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The Effects of Biochar Amendment on Soil Fertility


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Biochar is a black, C-rich, stable, solid product from pyrolysis of biomass materials. Although it was known as a soil C sequester for a considerable length of time, biochar is also recently advocated in agricultural applications for improving soil quality; therefore, its agronomic value is evaluated. This paper summarizes and discusses the potential of biochar amendment for soil fertility improvement and the effects on crop productivity by reviewing scientific studies performed around the globe. Researches have shown that biochar amendment significantly enhances the nutrient availability and nutrient retention of a wide range of soils. The soil fertility amelioration is achieved through improving soil physical, chemical, and biological properties. The capacity of a biochar to provide or enhance soil available nutrients, however, is determined by the feedstock and production conditions of the biochar. Biochars produced from nutrient-rich feedstocks contain comparatively high readily available nutrients. In general, biochar amendment improves soil fertility, yet the effect is more apparent for poor (e.g., acidic, highly leached) soils than for originally fertile soils. The impacts of biochar amendment on crop growth are largely positive, with mixed results dependent on the biochar quality, application rate, soil type, and crop species. Further research is needed to fully uncover the role of biochar in enhancing soil fertility and crop growth.
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Abbreviations: CEC, cation exchangeable capacity.
Avanthi Deshani Igalavithana (, Yong Sik Ok (,
and Sang Soo Lee, Korea Biochar Research Center and Dep. of Biological Environment and, Kang-
won National University, Chuncheon 24341, South Korea; A.R.A. Usman, Dep. of Soils and Water,
Faculty of Agriculture, Assiut University, Assiut 71526, Egypt (; Moham-
mad I. Al-Wabel, Soil Sciences Dep., College of Food and Agricultural Sciences, King Saud Univer-
sity, P.O. Box 2460, Riyadh 11451, Saudi Arabia (; Patryk Oleszczuk, Dep. of
Environmental Chemistry, Faculty of Chemistry, 3 Maria Curie-Skłodowska Square, 20-031 Lub-
lin, Poland ( *Corresponding author (sslee97@kangwon. A.D. Igalavithana and Y.S. Ok share first authorship.).
Agricultural and Environmental Applications of Biochar: Advances and Barriers. SSSA Special
Publication 63. M. Guo, Z. He, and M. Uchimiya, editors.
© 2015. SSSA, 5585 Guilford Rd., Madison, WI 53711, USA.
The Eects of Biochar Amendment
on Soil Fertility
Avanthi Deshani Igalavithana, Yong Sik Ok, Adel R.A. Usman,
Mohammad I. Al-Wabel, Patryk Oleszczuk, and Sang Soo Lee*
Biochar is a black, C-rich, stable, solid product from pyrolysis of biomass materials. Although
it was known as a soil C sequester for a considerable length of time, biochar is also recently ad-
vocated in agricultural applications for improving soil quality; therefore, its agronomic value
is evaluated. This paper summarizes and discusses the potential of biochar amendment for
soil fertility improvement and the eects on crop productivity by reviewing scientic studies
performed around the globe. Researches have shown that biochar amendment signicantly en-
hances the nutrient availability and nutrient retention of a wide range of soils. The soil fertility
amelioration is achieved through improving soil physical, chemical, and biological properties.
The capacity of a biochar to provide or enhance soil available nutrients, however, is determined
by the feedstock and production conditions of the biochar. Biochars produced from nutrient-
rich feedstocks contain comparatively high readily available nutrients. In general, biochar
amendment improves soil fertility, yet the eect is more apparent for poor (e.g., acidic, high-
ly leached) soils than for originally fertile soils. The impacts of biochar amendment on crop
growth are largely positive, with mixed results dependent on the biochar quality, application
rate, soil type, and crop species. Further research is needed to fully uncover the role of biochar
in enhancing soil fertility and crop growth.
Published November 12, 2015
2 Igalavithana et al.
Soil fertility is the ability of a soil to supply plant nutrients to maintain sustain-
able crop productivity. Soil fertility degradation and available nutrient depletion
is common in agroecosystems with environmentally detrimental amounts of
modern agricultural practices, which have imbalanced the responsible abiotic
and biotic soil fertility factors (Suzuki et al., 2014). Soil fertility enhancement and
maintenance are challenges nowadays, as soil nutrient availability and retention
have generally been declining. It is clearly urgent to reverse the trend to sustain
the soil fertility of agroecosystems. Application of organic amendments such as
compost and animal manure is a traditional practice to rehabilitate soil nutrient
retention. The traditional organic amendments, however, are of short life span in
soil; continuous application in bulk quantities diverts its aention of this practice.
Moreover, the increasing population pressure does not allow fallowing cropland
to gain the diminished soil fertility through natural rehabilitation (Achard and
Banoin, 2003).
Terra preta or Amazonian dark earths are fertile anthrosols generated by
ancient Amazonian inhabitants. The high fertility of terra preta has been investi-
gated in details by many scientists; a large amount of stored C with a high degree
of stability, as in a form of charcoal, has been identied for the aractive fertil-
ity (Petersen et al., 2001; Schmidt et al., 2014). From the archeological perspective,
terra preta aained its fertility as a result of the addition of charcoal and animal
bones (Petersen et al., 2001; Schmidt, 2010, 2013; Schmidt et al., 2014). In general,
the content and stability of soil organic C are known as very important factors
for maintaining soil fertility (Lal, 2004; Liu et al., 2013; Pan et al., 2009). Hence,
applying biochar to soils might have fertility enhancement eects as implicated
by charcoal abundance in terra preta soils (Akhtar et al., 2014).
Biochar is a C-rich, stable, anthropogenic product obtained by thermal
decomposition of biomass with lile or no available oxygen at relatively low
temperatures (<700°C; Lehmann and Joseph, 2009). Biochar shows enormously
greater stability in the soil than any other organic amendments (Domene et al.,
2014; Spokas, 2010), possessing the ability to play a similar role of charcoal in
terra preta. Many researchers have examined the inuence of biochar amend-
ment on fertility and nutrient status of soil and reported generally signicant
positive impacts. Nevertheless, the long-term role of biochar on soil fertility still
belongs to speculation (Glaser et al., 2002; Sohi et al., 2010).
