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Biochar
https://doi.org/10.1007/s42773-020-00067-x
REVIEW
Feedstock choice, pyrolysis temperature andtype inuence biochar
characteristics: acomprehensive meta‑data analysis review
JamesA.Ippolito1 · LiqiangCui1,2· ClaudiaKammann3· NicoleWrage‑Mönnig4· JoseM.Estavillo5·
TeresaFuertes‑Mendizabal5· MariaLuzCayuela6· GilbertSigua7· JeNovak7· KurtSpokas8· NilsBorchard9
Received: 2 June 2020 / Accepted: 19 August 2020
© The Author(s) 2020
Abstract
Various studies have established that feedstock choice, pyrolysis temperature, and pyrolysis type influence final biochar
physicochemical characteristics. However, overarching analyses of pre-biochar creation choices and correlations to biochar
characteristics are severely lacking. Thus, the objective of this work was to help researchers, biochar-stakeholders, and prac-
titioners make more well-informed choices in terms of how these three major parameters influence the final biochar product.
Utilizing approximately 5400 peer-reviewed journal articles and over 50,800 individual data points, herein we elucidate the
selections that influence final biochar physical and chemical properties, total nutrient content, and perhaps more importantly
tools one can use to predict biochar’s nutrient availability. Based on the large dataset collected, it appears that pyrolysis
type (fast or slow) plays a minor role in biochar physico- (inorganic) chemical characteristics; few differences were evident
between production styles. Pyrolysis temperature, however, affects biochar’s longevity, with pyrolysis temperatures > 500°C
generally leading to longer-term (i.e., > 1000years) half-lives. Greater pyrolysis temperatures also led to biochars containing
greater overall C and specific surface area (SSA), which could promote soil physico-chemical improvements. However, based
on the collected data, it appears that feedstock selection has the largest influence on biochar properties. Specific surface area
is greatest in wood-based biochars, which in combination with pyrolysis temperature could likely promote greater changes
in soil physical characteristics over other feedstock-based biochars. Crop- and other grass-based biochars appear to have
cation exchange capacities greater than other biochars, which in combination with pyrolysis temperature could potentially
lead to longer-term changes in soil nutrient retention. The collected data also suggest that one can reasonably predict the
availability of various biochar nutrients (e.g., N, P, K, Ca, Mg, Fe, and Cu) based on feedstock choice and total nutrient
content. Results can be used to create designer biochars to help solve environmental issues and supply a variety of plant-
available nutrients for crop growth.
Keywords Biochar· Total elemental analysis· Plant-available elemental analysis· Physico-chemical characteristics· Meta-
analysis
1 Introduction
Biochars are carbon (C) rich materials typically pro-
duced via biomass pyrolysis at relatively low temperatures
(300–700°C) under limited oxygen conditions (Lehmann
and Joseph 2009). Biomass, the feedstock for biochar
creation, is typically derived from agricultural and forestry
waste products, municipal waste, green and food waste. The
creation of biochar from these products places C into a recal-
citrant form which could last hundreds to over thousands
of years (Spokas 2010; Kuzyakov etal. 2014; Wang etal.
2016), suggesting that biochar could aid in climate change
mitigation (Tripathi etal. 2016) as one of the few nega-
tive greenhouse gas emission technologies with sustainable
development co-benefits (Smith etal. 2019).
Over shorter time scales (e.g., one to several years), bio-
chars have been proven to improve environmental quality by
sorbing heavy metals and organic contaminants (e.g., Sigua
etal. 2019; Cui etal. 2019; Novak etal. 2019a), positively
Electronic supplementary material The online version of this
article (https ://doi.org/10.1007/s4277 3-020-00067 -x) contains
supplementary material, which is available to authorized users.
* Nils Borchard
nils.borchard@luke.fi
Extended author information available on the last page of the article
Biochar
1 3
affect soil water relations (e.g., Lentz etal. 2019; Kammann
etal. 2011), reduce greenhouse gas emissions (e.g., Fuertes-
Mendizábal etal. 2019; Borchard etal. 2018; Jeffery etal.
2016), and improve crop growth (e.g., Laird etal. 2017;
Novak etal. 2016; Liu etal. 2013). Although creation of
biochars for the above purposes may seem simply based on
feedstock selection, biochar production for environmental
improvements is complex. Feedstock selection, pyrolysis
temperatures, and pyrolysis types can all greatly influ-
ence the final biochar product (Cao etal. 2017; Cha etal.
2016). Thus, increasing the understanding of the interaction
between feedstock, pyrolysis temperature, and production
technique (i.e., either fast or slow pyrolysis) would help bio-
char stakeholders make more well-informed choices for its
use.
In terms of feedstock, understanding how initial feedstock
properties influence final biochar characteristics is impor-
tant. Feedstocks have been shown to play a major role in cre-
ating biochars with distinctly different chemical properties
(Funke and Ziegler 2010; Novak etal. 2019b). In relative
terms, wood-based biochars contain more C and lower plant-
available nutrients, manure-based biochars show opposite
trends, and grass-based biochars typically fall somewhere in
between woody and manure biochars (Ippolito etal. 2015).
However, these properties may be altered by pyrolysis tem-
perature and pyrolysis technique used for biochar creation.
Pyrolysis temperature and production technique play key
roles in creating biochars with various chemical and struc-
tural properties. For example, nutrient availability changes
drastically as pyrolysis temperature is increased (Clough
etal. 2013; Nguyen etal. 2017). Specifically, with increas-
ing pyrolysis temperature one typically observes increasing
biochar C, P, K, Ca, ash content, pH, specific surface area
(SSA), and decreasing N, H, and O content (e.g., Weber and
Quicker 2018; Ippolito etal. 2015). These biochar character-
istics are driven by forcing C into more condensed, recalci-
trant forms, the creation of oxide/carbonate mineral phases
(e.g., P, K, Ca) leading to greater ash content and higher pH,
and the loss of N, H, and O via volatilization. Volatilization
losses further concentrate other remaining elements (Kim
etal. 2012; Kinney etal. 2012). When choosing pyrolysis
type, in general slow pyrolysis tends to produce biochars
with greater N, S, available P, Ca, Mg, surface area, and cat-
ion exchange capacity (CEC) as compared to fast pyrolysis.
