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Biochar effects on soil nutrient transformations

Authors:
15
Biochar effects on soil nutrient transformations
Thomas H. DeLuca, Michael J. Gundale, M. Derek MacKenzie
and Davey L. Jones
Introduction
A key aspect of biochar management is its
proposed effect on soil fertility and plant pro-
duction (Lehmann, 2007). Plant productivity
is directly influenced by nutrient availability,
which is a product of nutrient transforma-
tions in the soil environment (Marschner,
2006). For that reason, there is a great deal of
interest in how biochar influences nutrient
transformations and availability of those
nutrients for plant uptake. And although
increasing evidence suggests that biochar
addition to soil may enhance plant produc-
tion in a variety of natural and agricultural
environments (Lehmann and Rondon, 2006;
Atkinson et al, 2010; Jeffery et al, 2011), the
direct influence of biochar additions on soil
nutrient cycling are inconsistent and remain
somewhat poorly understood. This is par-
tially due to differences in the soils, crops and
biochar amendments used in experiments
and the predominance of short-term studies
in the literature.
The purpose of this chapter is to sum-
marize several general mechanisms through
which biochar affects nutrient availability to
plants and to specifically evaluate the effect
biochar has on nutrient cycling and specific
transformations within several key nutrient
cycles. Our aim is to complement other chap-
ters in this book as well as other reviews that
have focused on the chemical and physical
properties of biochar (Chapters 5 and 6)
(Atkinson et al, 2010; Shrestha et al, 2010),
its stability in the soil (Shrestha et al, 2010),
its effect on soil biota and plant eco-physiol-
ogy (Chapters 13 and 14) (Atkinson et al,
2010; Lehmann et al, 2011), its influence on
soil properties (Atkinson et al, 2010; Beesley
et al, 2011), its impact on trace gas fluxes
(Chapter 18) (Jones et al, 2011) and its use in
biofuel technology or soil C sequestration
(Chapter 10) (Lehmann, 2007; Lee et al,
2010; Macias and Arbestain, 2010). The
purpose of this review is to explore what is
and is not known about the effect of biochar
on soil nutrient transformations, which are
likely to have both short- and long-term
impacts on plant productivity in forest and
Biochar C15.indd 419 11/3/2014 9:04:29 AM
420 BIOCHAR FOR ENVIRONMENTAL MANAGEMENT
agricultural landscapes (Atkinson et al, 2010).
We specifically focus on the response of
nitrogen (N), phosphorus (P) and sulfur (S)
cycles in response to biochar amendment and
explore the implications for altered transfor-
mations within these cycles on the availability
of nutrients to plants and their long term
budgets across a range of ecosystems. In this
effort we will try to differentiate between
short-term and long-term effects of biochar
on ecosystem processes.
General mechanisms by which biochar inuences nutrient
turnover and transformations
The application of biochar to agricultural and
forest soils has been found to increase the
bio-availability and uptake of many nutrients
to plants (Glaser et al, 2002; Lehmann et al,
2003; Steiner et al, 2007; Jeffery et al, 2011;
Nelson et al, 2011). While some mechanisms
causing increased nutrient availability have
been extensively described and summarized
(Atkinson et al, 2010), very little research has
been conducted on the influence of biochar
on specific nutrient cycling mechanisms. For
instance, numerous studies have described
high concentrations of available nutrients on
the surface of newly created biochar made
over a wide range of temperatures and oxida-
tion conditions, and from a range of feed-
stocks, suggesting that biochars themselves
can have fertilization effects over short time-
scales (Chan and Xu, 2009; Jeffery et al,
2011). As an example, the direct contribution
of NH4
+ salts from newly formed biochar has
been described in numerous studies (see
Chapter 7; Gundale and DeLuca, 2006;
Chan and Xu, 2009; Spokas et al, 2012).
Considerably less attention has been given to
the effect of biochar on specific transforma-
tions, i.e. indirect alterations, within the N
cycle (Lehmann, 2007; Clough and Condron,
2010; Clough et al, 2013), for example bio-
logical N-fixation, N-mineralization, nitrifi-
cation and gaseous N losses (Clough and
Condron, 2010).
The effects that biochar may have on
nutrient transformations has consequences
for the long term effect of biochar on plant
productivity and on nutrient stocks (i.e. the
installation of a positive reinforcing feedback
loop, see Figure 15.1) and therefore have
important implications for the viability and
sustainability of biochar as a C mitigation
strategy (Lehmann, 2007; Roberts et al,
2010). In the following section we identify
three general mechanisms through which bio-
char may influence nutrient cycles: (i)
Increase in the pool size and turnover of labile
organic nutrients; (ii) Alteration of soil physi-
cal and chemical properties; and (iii) effects
on soil biota.
Increase in the pool size and
turnover of labile organic
nutrients
A primary mechanism by which biochar may
accelerate nutrient cycling over long time
scales is by serving as a short-term source of
highly available nutrients, which become
incorporated into living biomass and labile
soil organic pools (Jeffery et al, 2011). As
described above and in detail in Chapter 7,
new, unweathered biochar, especially that
generated from nutrient-rich material, can be
a source of highly available nutrient salts that
provide a direct short-term source of nutri-
tion to plants (Chan and Xu, 2009; Atkinson
et al, 2010). During the pyrolysis process,
heating causes some nutrients to volatilize
(e.g. N as nitrogen oxides (NOx)), especially
Biochar C15.indd 420 11/3/2014 9:04:29 AM
BIOCHAR EFFECTS ON SOIL NUTRIENT TRANSFORMATIONS 421
Figure 15.1 A conceptual model for the
influence of biochar on nutrient (Nr) turnover in
the soil environment
at the surface of the material, while other
nutrients become concentrated in the remain-
ing biochar (Gundale and DeLuca, 2006;
Nelson et al, 2011). Feedstock, formation
temperature, the time a material is held at a
given temperature, oxygen availability and
the heating rate directly influence the surface
residue chemistry of biochar (Gundale and
DeLuca, 2006; Atkinson et al, 2010). Some
specific elements are disproportionately lost
to the atmosphere, fixed into recalcitrant
forms or liberated as soluble oxides during
the heating process, affecting the chemical
composition of ash residues on the biochar
surface (Chan and Xu, 2009). For wood-
derived biochars, carbon (C) begins to vola-
tilize around 100ºC, N above 200°C, S above
375 ºC and potassium (K) and P between
700 and 800ºC (Neary et al, 2005), whereas
the volatilization of magnesium (Mg), cal-
cium (Ca) and manganese (Mn) only occurs
at temperatures above 1000ºC (Neary et al,
1999; Knoepp et al, 2005). These differences
in volatilization temperatures among ele-
ments cause shifts in the stoichiometry of bio-
char elemental concentrations, with total S
and N concentrations often decreasing rela-
tive to other elements due to their lower vola-
tilization temperatures (Knudsen et al, 2004;
Trompowsky et al, 2005). Correspondingly,
several nutrient salts accumulate on biochar
surfaces, with NH4
+ and SO4
-2 concentrations
increasing in low temperature biochars (<
500ºC) (Knudsen et al, 2004; Gundale and
DeLuca, 2006) and NO3
-, PO4
-3, Ca+2, Mg+2
and trace metals increasing, especially in bio-
chars formed at high temperatures (Gundale
and DeLuca, 2006; Chan and Xu, 2009;
Atkinson et al, 2010; Nelson et al, 2011).
Because soils generally contain a rela-
tively large total pool of most nutrients, bio-
char additions to soil usually provide only a
modest contribution to the total soil nutrient
capital (Chan et al, 2007). However, only a
small fraction of the total soil nutrient capital
is usually bio-available, meaning that the
addition of nutrient salts in biochar surface
residues can constitute a significant increase
in the bio-available pool of some nutrients
(Gundale and DeLuca, 2006; Yamato et al,
2006; Chan et al, 2007). This short-term
input of bio-available nutrients can enhance
plant productivity (i.e. total biomass) and
improve tissue quality (Kimetu et al, 2008;
Jeffery et al, 2011) and therefore influence
both the quantity and quality of nutrient-con-
taining plant residues returned to the soil
(Major et al, 2010). Plants’ C inputs to the
soil occur through root exudation and turno-
ver, and through senescence and death of
above-ground tissues. It is well known that
the nutrient concentrations of plant litter is a
Biochar C15.indd 421 11/3/2014 9:04:29 AM
422 BIOCHAR FOR ENVIRONMENTAL MANAGEMENT
strong control on nutrient mineralization
rates (Stevenson and Cole, 1999; Brady and
Weil, 2002). Therefore, larger inputs of
higher quality plant organic matter to the soil
in response to biochar derived nutrients likely
result in an increase in the labile nutrient pool
size, thereby in theory increasing the total
quantity of labile organic nutrients returned
back to the soil and available for mineraliza-
tion (DeLuca et al, 2006; Gundale and
DeLuca, 2007; Major et al, 2010). This feed-
back involving higher plant nutrient uptake, a
higher return of labile organic nutrients to the
soil and higher nutrient mineralization rates
could enhance nutrient availability to plants
over longer time scales as implied in Figure
15.1. The persistence of accelerated nutrient
turnover between plants and soil is likely
dependent on the size of the nutrient pool
added from biochar, the frequency of its
addition (e.g. single dose, multiple doses or
annual), the degree to which nutrient capital
is removed from a system during harvesting
activities (Jeffery et al, 2011), the degree to
which nutrients are fixed into recalcitrant
organic or insoluble mineral pools (Hedley et
al, 1982), the long-term losses in nutrient
capital through leaching or volatilization that
occur at a given site (Lehmann et al, 2003;
Yanai et al, 2007) and the long-term build-up
(or decline) of stable, recalcitrant organo-
mineral complexes beyond the pure biochar.
Alteration of soil physical and
chemical properties
In addition to its direct contribution of avail-
able nutrients to the soil, biochar has a variety
of physical and chemical properties that influ-
ence soil nutrient transformations. For a more
detailed review of biochar physical and chem-
ical properties, see Chapters 5 and 6, and
Atkinson et al (2010). Biochar is a high sur-
face area (Beesley et al, 2011), highly porous
(Keech et al, 2005), variable charge organic
material which often contains a surface resi-
due enriched in alkaline metals (Figure 15.2b)
(Atkinson et al, 2010). When added to soil,
biochar has the potential to alter the physical
and chemical properties of soil, which in turn
can influence nutrient transformation rates.
For instance, biochar has been shown to
increase soil water holding capacity, alter gas
exchange, increase cation exchange capacity
(CEC), increase surface sorption capacity,
increase base saturation of acidic mineral
soils and alter soil pH (Glaser et al, 2002;
Bélanger et al, 2004; Keech et al, 2005; Liang
et al, 2006; Atkinson et al, 2010). These bio-
char properties are highly dependent on
the temperature and duration of pyrolysis
(Gundale and DeLuca, 2006; Bornermann et
al, 2007; Joseph et al, 2007) and the feedstock
from which biochar is made (Gundale and
DeLuca, 2006; Streubel et al, 2011).
Many nutrient transformations are
enzyme mediated reactions carried out by
soil micro-organisms. Soil micro-organisms
require environments with appropriate water
potential and redox conditions to carry out
their metabolic activities (Alexander, 1991;
Briones, 2012). The physical structure of
biochar contains a range of pore sizes which
are inherited from the feedstock material
(Keech et al, 2005) and which can directly
influence the water potential and redox envi-
ronment of soil micro-organisms (Joseph et
al, 2010). Micropores, defined by soil scien-
tists as pores with < 30µm diameter (Brady
and Weil, 2002), serve as capillary spaces
with high surface area to volume ratios and
can retain water even when soil moisture is
strongly depleted (Kammann et al, 2011),
thereby creating moist microsites (Lehmann
and Rondon, 2006). Biochar also often con-
tains macropores (>75µm diameter) which
can serve as gas exchange channels (Keech et
al, 2005), thereby influencing the redox envi-
ronment for soil biota (Joseph et al, 2010;
Lehmann et al, 2011). Organic residues
Biochar C15.indd 422 11/3/2014 9:04:29 AM
BIOCHAR EFFECTS ON SOIL NUTRIENT TRANSFORMATIONS 423
decompose much more rapidly under aerobic
conditions and therefore biochar may
enhance nutrient mineralization in soils with
inherently poor gas exchange properties
(Gundale and DeLuca, 2006; Asai et al,
2009). Likewise, several specific nutrient
transformations require oxygen as an electron
acceptor, such as nitrification and S oxida-
tion, which suggests that the physical struc-
ture of biochar may increase oxidative
transformations in soils with inherently poor
gas exchange environments (DeLuca et al,
2006; Asai et al, 2009; Joseph et al, 2010).