The unique characteristics of biochar endow its ability to enhance soil physi-
cal, chemical, and biological properties; thereby, biochar application uplis the
overall soil fertility (Akhtar et al., 2014). This chapter presents a comprehensive
review on biochar as a fertilizer, biochar–soil nutrient cycle, and mechanisms of
biochar enhancing soil fertility and crop productivity.
Could Biochar Be Used as a Fertilizer?
In the 19th century, Liegbig, a German scientist, explained that plant growth
depends on the availability of 16 essential nutrients: 13 of from soil and the
remaining three (C, H, and O) from other sources. These 13 nutrients are divided
into three groups as primary (N, P, and K), secondary (Ca, Mg, and S) and micro (B,
Cl, Cu, Fe, Mn, Mo, and Zn) nutrients (Havlin et al., 2004). The rst identication
The Eects of Biochar Amendment on Soil Fertility
of micronutrients has been changed with new ndings. Cobalt, Si, Na, V, and
Ni also have been listed as micronutrients, which are essential for some plant
species (USDA, 2009). Application of biochar to soil has shown to increase plant
growth; however, its eects depended on the amount and type of biochar applied.
Lehmann and Rondon (2005) documented the signicant increases of plant pro-
ductivity (by 20–220%) using dierent biochars at dierent application rates. The
increase of plant productivity was related to rise in nutrients availability in soil,
leading to the question: Does biochar itself provide nutrients for plant growth or
facilitate the release of bound nutrients already present in the soil? To unveil the
biochar mystery on soil fertility, there is a rst need to disclose the chemical com-
position of biochar and its ability to provide nutrients.
Biochars chemical composition and nutrient arrangement rely mainly on
the feedstock and the production temperature (Qin et al., 2012; Spokas and
Reicosky, 2009). Moisture content of the raw biomass also aects the composi-
tion of the nal product (Galinato et al., 2011). For all biochars that are frequently
dened as the carbonaceous crude of biomass pyrolysis,the main constitu-
ent is C (Ahmad et al., 2014). This C is arranged into aromatic structures and
occasional piles of graphite-like layers (Zimmerman, 2010). Additionally, H, O,
and N are the main supportive elements for C to nalize the biochar structure
(Mimmo et al., 2014).
Gaskin et al. (2008) reported that biochar produced from poultry manure
contained more nutrients than biochars produced from others containing poor
nutrient contents. Likewise, Joseph et al. (2010) documented that dierent types
of manure-derived biochars generally contained signicant amounts of available
plant nutrients. However, manure-derived biochars produced at high temper-
atures have low hydrolyzable organic N and high aromatic and heterocyclic
structures (Cao and Harris, 2010; Clough et al., 2013; Lehmann, 2007). In general,
biochars produced at low temperatures (e.g., £300°C) are richer in nutrients than
those produced at high temperatures (e.g., ³600°C). Therefore, the biochars pro-
duced at relatively low pyrolysis temperatures are preferred as agricultural soil
amendments (Atkinson et al., 2010; Clough et al., 2013).
The nutrient contents of selected biochars are listed in the Table 1. Biochar
contained N, P and K in the ranges of 0.09 to 3.5, 0.03 to 7.3, and 0.1 to 5.9%, respec-
tively. There are no direct relationships between the pyrolysis temperature and
the N content of biochar; the N content mainly depends on the percentage of N
in the biomass feedstock (Ahmad et al., 2014); for the same feedstock, however,
biochars showed a decreasing trend in N content as the pyrolysis temperature
is elevated within 300 to 600°C (Song and Guo, 2012). Novak et al. (2009b) and
Granatstein et al. (2009) evidenced that the origin of biochar plays a major role in
its N content; biochars made from herbaceous feedstocks (e.g., switchgrass [Pani-
cum virgatum L.], digester ber, and peanut hulls) typically have lower C contents
and higher N contents and pH than biochars made from woody feedstocks. How-
ever, Lehmann and Joseph (2009) and Song and Guo (2012) observed a signicant
amount of N loss with increasing the pyrolysis temperature. The other two pri-
mary nutrients, P and K, showed an opposite trend of behavior as a temperature
function by retaining most part of the elements in the feedstock.
4 Igalavithana et al.
Table 1. Elemental composition of biochar produced with different feedstocks and pyrolysis temperatures.
Feedstock Temp.† C H O N P K Ca Mg S Fe B Cu Mn Mo Zn
———————————————————– g kg
—————————————————— ———————— mg kg
Poultry litter 400† 392 34.7 30.1 51.1 42.7 10.7 13.67 6.06 91.5 805 596 17.1 628
500† 392 30.9 35.9 58.6 50.4 12.9 13.93 8.03 100 1034 725 14.2 752
Peanut hulls 400† 732 24.3 1.83 15.2 4.62 2.19 0.56 1.00 32.5 16 116 4.78 35
500† 804 24.8 1.97 16.4 5.12 2.50 0.55 1.15 33.7 19 131 <1 37
Pine chips 400† 739 2.55 0.15 1.45 1.71 0.60 0.01 0.15 5.69 25 274 <1 15
500† 817 2.23 0.14 1.45 1.85 0.59 0.06 0.05 4.21 9 258 <1 18
600‡ 535 3.1 2.91 12.20 10.50 3.95 116
Green waste 450§ 360 1.8 0.2 8.19 0.04 0.13
Peanut shell 380–450¶ 725 18 1.84 18.2
Poultry litter 450# 380 20 25
700†† 258 7.5 48 30
Broiler cake 700†† 172 6.0 73 58
300‡‡ 695 42 245 9.0 0.5 2.7 4.6 1.4 0.20 0.00 100
450‡‡ 786 35 155 0.9 0.7 2.5 8.3 1.8 0.60 0.00 100
600‡‡ 765 29 183 8 0.8 1.5 9.1 2.1 0.50 0.00 100
Peanut hull 300‡‡ 739 39 191 16 0.9 8.6 3.2 1.3 0.00 0.00 0.00
450‡‡ 815 29 130 10 0.9 9.4 3.3 1.3 0.00 0.00 0.00
600‡‡ 864 14 100 9 1 7.1 3.4 1.2 0.00 0.00 0.00
300‡‡ 593 52 341 3 0.3 1 7.3 1.2 0.40 0.00 100
450‡‡ 756 36 172 3 0.7 2.5 13.2 2.3 0.50 0.00 0.00
600‡‡ 770 22 177 1 0.9 1.2 18.1 2.9 0.80 0.00 0.00
Bamboo 300‡‡ 662 47 277 4 2.4 3 2.2 1.4 0.00 0.00 100
450‡‡ 769 36 181 2 3.6 3.5 2.9
1.9 0.00 0.00 100
600‡‡ 809 24 149 2 5 5.2 3.4 2.3 0.00 0.00 100
Rice husks 450–550§§ 393 22 579 7 4.7 7.4 3.4 3.3
† Gaskin et al. (2008). ‡ Houben et al. (2013). § Chan et al. (2007). ¶ Magrini-Bair et al. (2009). # Chan et al. (2008).
