BIOCHAR - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 108

Biochar spatial structure and inner void volume is suggested as habitat for fungi and
bacteria, providing physical protection from soil predators (Lehmann et al., 2011; Warnock et
al., 2007). Yet, examining 3 year old field-aged biochar particles Quilliam et al. (2013a)
found microbial colonization to be evenly distributed along biochar particles transects with no
evidence for increase in microbial presence at the internal areas of biochar compared to
biochar-soil interface. Moreover, CO 2 evolution rates from the soil brushed from biochar
surface were similar to that of the bulk soil, both of which were higher than that of internal or
external surfaces of field-aged biochar, which were not significantly different from each other
(Quilliam et al., 2013a). Biochar also suppresses intercellular signaling and disrupts
communication within a growing multicellular microbial system, the degree of which was
positively correlated to biochar surface area and peak production temperature; this
phenomenon is attributed to the affinity of biochar for acyl-homoserine lactone, the
intercellular signaling molecule used in this experiment (Masiello et al., 2013). Several
studies had demonstrated the suppressive effect of biochar on development of powdery
mildew ( Leveillula taurica ) on tomato (Elad et al., 2010), and reductions in the percentage of
root lesions caused by Fusarium oxysporum f. sp. asparagi and F. proliferatum , where
biochar also showed to improve AM fungi root colonization and increase in root growth and
mass (Elmer & Pignatello, 2011). Biochar also increased abundance of genes encoding for
denitrification-associated enzymes and of denitrifying bacteria, resulting in lower N 2 O
emission during composting of organic waste (Wang et al., 2013). Soil pH is known to
significantly affect N 2 O emission (Firestone, 1982) and to affect abundance of genes
encoding for denitrification associated enzymes and of denitrifying bacteria (Cuhel et al.,
2010), similar to the above finding by Wang et al. (2013). Noteworthy, the observed
reduction in the proportion of N 2 O in N gas emission (i.e. N 2 O/[N 2 O + N 2 ]) was due to
increase in N 2 emission, amid a rather constant emission of N 2 O throughout the pH range
tested, 5.5 to 7.7 (Cuhel et al., 2010). Conversely, a sharp increase in soil N 2 O emission at
soil pH below 5.0-5.5 was reported by others where both biotic and abiotic denitrification
mechanisms, with nitrite playing a significant role in the abiotic pathway (Van Cleemput &
Samater, 1995; Morkved et al., 2007). Regardless of the mechanisms involved, their
proportion and/or relative significance, N 2 O emission from soil is tightly and inversely
correlated with soil pH. Inasmuch as biochar effect on soil pH may improve activity of N 2 O-
reducing organism (Yanai et al., 2007), biochar, because of its aromaticity (Figure 1), can act
as electron donor and acceptor (Joseph et al., 2010), facilitating the transfer of electrons
(―electron shuttle‖), and promoting the reduction of N 2 O to N 2 (Cayuela et al., 2013).
Biochar application also showed to affect positively soil physical properties, including
soil bulk density, aggregation, available water content, and soil hydraulic conductivity
(Novak et al., 2009a; Herath et al., 2013). Biochar application improved soil water holding
capacity in coarse texture soils but not in soils of high organic matter content or fine texture
(Novak et al., 2009a; Karhu et al., 2011; Uzoma et al., 2011a; Abel et al., 2013; Masto et al.,
2013). Biochar properties including polarity, surface area, total and micro porosity improve
some soil physical properties; soil available water content was improved with biochar of high
pyrolysis temperature (Mendez et al., 2013), whereas soil aggregation was improved with
increase in biochar hydrophilicity which improved over time (Novak et al., 2009a; Herath et
al., 2013). Yet, effect of biochar on soil nutrients, microbial growth, and mycorrhizal
colonization was found to be temporary as no significant effect was noted in these soil quality