The above aspects of biochar creation have led individual
researchers to pay attention to biochar end-product proper-
ties. Current literature contains an untapped wealth of infor-
mation regarding feedstock, pyrolysis type and temperature
choices. However, there is some uncertainty in the literature
with a vague description of how biochar characteristics are
influenced by feedstock choice, pyrolysis type, and tempera-
ture employed. Thus, we chose to provide in this review a
clearer picture by synthesizing existing literature to create
a true comprehensive review of biochar properties based
on feedstock choice, pyrolysis temperature, and pyrolysis
type. Presenting this type of data is paramount for improv-
ing our understanding of the factors used to create biochar
and characteristics within the final product. Establishing
these comparisons should aid biochar practitioners and
stakeholders in making well-informed decisions for biochar
use as amendments in soils and for environmental mitiga-
tion purposes in mine spoils or metal contaminated soils.
The objective of this work was focused on comprehensively
reviewing how different feedstocks, pyrolysis temperatures,
and production techniques affect biochar physicochemical
properties, total and available nutrient content, other char-
acteristics, and what these properties indicate when biochar
is used for agricultural benefits.
2 Materials andmethods
Data were compiled from literature that compared biochar
macro- and micro-nutrient concentrations, pH, SSA, electri-
cal conductivity (EC), cation and anion exchange capacity
(CEC and AES, respectively), calcium carbonate equivalent
(CCE), total pore volume (PV), average particle size (APS),
and ash content under different biochar production tem-
peratures and types. The literature examined was published
between January 2009 through December 2016, searching
electronic databases including Web of Science™ and Sco-
pus™ for the keyword “biochar”. Overall, 5394 publica-
tions presented reliable and valid physicochemical biochar
properties which were fed into a database obtaining 50,851
individual observations (see Supporting Table1 for refer-
ences cited). We chose not to collect data from 2016 onwards
because of the overwhelming points already collected from
between 2009 and 2016.
Data from the selected peer-reviewed literature should
provide the reader with overarching changes in biochar phys-
icochemical characteristics, and thus where appropriate, spe-
cific inferences were made based on logical comparisons
between biochar properties. The data are presented by feed-
stock choice, pyrolysis temperature, and pyrolysis type (i.e.,
either fast or slow pyrolysis). The data are further separated
into nutrient availability based on feedstock choice, in order
to provide biochar producers with guidance for preparing
biochars to meet plant nutrient needs.
2.1 Feedstock choice
Wood feedstock data were derived from literature reporting
chipped, shaved, bark, peeled, and other similar wood-based
biochar products. All wood data were initially combined into
one category because it has been previously shown that,
in general, hardwood and softwood biochars have similar
Biochar
1 3
characteristics (Ippolito etal. 2015). However, this concept
was revisited in the current manuscript due to the larger
dataset involved as compared to Ippolito etal. (2015); wood
feedstock data were further separated into either hardwood-
(including bamboo) or softwood-derived biochars for spe-
cific nutrient availability analysis presented below.
Crop waste data included biochars made from a variety
of agricultural crop residues, such as corn, wheat straw, rice
straw and husk, potato, soybean, sugarcane and bagasse, cot-
ton, grape, orange, peanut, and rape seed/straw. Based on the
dataset collected, the major crop wastes utilized to produce
biochars were corn, wheat straw, and rice straw/husk, and,
therefore, this datum was further categorized for derivation
of specific nutrient availability analyses presented below.
Other results from grasses were compiled from species
that were typically, but not entirely, used for bioenergy,
industrial production, or fodder. This dataset included grassy
and leafy species such as Miscanthus (Miscanthus spp.),
switchgrass (Panicatum virgatum), giant red (Arundo spp.),
common reed (Phragmites australis), Typha (Typha spp.),
water hyacinth (Eichhornia crassipes), and other minor grass
species. Opposite of other feedstocks, this dataset was not
further refined for nutrient availability analyses due to a lack
of dataset robustness.
The manures/biosolids dataset included biochars made
from papermill sludges, cattle and dairy manure, horse
manure, swine manure, poultry manure and litter, and bio-
solids. Among all feedstocks, poultry manure, pig manure,
cattle and dairy manure, and biosolids were the most com-
mon feedstocks employed to produce biochars. Thus, bio-
chars made from these four feedstock choices were further
separated for defining their specific nutrient availability as
presented below.
2.2 Pyrolysis temperature andtype
For ease of discussion, pyrolysis temperatures were grouped
as follows: < 300, 300–399, 400–499, 500–599, 600–699,
700–799, and > 800°C. A similar approach was utilized by
Ippolito etal. (2015) when describing changes in biochar
properties as affected by pyrolysis temperature. Pyrolysis
type was simply separated into either fast or slow pyrolysis
as indicated in the manuscripts evaluated.
2.3 Data interpretation
All individual data comparisons (e.g., total C, total O,
total, H, etc.) between fast or slow pyrolysis were analyzed
using a t test at α = 0.05. All individual data comparisons
between various feedstocks or all pyrolysis temperatures
were analyzed using analysis of variance (ANOVA). The
Shapiro–Wilk and Levene’s tests were also used to ana-
lyze for assumptions of normality and equal variance,
respectively. In cases where assumptions were violated,
data were transformed using either log10, natural log, or a
square root function and re-analyzed for meeting assump-
tions of normality and equal variance. Tukey’s Honestly
Significant Difference pairwise comparisons were utilized
to discern differences between various feedstocks or pyrol-
ysis temperatures for individual (non-)transformed data at
α = 0.05. The non-transformed data means are presented
below.
For more specific data interpretations, we utilized the
entire dataset, or specific feedstock subsets, along with
SigmaPlot 13.0 for graphical interpretations. Within Sig-
maPlot 13.0, we utilized regression fitting functions (lin-
ear, quadratic, exponential rise or decay, and exponential
growth equations) that best fit (e.g., best R2 values and
greatest p values) the presented data. We avoided data
interpretations that made no logical sense (e.g., sigmoi-
dal equations, sinusoidal equations, etc.) yet may have had
greater R2 values than regression equations that made logi-
cal, interpretable sense. When necessary, Pearson’s cor-
relations were utilized to help drive discussion for biochar
utilization from specific feedstock choices.