†† Lima and Marshall (2005). ‡‡ Yao et al. (2012). §§ Qian et al. (2013).
The Eects of Biochar Amendment on Soil Fertility
Biochar Decomposition and Plant Available Nutrients
The availability of nutrients in biochar relies on their structural stability, which
in turn is determined by the feedstock type, production conditions, and soil
environment (Asadullah et al., 2010; Jha et al., 2010). Elemental ratios of H/C, O/C,
and C/N are the main indicators of structural stability of biochar. Increasing the
pyrolysis temperature generally reduces H/C and O/C ratios while transforming
the biochar structure into chemically and biologically more stable arrangement
(Ahmad et al., 2014; Braadbaart et al., 2004; Mohan et al., 2014). Contrarily, the C/N
ratio rises with the increasing pyrolysis temperature and leads to a more stable
biochar structure (Baldock and Smernik, 2002).
Whereas biochar is highly resistant to biological and chemical decomposition,
studies have shown that biochar can be partially decomposed or mineralized via
abiotic and biotic factors of the natural environment (Cheng et al., 2008; Hamer
et al., 2004; Kuzyakov et al., 2009). Kuzyakov et al. (2009) examined the biochar
decomposition with
C-labeled biochar was produced from perennial ryegrass
(Lolium perenne L.) shoot lier. Biochar-added soil was incubated at 20°C and 70%
of water-holding capacity for 1181 d in a laboratory incubator. Decomposition of
biochar is comparatively fast during the rst few months following incorpora-
tion into the soil and then slows down with continuing the partial decomposition.
Some authors have observed enhanced biochar mineralization with the coappli-
cation of a labile C source such as glucose in laboratory experiments (Hamer et al.,
2004; Kuzyakov et al., 2009). However, it is not completely understood whether
this mineralization is only from biochar or includes the inherent soil organic
maer. Awad et al. (2013) reported 13.5% enhanced
C-labeled organic maer
mineralization following a commercial biochar addition in a laboratory incu-
bation experiment. Similarly, Awad et al. (2012) documented that the soils with
biochar addition did not show signicant increases in native C decomposition.
Jha et al. (2010) reported that corn (Zea mays L.)- and oak wood (Quercus spp.)-
derived biochars produced at 350 and 600°C showed rather slow mineralization
by 16 and 12% of total biochar C, respectively, within 1 yr under submerged and
alternative weing and drying conditions. A similar mineralization rate (16% per
year) was also observed for corn stover biochar by Kuzyakov et al. (2009) in 3.2 yr
incubation study at 70% water holding capacity. In a 60-d incubation study, 0.26%
of C in wood biochar produced at 350°C and 0.72% of C in maize biochar pro-
duced at 800°C were mineralized into CO
(Hamer et al., 2004). Biochars showed
higher mineralization rates in the alkaline soils than in the acidic soils (Aciego
Pietri and Brookes, 2008). Nevertheless, the decomposition rate of biochar could
not be considered as a signicant factor in evaluating biochar’s capacity to sup-
ply plant nutrients.
Luo et al. (2011) reported that the contents of water-extractable NH
–N in
Miscanthus (Miscanthus ´ giganteus J. M. Greef & Deuter ex Hodk. & Renvoize)
biochars produced at 350 and 700°C were 1.75 and 0.18 mg g
, respectively,
equivalent to 0.09 and 0.01 mg N g
soil, respectively, when the each biochar
was applied at 5% (w/w). Water-extractable NO
–N in the same biochars was not
measured. It has been reported by Lehmann et al. (2003) that biochar addition to a
Ferralsol lowered the soil N availability, mainly as a result of the high C/N ratios
of the tested biochars. There is no report on the availability or release of other
nutrients during biochar mineralization.
6 Igalavithana et al.
Elemental composition and biodegradability are the main factors determin-
ing the use of biochar as a fertilizer. Low available nutrient contents and poor
nutrient release capacity of biochar in short runs do not support the objective of
considering the material as a fertilizer. To be an eective fertilizer, biochar should
contain the sucient nutrients and be susceptible to microbial decomposition for
the release of available nutrients. In this context, feedstock type and pyrolyzing
condition should be strictly monitored to obtain the desired biochar. Although
biochar is not a well-known fertilizer so far, it has a potential to be a great soil
fertility enhancer recently proven by the laboratory experiment and long-term
eld studies.