The highly variable pore size distribution of
biochar thus assures the presence of a wide
variety of soil micro-sites with contrasting
moisture and redox conditions under variable
environmental conditions (Joseph et al,
2010). In all biological living systems from
microorganisms to plants, gradients and
potential-differences (concentrations, redox,
Eh, pH) are the prerequisites for material and
electron flow, i.e. for metabolism and energy
gain. The addition of biochars may thus
intensify microbial or root-associated gross
nutrient cycling processes by: (i) creating
more ‘micro-site opportunities’ with steeper
redox, pH or nutrient concentration gradi-
ents around or across biochar particles
(Briones, 2012; Joseph et al, 2013); and by
(ii) creating more such micro-scale metabo-
lism opportunities within the soil matrix. If
the ‘biochar micro-site metabolism opportu-
nities’ then meet higher organic (e.g. crop or
root residue) inputs, a positive feedback cycle
with intensified gross nutrient cycling may
result, improving soil fertility in the long run
(Figure 15.1).
Additional mechanisms through which
biochar amendments can alter nutrient trans-
formations is by: (i) Reducing nutrient loss
from the soil (Crutchfield et al, 2010; Ding et
al, 2010; Prendergast-Miller et al, 2011;
Ventura et al, 2013); (ii) Reducing fixation of
nutrients into insoluble mineral or recalci-
trant organic pools (Cui et al, 2011; Nelson et
al, 2011); (iii) Reduced gaseous losses of N,
be it as NH3, N2 or N2O (Prendergast-Miller
et al, 2011; Taghizadeh-Toosi et al, 2012a;
Spokas et al, 2012); (iv) By ameliorating
other constraints of nutrient cycling e.g. in
contaminated soils by its sorptive properties
(Figure 15.1). Biochar has been shown to
have a transient anion exchange capacity and
moderately high CEC that also changes with
time in the soil (Brewer et al, 2011). Biochar
also can ameliorate soil pH due to its surface
ash residue containing alkaline metals, espe-
cially in acidic soils (Brewer et al, 2011).
Some biochars can harbour relatively high
exchange capacity per unit mass (Atkinson et
al, 2010), therefore its addition to some soils
can increase surface soil exchange capacity.
Free nutrient ions can be lost from ecosys-
tems via leaching or runoff, resulting in a
decline in soil fertility through time. Biochar
can reduce leaching and volatilization losses
under some circumstances (Prendergast-
Miller et al, 2011; Taghizadeh-Toosi et al,
2012a; Spokas et al, 2012; Ventura et al,
2013) and thus increase the total pool of
nutrients available to plants or microbes. A
variety of studies suggests that biochar can
simultaneously reduce nutrient leaching and
volatilization losses through its influence on
soil pH (Bélanger et al., 2004, Atkinson et al.,
2010) and CEC (Crutchfield et al, 2010;
Ding et al, 2010); however, the alkaline
nature of some biochars may actually increase
NH3 volatilization in surface soils amended
with biochar (Chen et al, 2013).
An additional characteristic of biochar
that can influence nutrient cycling is its effect
on soil solution C chemistry (Figure 15.1) and
turnover (see Chapter 16). While biochar itself
has been shown to contain only a minor frac-
tion of bio-available C (Jones et al, 2010;
Major et al, 2010), several studies suggest that
it serves as a strong sorptive surface for a wide
range of C compounds. The high surface area,
Biochar C15.indd 423 11/3/2014 9:04:29 AM
424 BIOCHAR FOR ENVIRONMENTAL MANAGEMENT
porous (Figures 15.2 and 15.3) and often
hydrophobic nature of biochar directly after
production makes it an ideal surface for the
sorption of hydrophobic organic compounds
(Cornelissen et al, 2004; Keech et al, 2005;
Bornermann et al, 2007; Gundale and
DeLuca, 2007). Numerous studies have
shown a reduction in soluble or free phenolic
compounds when activated C is added to soils
(DeLuca et al, 2002; Wallstedt et al, 2002;
Berglund et al, 2004; Keech et al, 2005;
Gundale and DeLuca, 2006; MacKenzie and
DeLuca, 2006). Additional studies have dem-
onstrated that char formed during wildfires or
burning of agricultural residues also functions
to adsorb phenolic and various aromatic and
hydrophobic organic compounds (Yaning and
Sheng, 2003; Brimmer, 2006; DeLuca et al,
2006; Gundale and DeLuca, 2006; MacKenzie
and DeLuca, 2006; Bornermann et al, 2007).
Through these sorption reactions, biochar
may: (i) reduce the activity of compounds that
may be either inhibitory to nutrient transfor-
mation specialists, such as nitrifying bacteria
(White, 1991; Ward et al, 1997; Paavolainen
et al, 1998); (ii) reduce complexation of nutri-
ent-rich molecules such as proteins into tan-
nin-complexes (Kraus et al, 2003; Gundale et
al, 2010); or (iii) reduce the concentration of
bio-available C in the soil solution that would
otherwise enhance the immobilization of inor-
ganic N, P or S (Schimel et al, 1996; Stevenson
and Cole, 1999) (Figure 15.1). The interac-
tion of soluble soil C with biochar surfaces is a
key mechanism that may influence nutrient
availability and transformations, but has
received relatively little attention (MacKenzie
and DeLuca, 2006; Nelissen et al, 2012).
Alteration of microbial
communities
Biochar additions to soil have the potential to
change the biomass, community composition
and activity of soil microbes, all of which can
Figure 15.2 Electron micrographs of a high
sorption (a) and low sorption (b) char collected
from forest soils in northern Idaho (Brimmer,
2006). The high sorption char (immature char
formed in a recent fire) has open pores that
follow trachieds whereas the low sorption char
(mature char) has many of the pores occluded
with organics
influence nutrient mineralization from
decomposing plant residues, as well as several
specific nutrient transformations. For a com-
plete review of biochar effects on soil micro-
bial communities, see Chapter 13. There are
several mechanisms proposed by which bio-
char can influence soil microbes, including
the porous structure of biochar which pro-
vides a habitat for microbes (Pietikäinen and
Fritze, 1993), its effects on plant growth and
associated plant C inputs (Major et al, 2010),
its source of trace minerals (Rondon et al,
Biochar C15.indd 424 11/3/2014 9:04:29 AM
BIOCHAR EFFECTS ON SOIL NUTRIENT TRANSFORMATIONS 425
Figure 15.3 The pH, electrical conductivity (EC), cation exchange capacity (CEC) and density of
biochar produced from Douglas-fir or ponderosa pine wood or bark at 350 or 800°C (from Gundale
and DeLuca, 2006). Data meeting the assumptions of normality were compared with one-way
ANOVA followed by the Student-Neuman-Kuels post hoc procedure where letters indicate pairwise
differences. Non-normal data were compared using the Kruskal-Wallis (K-W) statistic
2007), its sorption of microbial signalling
compounds or inhibitory plant phenolic com-
pounds (DeLuca et al, 2006; Ni et al, 2010),
as well as its effect on soil physical and chem-
ical properties (described on page 422). Very
few studies have attempted to isolate the rela-
tive importance of these factors and substan-
tial uncertainty remains regarding the
mechanisms through which biochar influ-
ences soil microbial community properties
(Lehmann et al, 2011).
Despite mechanistic uncertainty, several
studies have shown that increases in micro-
bial biomass appear to occur in response to
soil biochar amendments. O’Neill et al (2009)
and Liang et al (2010) showed that
Amazonian Anthrosol soils rich in pyrogenic
C (PyC) contained between one and two
orders of magnitude greater microbial bio-
mass than adjacent soils with low PyC con-
centrations. In short-term studies with
biochar amendments, Anderson et al (2011)
showed somewhat more modest increases of
between 5–14 per cent in the abundance of a
variety of microbial taxonomic groups in
response to biochar amendment in a temper-
Biochar C15.indd 425 11/3/2014 9:04:29 AM
426 BIOCHAR FOR ENVIRONMENTAL MANAGEMENT
ate pasture soil. Pietikäinen et al (2000) also
showed that microbial respiration and bio-
mass increased in response to additions of
pyrogenic carbonaceous matter (PCM) in
boreal soils. However, other studies have
shown no significant shift in microbial activ-
ity with biochar amendments to soils (Jones et
al, 2012). Although soil microbes are the pri-
mary driver of organic nutrient mineraliza-
tion and oxidative or reductive nutrient
transformations, these studies suggest that
biochar-induced changes in microbial com-
munities likely have consequences for nutri-
ent turnover rates between plants and soil.
In addition to observed shifts in micro-
bial biomass in response to biochar, a variety
of studies have shown that microbial commu-
nity composition can be altered by biochar
(Anderson et al, 2012; Jones et al, 2012;
Ducey et al, 2013), sometimes resulting in
increased abundance of functional groups
that have key roles in nutrient cycling and
plant nutrient acquisition (Lehmann et al,
2011). Mycorrhizal fungi, which play a key
role in extracting nutrients from recalcitrant
organic or insoluble mineral pools, have been
observed to both increase (Saito, 1990;
Makoto et al, 2010; Solaiman et al, 2010) and
decrease (Warnock et al, 2007; Lehmann et
al, 2011) in response to biochar addition to
soil. Given the specific functional role of
mycorrhizae in nutrient acquisition, changes
in mycorrhizal biomass and colonization
likely influence the flux of nutrients from
unavailable nutrient pools (i.e. recalcitrant
organic matter and insoluble minerals, in par-
ticular P) into biomass and therefore labile
organic pools that actively turn over between
plants and soil, although studies identifying
the effect of biochar on these fluxes are lack-
ing. In addition to mycorrhizae, several spe-
cific nutrient transformations have been
shown to either increase or decrease in
response to soil biochar amendments and in
some cases altered transformation rates have
been linked to changes in the abundance of
specific soil biota. One of the clearest exam-
ples of this is the frequently observed increase
of nitrification rates in biochar amended for-
est soils (DeLuca et al, 2006; Gundale and
DeLuca, 2007), which has been linked to
larger populations of nitrifying bacteria in
biochar pore spaces (Ball et al, 2010;
described in further detail below). While an
increasing number of studies have described
changes in either microbial community com-
position or changes in nutrient transforma-
tion rates in response to biochar amendment
(Lehmann et al, 2011), there remain a rela-
tively small number that explicitly link altered
nutrient transformation rates to functional
changes in the soil microbial community (Ball
et al, 2010; Ducey et al, 2013).
Inuences of biochar on specic nutrient transformations
As previously described, there are a range of
mechanisms through which biochar can
influence the loss of nutrients from forest or
agricultural ecosystems, as well as the gross
annual turnover between soils and plants.
However, plant nutrients differ substantially
in many key physical and chemical proper-
ties, such as the number of molecular species
that exist, the mass and potential energy of
those molecular species and the ability of
microbes to transform molecular species to
acquire energy under given soil conditions
(i.e. pH and redox potential). These individ-
ualistic properties of different nutrient ele-
ments can determine how the cycles of
specific elements respond to soil biochar
amendments. In the following sections we
review the influence of biochar on N, P and S
Biochar C15.indd 426 11/3/2014 9:04:29 AM
BIOCHAR EFFECTS ON SOIL NUTRIENT TRANSFORMATIONS 427
cycles. Biochar always contains some quan-
tity of soluble inorganic N and P (see Chapter
7 and Figure 15.4) which can be released rap-
idly or slowly into the soil; however, in this
section we will focus on the influence of bio-
char on transformations of nutrients in the
soil as opposed to nutrient delivery.