3 Results anddiscussion
3.1 Biochar physicochemical properties
3.1.1 Pyrolysis type
In terms of the general utility in choosing pyrolysis
type, slow pyrolysis uses a slow temperature heating
rate (0.01–2°Cs−1) as compared to fast pyrolysis, and if
adjusted properly can produce approximately equal ratios
of solid (i.e., biochar), gas, and liquid products (Sohi etal.
2009). Fast pyrolysis uses higher heating rates (> 2°Cs−1)
and shorter residence times (< 2s) during the thermal
conversion process, which provides greater bio-oil yields
(75%) but lower gas and biochar quantities (Qambrani
etal. 2017).
The influence of pyrolysis type on final biochar physico-
chemical properties is presented in Table1. Fast pyrolysis
led to biochars containing greater SSA and lower APS as
compared to slow pyrolysis, both parameters likely a func-
tion of the relatively small initial feedstock particle size uti-
lized during fast pyrolysis in fluidized bed reactor (Asadul-
lah etal. 2010). Slow pyrolysis led to biochars containing
greater CCE and ash content as compared to fast pyrolysis.
Increasing ash content and CCE are related, as acidic func-
tional groups are reduced (Novak etal. 2009) and mineral
hydroxide and carbonate phases are increased with increas-
ing ash content (Knicker 2007).
Biochar
1 3
3.1.2 General feedstock choice
Various feedstock sources also influence final biochar
properties (Table1). Wood-based biochars typically con-
tained a greater SSA and PV as compared to other feed-
stock choices. In terms of SSA and PV, this is a function
of reducing relatively large wood-based cell structures to
smaller pores and thus increasing overall SSA (Weber and
Quicker 2018; Downie etal. 2009) and, consequently, PV.
Increasing SSA and PV may also be associated with gas or
water volatilization processes during pyrolysis and the loss
of micro-molecule organic compounds, both of which can
create voids within the biochar matrix during pyrolysis (Guo
and Lua 1998). Contrarily, biochars produced from manures/
biosolids typically exhibited relatively low SSA, likely due
to the development of deformation, structural cracking or
micropore blockage (Ahmad etal. 2014; Lian etal. 2011),
along with less distinct porous structures in the feedstock as
compared to wood-based biochars.
Crop waste, other grasses, and manures/biosolids bio-
chars had a greater CEC and pH compared to wood-based
biochars. CEC can be generated during pyrolysis, as oxy-
genated surface and inorganic functional groups are formed
(Briggs et al. 2012). The increased CEC may also be
attributed to elevated pH leading to pH-dependent charge,
or insoluble precipitates present in the ash that act as reac-
tion sites (Ippolito etal. 2017). Others have related increased
CEC to increases in SSA (Kloss etal. 2012; Qambrani etal.
2017; Liang etal. 2006), yet the data presented here contra-
dict these findings. Concomitant with increasing ash content
from wood, to crop, to other leafy-grassy, to manures/biosol-
ids biochars, the CCE is also greatest in manure- biosolids-
derived biochars. This is likely due to oxide and hydroxide
mineral phase precipitation during pyrolysis (e.g., Ippolito
etal. 2012).
3.1.3 Pyrolysis temperature
Increasing pyrolysis temperature also influences final bio-
char composition (Table1).
Specific surface area increased with increasing pyrolysis
temperature, as shown by others (Domingues etal. 2017;
Luo etal. 2015). This is a function of shrinking the solid
matrix, causing relatively large pores to become smaller and
thus increasing overall SSA (Weber and Quicker 2018; de
Mendonça etal. 2017). Surface area has been previously
correlated with sorption/retention of nutrients and contami-
nants, while pore volume (which, in general increases with
Table 1 Basic biochar mean physicochemical properties (± standard error of the mean) based on pyrolysis type, feedstock source, and pyrolysis
temperature, on a dry weight basis
SSA specific surface area, CEC cation exchange capacity, AES anion exchange capacity, CCE calcium carbonate equivalent, PV total pore vol-
ume, APS average particle size, EC electrical conductivity, ND no data
Different letters within a column for either pyrolysis type, feedstock source, or pyrolysis temperature, indicate a significant difference (p < 0.05);
no letters present indicate no significant difference
SSA CEC AEC CCE PV APS Ash pH EC
(m2g−1) (cmolkg−1) (cmolkg−1) (%) (m3t−1) (nm) (%) (dSm−1)
Pyrolysis type
Fast 183 ± 17.3a 44.9 ± 3.62 4.90 ± 3.45 6.10 ± 1.12b 2.04 ± 0.81 52.3 ± 40.2b 19.2 ± 0.62b 8.7 ± 0.1 4.43 ± 0.50
Slow 98.6 ± 3.53b 48.1 ± 3.12 5.33 ± 1.51 11.2 ± 0.98a 3.66 ± 1.27 1190 ± 565a 22.0 ± 0.51a 8.7 ± 0.0 5.85 ± 1.58
Feedstock
source
Wood based 184 ± 11.4a 23.9 ± 1.87b 5.65 ± 1.80 9.04 ± 1.17b 7.01 ± 3.07a 74.6 ± 44.4a 10.2 ± 0.43d 8.3 ± 0.1b 6.20 ± 2.85
Crop wastes 98.2 ± 5.45b 56.3 ± 3.92a 4.51 ± 1.96 6.12 ± 0.97b 2.05 ± 0.91b 2320 ± 1,150a 21.1 ± 0.54b 8.9 ± 0.1a 5.72 ± 0.67
Other
grasses