Composted Biochar and Soil Fertility
The recalcitrant nature of biochar limited its use as a fertilizer because of insuf-
cient release of nutrients in soil, particularly for the biochars produced from
the feedstocks containing poor nutrients and at high pyrolysis temperature. To
overcome this limitation, the mixed addition of biochar with organic amend-
ments, such as compost, is recently in practice (Schulz et al., 2013). Signicant
plant-nutrient buildup has been observed in soils receiving biochar and compost
mixtures. Composted biochar is a quite recent approach in agronomic adapta-
tion of biochar and it has demonstrated promising results for increasing plant
nutrients in soil (Dias et al., 2010; Prost et al., 2013; Schulz and Glaser 2012; Schulz
et al., 2013). Schulz et al. (2013) produced composted biochars using dierent
char/biomass ratios and observed higher plant nutrient availability in soils when
amended. Biochar was made from beech (Fagus sylvatica L.) wood by pyrolyzing
at 350 to 450°C, traditionally in a charcoal kiln. Six dierent rates of biochar were
blended with the composting materials to obtain 0 to 50% (w/w) biochar con-
tents in nal product. A pot experiment was conducted with oats (Avena sativa
spp.) by incorporating the six dierent composted biochars at the rates of 50, 100,
and 200 Mg ha
of soil. Compost with the relatively high amounts of biochar
addition (in the range of 4050% [w/w]) showed the greater nutrient availability
and the enhanced eect with higher application rate (Schulz et al., 2013). Khan et
al. (2014) reported enhanced nitrication and reduced NH
emission in compost
preparation with biochar relative to compost alone. Their observation was based
on six dierent composted biochars produced with three dierent raw biochars
originated from nutshell hardwood shavings and chicken lier based on wood
shavings and two application rates of 5 and 10% (w/w). Biochar addition enhances
humication and reduces organic maer decomposition during composting. The
elevated proportion of humic substances improves the quality of compost (Dias
et al., 2010; Hua et al., 2009; Ishizaki and Okazaki, 2004).
Biochar and the Nutrient Cycle
Biochar amendment can result in substantial changes in soil nutrient cycles
(Prommer et al., 2014). The eects of biochar amendment on soil organic N cycle
have been discussed by a few studies but not in detail (Singh et al., 2010). Singh
et al. (2010) and DeLuca et al. (2009) showed that biochar had the ability to inu-
ence the N cycle of agroecosystems. The authors found that soil-incorporated
biochar could decrease the soil’s net N mineralization, NO
emission, and NO
leaching. Similar ndings were observed by Kolb et al. (2009). However, Jones
The Eects of Biochar Amendment on Soil Fertility
et al. (2012) presented divergent results from a long-term (3 yr) eld experiment
using temperate agricultural soils. They concluded that biochar amendment did
not aect the NO
and NH
pool size, the dissolve organic N content, and the
N mineralization rate of soil. Evidently, the short- and long-term eects of bio-
char amendment on soil nutrient cycling can be dierent. There is a strong need
for conducting long-term eld studies to clarify the potential eects of biochar
amendment on soil nutrient cycling.
It has been indicated that biochar can be applied to soil to decrease inorganic
N leaching, N
O emissions, and NH
volatilization as well as to increase biologi-
cal N xation (Chen et al., 2010; Clough et al., 2013; Rondon et al., 2007; Singh
et al., 2010; Spokas et al., 2009; Steiner et al., 2010; Ventura et al., 2013; Yao et al.,
2012). Hu et al. (2014) reported the addition of wheat (Triticum aestivum L.) straw
biochar produced at 450°C reduced N
O emission in laboratory incubation study
conducted in dark at 25°C. Moreover, NO
–N in soil was continually increased
during 15 mo aer biochar addition as a result of the enhanced gross nitrication
rate by 10% over the control. In a eld study to investigate the eect of biochar
on short-term NO
leaching from the A horizon soil of an apple (Malus domestica
Borkh.) orchard, the biochar addition signicantly decreased NO
leaching from
the surface soil layer, while NH
leaching was unaected (Ventura et al., 2013).
Chen et al. (2010) reported the similar decreases of NO
N concentration in per-
colating water from bagasse biochar-amended soils.
The reduction of N losses can be ascribed to increased soil water holding
capacity and NH
adsorption as well as enhanced N immobilization by bio-
char amendment (Zheng et al., 2010). Dempster et al. (2012b) found that biochar
addition decreased NO
leaching more signicantly from coarse-textured soils
than from ne-textured clay soils, mainly because of a decrease of nitrication.
However, they noticed that the biochar addition signicantly decreased the
cumulative NH
leaching from soils, but leaching of dissolved organic N was
lile inuenced. Güereńa et al. (2013) reported the lower gaseous N loss (e.g., via
ammonia volatilization and denitrication) from soils aer addition of biochar.
A similar observation was also obtained by Taghizadeh-Toosi et al. (2011) in lab-
oratory experiments using pasture soils amended with ammonia-impregnated
biochar. The same authors have documented reduced ammonia volatilization
with respect to biochar application (Taghizadeh-Toosi et al., 2012a).
Depending on its quality, biochar may aect soil N dynamics through alter-
ing soil chemical and biological properties following land application. The type
of soil or feedstock, pyrolysis conditions, and application rate are all the factors
of biochar soil amendment that aect soil N dynamics. Indeed, the reductions in
and NO
losses depend on the source of N and the biochar characteristics.
Short-term lysimeter studies showed the reductions of NO
and NH
with the biochar application, while NH
exhibited the highest retention (Güereńa
et al., 2013). However, Dempster et al. (2012a) assumed that fresh biochar had a
beer ability to retain NO
with its high anion retention capacity. Aer several
years, biochars anion retention capacity would be negligible as a result of natu-
ral aging (Cheng et al., 2008; Silber et al., 2010). Nitrogen retention in a soil could
be increased by incorporation of biochar (Güereńa et al., 2013). The incorporation
of biochar into soil might increase the overall net-soil surface area and subse-
quently result in increasing nutrient retention via adsorption (Chan et al., 2007).
Lehmann et al. (2002) suggested two basic approaches for reducing nutrients’
8 Igalavithana et al.
leachability and increasing their retention: (i) biochar may act as a slow-releasing
nutrients’ agent, and (ii) the adsorption sites increased because of biochar appli-
cation resulting in increasing retention of inorganic nutrients.
Applying biochar to soil can alter the C/N ratio of the soil, thus inuenc-
ing N mineralization and immobilization. Several researchers indicated that the
high-C-mineralization biochar at the beginning resulted in short-term N immobi-
lization as a result in an increase in soil C/N ratio (Lehmann et al., 2003; Nelson et
al., 2011; Novak et al., 2010). However, this short-term eect is temporary, mainly
due to the fact that the readily available fraction of biochar C would decrease
with time and only the highly recalcitrant C fraction persists (Nelson et al., 2011;
Novak et al., 2010).