Nitrogen
Nitrogen is the single most limiting plant nutri-
ent in most cold or temperate terrestrial eco-
systems (Vitousek and Howarth, 1991) and
also most frequently limits agricultural pro-
ductivity. In soils, the majority of N exists in
complex organic forms that must be mineral-
ized (converted from organic N to NH4
+ or
NO3
-) prior to uptake by most agricultural
plants (Stevenson and Cole, 1999), although it
is increasingly recognized that most plants also
take up organic N (Jones et al, 2002; Schimel
and Bennett, 2004). Recent studies have dem-
onstrated that the addition of biochar to sur-
face mineral soils may directly influence N
transformations. Here we review the evidence
for the direct and indirect influences of biochar
on ammonification, nitrification, volatilization,
denitrification, N2O emission (see also Chapter
17) and N2-fixation, while providing potential
mechanisms that may be driving these
transformations.
Ammonication and nitrication
Nitrogen mineralization is the process by
which organic N is converted to inorganic
forms (primarily NH4
+ and NO3
-). The con-
version of organic-N to NH4
+ is generically
termed ammonification. This process is driven
by a broad consortium of organisms capable of
enzymatic denaturation of proteins and the
removal of amide groups from organic com-
pounds (e.g., amino acids and amino sugars).
Nitrification represents the oxidation of
organic N (via heterotrophic organisms) or
NH4
+-N to NO3
- by autotrophic bacteria and
Figure 15.4 The soluble PO4
-3, NH4
+ and
NO3
- concentration in biochar produced from
Douglas-fir or Ponderosa pine wood or bark at
350 or 800ºC (from Gundale and DeLuca,
2006). Data meeting the assumptions of
normality were compared with one-way
ANOVA followed by the Student-Neuman-
Kuels post hoc procedure where letters indicate
pairwise differences. Non-normal data were
compared using the Kruskal-Wallis (K-W)
statistic
archaea as well as certain fungi (Stevenson and
Cole, 1999; Leininger et al, 2006). Biochar
addition to temperate and boreal forest soils
has been found to increase net nitrification
Biochar C15.indd 427 11/3/2014 9:04:30 AM
428 BIOCHAR FOR ENVIRONMENTAL MANAGEMENT
rates in soils that otherwise demonstrate little
or no net nitrification (Berglund et al, 2004;
DeLuca et al, 2006); whereas, there has been
little evidence for such an effect in grassland
(DeLuca et al, 2006) or agricultural soils
(Lehmann et al, 2003; Rondon et al, 2007),
which may already accommodate an active
nitrifying community. Results from the litera-
ture are summarized in Table 15.1, which spe-
cifically focuses on ammonification and
nitrification resulting from biochar or activated
carbon amended soil samples, field plots, or
mesocosms, as compared to unamended
controls.
Several studies in forest ecosystems have
aimed to understand the mechanisms under-
lying increased nitrification following PCM
addition. Using forest soils with very low
inorganic N concentrations, DeLuca et al
(2002) showed that ammonification was
enhanced when a labile organic N substrate
(i.e. glycine) was added to the soil, indicating
that ammonification was substrate limited. In
contrast, the large increase in NH4
+ that
resulted from the glycine addition did not
cause soil NO3
- concentration to increase,
suggesting that nitrification was not substrate
limited (DeLuca et al, 2002); rather, nitrifica-
tion rates exceeded ammonification rates. In
the same study, the injection of activated car-
bon into the organic horizon induced a slight
stimulation of nitrification (see Table 15.1),
but the injection of glycine with activated car-
bon consistently stimulated high rates of
nitrification, demonstrating that biochar in
some way alleviated the factor limiting nitrifi-
cation (DeLuca et al, 2002; Berglund et al,
2004). Char collected from recently burned
forests (DeLuca et al, 2006; MacKenzie and
DeLuca, 2006) or generated in laboratories
under controlled conditions (Gundale and
DeLuca, 2006) were found to stimulate net
nitrification in laboratory incubations and in
short-term (24hr) nitrifier activity assays.
One possible mechanism is that activated car-
bon adsorbed organic compounds (and spe-
cifically terpenes) that either inhibited net
nitrification (White, 1991; Ward et al, 1997;
Paavolainen et al, 1998) or caused immobili-
zation of NH4
+ (McCarty and Bremner,
1986; Schimel et al, 1996; Ward et al, 1997;
Uusitalo et al, 2008). The rapid response of
the nitrifier community to biochar additions
in soils with low nitrification activity and the
lack of a stimulatory effect on actively nitrify-
ing communities suggest that biochar may be
adsorbing inhibitory compounds in the soil
environment (Zackrisson et al, 1996) that
then allows nitrification to proceed. Similarly,
fire induces a short-term influence on N
availability, but biochar may act to maintain
that effect for years to decades after a fire. It
is also possible that the presence of biochar in
these forest soils enhances the numbers of
ammonia oxidizing bacteria by creating con-
ditions conducive to their growth (increased
pH, reduced inhibitory compounds, micro-
sites, redox potential, external electron trans-
fer) (Ball et al, 2010).
In another study seeking to explain char-
induced increased nitrification rates in nutri-
ent poor conifer forests, DeLuca et al (2006)
evaluated gross nitrification rates in char-
treated and untreated forest soils. Gross nitri-
fication rates in the char-amended forest soils
were nearly four times that in the untreated
soil, demonstrating the stimulatory effect of
char on the nitrifying community rather than
reduced immobilization. We also found that
sterilized soils treated with biochar also exhib-
ited a modest increase in nitrifier activity
(DeLuca, unpublished data) suggesting that
the oxide surfaces on biochar may stimulate
some quantity of auto-oxidation of NH4
+
(DeLuca et al, 2006). Wood ash commonly
contains high concentrations of metal oxides
including CaO, MgO, Fe2O3, TiO2 and CrO
(Koukouzas et al, 2007). Exposure of biochar
to solubilized ash may result in the retention
of these potentially catalytic oxides on active
Biochar C15.indd 428 11/3/2014 9:04:30 AM
Table 15.1 The effect of biochar (natural biochar, lab-generated biochar, or activated carbon) on nitrogen mineralization, nitrification and
immobilization from studies performed in soils of different ecosystems around the world
Ecosystem Biochar Type Nutrient Source
and Incubation
Control Biochar Addition Statistical
Difference
Reference
NH4
+ - N NO3
- - N NH4
+ - N NO3
- - N
Forested
Ponderosa pine,
Western MT
Wildre
Biochar,
Ponderosa pine
wood
Glycine in
greenhouse,
resin collected,
30 days
150 ± 200
(µg N cap-1) ‡
200 ± 100 700 ± 400 1200 ± 500 NO NH4
+
YES NO3
-
MacKenzie
and DeLuca
(2006)
Ponderosa pine,
Western MT
Lab Biochar,
Ponderosa pine
wood
(NH4)SO4 and
H2PO4 in lab,
aerobic
incubation,
15 days
NA
(µg N g soil -1)
40 ± 5 NA 70 ± 3 YES NO3
-DeLuca et al
(2006)
Ponderosa pine,
Western MT
Lab Biochar,
Ponderosa pine
(wood and
bark),
Douglas-r
(wood and
bark)
Glycine in lab,
aerobic
incubation,
14 days
47 ± 4
(µg N g soil -1)
5 ± 1 ppw † 20 ± 5
ppb 25 ± 6
dfw 32 ± 8
dfb 27 ± 3
ppw 21 ± 4
ppb 20 ± 8
dfw 11 ± 8
dfb 16 ± 4
YES NH4
+
YES NO3
-
YES NH4
+
YES NO3
-
NO NH4
+
NO NO3
-
NO NH4
+
YES NO3
-
Gundale and
DeLuca
(2006)
Scots Pine,
Sweden
Activated
Carbon
Glycine in Field,
resin collected,
30 days
20 ± 13
(µg N cap-1) ‡
0.06 ± 0.02 low§ 410 ± 99
high 780 ± 302
low 0.12
± 0.03
high 1.89
± 1.1
YES NH4
+
YES NO3
-
YES NH4
+
YES NO3
DeLuca et al
(2002)
Scots Pine,
Sweden
Activated
Carbon
Glycine in lab,
aerobic
incubation, 60
days
46 ± 6
(µg N g soil -1)
2.8 ± 0.4 1350 ± 50 5.5 ± 0.6 YES NH4
+
YES NO3
-
Berglund et al
(2004)
Biochar C15.indd 429 11/3/2014 9:04:30 AM
Table 15.1 continued
Ecosystem Biochar Type Nutrient Source
and Incubation
Control Biochar Addition Statistical
Difference
Reference
NH4
+ - N NO3
- - N NH4
+ - N NO3
- - N
Forested continued
Scots Pine,
Sweden
continued
Glycine in Field,
resin collected,
75 days
20 ± 3
(µg N cap-1) ‡
0.20 ± 0.20 146 ± 42 0.6 ± 0.1 YES NH4
+
NO NO3
-
Agricultural
Corn Production
South Carolina
Pecan Shell
Biochar
49 kg ha-1 UAN
(28-0-0),
aerobic, 25 days
4.74
(mg L-1)
256.85 25 days 2.25
67 days ND
78.67
43.98
NO NH4
+
YES NO3
-
NO NH4
+
NO NO3
-
Novak et al
(2010)
Winter Wheat
Kandsol Soil
Australia
Perennial Rye
Eutric Camisol
Wales, UK
Wheat Residue
Biochar
Mixed
Harwood
Biochar
None, aerobic,
7 days
None, aerobic,
7 days
3.70 ± 0.38
(mg N kg-1)
15.0 ± 14.2
(mg N kg-1)
2.02 ± 0.31
26.8 ± 12.2
fresh 1.42 ± 0.21
old 3.87 ± 0.76
fresh0.63 ± 0.45
old 5.16 ± 3.50
1.05 ± 0.05
1.74 ± 0.30
0.24 ± 0.08
30.7 ± 12.6
Not Reported
Not Reported
Dempster et
al (2012)
Dempster et
al (2012)
5 agronomic
soils (S, SiL),
Washington
Area
Four feed-
stocks,
Douglas-r
wood,
Douglas-r
bark, Switch
grass, Digested
bre
None, Aerobic
49 days
Mineralizable N 30 to 70
(mg N kg-1)
Mineralizable N Lower Signicantly
lower in most
cases
Streubel et al
(2011)
Ionic resin analysis used approximately 1g mixed bed resin in nylon mesh capsules approximately 25.4mm in diameter
ppw – Ponderosa pine wood; ppb – Ponderosa pine bark; dfw – Douglas-r wood; dfb – Douglas-r bark biochar produced at 350ºC
§ Low biochar application rate of 1,000kg ha-1, high application rate was 10,000kg ha-1
!! Sand (S) and silt loam (SiL) textured soils
Biochar C15.indd 430 11/3/2014 9:04:30 AM
BIOCHAR EFFECTS ON SOIL NUTRIENT TRANSFORMATIONS 431
surfaces of the biochar (Le Leuch and
Bandosz, 2007). These oxide surfaces may in
turn effectively adsorb NH4
+ or NH3 and
potentially catalyse the photo-oxidation of
NH4
+ (Lee et al, 2005). More work is required
to understand these variable mechanisms on
nitrification in forest soils.
In contrast to forested ecosystems, bio-
char additions in agricultural systems have
yielded mixed results, partially based on the
variety of feedstocks tested in agricultural tri-
als. Biochar additions to agricultural soils
have been found to reduce, have no effect or
in some cases increase net N mineralization
(Yoo and Kang, 2010; Streubel et al, 2011;
Güereña et al, 2013). Streubel et al (2011)
tested 5 different soils from the agronomic
regions of Washington state, ranging in tex-
ture from sand to silt loam (Table 15.1) and
amended with three rates of biochar (9.8,
19.5 and 39.0Mg ha−1), produced from four
different feedstocks (Douglas-fir wood and
bark, switchgrass stubble and digested fibre).