63.4 ± 8.84b 63.3 ± 16.4a 2.05 ± 1.05 ND 3.36 ± 3.30a 268 ± 125a 18.0 ± 1.01c 8.9 ± 0.1a 5.20 ± 0.93
Manures/
Biosolids
52.2 ± 4.23c 66.1 ± 8.00a 7.77 ± 7.52 14.2 ± 1.56a 0.82 ± 0.30b 27.3 ± 12.5b 44.6 ± 0.97a 8.9 ± 0.1a 3.98 ± 0.41
Pyrolysis temp (oC)
<300 27.1 ± 5.45c 44.4 ± 6.43ab ND 7.16 ± 0.81 0.06 ± 0.02ab 8.16 ± 1.57 12.3 ± 0.96e 6.0 ± 0.1f 3.60 ± 1.00
300–399 57.2 ± 13.1c 52.8 ± 4.96a 3.65 ± 0.35 9.17 ± 1.84 3.45 ± 1.71ab 2340 ± 2140 17.8 ± 0.87d 7.8 ± 0.1e 5.72 ± 2.15
400–499 108 ± 13.7b 35.0 ± 3.85b ND 9.08 ± 1.67 1.18 ± 0.61b 78.0 ± 69.2 19.0 ± 0.82d 8.5 ± 0.1d 2.77 ± 0.28
500–599 97.2 ± 8.48b 56.4 ± 5.69a 3.38 ± 1.22 10.1 ± 1.29 4.68 ± 2.47ab 1140 ± 938 23.2 ± 0.74c 9.0 ± 0.1c 8.05 ± 3.82
600–699 178 ± 8.71a 33.7 ± 4.88b ND 9.50 ± 3.82 1.77 ± 1.04ab 2000 ± 1360 23.5 ± 1.09bc 9.5 ± 0.1b 4.85 ± 0.92
700–799 204 ± 14.1a 53.0 ± 9.31a 5.27 ± 3.66 12.9 ± 2.65 8.87 ± 5.99a 9.19 ± 1.50 26.6 ± 1.56ab 10.0 ± 0.1a 4.29 ± 0.96
>800 208 ± 22.2a 85.3 ± 27.7a 8.83 ± 5.14 19.6 ± 16.2 0.09 ± 0.02ab 8.45 ± 1.89 28.5 ± 2.31a 9.9 ± 0.1a 6.44 ± 1.41
Biochar
1 3
pyrolysis temperature) is assumed to affect water avail-
ability and soil aeration (Ajayi and Horn 2016; Qambrani
etal. 2017). Increasing pyrolysis temperature also clearly
increased biochar ash content and pH, as solid phase hydrox-
ide and carbonate phases increase within the ash, causing pH
values to concomitantly increase. This concept is described
in more detail in the biochar physicochemical correlations,
Sect.3.1.4 below.
3.1.4 Biochar physicochemical correlations
Correlations between biochar pH and ash content, pyrolysis
temperature and pH, and pyrolysis temperature and SSA,
based on all pertinent data collected, are shown in Fig.1.
Increasing biochar pH generally correlates with an increase
in ash content (Fig.1a) as also shown by Lehmann (2007).
This correlation could be useful for practitioners design-
ing pyrolysis systems for creating biochars needed for soil
liming purposes (e.g., in acidic or acid generating mines
soils; Ippolito etal. 2017; Sigua etal. 2019; Godlewska etal.
2017). Increasing pyrolysis temperature caused biochar pH
to increase (Fig.1b), likely due to loss of acidic functional
groups (Novak etal. 2009) and the formation of Ca- Mg-,
Na-, and K-bearing oxide, hydroxide, and carbonate min-
eral phases (Cao and Harris 2010) that can raise the pH to
ranges extending from 9.9 to 13 (aqion 2019). Ngatia etal.
(2017) also illustrated biochar pH correlations to alkali earth
elements such as those mentioned above. Increasing pyroly-
sis temperature also increased biochar specific surface area
(Fig.1c), as observed by others (e.g., Lu etal. 2012; Hass
etal. 2012). Increasing specific surface area appears to be
a function of decreases in cell pore diameter (Ahmad etal.
2012), along with tar, oils, H and O removal with increasing
pyrolysis temperatures (Kloss etal. 2012; Chen etal. 2008).
4 Biochar total elemental analysis
4.1 Pyrolysis type, general feedstock choice,
andpyrolysis temperature
Changes in biochar total macro-elements as a function of
pyrolysis type, general feedstock choice, and pyrolysis tem-
perature, are shown in Table2. Fast pyrolysis favored total
S, K, Ca, and Mg content as compared to slow pyrolysis.
However, in general, pyrolysis type had little influence on
total macro-elements as compared to feedstock choice and
temperature; total macro-elements have been previously
correlated with feedstock choice and pyrolysis temperature
(Zhang etal. 2017b). In terms of feedstock choice, wood-
based feedstocks led to greater C content over other feed-
stock choices. If C storage was a goal, wood-based biochars,
especially with high aromatic-C character (Wang etal. 2016)
and low O/C and H/C ratios (Spokas 2010) should be applied
to soils. Grass-based feedstocks contained relatively elevated
K and Ca content as compared to other feedstocks, while
manures/biosolids-based feedstocks contained the great-
est N, S, P, Ca, and Mg concentrations over biochars from
other feedstocks, similar to findings by Amoah-Antwi etal.
(2020). At first glance, it appears that if N–P–K fertilizer
use was a goal, grass- or manure/biosolids-based biochars
could be utilized (Lin etal. 2017; Gondek and Mierzwa-
Hersztek 2016; Wang etal. 2013; Brewer etal. 2012); this
concept is revised within the context of specific feedstock
choices in Sect.6.5 below. In terms of pyrolysis temperature,
increasing temperature increased C, P, Ca, and Mg concen-
trations, also as suggested by Chen etal. (2016). Specifics,
with respect to biochar total elemental analysis, are also
discussed below.
4.2 Carbon, hydrogen, andoxygen
For biochars, total C content is often elevated as most feed-
stocks contain appreciable C concentrations, yet feedstock
choice significantly affects biochar C content (Table2).
Wood-based biochars contained greater C as compared to
biochars made from other feedstock choices, simply due to
a lack of other elements (e.g., N, S, P, K, Ca, and P) leading
to a smaller C-dilution effect in wood-based biochars.