Taghizadeh-Toosi et al. (2012b) found that soil incorporation of biochar
resulted in signicant decreases in NH
–N volatilization from ruminant urine
applied to soil as a result of adsorption of NH
onto biochar. The authors fur-
ther demonstrated that the adsorbed NH
was plant available, thus indicating
improved soil fertility. Combined application of biochar and chemical fertilizers
has recently been studied to illustrate the eect of biochar on nutrient availability.
Güereńa et al. (2013) investigated the N losses from soil received 54 and 108 kg N
of N fertilization in addition to biochar amendment at 0 and 12 t ha
. Biochar
was produced with maize stover at 600°C. No signicant dierences in N losses
were detected between the low-N-fertilization treatments with and without bio-
char amendment. At the high-N-fertilization level, however, biochar addition
signicantly reduced the soil N losses. Similar results were obtained by other
researchers (Dempster et al., 2012a; Laird et al., 2010; Novak et al., 2009a). Nelson
et al. (2011) emphasized that the biochar amendment alone (e.g., at 20 g kg
could not adequately increase the availability of plant nutrients in soil; therefore,
the additional chemical fertilization in combination with biochar amendment
would be needed to maximize crop production.
Despite of the direct eects on N mineralization in soil, biochar may indi-
rectly aect the N dynamics by improving certain soil physicochemical properties,
simulating microbial activities and subsequently enhancing the mineralization
of soil organic maer. Many researchers reported that the biochar application
increases soil microbial biomass and activity (ereńa et al., 2013; Jones et al.,
2012; Kolb et al., 2009; Kuzyakov et al., 2009; Steiner et al., 2004). The enhanced
microbial population, in turn, improves mineralization of labile organic com-
pounds in biochar (Kuzyakov et al., 2009, 2014; Lehmann et al., 2009) and soil
organic maer (Kuzyakov et al., 2009).
Biochar exhibits the direct impacts on the soil C cycle. An earlier study by
Kuzyakov et al. (2009) aempted to disclose the role of biochar in the C cycle and
discussed the priming eect of biochar. The priming eect can be dened as
changes in the mineralization of native soil organic maer due to the addition of
new substrates” (Zimmerman et al., 2011). The priming eect could be positive or
negative (Bell et al., 2003; Kuzyakov et al., 2000; Noingham et al., 2009). Biochar
can generate the positive priming eects if the product contains high amount of
mineralizable C and provides the signicant amounts of N, P, and micronutrients
(Chan and Xu, 2009). Ahmad et al. (2012) reported a high biologically active C in
a soil as a result of the application of oak wood biochar produced at 400°C at a
rate of 5% (w/w). Negative priming eects on C cycle were observed with addi-
tion of biochar produced at high temperatures and nutrient-poor feedstocks. This
The Eects of Biochar Amendment on Soil Fertility
primarily is due to the organic maer preservation mechanism via sorption to
biochar pores or onto external biochar surface (Kuzyakov et al., 2009; Novak et al.,
2010; Spokas et al., 2009; Zimmerman et al., 2011). However, the laboratory incuba-
tion study conducted at 25°C for 60 d using the nutrient-rich-pig-manure biochar
produced at 420°C promoted the soil organic C concentration and stabilization in
Regosol, Luvisol, and Kastanozem (Yanardağ et al., 2015).
So far, lile has been known about the role of biochar on the P cycle in
soil. The reported eects of biochar on soil P availability are inconsistent. Many
researchers observed enhanced P bioavailability and plant growth in soils
through biochar amendment (DeLuca et al., 2009; Lehman et al., 2003; Nelson
et al., 2011). Contrarily, the immobilization of soil P by biochar has also been
reported (Novak et al., 2009a). In general, biochars containing high P contents,
such as those derived from poultry waste, have the net release of soluble P and
consequently enhance soil P availability. As a maer of fact, soil available P can
be adsorbed onto biochar and become unavailable to plants. The mechanism of
P sorption to biochar is pH dependent. Xu et al. (2014) indicated that in acidic
soils, more P was sorbed onto the solid phase with increasing the biochar amend-
ment rate, while in alkaline soils, the sorption decreased slightly. The authors
suggested that precipitation or Ca-induced P sorption resulted in retention of
available P.
Other Chemical Parameters of Biochar
Improving Soil Fertility
Biochar has been recognized as a soil fertility enhancer and rehabilitator. Appli-
cation of biochar would improve soil quality and subsequently increase crop
productivity (Gaskin et al., 2010; Lehmann et al., 2006; Novak et al., 2009a).
Though biochar does not have the immediate eects equivalent to that of chem-
ical fertilizers, the enhancement of soil physicochemical properties by biochar
may be considered as the cause for the favorable eects on soil productivity. The
long-lasting life-span and desirable chemical and surface properties of biochar
facilitate the soil fertility improvement. The eects of biochar amendment on soil
moisture retention, aggregate stability, pH, cation exchangeable capacity (CEC),
nutrient retention, priming eect, microbial growth, and enzymatic activities are
considered to be directly or indirectly related to the soil fertility enhancement.
In the following section, we will discuss the inuence of biochar on soil pH and
CEC in relation to nutrient availability and soil fertility enhancement.
The available pool of soil nutrients, which directly relates to soil fertility, is pH
dependent. Elevation of soil pH by biochar amendment has been well docu-
mented. Generally, the pH of biochar ranges from 5.9 to 12.3, with a mean value
of 8.9 (Ahmad et al., 2014). The alkaline nature of biochar is due to the existence of
inorganic alkali salts that are determined by the feedstock type and positively cor-
related with the pyrolysis temperature. Application of alkaline biochar to acidic
soils reduces soil acidity and increases soil pH, thereby enhancing the availabil-
ity of alkaline cations such as Mg
, Ca
, and K
(Atkinson et al., 2010; Glaser et al.,
2002; Major et al., 2010). At the same time, it decreases the exchangeable Al (Van
10 Igalavithana et al.
Zwieten et al., 2010; Yamato et al., 2006). Biochars have shown the liming eect
on acidic soils and the capability for buering soil pH (Kimetu et al., 2008; Van
Zwieten et al., 2010). As biochar persists over a long time in a soil, relative to other
liming materials, biochar could long-lastingly mediate soil pH while maintain-
ing soil pH in the optimal level for beer nutrient availability (Ahmad et al., 2014).