In this study, biochar had no significant
effect, or reduced N mineralization regard-
less of feedstock, for all but the sandy soil
amended at the highest quantity of switch-
grass biochar, which had significantly higher
NH4
+ and NO3
- production. Contrasting
results were reported in alkaline, calcareous
agricultural soils amended at a rate of 1–10
per cent switchgrass biochar in a laboratory
incubation, wherein biochar applications
reduced NH4
+ and NO3
- accumulation
(Ducey et al, 2013). However, when soils are
treated with biochar produced from a N-rich
feedstock (e.g. swine manure), increases in
net N mineralization and net nitrification
have been observed in laboratory incubations
(Yoo and Kang, 2010). Importantly, barley
straw biochar amendments to the same soils
had no significant effect on N mineralization.
Using molecular analyses (TRFLP and 454
pyrosequencing) microbial response to bio-
char additions were studied in agricultural
soils; the presence of Nitrosovibro (NH4
+
NO2
-) was found to decrease in the presence
of biochar while Nitrobacter (NO2
- NO3
-)
was observed to increase in the presence of
biochar (Anderson et al, 2012). However,
these shifts could have little consequence for
nitrification rates as molecular analyses have
also demonstrated little or no relationship
between gene abundance of ammonia oxidiz-
ing bacteria and rates of NO3
- accumulation
(Ducey et al, 2013). Such results emphasize
the contrast between the strong positive
effects biochar amendment has on forest
soils, where little or no net nitrification occurs,
compared to absence of effects in agricultural
soils, that already exhibit inherently high
rates of net nitrification and NO3
- accumula-
tion (e.g. over 113mg NO3
- -N kg-1 in the
control, Ducey et al, 2013) prior to biochar
additions. Interestingly, Nelissen et al (2012)
reported a significant increase in gross
ammonification and nitrification rates in
sandy soils amended with maize biochar with
the increase in nitrification being attributed
to greater substrate availability for auto-
trophic nitrifying bacteria.
The length of time that biochar resides in
the soil environment has also been shown to
affect N mineralization potential which may
be related to its occlusion with organic matter
over time as postulated by Zackrisson et al
(1996). Dempster et al (2012) found that
soils amended with ‘old’ biochar resulted in
greater inorganic N accumulation than soils
amended with ‘fresh’ biochar in different
agronomic soils from both Australia and the
UK (Table 15.1). This might have significant
implications for management practices that
are using biochar to retain inorganic N ferti-
lizer on-site. Regular additions of ‘fresh’ bio-
char to agricultural systems might be needed
to help retain inorganic N fertilizers and this
practice may also sequester large amounts of
C. In contrast, Novak et al (2010) reported a
modest increase in net N mineralization when
Biochar C15.indd 431 11/3/2014 9:04:30 AM
432 BIOCHAR FOR ENVIRONMENTAL MANAGEMENT
fresh wood biochar was added to acidic agri-
cultural soils. Biochar additions to agricul-
tural soils of the tropics have been reported to
either reduce N availability (Lehmann et al,
2003) or to increase N uptake and export in
crops (Steiner et al, 2007; Cornelissen et al,
2012). Reduced N availability may be a result
of the high C:N of biochar and thus greater
potential for adsorption of NH4
+ to biochar
which in turn reduces the potential for
N leaching losses and sustained higher N fer-
tility over time in surface soils (Steiner
et al, 2007). Alternatively, a biochar-induced
increase in microbial biomass could result in
net immobilization of N as demonstrated in
15N fertilizer trials on corn fields in New York
(Güereña et al, 2013).
Several studies have suggested that bio-
char can adsorb NH4
+ from the soil solution
(Lehmann et al, 2011; Spokas et al, 2012;
Taghizadeh-Toosi et al, 2012a), thus reduc-
ing the availability of NH4
+ for autotrophic
conversion to NO3
-; however, this hypothesis
has not been adequately tested. Increased
sorption of NH4
+ could, at least temporarily
create localized concentrations for microbial
use or plant uptake. Although reduced N2O
emissions with biochar additions have been
ascribed to increased sorption of NO3
- by
biochar (van Zwieten et al, 2010), NO3
- sorp-
tion to wood biochar has also been reported
to be insignificant (Jones et al, 2012). In addi-
tion to sorption of inorganic N, biochar also
has the potential to adsorb organic N com-
pounds (amino acids, peptides, proteins)
which could reduce N net mineralization or
nitrification, or stimulate N-fixing microbial
growth around and within biochar particles,
coating them with N-retaining microbes.
Moreover, biochar in soil ultimately becomes
occluded with organic matter and may aggre-
gate both mineral and organic matter frac-
tions together into physically protected pools
(Brodowski et al, 2006), N present in these
organic pools would likely remain unavailable
for some period of time and be protected
against transformation.
Immobilization
Biochar from wood or other N-poor feed-
stocks is an N-depleted material with a high
C:N ratio; however, biochars generated from
N-rich feedstocks can serve as a N source
(Lehmann et al, 2006). It has generally been
found that some decomposition occurs when
fresh biochar is added to soil (Schneour,
1966; Spokas et al, 2009; Jones et al, 2011),
although it is also well known that wood bio-
char is highly recalcitrant (DeLuca and Aplet,
2008). It is therefore uncertain whether bio-
char amendments provide sufficient bio-
available C to stimulate immobilization
(although this argument is often cited).
Several studies have demonstrated increased
respiration rates with biochar additions to soil
and suggested that the biochar was being
degraded or that the biochar induced priming
of resident soil C or fresh C (Wardle et al,
2008; Spokas et al, 2009; Novak et al, 2010).
However, recent studies have shown that
increased CO2 evolution, which is usually
indicative of increased microbial activity,
upon biochar additions was actually partly
due to emission of inorganic C (i.e. carbon-
ates) from within the applied biochar (Jones
et al, 2011). Low-temperature biochars, in
particular, would be more likely to induce net
nutrient immobilization, because they con-
tain higher concentrations of bioavailable C
and residual bio-oils (Steiner et al, 2007;
Nelissen et al, 2012; Clough et al, 2013) or
surface functional groups (Liang et al, 2006)
that can serve as microbial substrates. Higher
temperature biochars, in contrast, contain
much higher concentrations of graphene
structures which are much more resistant to
microbial degradation and less residual vola-
tiles. When biochars do provide a significant
concentration of bioavailable C (see Chapter
16), any immobilization stimulated by bio-
Biochar C15.indd 432 11/3/2014 9:04:30 AM
BIOCHAR EFFECTS ON SOIL NUTRIENT TRANSFORMATIONS 433
char would likely lead to only short-term
reductions in available inorganic N pools that
could reduce nitrification and N2O emissions
(Chapter 17) (Steiner et al, 2007).
Gaseous nitrogen emissions
Over the past several years there has been an
increasing interest in understanding how bio-
char influences the gaseous soil N transfor-
mations in order to understand ecosystem N
budgets and effects of biochar management
on greenhouse gas emissions. Much interest
has focused on the influence of biochar on
N2O flux (i.e., it has a global warming effect
per molecule that is 298 times greater than
CO2) (Yanai et al, 2007; Spokas et al, 2009;
Clough et al, 2010; Cornelissen et al, 2012),
because of its importance as a greenhouse gas
(Hansen et al, 2005) and ozone-depleting
substance (Ravishankara et al, 2009). Several
studies have also addressed the influence of
biochar applications on denitrification and
NH3 volatilization potential to evaluate the
influence of biochar on N conservation in
agricultural soils (Jones et al, 2012;
Taghizadeh-Toosi et al, 2012a). Nitrous
oxide emissions from soil are associated with
the processes of nitrification and denitrifica-
tion and this topic is covered in detail in
Chapter 17.
To date there have been a number of
papers devoted to assessing N2O generation
(as a greenhouse gas) on biochar-amended
agricultural soils, but far less effort geared
towards assessing the influence of biochar on
denitrification potential. Kammann et al
(2012) reported a significant decrease in N2O
emissions under ‘denitrification inducing
conditions’ following the addition of 50Mg
ha-1 of peanut hull biochar to an agricultural
Luvisol in Germany. However, when the bio-
char was added with 50kg N ha-1 as NH4NO3,
N2O emissions actually increased with bio-
char additions (Kammann et al, 2012). The
latter results are similar to the findings of
Jones et al (2012) which demonstrated an
increase in denitrification enzyme activity
DEA in north Wales where soils had been
treated with 50Mg wood biochar ha-1 and
100kg N ha-1 as NH4NO3 two years prior to
sampling. Studies have also demonstrated an
increase in denitrifying bacterial communities
with biochar additions to soil (Anderson et al,
2012; Ducey et al, 2013).
As indicated above, biochar applications
to agricultural or grassland soils that exhibit
high rates of nitrification have generally been
found to have no effect or a negative effect on
net nitrification rates (DeLuca et al, 2006;
Rondon et al, 2007; Dempster et al, 2012;
Jones et al, 2012) which would act as to
reduce denitrification potential. In contrast,
forest soils that otherwise express little or no
net nitrification respond to biochar or acti-
vated carbon additions by exhibiting an
increase in net nitrification and nitrifier activ-
ity (Berglund et al, 2004; DeLuca et al,
2006). Further, accumulation of NO3
- in soils
treated with soluble C-rich biochar would act
to increase denitrification potential under
anaerobic conditions (McCarty and Bremner,
1992). Hydochar produced under hydrother-
mal conditions increases soluble C additions
and has the potential to increase respiration
(Kammann et al, 2012) and denitrification
potential. However, application of wood bio-
char likely results in a long-term net decrease
of soluble organic C (see Chapter 16), which
would in turn reduce denitrification
potential.
Several recent studies have also evaluated
the influence of biochar on NH3 volatilization
(Steiner et al, 2010; Doydora et al, 2011;
Jones et al, 2012; Taghizadeh-Toosi et al,
2012a, b; Chen et al, 2013). Ammonia vola-
tilization in agricultural soils is favoured at
alkaline pH and when high concentrations of
NH4
+ are present and is reduced in soils with
high CEC (Stevenson and Cole, 1999).
Biochar and biochar mixed with ash are
Biochar C15.indd 433 11/3/2014 9:04:30 AM
434 BIOCHAR FOR ENVIRONMENTAL MANAGEMENT
known to temporarily increase soil pH (Glaser
et al, 2002; Jones et al, 2012), but usually not
to a high enough level to increase NH3 vola-
tilization. Taghizadeh-Toosi et al (2012a,b)
have shown instead that NH3 is effectively
sorbed to the surface of wood biochar, but
also demonstrate that it can be desorbed into
solution as NH4
+ thereby preventing N losses
to the atmosphere.
Biochar additions to agricultural soils as
well as acid forest soils have been found to
reduce NH4
+ concentrations (Le Leuch and
Bandosz, 2007; Taghizadeh-Toosi et al,
2012a) which reduces the potential for NH3
volatilization. Steiner et al (2010) found a
clear reduction in NH3 evolution during
poultry litter composting when biochar
amendment rates were 20 per cent (w/w).
Doydora et al (2011) found 50–60 per cent
reductions in NH4
+ available for volatilization
when composting poultry litter was cut 1:1
with biochar prior to incorporation into soil.
This finding is supported to some degree by
Jones et al (2012) who found a clear capacity
of biochar to adsorb NH4
+. Furthermore, in
field trials the researchers showed a reduction
in NH3 volatilization at rates of 50Mg biochar
ha-1, but not at 25Mg biochar ha-1 (Jones et al,
2012). In agricultural soils, it appears that
biochar generally results in a reduced pres-
ence of extractable NH4
+, likely as a result of
sorption of soluble NH4
+ to biochar surfaces.
However, the reduced occurrence of NO3
-
formation in agricultural soils treated with
biochar suggests that the reduced oxidative
pathway may leave more NH4
+ present and
available for immobilization. Further studies
are clearly required to determine the capacity
of biochar to reduce volatilization of soil or
applied NH4
+.
Biological nitrogen xation
Biological N2 fixation historically provided
the vast majority of N inflow into agroecosys-
tems (Galloway et al, 2008). Today it is man-
datory in low-input agroecosystems where
external N inputs are minimal. A thorough
understanding of the influence of biochar on
both symbiotic and free-living N2 fixing
organisms is needed. The influence of bio-
char on N2 fixation in leguminous plants was
studied with some intensity over half a cen-
tury ago, as researchers investigated the role
of charcoal as a soil amendment. Although
char was noted to have positive influence on
soil physical properties (Tryon, 1948), there
has been no consistent observed influence of
biochar on N2 fixing leguminous plants.