Biochar C compounds can be grouped into relatively
condensed (i.e., stable, non-mineralizable) aromatic C com-
pounds, compared to easier-degradable, micro-molecular
or water-soluble C (Lehmann etal. 2011). During pyroly-
sis, dehydration, cleavage, and polymerase reactions cause
easily degradable C compounds to be restructured, while
other elements may be lost to volatilization, and thus overall
biochar total C content increases with increasing pyrolysis
temperature (Weber and Quicker 2018; Antal and Grønli
2003; Table2). Biochar C bioavailability is temperature
dependent, with higher pyrolysis temperatures related to
larger non-labile C fractions (Nelissen etal. 2012). Greater
pyrolysis temperatures tend to create relatively stable, aro-
matic C compounds and silicate–carbon complexes that
are usually regarded as recalcitrant to microbial oxidation
(Guo and Chen 2014). When placed in soils, recalcitrant C
could last hundreds to thousands of years, and as such, bio-
char land application may play a role in climate mitigation
(Schmidt etal. 2019; Werner etal. 2018; Woolf etal. 2018;
Bolan etal. 2012).
Increasing pyrolysis temperature significantly increased
biochar C content via volatilization losses of other elements,
especially H and O (Table2). As pyrolysis temperature
increases, water, organic surface functional groups, and
tars are lost, all of which contain H and O atoms (Ahmad
etal. 2014; Cantrell and Martin 2012). During pyrolysis,
O is released at a greater rate than H, with the final biochar
Biochar
1 3
Fig. 1 The relationship between
a pH and ash content, b
pyrolysis temperature and pH,
and c pyrolysis temperature and
specific surface area
pH
246810 12 14
Ash Content (%)
0
20
40
60
80
100a
Ash Content (%) = 0.4075 e(0.4075*pH)
R2 = 0.098
Pyrolysis Temperature (oC)
0200 400 600800 1000 1200
pH
2
4
6
8
10
12
14
pH = 10.49(1 - e[-0.004*Pyrolysis Temp]); R2 = 0.329
b
Pyrolysis Temperature (
o
C)
100200 300 400500 600700 800900
1000
Specific Surface Area (m
2
/g)
0
100
200
300
400
500
600
700
800
900
1000
c
SSA = -30.875 + 0.151(pyrol. temp) + 0.0002(pyrol. temp)2
R2 = 0.147
Biochar
1 3
product characterized by a decrease in H/C-ratio and con-
taining low oxygen-content. Thus, understanding the ratios
between H, C, and O, as depicted in the Van-Krevelen dia-
gram, may be useful for discerning biochar longevity in soil
systems (Schimmelpfennig and Glaser 2012; Spokas 2010).
Specifically, the atomic ratios of O/C to H/C have been
used to describe the pyrolysis carbonization process (Weber
and Quicker 2018), and more specifically to describe several
key biochar environmental longevity factors as a function
of these ratios. Figure2 illustrates how the O/C and H/C
Table 2 Biochar mean total macro-element concentrations (± standard error of the mean) based on pyrolysis type, feedstock source, and pyroly-
sis temperature, on a dry weight basis
Different letters within a column for either pyrolysis type, feedstock source, or pyrolysis temperature, indicate a significant difference (p < 0.05);
no letters present indicate no significant difference
C H O N S P K Ca Mg
(%) (gkg−1)
Pyrolysis type
Fast 60.6 ± 0.47 3.37 ± 0.08 19.1 ± 0.38 1.63 ± 0.06 0.85 ± 0.09a 14.2 ± 0.72 46.8 ± 4.69a 44.3 ± 4.01a 43.5 ± 12.1a
Slow 60.8 ± 0.34 3.36 ± 0.09 18.4 ± 0.29 1.63 ± 0.04 0.55 ± 0.04b 12.0 ± 0.56 22.8 ± 1.33b 29.1 ± 1.68b 5.73 ± 0.30b
Feedstock
source
Wood based 70.5 ± 0.39a 3.38 ± 0.08b 17.7 ± 0.35bc 0.95 ± 0.03d 0.44 ± 0.07b 4.00 ± 0.46d 19.3 ± 2.62c 26.3 ± 2.60b 5.18 ± 0.84b
Crop wastes 61.4 ± 0.41c 3.28 ± 0.10b 18.1 ± 0.38b 1.54 ± 0.06c 0.39 ± 0.06b 8.00 ± 0.97c 40.9 ± 3.62b 20.7 ± 2.16b 6.06 ± 0.76b
Other
grasses
63.6 ± 0.72b 5.11 ± 0.50a 20.9 ± 0.74a 1.80 ± 0.14b 0.51 ± 0.21b 20.1 ± 6.08b 59.1 ± 12.2a 45.9 ± 12.0a 34.3 ± 12.7b
Manures/
Biosolids
41.6 ± 0.68d 2.73 ± 0.10c 16.5 ± 0.70c 2.42 ± 0.06a 0.89 ± 0.06a 25.7 ± 1.44a 25.3 ± 1.79c 52.7 ± 3.64a 57.8 ± 20.5a
Pyrolysis
Temp (oC)
<300 54.1 ± 0.59e 5.62 ± 0.25a 30.6 ± 0.60a 1.70 ± 0.10ab 0.43 ± 0.06 9.03 ± 1.32b 26.7 ± 5.24 25.0 ± 4.67bc 5.41 ± 0.88ab
300–399 58.0 ± 0.58d 4.70 ± 0.24b 23.6 ± 0.50b 1.81 ± 0.09a 0.44 ± 0.07 9.60 ± 1.56b 23.8 ± 4.04 23.0 ± 4.03c 43.0 ± 22.1a
400–499 62.3 ± 0.59bc 3.78 ± 0.19c 18.1 ± 0.41c 1.61 ± 0.08b 0.54 ± 0.08 10.1 ± 1.40b 32.7 ± 3.93 34.7 ± 4.80bc 9.61 ± 3.44ab
500–599 62.5 ± 0.59bc 2.83 ± 0.09d 14.2 ± 0.40d 1.34 ± 0.04c 0.54 ± 0.09 11.8 ± 1.36b 32.6 ± 3.93 28.6 ± 2.84c 24.3 ± 9.22b
600–699 65.8 ± 0.87a 2.31 ± 0.11e 12.7 ± 0.52e 1.32 ± 0.07c 0.60 ± 0.10 12.6 ± 2.29b 26.8 ± 4.93 36.0 ± 5.25abc 9.87 ± 3.51ab
700–799 64.7 ± 1.30ab 1.77 ± 0.12ef 13.0 ± 0.90de 1.26 ± 0.07c 0.63 ± 0.14 18.8 ± 2.49a 34.1 ± 8.68 43.0 ± 6.42ab 10.1 ± 4.25ab
>800 61.0 ± 1.82c 1.45 ± 0.12f 9.51 ± 1.00f 1.51 ± 0.26abc 0.36 ± 0.07 14.5 ± 3.68ab 34.5 ± 6.21 54.1 ± 11.8a 12.7 ± 3.50ab
Fig. 2 The relationship between
the molar ratio of O/C and H/C
and pyrolysis temperature (Van
Krevelen Diagram). Biochars
with O/C ratios < 0.2 are highly
stable (half-life > 1000years),
between 0.2 and 0.6 are moder-
ately stable (half-life between
100 and 1000years), and > 0.6
are relatively unstable (half-life
less than 100years; Spokas
2010). Biochars with H/C
ratios < 0.7 have greater fused
aromatic ring structures and
have been thermochemically
altered as compared to biochars
with H/C ratios > 0.7 (IBI 2015)
Biochar
1 3
ratios are altered as a function of pyrolysis temperature.