A meta-analysis conducted by Jeery et al. (2011) reported that alkaline
biochar addition could increase the pH of acidic soils by 0.1 to 0.2 units. Van
Zwieten et al. (2010) and Hossain et al. (2010) even demonstrated that designed
biochars, if applied at high rates, could enhance the pH of acidic soils by 2.0
units. Paper mill wastes (enhanced solids reduction and clarier sludge) and
waste wood chips were used by Van Zwieten et al. (2010) to produced biochar at
550°C (Table 2), whereas Hossain et al. (2010) have used wastewater sludge as the
feedstock and produced biochar at the same temperature. Indeed, the capacity
of biochar for elevating soil pH depends on the application rate and its chemical
properties (Table 2). It can also be deduced from Table 2 that an elevated soil
pH is generally accompanied with an increased primary nutrient availability of
the soil. The liming eects of alkaline biochar and the concurrently introduced
mineral nutrients (e.g., Ca
, Mg
, and K
) are possibly the main mechanism
through which biochar amendment increases the crop productivity of acidic
soils. However, depending on the feedstock type and pyrolysis temperature, the
liming capacity of biochar varies with its acid-neutralizing capacity (Ahmad et
al., 2014). In most reported studies, alkaline biochar has been applied to acidic
soils. Limited information is known about biochar application to alkaline soils
in the arid and semiarid regions. Recently, Liu and Zhang (2012) showed that
application of alkaline biochar (pH 8.4) produced from Chinese pine (Pinus spp.)
and locust (Robina spp.) at 600°C to alkaline soils (pH 8.79.0) decreased soil pH
by up to 0.2 units aer 4 mo of incubation. The pH reduction was enhanced with
increasing biochar application rate and incubation time, most likely a result of
the production of acidic materials from biochar oxidation. These results implicate
that biochars containing high labile C contents (generally produced at low
pyrolysis temperature of <400°C) may be applied to alkaline and calcareous soils
to facilitate the nutrient availability. Furthermore, low-temperature-produced
biochars typically contain the signicant amounts of biodegradable materials that
would stimulate microbial activity. Application of biochar with organic maer
enhances the biochar oxidation and forms more surface carboxylic functional
groups (Cheng et al., 2006). Meanwhile, biochar promotes the oxidation of organic
maer and could produce acidic compounds (Zavalloni et al., 2011). It is, therefore,
suggested to use biochar–organic maer mixture in alkaline and calcareous soils
of arid regions for soil fertility.
Cation Exchangeable Capacity and Nutrient Retention
Plant nutrients can be easily washed o from the soils having low nutrient-reten-
tion capacities (Giardina et al., 2000). Biochar as a soil additive can increase soil
CEC and improve the ability of soils to retain nutrients. Anthrosols rich in bio-
char were found to possess the greater values of CEC than the adjacent soils
(Liang et al., 2006). The high CEC was aributed to oxidation of biochar particles
and adsorption of highly oxidized organic maer to biochar surfaces (Glaser et al.,
2003; Lehmann et al., 2005; Liang et al., 2006). Biochar surfaces are generally nega-
tively charged, facilitating the electrostatic araction of cations. Therefore, higher
The Eects of Biochar Amendment on Soil Fertility
Table 2. pH, cation exchange capacity (CEC), and primary nutrients in biochar-treated soils and controls.
pH CEC Primary nutrients in soil
Biochar Soil Biochar Soil Total N Total P Exchangeable K Total K
g kg
mg kg
mg kg
32.6% enhanced solids
reduction sludge + 18.8%
clarifier sludge + 48.6%
waste wood chips†
550 2% (w/w) 9.4 5.9 9.0 10.5 0.66
19.5% enhanced solids
reduction sludge + 11.2%
clarifier sludge + 69.3%
waste wood chips†
550 2% (w/w) 8.2 5.4 18 7.57 0.14
0 4.2 4.03 0.11
Wheat straw‡ 350–550 10 t ha
6.7 2.12
40 t ha
6.9 2.48
0 6.5 1.78
Miscanthus ´ giganteus§
600 1% (w/w) 10.2 5.7 29.47 5.45 17 116
5% (w/w) 6.2 5.94 21 317
10% (w/w) 6.7 6.16 34 646
0 5.6 5.54 16 42
† Van Zwieten et al. (2010).
‡ Zhang et al. (2010).
§ Houben et al. (2013).
12 Igalavithana et al.
cation retention can be expected from biochar application. This is in agreement
with the ndings of DeLuca et al. (2009) and Lehmann et al. (2003) who found the
enhanced soil nutrient availability and plant uptakes of P, K, Ca, Zn, and Cu with
respect to biochar application, and soil N also showed reduced leaching losses.
Long-term natural oxidation of biochar can assist in developing surface func-
tional groups, resulting in increased surface negative charges or reduced surface
positive charges (Cheng et al., 2008). Thus, it facilitates biochar-containing soils
to retain exchangeable bases. However, phosphate via anion retention capacity
may be decreased because of the increase in surface negative charge. On the other
hand, DeLuca et al. (2009) claried that reduced soluble forms of Al and Fe might
be a main factor for the enhanced P availability of biochar treated soils.
Soil CEC can be signicantly increased by adding biochars with high CEC
values (Table 2). Microbial activity generally increases with increasing soil CEC
as a result of high availability of nutrients, further promoting soil fertility. The
feedstock type and the pyrolysis conditions greatly aect the CEC value of
biochar products. In general, biochars produced at higher pyrolysis temperatures
exhibit higher CECs relative to the same feedstock-derived products from lower
pyrolysis temperatures (Guo and Rockstraw, 2007). Jiang et al. (2014) reported
that the biochars produced from nonlegume straws had a higher CEC than those
produced from legume straws. Aging is another factor that aects the biochar
CEC (Hale et al., 2011). Freshly prepared biochars usually possess minimal
CEC. Aer aging in soil by exposing to oxygen and moisture, and undergoing
spontaneous oxidation reactions, the biochar can signicantly increase its CEC.