Table 15.2 provides a summary of results of
studies on the influence of PCM applications
on nodulation and N2 fixation in leguminous
plants. Several of these studies are described
in the following section.
Vantis and Bond (1950) found that the
addition of wood biochar to soils at a rate of 1
per cent (v/v) resulted in a reduction in the
number of nodules on clover, but increased
the total nodule mass and total N2 fixed in
Pisum sativum (L.). However, at higher rates
of biochar (greater than 2 per cent) there was
no effect or a negative effect of biochar on
nodulation (Vantis and Bond, 1950). Turner
(1955) found a significant increase in the
number of root nodules in clover (Trifolium
pratense L.), but only after an initial reduction
compared to the control. Their work went on
to show that boiled biochar further increased
nodulation and suggested that inhibitory com-
pounds can be removed by various forms of
pretreatment of biochar (Turner, 1955) (this
treatment may have influenced phytohor-
mone-like chemicals, see Chapter 14).
Investigation of composts with or without bio-
char added (5% w/w) as a growth medium
suggested that the biochar additions resulted
in a significant decrease in nodule number and
size (Devonald, 1982), however, there is no
discussion on pretreatment of the biochar or
its polyaromatic hydrocarbon (PAH) content.
Biochar C15.indd 434 11/3/2014 9:04:30 AM
Table 15.2 Summary of research findings on the influence of biochar or activated C on growth, nodulation and N2 fixation in
leguminous crops. For each study, percentage change in individual variables were calculated relative to an experimental control. All
studies are pot trials with the exception of Quilliam which combines field application of biochar with a growth chamber pot trial
Biochar type and rate Response plant Growth response Nodulation Nitrogenase
Activity
Source
Wood biochar 2% Pisum sativum + 37% + 25% NA Vantis and Bond (1950)
Wood biochar 4% + 45% - 11% NA
Wood biochar 8% + 8% - 31% NA
Activated carbon 1% - % NA
Animal biochar 2% NS or neutral - % NA
Wood biochar 1% –2% Trifolium pratense NA + 97% NA Turner (1955)
Wood biochar powder 1:1 P. sativum - 24% - 39% NA Devonald (1982)
Wood bark biochar ~ 1% Medicago sativum +70% NA +517% Nishio and Okano (1991)
Wood biochar 3% Phaseolus vulgaris + 25% NA + 42% Rondon et al (2007)
Wood biochar 6% + 39% NA + 64%
Wood biochar 9% NS NA NS
Chicken manure biochar ~ 0.4% Glycine max +5% +100% NA Tagoe et al (2008)
Chicken manure biochar ~ 0.8% +41% +190% NA
Wood biochar ~2.5% Trifolium repens Neutral NA + 250% Quilliam et al (2012)
Wood biochar ~ 5% Trifolium repens Neutral -70% + 350% Quilliam et al (2012)
NA: Not available
NS: Not signicant at P < 0.05
Biochar C15.indd 435 11/3/2014 9:04:30 AM
436 BIOCHAR FOR ENVIRONMENTAL MANAGEMENT
These findings are supported by more
recent studies that demonstrate a noted inhib-
itory effect of activated carbon on nodulation
in Lotus corniculatus (L.) (Wurst and van
Beersum, 2008). On the other hand, the
application of a nutrient-rich biochar (car-
bonized chicken manure) to silt loam soils in
a greenhouse experiment was found to
increase nodule number and mass in soy-
beans (Glycine max L.) and increase total N
yield (Tagoe et al, 2008). In a recent field
study (Quilliam et al, 2013), high rates of
wood biochar were applied to temperate agri-
cultural soils, (total applications of 25, 50 and
100kg biochar ha-1), soils were collected and
placed in pots and seeded to clover (T.
repens). Clover plants grown in the presence
of high rates of biochar were observed to have
reduced numbers of nodules, but the mass of
nodules was increased as was nitrogenase
activity (Quilliam et al, 2013).
Rondon et al (2007) tested the effect of
adding different amounts of wood (eucalypt)
biochar to nodulating and non-nodulating
varieties of the common bean, Phaseolus vul-
garis, inoculated with Rhizobium strains and
measured changes in N uptake using an iso-
tope pool dilution technique. Biochar was
found to significantly increase N2 fixation and
bean productivity at application rates of 30 or
60g biochar kg-1 compared to a control, but
the highest application rate, 90g biochar kg-1
soil reduced bean productivity (Rondon et al,
2007). All biochar treatments increased the
percentage of N in bean tissue derived from
N2 fixation. The study further indicates that
biochar may stimulate N2 fixation as the result
of increased availability of trace metals such
as nickel (Ni), iron (Fe), boron (B), titanium
(Ti) and molybdenum (Mo). The highest
rates of biochar application decreased the
magnitude of the effect and if taken to the
extreme might interfere with N2 fixation.
It is possible that lack of consistent effects
of biochar on legume performance and nodu-
lation is due to differences in nutrient con-
tents of the various biochars and their
respective potential to adsorb signalling com-
pounds. There is certainly variation in the
nutrient content and sorption capacity of
various types of biochar. Nodule formation in
leguminous plants is initiated by the release of
signalling compounds, often flavonoids (Jain
and Nainawatee, 2002). Such polyphenolic
compounds are readily sorbed by biochar
(Gundale and DeLuca, 2006). This might
explain why some studies have shown that
activated carbon reduces nodulation, while
low sorption P-rich biochars increased nodu-
lation, which is presumably the result of alle-
viating P-limitation of nodulating bacteria
with high P demands, such as Rhizobium spp.
(Rondon et al, 2007).
Numerous studies have been conducted
to evaluate the potential for increasing the
activity of free living N2 fixing bacteria in
agroecosystems, however, this has only been
directly evaluated in a few papers (Table
15.2). One methodological limitation to stud-
ying this is that biochar additions to soil likely
increase ethylene production (Spokas et al,
2010; see also Chapter 14), which is used as a
surrogate for N2 fixation activity in the acety-
lene reduction assay, the most commonly
used technique to estimate nitrogenase activ-
ity. It is well understood that excess soluble N
in the soil solution reduces N2 fixation rates in
free-living N2-fixing bacteria (Kitoh and
Shiomi, 1991; DeLuca et al, 1996) and avail-
able soil P can stimulate N2 fixation (Chapin
et al, 1991). Therefore, it is possible that the
activity of free living N2-fixing bacteria could
be increased by biochar-induced increases in
P solubility (Lehmann et al, 2003; Steiner et
al, 2007) and reduced soluble soil N concen-
trations (due to immobilization or surface
adsorption of NH4
+). Biochar therefore
potentially represents a good carrier or
medium for the growth and proliferation of
free-living N2-fixing bacteria. Wood and
Biochar C15.indd 436 11/3/2014 9:04:30 AM
BIOCHAR EFFECTS ON SOIL NUTRIENT TRANSFORMATIONS 437
cellulose based biochars are low N media, yet
serve to sorb soil P (see Chapter 7).
Conversely, however, in low inorganic N
environments, biochar is known to stimulate
net nitrification (e.g., DeLuca et al, 2006)
and thus may ultimately down-regulate N2
fixation by free-living N2-fixing bacteria.
While many of these mechanisms may influ-
ence the activity of free living N2-fixing bac-
teria, very little work has been done on this
topic.
Phosphorous
Biochar additions to soil have been found to
both increase and decrease the availability of
soil P (Steiner et al, 2007; Nelson et al, 2011).
After N, P tends to be the next major nutrient
limiting primary production in most ecosys-
tems, except in the tropics where it is often
the primary limitation (subsequently limiting
microbial N2 fixation). Unlike N, there is little
evidence for the direct uptake of organic P by
plants and therefore soil organic matter con-
taining organic P polymers (e.g. phospholip-
ids, DNA, phosphorylated proteins etc.)
must be enzymatically broken down outside
the cell prior to the uptake of inorganic P (Pi).
Inorganic P is most commonly taken up by
plants in the HPO4
-2 or H2PO4
- form. Some
low molecular weight organic P can be
directly taken up by microbial cells (e.g.
adenosine phosphates), however, this path-
way is probably small in comparison to the
uptake of Pi. In contrast to N, however, the
solubility and rate of diffusion of Pi in soils is
typically extremely low due to strong sorption
to the mineral phase (e.g. on Fe and Al oxy-
hydroxide surfaces) and its potential to form
mineral precipitates (e.g. Ca-P). Although
biochar itself can provide a readily available
source of P, it may also directly and indirectly
influence P behaviour in soil by a range of
other mechanisms including: (i) shifts in soil
pH; (ii) alteration in enzyme efficiencies; (iii)
formation of organo-mineral complexes that
increase P solubility; (iv) shifts in plant and
microbial community structure.
Release of P from biochar and impacts
on P leaching
Most biochars contain an appreciable amount
of P and the release of P from biochar has
long been recognized (Tryon, 1948). The P
contained in biochar feedstocks typically
ranges from 0.01–0.1 per cent for wood resi-
dues, 0.1–0.4 per cent for crop residues and
0.5–5 per cent for manures and biosolids
(Barrelet et al, 2006; Liu et al, 2011; Wang et
al, 2012). Within each feedstock, P can be
contained in different chemical forms which
may affect its subsequent availability after
entering the soil. When plant residues are
pyrolysed, organic C begins to volatilize at
approximately 100°C; whereas, P does not
volatilize until approximately 700°C (Knoepp
et al, 2005). Combustion or charring of
organic materials can greatly enhance P avail-
ability from plant tissue by disproportionately
volatilizing C and by cleaving organic P
bonds, resulting in a residue of soluble P salts
associated with the charred material. Pyrolysis
leads to the formation of a range of mineral P
forms of which complexes with Fe, Al, Ca
and Mg predominate. It is likely that biochars
derived from biosolids (sewage sludge) will
have a high proportion of Fe and Al phos-
phates which will be less soluble than Ca and
Mg phosphates. Biochar therefore contains
three pools of P, one which is freely soluble,
one which is strongly bound to Fe and Al and
one which remains organically bound as a
residue of the original feedstock. The propor-
tion of each is dependent on feedstock and
pyrolysis conditions (covered in detail in
Chapter 6) (Liu et al, 2011), however, a
number of studies have shown that a large
proportion of the P contained in wood-
derived biochars is immediately soluble and
readily released into soil solution (e.g.
Biochar C15.indd 437 11/3/2014 9:04:30 AM
438 BIOCHAR FOR ENVIRONMENTAL MANAGEMENT
Gundale and DeLuca, 2006). Experimental
biochar addition rates of 10–50kg biochar
ha-1 would result in the addition of 1 to 2500
kg P ha-1 depending on the feedstock of which
approximately 5–20 per cent can be assumed
to be available depending on feedstock (see
Chapter 7). When considering that typical
synthetic fertilizers are added at 5 to 50kg P
ha-1 there is considerable potential for over-
application with some biochars. However,
there has been little evidence for increased
leaching of P in laboratory trials (Laird et al,
2010; Borchard et al, 2012a; Schultz and
Glaser, 2012). Quilliam et al (2012) described
a significant increase in available soil P (0.5M
acetic acid extraction) with reapplication of
wood biochar (25 and 50Mg biochar ha-1) on
top of an existing biochar application of 25
and 50Mg biochar ha-1 (resulting in a 0, 25,
50, 25+25 and 50+50Mg biochar ha-1 experi-
ment) in an agricultural Inceptisol. However,
this noted increase in P availability did not
translate to an increase in foliar P concentra-
tions in the test crop (Quilliam et al, 2012).
Effect of biochar on phosphatase enzymes
and P solubilizing bacteria
Biochar can induce significant shifts in the
size, structure and activity of the soil micro-
bial community (Lehmann et al, 2011).
Despite the significant amount of functional
redundancy in the microbial population, this
may cause changes in rates of P cycling.
Biochar has been observed to influence myc-
orrhizal colonization of plant roots which in
turn may alter soil P uptake (Warnock et al,
2007; Lehmann et al, 2011); however, this
topic is covered in detail in Chapter 13.
Short-term laboratory studies have
shown that biochar addition induces an
increase in phosphatase activity (Bailey et al,
2010; Yoo and Kang, 2010; Jindo et al, 2012)
which would increase the release of P from
soil organic matter and organic residues.