Spokas (2010) described biochars with O/C ratios: (a) < 0.2
as highly stable (half-life > 1000years); (b) between 0.2
and 0.6 as moderately stable (half-life between 100 and
1000years); and (c) > 0.6 as relatively unstable (half-life less
than 100years). Meanwhile, biochars with H/C ratios < 0.7
have greater fused aromatic ring structures and have been
thermochemically altered as compared to biochars with
H/C ratios > 0.7 (IBI 2015). Biochar H/C ratio has been
also found to be a key factor defining its N2O mitigation
potential, with biochars with H/C ratios < 0.3 being the most
effective (Cayuela etal. 2015). Based on the above infor-
mation and the data presented in Fig.2, biochars created
at pyrolysis temperatures > 600°C would typically be the
most recalcitrant when placed in soils and, at the same time,
among the most effective in mitigating N2O emissions (e.g.,
see: Borchard etal. 2018; Cayuela etal. 2015). Biochars
created between 500°C and 599°C would typically have
half-lives of 100–1000years when placed in soils (Pari-
yar etal. 2020). Biochars created at temperatures < 500°C
should have relatively lower half-lives when placed in soils
due to these materials only being partially thermochemically
altered (e.g., see Table2 in Spokas 2010). Similar observa-
tions have been found by Wolf etal. (2013) when combust-
ing various feedstocks over increasing temperatures. Com-
paring 128 observations from 24 studies, Wang etal. (2016)
found that the mean residence time of recalcitrant biochar C
pools was 556years. It is obvious that understanding pyroly-
sis temperature is important for the C sequestration potential
of biochar (Wang etal. 2016).
4.3 Total macro‑nutrient concentrations
Total N and P contents are comparable between slow and
fast pyrolysis, yet fast pyrolysis favored greater S, K, Ca,
and Mg concentrations (Table2). Feedstock choice dic-
tated total N content, in the order of wood biochars < crop
waste biochars < other grasses < manures/biosolids biochars.
Greater biochar N content is likely a function of greater
amino acids and proteins present in these materials (Tsai
etal. 2012). As suggested by Cantrell etal. (2012), this pro-
vides an advantage to greater N-containing biochars, such
as manures/biosolids biochars, to act as a fertilizer (e.g., N)
source. Contrarily, substantial N amounts are released as
gaseous forms (e.g., NO, N2O, NO2, NH3, N2; > 60%) with
increasing pyrolysis temperature as illustrated in Table2.
The same response, at the same temperatures, were reported
by Ippolito etal. (2015) when comparing pyrolysis tempera-
ture effects on N within a smaller biochar dataset (n < 100).
Feedstock choice has been noted to typically be the pri-
mary determinant on biochar total S content (Cheah etal.
2014); our meta-analysis results suggest that only manures/
biosolids-based biochars contain a greater S content as
compared to biochars made from other feedstocks (Table2).
Biochars containing elevated S content (e.g., manures; Sager
2012) have been shown to increase soil S bioavailability
(Blum etal. 2013). Relatively lower pyrolysis temperatures
(e.g., < 500°C) have been shown to keep total biochar S
content intact, yet greater temperatures can lead to gase-
ous S losses (Wang etal. 2013). However, data presented
in Table2 do not support this contention, showing no sig-
nificant difference in S content when varying pyrolysis
temperature. Pyrolysis temperature has also been shown
to be a main determinant of the S forms found in biochar.
Biochar S is mainly found in the organic fraction, such as
dibenzothiophene (59% of total sulfur) and dibenzyldisulfide
(14% of total sulfur), both of which can be bound to bio-
char-borne C (Cheah etal. 2014). As pyrolysis temperature
increases, these organic-S bearing phases are converted to
gases and lost (Carpenter etal. 2010). However, some S still
remains, likely in a recalcitrant form bound to Ca, K, Mg,
and Si at higher pyrolysis temperatures (> 800°C) (Knud-
sen etal. 2004). Perhaps S data presented in Table2 reflect
these recalcitrant S forms present with respect to increasing
pyrolysis temperature.
Biochar total P, K, Ca, and Mg concentrations are also
affected by feedstock choice (Table2). Manures/biosolids-
based biochars typically contained greater P, Ca, and Mg
concentrations, other grass-based biochars contained appre-
ciable K and Ca, while crop wastes- and wood-based bio-
chars contained the least quantities of these four elements.
In general, increasing pyrolysis temperature increased P and
Ca content, had mixed effects with respect to Mg content,
and had no significant impact on K concentration. The P,
K, Ca, and Mg feedstock and pyrolysis temperature find-
ings are likely a result of the initial elemental concentra-
tions present in various feedstock, as well as increasing ash
content with increasing pyrolysis temperature (Table1). As
ash content increases, Ca oxides, hydroxides, and carbonate
mineral phases precipitate, which leads to increased total
Ca concentration. In terms of P, as pyrolysis temperature
increases biochar P content typically increases as well (e.g.,
Ippolito etal. 2015), likely due to P forming associations
with carbonate phases. Although not strongly illustrated in
Table2, it is important to note that P-containing compounds
can volatilize above 760°C (Knicker 2007) causing total P
concentrations to decrease.