Crop Growth Enhancement with Biochar
Biochar application in agricultural elds as a soil amendment has been shown
to promote plant growth in common cropping systems. Moreover, a long-life-
span biochar carries extraordinary agronomic benets for crop productivity
in a sustainable manner (Chan et al., 2008). Generally, the increased crop yield
and nutrients uptake might be mainly due to direct nutrient additions from the
applied biochar containing K, P, Ca, Zn, and Cu (Lehmann et al., 2003). Bagasse
biochar addition decreased soil bulk density and increased soil water retention,
thereby subsequently increasing yields and sugar content of sugarcane (Saccha-
rum ocinarum L.) (Chen et al., 2010). Zheng et al. (2010) also found that biochar
addition to a soil stimulated the above- and ground-biomass yields of maize.
Under nursery conditions, Dharmakeerthi et al. (2012) found that application of
rubber wood biochar to a soil at 2% (w/w) signicantly improved the growth of
Hevea [Hevea brasiliensis (Willd. ex A. Juss.) ll. Arg.] plants with only N and Mg
fertilizers. However, a few researchers reported negative impacts of biochar soil
amendment on crop growth (Asai et al., 2009; Kishimoto and Sugiura, 1985). The
negative observations can be explained by the following reasons: (i) decreased
N availability as a result of the high C/N ratios of biochars and (ii) increased pH
of neutral to alkaline soils (Kishimoto and Sugiura, 1985; Lehmann et al., 2003;
Tryon, 1948). Enhancement of plant growth would be more signicant when bio-
char is applied to acidic, highly leached, infertile soils.
Crop responses to biochar in a soil depend on the biochar type, plant species,
and soil type. Table 3 clearly illustrates that dierent types of biochars applied
at similar rates were not equally eective in increasing the crop yield. Houben
The Eects of Biochar Amendment on Soil Fertility
Table 3. Crop productivity improvements with the application of biochar to soil.
Yield increment
over the control
32.6% enhanced solids reduction sludge + 18.8% clarifier sludge +
48.6% waste wood chips†
2% (w/w) Wheat 33.33
19.5% enhanced solids reduction sludge + 11.2% clarifier sludge +
69.3% waste wood chips†
32.6% enhanced solids reduction sludge + 18.8% clarifier sludge +
48.6% waste wood chips†
Soybean 50.00
19.5% enhanced solids reduction sludge + 11.2% clarifier sludge +
69.3% waste wood chips†
Commercial biochar from wood residues (Teak [Tectona grandis L.] and
rosewood [Pterocarpus macrocarpus Kurz])‡
4 t ha
Rice cultivar: IR55423–01 (Apo: improved
8 t ha
16 t ha
4 t ha
Rice cultivars: Vieng (a traditional cultivar) −28.57
8 t ha
16 t ha
Wheat straw 350–550°
10 t ha
Rice (Oryza sativa L. ‘Wuyunjing 7’) 11.62
40 t ha
Lantana camara L.¶ 4 t ha
Wheat 11.42
Unknown# 15 g kg
French bean (P. vulgaris var. Anupama) 142.74
Fraxinus excelsior L., Fagus sylvatica L., and Quercus robur L., 450°C††
25 t ha
Dactylis glomerata 71.05
50 t ha
† Van Zwieten et al. (2010).
‡ Asai et al. (2009).
§ Zhang et al. (2010).
¶ Masto et al. (2013).
# Saxena et al. (2013).
†† Jones et al. (2012).
14 Igalavithana et al.
et al. (2013) observed a positive relationship between rapeseed (Brassica napus L.)
productivity and application rate of Miscanthus straw-derived biochar to soil. Van
Zwieten et al. (2010) reported 33 and 67% increases in wheat and soybean [Glycine
max (L.) Merr.] yields, respectively, at 2% (w/w) application of biochar to a soil,
indicating dierent responses of dierent crops (Table 3).
Recent meta-analysis conducted by Liu et al. (2013) for the biochars eect on
crop productivity showed that the biochar application rate was practically <30 t
and it would increase crop productivity by 11% on average irrespective to the
type of biochar. However, crop responses diverged with the experimental con-
ditions. Biochar performed beer in promoting crop growth in pot experiments
than in eld experiments in dryland crops than in wetland crops (rice [Oryza
sativa L.]) in sandy soils than in the loam and silt textured soils and in acid soils
than in neutral soils (Liu et al., 2013). The meta-analysis conducted by Jeery et
al. (2011) revealed that if the pH value of a soil (e.g., strongly acidic, pH < 5.0 soils
with high acidity) was not signicantly elevated through biochar amendment as
a result of the limited liming capacity of the test biochars applied at inadequate
rates, crop responses were barely signicant. The authors further synthesized
that the main mechanisms for biochar amendment to promote crop growth may
be through a liming eect and an improved water holding capacity of the soil,
along with improved crop nutrient availability.In a eld trial growing durum
wheat (Triticum turgidum L.) in plots of pH 5.2 silt loam soils amended with 500°C
pyrolyzed wood charcoal at separately 30 and 60 t ha
, Vaccari et al. (2011) found
that biochar application increased the wheat biomass production and grain yield
by 30% relative to the unamended control treatment; the dierences between the
two amendment-rate treatments were not signicant. In addition, the biochar
eects on durum wheat growth remained into the next crop season. It suggested
that the eect of biochar amendment on crop productivity was long lasting and a
30 t ha
application rate was essentially sucient for wood charcoal amendment
in durum wheat production.
Jones et al. (2012) investigated the eects of biochar amendment on crop pro-
duction and soil quality in terms of C and N cycles. In a 3-yr study, the wood
biochar produced at 450°C was applied to crop eld having a sandy clay loam
soil at 0, 25, and 50 t ha
and fodder maize was grown in the rst year followed
by forage and hay grasses in the second and third year, respectively. The results
showed that biochar application promoted plant growth, increasing the foliar N
level in the second year and the aboveground biomass production in the third
year. However, the addition of biochar did not show any impact on dissolved
organic C and N, and NO
or NH
pools of the soil.