Other studies, however, have revealed only
minor influence on soil phosphatase (Jones
et al, 2010). Molecular analyses of soils
amended with biochar revealed increased
presence of bacteria genes for genera of bac-
teria that have been observed to produce P
solubilizing compounds (Hamdali et al, 2008;
Anderson et al, 2012); however, this is indi-
rect evidence for biochar induced enhance-
ment of P solubilizing bacteria and further
studies are needed to determine if there is any
direct influence on bacterial production of P
solubilizing compounds.
In addition to directly releasing soluble P,
biochar can have a high CEC (Liang et al,
2006). Sorbed Al, Fe or Ca may influence P
solubility (see page 439 and Chapter 9). It
has been demonstrated that fresh biochar has
an abundance of transient anion exchange
capacity in the acid pH range (Cheng et al,
2008), which can be in excess of the total
CEC of the biochar. These exchange sites
have the potential to compete with Al and Fe
oxides (e.g. gibbsite and goethite) for sorp-
tion of soluble P, similar to that observed for
humic and fulvic acid extracts (Sibanda and
Young, 1986; Hunt et al, 2007). To date,
there is a noted lack of studies evaluating the
effect of biochar and variable charge surfaces
(short-term anion exchange capacity) on P
cycling and availability.
As biochar ages, the positive exchange
sites on biochar surfaces decline and negative
charge sites develop (Cheng et al, 2008). The
biochemical basis for the high CEC is not
fully understood (see Chapters 5, 6 and 9),
but is likely due to the presence of oxidized
functional groups (such as carboxyl groups),
whose presence is indicated by high surface
O/C ratios that form on the surface of charred
materials following microbial degradation
(Liang et al, 2006; Cheng et al, 2008; Preston
and Schmidt, 2006). Phosphorus availability
and recycling may be influenced by the bio-
char CEC over long time scales and in soils
that have inherently low exchange capacities.
Biochar C15.indd 438 11/3/2014 9:04:30 AM
BIOCHAR EFFECTS ON SOIL NUTRIENT TRANSFORMATIONS 439
By reducing the presence of free Al+3 and
Fe+3 near root surfaces, biochar may promote
the formation and recycling of labile P frac-
tions. This is also an area of research that
deserves greater attention.
Complexation
A significant component of the P cycle con-
sists of a series of precipitation reactions that
influence the solubility of P, ultimately influ-
encing the quantity of P that is available for
uptake and actively recycled between plants
and microbes. The degree to which these pre-
cipitation reactions occur is strongly influ-
enced by soil pH, due to the pH dependent
activities of the ions responsible for precipita-
tion (Al3+, Fe3+ and Ca2+) (Stevenson and
Cole, 1999). In alkaline soils, P solubility is
primarily regulated by its interaction with
Ca2+, where a cascading apatite mineral path-
way develops. In acid soils, P availability is
primarily regulated by its interaction with Al3+
and Fe3+ ions, where highly insoluble Al- and
Fe- phosphates form. Biochar may influence
precipitation of P into these insoluble pools
by altering the pH and thus the strength of
ionic P interactions with Al3+, Fe3+ and Ca2+
(Lehmann et al, 2003; Topoliantz et al, 2005)
or by sorbing organic molecules that act as
chelates of metal ions that otherwise precipi-
tate P (DeLuca, unpublished data, Figure
15.4). The latter pathway may be of particu-
lar importance for plant P availability if bio-
char enhances formation of stabilized organic
matter from decomposing organic matter as
suggested by some composting studies
involving biochar (Dias et al, 2010) (see also
Chapter 25), or by altered SOC turnover pat-
terns in Terra Preta (Liang et al, 2010).
Numerous studies have demonstrated
that biochar can modify soil pH, normally by
increasing pH in acidic soils (Mbagwu, 1989;
Matsubara et al, 2002; Lehmann et al, 2003).
There are few, if any, studies that have dem-
onstrated a reduction in pH with biochar
addition in alkaline soils, however, the addi-
tion of acid biochar to acidic soils has been
observed to reduce soil pH (Cheng et al,
2006). An increase in pH associated with
adding biochar to acid soils are due to an
increased concentration of alkaline metal
(Ca2+, Mg2+ and K+) oxides in the biochar
and a reduced concentration of soluble soil
Al3+ (Steiner et al, 2007). Adding these alka-
line metals, both as soluble salts and associ-
ated with biochar exchange sites, is likely the
single most significant effect of biochar on P
solubility in the short term, particularly in
acidic soils where subtle changes in pH can
result in substantially reduced P precipitation
with Al3+ and Fe3+. In contrast, adding bio-
char (and associated ash residue) to neutral
or alkaline soils may have a limited effect on P
availability because adding alkaline metals
would only exacerbate Ca driven P
limitations.
In addition to its effect on soil pH, bio-
char may also influence the bioavailability of
P through several other mechanisms associ-
ated with P precipitation, such as biochar-
induced surface sorption of chelating organic
molecules. Biochar is an exceptionally good
surface for sorbing polar or non-polar organic
molecules across a wide range of molecular
mass (Sudhakar and Dikshit, 1999; Schmidt
and Noack, 2000; Preston and Schmidt,
2006; Bornermann et al, 2007). Organic mol-
ecules involved in chelation of Al3+, Fe3+ and
Ca2+ ions will potentially be sorbed to hydro-
phobic or charged biochar surfaces so that, in
the long run, organo-biochar or organo-min-
eral-biochar complexes begin to form over
time that may aid in the retention and
exchange of soluble P around aged biochar
particles (Briones, 2012; Joseph et al, 2013).
However, in the short term, decreased P solu-
bility may result via the following mecha-
nisms. Examples of such chelates include
simple organic acids, phenolic acids, amino
acids and complex proteins or carbohydrates
Biochar C15.indd 439 11/3/2014 9:04:30 AM
440 BIOCHAR FOR ENVIRONMENTAL MANAGEMENT
(Stevenson and Cole, 1999). The sorption of
chelates may have a positive or negative influ-
ence on P solubility. A clear example of this
type of interaction is provided in Figure 15.5.
Here, two compounds that have been
reported as possible allelopathic compounds
released as root exudates from Centaurea spe-
cies: catechin and 8-hydroxy-quinoline
(Vivanco et al, 2004; Callaway and Vivanco,
2007) have also been reported to function as
potent metal chelates (Stevenson and Cole,
1999; Shen et al, 2001) that may indirectly
increase P solubility. Catechin effectively
increased P solubility in an alkaline (pH 8.0)
calcareous soil and the 8-hydroxy-quinoline
increased P solubility when added to an acidic
(pH 5.0) Al-rich soil (Figure 15.5). The
addition of biochar to these soils eliminated
the presence of soluble chelate in the soil sys-
tem and in turn eliminated the effect of the
chelate on P solubility. This interaction may
explain the observed reduction in P sorption
by ionic resins with increasing biochar appli-
cation rates in the presence of actively grow-
ing Koleria macrantha (Gundale and DeLuca,
2007). Such indirect effects of biochar on P
solubility would vary with soil type and veg-
etative cover and underscores the complexity
of plant-soil interactions.
Sulfur
To date, there have been few studies that
have focused on the influence of biochar soil
amendments on soil S transformations. Sulfur
plays an extremely important role in the bio-
chemistry of soils and the physiology of plants
(Stevenson and Cole, 1999; Marschner,
2006). Sulfur is a component of two amino
acids (cysteine and methionine), is required
in protein synthesis and is a fundamental
component of energy transformations in all
living organisms. Sulfur also represents a
source of energy for autotrophic organisms
and an alternative electron acceptor for oxi-
dative decomposition under anaerobic condi-
tions (Stevenson and Cole, 1999). Although
biochar produced from high S feedstocks has
the potential to release S into the soil solution
(Uchimiya et al, 2010), there is little evidence
for enhanced oxidation or reduction of soil S
with biochar applications. Given the similari-
ties between the S and N cycles (Stevenson
and Cole, 1999), there is certainly the poten-
tial for biochar to influence S mineralization
and oxidation activity in the soil. Although
the majority of soil S originates from the geo-
logic parent material, most soil S exists in an
organic state and must be mineralized (con-
verted from organic S to SO4
-2) prior to plant
uptake (Stevenson and Cole, 1999). Organic
S exists as either ester sulfate or as carbon-
bonded S, the latter having to be oxidized to
SO4
-2 prior to plant uptake. To date, no stud-
ies have directly assessed the influence of bio-
char on transformations of organic S already
in agricultural or forest soils (separately from
S release from the biochar discussed below).
However, numerous studies involving bio-
char or biochar additions to soils have
recorded changes in the soil environment that
suggest that biochar additions could change
the turnover of soil organic S.
One of the few studies that have directly
investigated the influence of biochar on S
availability was conducted with two soil types,
four crop residue amendments and performed
in the laboratory in PVC columns (Churka
Blum et al, 2013). In this study, S, C and N
mineralization was assessed following addition
of corn husk biochar to soil compared with
fresh residues of corn husks, pea and rape resi-
dues. Although C mineralization and N min-
eralization were notably low with the biochar
amendment, the highest rate of S mineraliza-
tion for all amendments was observed with the
corn husk biochar. The authors conclude that
the release of S from the residues is likely a
function of the S compounds within the resi-
dues. The high concentrations of ester S and
Biochar C15.indd 440 11/3/2014 9:04:30 AM
BIOCHAR EFFECTS ON SOIL NUTRIENT TRANSFORMATIONS 441
Figure 15.5 Soluble P leached from columns filled with (a) calcareous soil (pH = 8) amended with
catechin alone or with biochar or (b) acid Al rich soil (pH = 6) amended with 8-hydroxy quinoline
alone or with biochar (DeLuca, unpublished data). Studies were conducted by placing 30g of soil
amended with 50mg P kg-1 soil as rock phosphate into replicated 50mL leaching tubes (n = 3). Soils
were then treated with nothing (control), chelate, or chelate plus biochar (1% w/w), allowed to incubate
for 16 h moist and then leached with 3 successive rinsings of 0.01M CaCl2. Leachates were then
analysed for orthophosphate on a segmented flow Auto Analyzer III. Data were subject to ANOVA by
using SPSS
Biochar C15.indd 441 11/3/2014 9:04:30 AM
442 BIOCHAR FOR ENVIRONMENTAL MANAGEMENT
soluble SO4
-2 in the biochar amendment com-
bined with the modest increase in biotic activ-
ity with the biochar amendment suggests that
soluble SO3
-2 and SO4
-2 readily liberated from
the ester S allowed for rapid accumulation of
inorganic S in soils treated with biochar
(Churka Blum et al, 2013).
Biochar additions to acid agricultural
soils have been observed to yield a net
increase in soil pH (see Chapter 7), poten-
tially as a function of the alkaline oxides
applied along with the biochar or potentially
as a result of the influence on free Al:Ca
ratios in soils amended with biochar (Glaser
et al, 2002; Topoliantz et al, 2005). Sulfur
mineralization is favoured at slightly acid to
neutral pH. Sulfur mineralization rates have
been found to increase following fire in pine
forest ecosystems (Binkley et al, 1992),
much the same as that observed for N
(Smithwick et al, 2005). Separating the
effect of fire from the effect of the natural
addition of char is difficult, but this effect is
most likely due to the release of soluble S
from litter following partial combustion dur-
ing fire or heating events at temperatures in
excess of 200ºC (Gray and Dighton, 2006).
Sulfur oxidation is carried out by both
autotrophic (e.g. Thiobacillus spp.) and het-
erotrophic organisms. Sulfur oxidation by
acidophilic Thiobacillus spp. would not be
favoured by pH increases induced by the
presence of biochar. However, these auto-
trophic organisms have uniquely high
requirements for certain trace elements that
are in relatively high concentrations in bio-
char (see Chapter 13) and are increased in
soil when biochar is added (Rondon et al,
2007). Biochar additions to soil that ulti-
mately reduce the surface albedo of mineral
soils and result in faster warming of soils in
springtime (Meyer et al, 2012) may in turn
increase S oxidation or mineralization rates
(Stevenson and Cole, 1999).