4.4 Total micro‑nutrient concentrations
Biochar total micro-nutrient concentrations, based on
pyrolysis type, feedstock source, and pyrolysis tempera-
ture, are shown in Table3. Only total Cu and Zn con-
centrations were affected by pyrolysis type, with fast
pyrolysis favoring greater concentrations over slow pyrol-
ysis. As with total macro-nutrient concentrations, total
Biochar
1 3
micro-nutrient concentrations were almost always sig-
nificantly greater in manures/biosolids-based biochars as
compared to other biochars. This is a function of manures/
biosolids feedstocks being fortified with micro-nutrients
that were not assimilated by livestock or as a waste prod-
uct from municipal/industrial sources (Sistani and Novak
2006). Thus, manure-based feedstocks contain inherently
greater micro-nutrient concentrations than other feed-
stocks. This could also be a function of ash content pre-
sent based on feedstock choice (Table1) creating micro-
nutrient oxide, hydroxide, and carbonate phases (e.g.,
CuO, Cu(OH)2, or CuCO3; Ippolito etal. 2012; Zhang
etal. 2017a). Likewise, increasing pyrolysis temperature
was shown to affect ash content (Table1), with relatively
similar connections to increasing micro-nutrient concen-
trations as a function of temperature (Table3).
Increasing micro-nutrient concentrations within bio-
chars suggest that they may be used as a micro-nutrient
fertilizer source. Chang etal. (2015) showed that a bio-
char containing Fe, Cu, Zn, Mn, and Co could potentially
be used to supply micro-nutrients to plants. More spe-
cifically, Sigua etal. (2016) utilized poultry litter biochar
addition to soil, observing an increase in extractable Fe,
Mn, Cu and Zn by 19, 46, 68 and 32%, respectively, as
compared to a control. Additionally, Zhao etal. (2018)
reported that although a pig manure biochar contained
excessive total Mn (1230mgkg−1), Cu (780mgkg−1),
and Zn (1010mgkg−1), their bioavailability was up to
several orders of magnitude lower.
5 Biochar available nutrient analysis
asafunction ofpyrolysis type, feedstock,
andpyrolysis temperature
Biochar total elemental analysis only describes maximum
nutrient concentrations present, which is not truly indicative
of the nutrient availability when applied to soil. Available
nutrients are those elements that may be readily absorbed
by plants, as determined using various extractants (e.g.,
water, 1M KCl, 0.01M CaCl2, DTPA, Morgan, Mehlich, or
Olsen extracting solutions). Although these extractants were
originally developed for use in soils, they have been widely
used with other soil amendments, including biochars and
in biochar-amended soils (e.g., Lehmann etal. 2003; Lentz
and Ippolito 2012). Changes in biochar available macro- and
micro-elements, as a function of pyrolysis type, feedstock
choice, and pyrolysis temperature, are shown in Table4.
5.1 Pyrolysis type
Out of the ten available nutrients studied, only two were
affected by pyrolysis type (Table4). Biochars created via
slow pyrolysis favored greater Fe and NO3 availability over
Table 3 Biochar mean total micro-element concentrations (± standard error of the mean) based on pyrolysis type, feedstock source, and pyroly-
sis temperature, on a dry weight basis
Different letters within a column for either pyrolysis type, feedstock source, or pyrolysis temperature, indicate a significant difference (p < 0.05);
no letters present indicate no significant difference
Fe Cu Zn B Mn Mo Co Cl
(gkg−1) (mgkg−1)
Pyrolysis type
Fast 7.74 ± 1.76 314 ± 77.0a 1140 ± 236a 20.7 ± 3.36 391 ± 47.1 4.37 ± 0.90 5.51 ± 0.89 3140 ± 527
Slow 7.53 ± 0.89 159 ± 15.9b 356 ± 32.4b 32.2 ± 5.78 383 ± 28.4 3.22 ± 0.75 4.02 ± 0.82 4390 ± 648
Feedstock source
Wood based 2.72 ± 0.37b 53.7 ± 10.4b 406 ± 144b 15.5 ± 3.13a 227 ± 24.2c 1.12 ± 0.37b 2.17 ± 0.67b 1060 ± 176c
Crop wastes 3.84 ± 0.52b 52.3 ± 14.8b 152 ± 43.9b 13.8 ± 2.65a 353 ± 58.6b 2.23 ± 0.65b 4.09 ± 1.52ab 4760 ± 848b
Other grasses 3.64 ± 0.86b 65.6 ± 21.0b 123 ± 24.5b 9.48 ± 4.31a 348 ± 62.5bc 0.80 ± 0.24b 0.48 ± 0.15b 3020 ± 1,560bc
Manures/Biosolids 21.6 ± 3.83a 565 ± 92.4a 946 ± 76.9a 57.7 ± 11.0b 584 ± 49.6a 6.96 ± 1.26a 6.27 ± 1.03a 10,050 ± 1,300a
Pyrolysis temp (oC)
<300 8.86 ± 2.91 873 ± 469a 431 ± 191a 55.7 ± 27.8ab 71.5 ± 37.5bc 0.38 ± 0.23 ND 2830 ± 779b
300–399 3.21 ± 1.27 177 ± 50.0b 260 ± 48.0b 33.2 ± 12.3ab 236 ± 45.9c 2.49 ± 1.36 1.88 ± 1.31 1810 ± 1,130b
400–499 8.36 ± 2.86 213 ± 44.5b 864 ± 256a 39.2 ± 8.51a 412 ± 64.2b 3.32 ± 1.17 4.28 ± 1.10 4190 ± 1,080ab
500–599 7.71 ± 1.93 176 ± 34.9b 392 ± 42.5b 26.8 ± 4.72ab 356 ± 32.2bc 3.59 ± 0.66 4.06 ± 1.03 3150 ± 848b
