many environmental factors such as soil texture, weather, and microbial community may affect plant growth, a certain biochar may contain any compounds that may be harmful to soil microorganisms and may inhibit the growth. Biochar from different feedstocks and process conditions such as pyrolysis temperature may contain toxic compounds such as polycyclic aromatic hydrocarbons (PAHs) and dioxins [4, 5]. Some other contaminants such as potentially toxic elements i.e. trace metals (Cu, Cd, Pb, Cr, Ni, Zn, As, etc) may also be found in biochars [6, 7]. A study conducted on biochar properties regarding to contents of contaminants revealed that biochar from miscanthus was characterised by higher levels of Cd, Ni, Zn and Cr [8].

    Fertilizers produced from seaweed has been found to be superior to chemical fertilizers due to its high organic matter content and are more economical [9]. Commercial seaweed extracts such as Maxicrop (Sea born), Algifert (Marinure), Goemar GA14, Kelpak 66, Seaspray, Seasol, SM3, Cytex and Seacrop 16 has been found to stimulate plant growth and increase yield as well as quality of crops [10]. Seaweed applied as farmyard manure repels slugs and other pests. Charred seaweed could have several added benefits to crop growth and yield due to high nutrient contents.

    However, so far, the effects of seaweed biochar on plant growth have not been studied. In this study, kelp seaweed biochar (KBC) and fir wood pellet biochar (FBC) were produced and applied in corn cultivation to ascertain their effect on its growth. The cultivation of the corn was done with or without the biochars and/or compost fertilizer. A cell viability study of the biochar extracts at different exposure times and pre-washing conditions of the biochar prior to extraction were also investigated with a representative soil bacterium, Pseudomonas putida (K-5). This biological test would to some extent give evidence on the presence or absence of toxic effect to microbial colonies in soils in which biochars are applied.

    2. Materials and methods

       2.1. Production of biochar

    Two different types of biomass, fir wood pellet and kelp seaweed, were purchased from a local market in Daejeon, South Korea. A 40 L aluminium can was used for the pyrolysis of biomass in field. Four square holes (10 cm × 10 cm) were punched in even distribution under the can to allow the passage of air. To produce biochar 500 g of biomass was loaded in a stainless steel bowl with a lid having 7 holes, with each hole having a 0.5 mm diameter. The stainless steel bowls were packed in the aluminium can and heated with wood waste as fuel for about 3 h to char. After charring the biomass, the biochar produced were ground into - 1000 μm to + 212 μm for the entire experiment.

       2.2. Characterization of biochar