The utility of biochar, activated carbon
and graphite in the high temperature,
chemical reduction of SO2 to C adsorbed
episulfide has been studied intensely
(Humeres et al, 2005) to evaluate these
materials as scrubbers for removing SO2
from pollution streams. This has limited
relevance for soils, except that the very salts
demonstrated to enhance catalytic reduc-
tion of SO2 in the presence of activated car-
bon (e.g. Na+ and NO3
-) are often present
in soils in relatively high concentrations.
However, there are no published reports of
enhanced SO4
-2 reduction in soils in the
presence of biochar.
Biochar additions to mineral soils may
also directly or indirectly affect S sorption
reactions and S reduction. However, as
with NO3
-, non-aged, production-fresh bio-
char may lack any significant capacity to
adsorb SO4
-2 (Borchard et al, 2012b). As
noted in Chapter 5, biochar improves soil
physical properties through increased spe-
cific surface area, increased water holding
capacity and improved surface drainage.
Increased soil aeration through these
improvements in soil physical condition
would in turn reduce the potential for dis-
similatory S reduction (Stevenson and
Cole, 1999). Sulfur is readily adsorbed to
mineral surfaces in the soil environment
and particularly to exposed Fe and Al
oxides. Once Fe and Al have been sorbed to
biochar surfaces, SO4
-2 may interact with
the exposed metal oxides. Conversely,
organic matter additions to soil have been
shown to reduce the extent of SO4
-2 sorp-
tion in acid forest soils (Johnson, 1984),
therefore biochar amendments could act to
increase solution concentrations of S in
acidic iron-rich soils. The lack of studies
devoted to the evaluation of S transforma-
tions following biochar addition to soils
calls for additional research in this area.
Biochar C15.indd 442 11/3/2014 9:04:30 AM
BIOCHAR EFFECTS ON SOIL NUTRIENT TRANSFORMATIONS 443
Future research directions
The application of biochar to agricultural
soils has the potential to greatly improve soil
physical, chemical and biological conditions.
In this chapter we reviewed biochar as a mod-
ifier of soil nutrient transformations and dis-
cussed the known and potential mechanisms
that drive these modifications. Biochar addi-
tions to soils may directly or indirectly alter
nutrient cycling. Biochar applications may
increase NH4
+ retention in soil and have often
been observed to increase N uptake by crop
plants; however, there is little evidence for an
increase in N availability following crop har-
vest. It is important to note that biochar has
few negative impacts on soil nutrient cycling.
The observed increases in net nitrification in
forest soils occur at a level that would have
minimal influence on net N leaching and
N2O emissions. Although biochar additions
could increase net ammonification observa-
tions have not been consistent. While P solu-
bility appears to generally increase with
biochar additions, this may be primarily a
result of direct P addition with the applied
biochar than altered P cycling. There is a dis-
tinct need for studies directed at explaining
mechanisms for increased P uptake with bio-
char additions to agricultural soils. It is pos-
sible that biochar additions to soils stimulate
mycorrhizal colonization, which may increase
P uptake, but when applied with P-rich mate-
rials, this effect may be lost. There is a great
need for additional studies that elucidate the
effect of biochar on soil nutrient transforma-
tions, in the short term directly after applica-
tion as well as in the long term, e.g. in aged
PyC-rich soils. Some key areas that require
attention include: (1) Under what conditions
does biochar stimulate or reduce N minerali-
zation, nitrification and immobilization in dif-
ferent ecosystems? (2) Does NH4
+ adsorption
by biochar greatly reduce N availability or
does it concentrate N for plant and microbial
use? (3) By what mechanisms does biochar
addition to mineral soils stimulate P availabil-
ity? (4) Do enzymes sorb to biochar and
retain their activity? (5) How does biochar
affect S availability and by what
mechanism(s)? The answers to these ques-
tions can only be obtained through rigorous
investigation of biochar as a soil conditioner
and agricultural amendment.
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... The effect of biochar on the P status of the amended soil is inevitably influenced by biochar properties and dosage, amended soil types, and agricultural practices (Nelson et al. 2011;Qian et al. 2013;DeLuca et al. 2015;Zhu et al. 2018). A meta-analysis revealed the positive effect of biochar on soil available P supply up to a biochar dosage of more than above 10 Mg ha −1 (Glaser and Lehr 2019), and excessive biochar addition inevitably led to potential P loss and soil alkalization risks . ...
... Soil P forms and their cycling and dynamics are significantly influenced by biochar amendment, resulting in an altered P availability (Topoliantz et al. 2005;DeLuca et al. 2015). As mentioned earlier, Fe/Al (hydr)oxides bound P is the main available P pool in intensively weathered soil (Hong and Lu 2018), and the incorporated biochar can increase soil pH, decrease soil exchangeable acidity, facilitate P release from metal (hydr)oxides (Jiang et al. 2015), and reduce the transformation of Fe/Al (hydr)oxides-P to occluded P (O-P) (Ch'ng et al. 2014). ...
... In the recent decade, a substantial number of studies have found that biochar is effective in increasing the soil P content and availability, and decreasing P leaching (Cui et al. 2011;DeLuca et al. 2015;Eduah et al. 2019). Therefore, scientometric analysis of the current studies and future efforts was performed using Citespace 5.8R3 based on bibliographic records from the Web of Science Core Collection. ...
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Purpose Phosphorus (P) retrieval from crop residues has attracted significant attention in sustainable management of P resources. Biochar has the potential to enhance soil P availability and enlarge P pools. However, only few reviews have been reported on the factors and mechanisms of the effect of biochar on replenishing soil P and improving P availability. Materials and methods The current studies on biochar effects on improving soil P level, as well as the underlying factors and mechanisms were reviewed. Results and discussion Biomass (especially livestock manure and municipal sewage) derived biochar contains abundant nutrients and, hence, can directly increase soil available P levels. Most of the amended biochar could change soil physical and chemical properties, such as soil porous structure, pH, cation exchange capacity, and adsorption potential toward P. These variations are associated with P forms and availability in soil matrix. Moreover, soil biota and phosphatase, which increased in the presence of biochar, could solubilize insoluble inorganic P and mineralize organic P, thus enhancing P availability. However, the efficiency of biochar is governed by the properties of biochar and amended soil, and cultivation strategies. Conclusions Studies illustrating the available P sources in biochar-amended soil, quantifying the contribution of biochar-amended soil microorganisms in improving P level, enhancing the slow-release potential of biochar formulations, and inspecting the effects against comprehensive long-term field analyses are considered to expand our knowledge on the effect of biochar amendment on P supplementation and availability in soil.
... This increased carbon sequestration in the soil also improves soil quality due to vital role of carbon in biological, physical and chemical soil. DeLuca et al., (2009) found that augmentation of biochar in the soil results in increased biological availability of N, P, K nutrients and other metal ions in poor soils. Adding biochar in soil improves vital chemical and physical features of the soil. ...
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World population is increasing with massive rate and to achieve the goal of feeding 8.6 billion people by 2030, development of Good Agricultural practices (GAP) is imperative. The subject study was executed to appraise the impact of zeolite for improving soil property and quality which will ultimately enhance crop yields. For this purpose, zeolite (at rate of 1, 3 & 05 tons ha-1) blended with nitrogen (at rate of 0 & 140 kg-1) was administered in the soil and its residual effects were evaluated for 3 consecutive years. All treatments were applied with equal amount of phosphorus and potassium. The treatment with the highest rate of zeolite (Z 3 = 05 tons ha-1) gave promising results and improved the soil electrical conductivity (EC) by 24%, bulk density by 2.5%, soil water holding capacity by 20.6% and total carbon by 22% as compared to control. Zeolite addition has also increased total nitrogen in soil up to 1.1 times, available phosphorus by 1.3 times and extractable potassium by 2.4% over the control. Zeolite performance was almost persistent through all 3 years. In all 3 years zeolite showed no significant effect over pH of the soil. Treatments of zeolite blended with nitrogen depicted similar results as of sole zeolite treatments, except total nitrogen which is because of more nitrogen supply into soil in some treatments. Zeolite application improved soil properties due to its porous structure which conserves moisture and also increased the fertilizer use efficiency. Increase in total nitrogen may be the result of increased microbial activity in the soil.
... Biochar is also used to modify sand-based turfgrass root zones, where it lowers saturated hydraulic conductivity, reduces rooting depth, and enhances soil water retention in sand for plants in sand-based root zones (Brockhoff, 2010). Biochar influences nitrogen, phosphorus, and Sulphur changes in the soil ecosystem; the biochar mechanism modifies the transformation of soil nutrients (DeLuca et al., 2009). Pecan-based biochar that is not activated with ground switchgrass (Panicum virgatum) is utilized to increase the soil carbon content, infiltration, aggregation, and water-holding capacity of Norfolk Loamy Sandy soils with poor physical properties and low soil carbon content (Influence of Pecan Biochar on Physical Properties of a Norfolk Loamy Sand, 2010). ...
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Magnetic biochar made from agricultural biomass waste such as SRC willow, which is a densely planted, high-yielding energy crop and one of the leading sources of renewable energy production, combined with iron (II) chloride and iron (III) chloride, is a multi-functional material for land remediation and agricultural applications. Two magnetic biochar's (1.0 M iron solution magnetic biochar and 0.1 M iron solution magnetic biochar) were prepared by the chemical mixture and co-precipitation of iron (II) chloride tetrahydrate and iron (III) chloride on SRC willow with a particle size of less than 2 mm (about 0.08 in). The mixture of SRC willow with iron (II) chloride tetrahydrate and iron (III) chloride was then dried in the oven and pyrolyzed at 400 degrees Celsius. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction research on the 1.0 M iron solution magnetic biochar and the 0.1 M iron solution magnetic biochar reveal a greater concentration of iron compounds in the 1.0 M iron solution magnetic biochar. Ultraviolet infrared spectrometry was performed on iron (II) chloride tetrahydrate, iron (III) chloride, and copper (II) sulphate pentahydrate. Atomic absorption spectroscopy and ultra-violet spectrometry were performed on copper (II) sulphate pentahydrate and deionized water mixed with 1.0 M iron solution magnetic biochar, 0.1 M iron solution magnetic biochar, and activated for atomic absorption spectroscopy, 0.1 M iron solution magnetic biochar has a greater adsorption capacity than 1.0 M iron solution magnetic biochar for copper (II) sulphate pentahydrate solution. For ultra-violet infrared spectroscopy, the adsorption capacity of magnetic biochar in a 1.0 M iron solution is greater than that of magnetic biochar in a 0.1 M iron solution. Based on these results, both the 1.0 M iron solution magnetic biochar and the 0.1 M iron solution magnetic biochar are good options for removing metal pollutants like copper and restoring land.
... The biochar application enhanced the availability of P in soil (Table 3) as biochar has the ability to adsorb and desorb P and influenced the P adsorption and desorption of soil (Chintala et al., 2014). The biochar application in the soil which has high pH and CEC, increased the P adsorption activity by oxides of iron, aluminum, and reduce the calcium (DeLuca, Gundale, MacKenzie, & Jones, 2015). Biochar transforms the physical, chemical, and morphological characteristics of P and enhances the availability of P in the soil. ...
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It has been demonstrated that biochar has a great potential to reduce volatilisations of ammonia (NH3) from fertilised agricultural soils. While there have been several laboratory studies to demonstrate the effects of biochar on gaseous NH3 emissions, there is hardly any data on the influence of biochar amendments on NH3 volatilisations from the soils under a field environment. Modifying biochar or enriching it with nitrogen (N) may maximise its capacity to abate gaseous NH3 emissions from the soil. Three biochars, i.e. SAB, HPB, and KHB modified through post-pyrolysis treatment with sulphuric acid, hydrogen peroxide, and potassium hydroxide, respectively as well as two biochars enriched with either molten urea (URB) or ammonium nitrate (ANB), were used alongside the pristine biochar (PRB) for comparisons. The quantity of gaseous NH3 evolved from each the biochar amendments including their effects on the growth and yield of the Chinese cabbage plus selected soil chemical properties were evaluated through a field experiment. The control experiment consisted of urea applied alone. In comparison with the control, PRB, KHB, HPB, SAB, URB, and ANB amendments abated NH3 volatilisations from the soil by 44.18%, 45.91%, 63.23%, 65.62%, 72.66%, and 76.71%, respectively. Additionally, PRB, SAB, KHB, HPB, ANB, and URB amendments increased Chinese cabbage yields by 138.5%, 172.0%, 117.3%, 181.1%, 194.0%, and 181.1%, respectively in comparison with the control. The strong linear relationship (r² = 0.97) between cumulative NH3 emissions and nitrogen use efficiencies indicates that biochar-induced reductions in emissions of gaseous NH3 concomitantly increased the use-efficiencies of the applied N.