Based on the meta-analysis, Liu et al. (2013) emphasized that all biochars
did not show the same eect on crop production. For example, wood biochar,
crop residue biochar, manure biochar, and municipal waste biochar applied at
2% of soils improved crop productivity on average by 12.1, 2.6, 29.0, and 12.8%,
respectively. The authors further suggested that higher crop productivity could
be obtained by applying biochars produced at 350 to 550°C pyrolysis tempera-
tures (Liu et al., 2013). Ma et al. (2012) observed that wheat growth and N uptake
were stimulated signicantly following the biochar additions at the rates of 0.5, 1,
and 2% and the highest wheat growth and N uptake were recorded with biochar
produced at 750°C. In short, a biochar is an eective soil amendment to increase
N availability, decrease N loss, and improve the fertilizer use eciency.
The Eects of Biochar Amendment on Soil Fertility
The promotive eect of biochar amendment on crop growth is long last-
ing, extending over years (Zhang et al., 2012). The recalcitrant C in biochar could
remain in a soil for hundreds of years (Spokas, 2010); hence, the application of bio-
char to a soil is a long-term investment for agroecosystems.
Application of biochar to alkaline and calcareous soils in the arid and semi-
arid regions is generally limited as a result of its high pH value. Since these soils
are decient in organic maer and plant-available nutrients, the potential capac-
ity of biochar supplying nutrients could not be ruled out. However, appropriate
selection of suitable biochar is very important for improving the soil quality. For
instance, Ippolito et al. (2015) produced the designer biochar from mature switch-
grass at 350°C under N
gas supply and then activated with steam at 800°C. Low
pyrolysis temperature kept the acidic functional groups and reduced the ash con-
tent in biochar. Steam activation reduced the tar-like compounds in biochar and
led to enhance the biochar surface area; therefore, the biochar became more acidic
and possessed with high surface area (Borchard et al., 2012; Novak et al., 2009b).
They applied this biochar into the calcareous soil at the rates of 0, 1, 2, and 10%
(w/w) and monitored the changes of soil properties over 6 mo. Soil pH was not
decreased with any application rate because of a buering capacity of calcareous
soil. The contents of soil available Mn, Zn, and P increased slightly at the begin-
ning of the experiment; however, these contents gradually decreased with time as
a result of the formation of more stable minerals. The content of soil NO
–N also
decreased signicantly with increasing biochar application rate.
Low-temperature-produced biochars containing noncarbonized material
could be subjected to greater microbial activity, thus releasing nutrients to a soil
for plant uptake. Additionally, during the decomposition of noncarbonized frac-
tion, the value of soil pH goes down because of generated organic acids (Liu and
Zhang, 2012). Another important way of applying biochar to calcareous soils is
by compositing it with other organic or inorganic fertilizers. Zhang et al. (2012)
reported that the grain yield of maize grown in eld plots of a calcareous loamy
soil was increased by 7.3 to 15.8% by wheat-straw-derived biochar at 20 to 40 t ha
however, additional 300 kg N ha
fertilization increased its grain yield by 11.6 to
18.2%. Moreover, Lehmann et al. (2003) suggested that the application rate of bio-
char should be adjusted to meet the appropriate C/N ratio of soil for specic crop
production; otherwise, the N availability could be decreased under high biochar
application rates.
Studies have proved that biochar amendment has a great potential to enhance
soil fertility and crop yield by reducing soil acidity, increasing soil CEC and
nutrient retention, and improving plant nutrient availability. The enhancement,
however, is dependent on the biochar type, the application rate, and soil type.
The feedstock material and the production conditions of biochar are the main
factors manipulating its eect on soil fertility. Dependent on the nature of the
biochar, amendment rate, and original fertility of the soil, crop responses to
biochar amendment can be positive, negative, or neutral. Many of the reported
investigations were performed for short time periods; however, long-term eld
experiments are essential to validate the eects of biochar application on soil
fertility and crop growth and the related mechanisms. Overall, the benets and
16 Igalavithana et al.
capabilities of biochar as a soil rehabilitator and ameliorator are conrmed with-
out doubt. The long lifespan of biochar in a soil is a superior character of this soil
amendment over other organic amendments. Hence, production and use of bio-
char from organic residues is an eective approach for long-term maintenance
and improvement of soil fertility.
This study was supported by the National Research Foundation of Korea (NRF)
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... Biochar is a carbon-based solid product produced from agricultural and food processing waste, manure, or sewage sludge Domingues et al., 2017a;Lee et al., 2019;Qin et al., 2019;Kumar et al., 2021;Marinos et al., 2022;Rangabhashiyam et al., 2022) and it is derived from the heat-treatment of these biomasses under limited or absent oxygen supply. Biochar is known to affect atmospheric carbon sequestration by working as a CO 2 sink (Domingues et al., 2017b), to favour water and nutrient retention and for improving soil quality (Igalavithana et al., 2015),and fertility (Ding et al., 2016) and health also for stimulating soil microbiota (Gujre et al., 2021;He et al., 2021a). Moreover, biochar has the capacity to trap important toxic elements (i.e. ...
... At the European level, biochar must be characterized following the European Biochar Certificate (European Biochar Foundation (EBC), 2021) and at international level following the IBI directory (International Biochar Initiative, 2015). All the intrinsic physical, chemical and biological properties of biochar depend upon the feedstock material and productions technique (Igalavithana et al., 2015;Xie et al., 2015;Yargicoglu et al., 2015;Marmiroli et al., 2018;Lu et al., 2020). This study aims to provide a valuable investigation of correlation between the properties of biochar and feedstock material/production conditions, focusing on gasification temperatures which can influence biochar structure and quality (Titiladunayo et al., 2012;Song et al., 2014;Ippolito et al., 2020;Natasha et al., 2021): a deeper understanding of biochar's properties can help organic agriculture towards increasing sustainability and smarter improvement (Phillips et al., 2020). ...