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Biochar, a promising exogenous material, is of great interest due to its ability to retain soil nutrients. Understanding the nutrient retention and release characteristics of biochar in soil is crucial to avoid environmental risks. In the current study, batch adsorption experiments were used to explore the adsorption capacity of ammonium (NH4⁺-N) and phosphate (PO4³⁻-P) on Erythrina arborescens biochars produced at 300–700 °C. The biochar produced at 600 °C (BC600) was used to conduct the column leaching experiments under different addition ratios (0, 1%, 3%, 5%, and 10%) to evaluate the effects of biochar on nutrient leaching and soil quality over the short period of time. The results found that BC600 at different addition ratios owned the best adsorption ability to NH4⁺-N, and the highest removal rate was up to 49%. Column leaching experiments displayed that compared to pure soil, the introduction of 1% biochar could reduce the cumulative NH4⁺-N in the leachate by 30.7%. The adsorption of PO4³⁻-P on different biochars was poor, and with the increase of biochar addition ratio, the phenomenon of negative PO4³⁻-P removal rate appeared. Column leaching experiments found that when the biochar addition rate was 1%, the cumulative PO4³⁻-P in the leachate was reduced by 12.9% compared to that in pure soil. Meanwhile, the application of BC600 in soil also improved soil pH, electrical conductivity, cation exchange capacity, and organic matter. These findings suggested that the application of Erythrina arborescens biochar with the appropriate ratio in soil could benefit to mitigate nutrient loss.
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Nitrous oxide (N2O) emission from agriculture is increasing alarmingly due to intensive application of inorganic and organic fertilizers. Recently, biochar has been identified as a promising additive to improve agriculture by enhancing soil function and mitigate greenhouse gas emission. However, it is unclear how biochar of different size fractions influences N2O emission from agricultural soil. The current experiment aims to understand how the size of biochar (BC) and organic fertilizers interactively influence N2O emission from a tropical vertisol. BC was prepared using pigeon pea (Cajanus cajan) stalks and further processed to obtain two size fractions (<0.25 mm or 0.25–2.00 mm). Organic fertilizers (vermicompost [VC], poultry manure [PM], or farmyard manure [FYM]) and BC were added to soil to evaluate N2O emission potential. BC was added to soil at 10% (w/w), whereas the organic fertilizers were added at 80 kg N ha–1. Emission of CO2 and the abundance of 16S rRNA and amoA gene copies were estimated after incubation period. The interactive effect of BC size fractions and organic fertilizers were statistically evaluated. Both BC and organic fertilizers stimulated N2O emission in soil. BC of larger size stimulated N2O emission (µg N2O produced g–1 soil d–1) more than smaller size. Of the three organic fertilizers, PM resulted highest N2O (0.380) emission followed by FYM (0.240) and VC (0.210). BC (0.25 mm) + PM produced least N2O. Abundance of heterotrophic bacterial 16S rRNA gene copies and ammonia‐oxidizing bacterial (AOB) amoA gene copies were highest in PM + BC and lowest in control. Significant relation (p < 0.0001) existed among N2O emission, CO2 emission, and microbial abundance. BC of small size fraction along with organic fertilizers can be an effective strategy to mitigate N2O emission from tropical vertisol.
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Heavy metals (HMs) accumulation in soil poses a severe threat worldwide for soil, plants, and humans. The accumulation of HMs in soil and uptake by plants leads to disrupt physiological and biochemical metabolisms. As a potential and sustainable soil amendment, biochar has attained huge attention to reduce HMs toxicity in soil and improve plant growth influenced by HMs stress. Despite an array of research studies, there is a lack of knowledge on how biochar interacts with HMs, moderate plant defence system, induce HMs stress signals pathways and promote plant growth. At first, the review highlights the possible effects of HMs on soil and plant and their consequences on plant signaling network. Secondly, the biochar's impact on soil physiochemical properties and the sorption of HMs on biochar surface through direct and indirect mechanisms are reviewed. Finally, the review shows the key roles of biochar in soil improvement to enhance plant growth and signaling response to HMs by enhancing the activities of antioxidants and reducing chlorophyll injury, reactive oxygen species (ROS) accumulation, and cell membrane degradation under HMs stress. However, future studies are needed to evaluate the role of biochar in diverse climatic conditions as well as the long-term effects of biochar on HMs persistency in soil and crop productivity. This review will provide new avenues for future studies to address and quantify the advancement in biochar's role in alleviating plant's HMs stress on a sustainable basis.
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Biochar, an environmentally friendly soil amendment, is created via a series of thermochemical processes from carbon-rich organic matter. The biochar addition enhances soil characteristics dramatically and increases crop growth and yields. However, the mechanism by which biochar improves plant lodging resistance, which is heavily influenced by cell walls, remains unknown. Three rice cultivars were grown in an experimental field provided with four concentrations of biochar (10, 20, 30, 40 t ha⁻¹). The biochar application enhanced biomass production and lodging resistance in all three cultivars by up to 29 % and 22 %, respectively, with the largest improvement at a biochar application rate of 30 t ha⁻¹. Biochar application significantly enhanced stem cell wall-related characteristics, with an increase in stem breaking force, wall thickness, and plumpness of 52 %, 32 %, and 21 %, respectively, which are suggested to be major contributors to enhanced lodging resistance and biomass yield. Notably, cell wall composition and silica content analysis indicated a significant increase in hemicellulose, lignin, and silica content in biochar-treated samples up to 36 %, 13 %, and 58 %, respectively, when compared to plants not treated with biochar. Integrative analysis suggested that silica, hemicellulose, and lignin were co-deposited in cell walls, which influenced biomass production and lodging resistance. Furthermore, the transcriptome profile revealed that biochar application increased the expression of genes involved in biomass production, cell wall formation, and silica deposition. This study suggests that biochar application might improve both biomass production and lodging resistance by promoting the co-deposition of silicon with hemicellulose and lignin in cell walls.
Article
The use of M. × giganteus in phytoremediation requires treatment of the contaminated biomass, which can be done by pyrolysis to produce biochar. Due to its potentially detrimental properties, the application of biochar in soil remediation must first be evaluated on a test plant to infer how the growth process was affected by the impact on soil parameters. The main goal of the current research was to investigate the effects of waste-derived Miscanthus biochars (from contaminated rhizomes (B1) and aboveground biomass (B2)) on soil properties and evaluate the impact of biochar doses and properties on Spinacia oleracea L. growth. It was revealed that incorporation of B1 at a dose of 5% and B2 at doses of 1, 3, and 5% increased soil organic carbon, pH, K (at 3 and 5%), and P2O5 (at 5% B2). Cultivation of S. oleracea reduced organic carbon, soil pH as a function of biochar dosage, and K, P2O5, NH4, and NO3 content in all treatments tested. The highest biomass yield was recorded at 3% B2. The photosynthetic parameters indicated that the doses of 3 and 5% B2 led to dissociation of light-harvesting complexes. Increasing the biochar dose did not necessarily increase yield or improve photosynthetic parameters. S. oleracea adapted to the initial stress by incorporating biochar and managed to establish a balance between nutrients, water supply, and light. It is recommended that the effects of biochar on the development of the target crop be evaluated through preliminary trials before biochar is applied at field scale.
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This review highlights the ubiquity of black carbon (BC) produced by incomplete combustion of plant material and fossil fuels in peats, soils, and lacustrine and marine sediments. We examine various definitions and analytical approaches and seek to provide a common language. BC represents a continuum from partly charred material to graphite and soot particles, with no general agreement on clear-cut boundaries. Formation of BC can occur in two fundamentally different ways. Volatiles recondense to highly graphitized soot-BC, whereas the solid residues form char-BC. Both forms of BC are relatively inert and are distributed globally by water and wind via fluvial and atmospheric transport. We summarize, chronologically, the ubiquity of BC in soils and sediments since Devonian times, differentiating between BC from vegetation fires and from fossil fuel combustion. BC has important implications for various biological, geochemical and environmental processes. As examples, BC may represent a significant sink in the global carbon cycle, affect the Earth's radiative heat balance, be a useful tracer for Earth's fire history, build up a significant fraction of carbon buried in soils and sediments, and carry organic pollutants. On land, BC seems to be abundant in dark-colored soils, affected by frequent vegetation burning and fossil fuel combustion, thus probably contributing to the highly stable aromatic components of soil organic matter. We discuss challenges for future research. Despite the great importance of BC, only limited progress has been made in calibrating analytical techniques. Progress in the quantification of BC is likely to come from systematic intercomparison using BCs from different sources and in different natural matrices. BC identification could benefit from isotopic and spectroscopic techniques applied at the bulk and molecular levels. The key to estimating BC stocks in soils and sediments is an understanding of the processes involved in BC degradation on a molecular level. A promising approach would be the combination of short-term laboratory experiments and long-term field trials.
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This state-of-knowledge review about the effects of fire on soils and water can assist land and fire managers with information on the physical, chemical, and biological effects of fire needed to successfully conduct ecosystem management, and effectively inform others about the role and impacts of wildland fire. Chapter topics include the soil resource, soil physical properties and fire, soil chemistry effects, soil biology responses, the hydrologic cycle and water resources, water quality, aquatic biology, fire effects on wetland and riparian systems, fire effects models, and watershed rehabilitation.
Article
The application of bio-char (charcoal or biomass-derived black carbon (C)) to soil is proposed as a novel approach to establish a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems. Apart from positive effects in both reducing emissions and increasing the sequestration of greenhouse gases, the production of bio-char and its application to soil will deliver immediate benefits through improved soil fertility and increased crop production. Conversion of biomass C to bio-char C leads to sequestration of about 50% of the initial C compared to the low amounts retained after burning (3%) and biological decomposition (< 10–20% after 5–10 years), therefore yielding more stable soil C than burning or direct land application of biomass. This efficiency of C conversion of biomass to bio-char is highly dependent on the type of feedstock, but is not significantly affected by the pyrolysis temperature (within 350–500 ∘C common for pyrolysis). Existing slash-and-burn systems cause significant degradation of soil and release of greenhouse gases and opportunies may exist to enhance this system by conversion to slash-and-char systems. Our global analysis revealed that up to 12% of the total anthropogenic C emissions by land use change (0.21 Pg C) can be off-set annually in soil, if slash-and-burn is replaced by slash-and-char. Agricultural and forestry wastes such as forest residues, mill residues, field crop residues, or urban wastes add a conservatively estimated 0.16 Pg C yr−1. Biofuel production using modern biomass can produce a bio-char by-product through pyrolysis which results in 30.6 kg C sequestration for each GJ of energy produced. Using published projections of the use of renewable fuels in the year 2100, bio-char sequestration could amount to 5.5–9.5 Pg C yr−1 if this demand for energy was met through pyrolysis, which would exceed current emissions from fossil fuels (5.4 Pg C yr−1). Bio-char soil management systems can deliver tradable C emissions reduction, and C sequestered is easily accountable, and verifiable.
Book
An understanding of the mineral nutrition of plants is of fundamental importance in both basic and applied plant sciences. The Second Edition of this book retains the aim of the first in presenting the principles of mineral nutrition in the light of current advances. This volume retains the structure of the first edition, being divided into two parts: Nutritional Physiology and Soil-Plant Relationships. In Part I, more emphasis has been placed on root-shoot interactions, stress physiology, water relations, and functions of micronutrients. In view of the worldwide increasing interest in plant-soil interactions, Part II has been considerably altered and extended, particularly on the effects of external and interal factors on root growth and chapter 15 on the root-soil interface. The second edition will be invaluable to both advanced students and researchers.