600–699 8.63 ± 2.38 169 ± 60.9b 414 ± 95.1b 23.2 ± 6.14ab 337 ± 54.4bc 0.75 ± 0.38 3.85 ± 1.22 6090 ± 1,280a
700–799 9.44 ± 3.38 301 ± 113b 343 ± 88.7b 21.0 ± 13.9ab 348 ± 87.9bc 4.60 ± 4.35 6.05 ± 3.95 2290 ± 780b
>800 9.38 ± 3.17 162 ± 45.4b 779 ± 215a 10.4 ± 5.14b 685 ± 206a ND†ND 4520 ± 1,520ab
Biochar
1 3
Table 4 Biochar mean available macro- and micro-element concentrations (extracted with either H2O, 1M KCl, 0.01M CaCl2, DTPA, Morgan, Mehlich, or Olsen extracting solutions; ± stand-
ard error of the mean) based on pyrolysis type, feedstock source, and pyrolysis temperature, on a dry weight basis
Different letters within a column for either pyrolysis type, feedstock source, or pyrolysis temperature, indicate a significant difference (p < 0.05); no letters present indicate no significant differ-
ence
P K Mg Ca Fe Mn Zn Cu NO3−NH4+
(mgkg−1)
Pyrolysis type
Fast 404.0 ± 145 4490 ± 720 450 ± 90.6 1670 ± 382 22.2 ± 7.90b 34.9 ± 11.8 60.6 ± 24.3 4.27 ± 1.89 19.8 ± 3.40b 265 ± 106
Slow 640.5 ± 117 6050 ± 686 675 ± 102 2450 ± 365 290 ± 59.8a 28.9 ± 8.20 30.4 ± 5.90 9.21 ± 3.78 66.4 ± 19.9a 295 ± 185
Feedstock source
Wood based 118 ± 17b 1660 ± 289d 232 ± 43.4b 1780 ± 444b 134 ± 53.3 19.6 ± 3.8b 39.1 ± 28.6c 3.3 ± 0.9b 32.0 ± 10.7b 16.3 ± 4.5b
Crop wastes 517 ± 125b 9019 ± 1,220b 722 ± 137a 1285 ± 185b 309 ± 95.0 26.0 ± 9.2b 15.3 ± 3.5c 1.9 ± 0.5b 15.7 ± 3.1b 43.9 ± 12.3b
Other grasses 411 ± 57b 16,290 ± 3,140a 1060 ± 617a 1410 ± 351b 0.5 ± 0.1 3.6 ± 1.1b 0.5 ± 0.3d 2.7 ± 2.5b 9.8 ± 6.7b 14.4 ± 5.2b
Manures/Biosolids 1380 ± 369a 4316 ± 670c 993 ± 230a 4488 ± 1,000a 68.4 ± 23.1 79.9 ± 34.3a 91.4 ± 17.4a 20.7 ± 11.4a 143.7 ± 54.8a 1005 ± 472a
Pyrolysis temp (oC)
<300 25.1 ± 9.72c 1120 ± 730b 132 ± 45.9b 195 ± 53.9b 29.2 ± 15.1 6.38 ± 2.30 1.52 ± 0.67 1.02 ± 0.24 65.6 ± 39.6 67.2 ± 24.4
300–399 517 ± 183b 4930 ± 997b 641 ± 189b 2180 ± 780a 216 ± 94.0 40.8 ± 23.9 2.85 ± 1.07 6.35 ± 3.77 99.4 ± 51.7 722 ± 303
400–499 424 ± 162c 3810 ± 637b 492 ± 107b 1930 ± 515a 188 ± 82.0 31.1 ± 7.77 62.7 ± 33.6 2.17 ± 0.61 44.9 ± 30.8 801 ± 570
500–599 682 ± 214b 6480 ± 1,030b 480 ± 111b 1920 ± 475b 215 ± 107 18.9 ± 7.56 42.4 ± 10.5 16.6 ± 12.8 38.8 ± 17.2 40.0 ± 13.6
600–699 365 ± 86.1b 5010 ± 1,420b 747 ± 239b 3130 ± 989a 133 ± 46.5 41.4 ± 19.7 34.4 ± 15.8 7.85 ± 2.47 72.8 ± 64.9 81.1 ± 36.6
700–799 1230 ± 575a 13,420 ± 4,400a 1510 ± 616a 3270 ± 1,040a 85.4 ± 44.7 73.2 ± 62.7 52.6 ± 37.8 8.80 ± 3.29 58.4 ± 55.5 43.4 ± 39.0
>800 245 ± 105b 5580 ± 2,310a 537 ± 422a 1300 ± 599a 6.55 ± 3.95 2.05 ± 0.95 0.45 ± 0.35 0.25 ± 0.15 7.48 ± 3.40 35.0 ± 17.6
Biochar
1 3
fast pyrolysis. Depending on the extractant used, nutrient
availability may be either over- or under-estimated (e.g., the
use of Morgan or Mehlich extractants, which contain weak
acids, for use with alkaline-containing materials could over-
estimate availability). In the current study, we grouped all
data together and did not model effect of extractants used
for nutrient availability determination; this would be worth
exploring in the future.
5.2 Feedstock choice
In general, manure/biosolids-based biochars typically
contained the greatest available nutrient concentrations as
compared to other biochars (Table4). This is not surprising
given that these feedstocks contain, overall, greater nutri-
ent contents as compared to other feedstocks (e.g., Williams
etal. 2017). All other feedstock-based biochars generally
were grouped together in terms of nutrient availability,
potentially a consequence of lower ash content leading to
lower nutrient retention (e.g., Williams etal. 2016).
5.3 Pyrolysis temperature
Increasing pyrolysis temperature increased only the macro-
elements P, K, Mg, and Ca (Table4). As mentioned in the
biochar total elemental analysis discussion (Sect.4, above),
as pyrolysis temperature increases, water, volatile bio-oil
compounds, acids, organic surface functional groups and
tars are lost, all of which contain H and O resulting in their
losses as well (Ahmad etal. 2014; Cantrell and Martin 2012;
Antal and Grønli 2003). This concentrates other elements in
the final product, with macro-nutrient availability appearing
to be a function of pyrolysis temperature. This concept is
explored in more detail below.
6 Available nutrient analysis correlations
Ippolito etal. (2015) suggested that total elements present
in biochars cannot accurately predict nutrient availability.
However, their dataset utilized was based only on approxi-
mately 80 published biochar articles. It is worth to revisit
this concept, as well as other correlations, based on nearly
5400 published articles reviewed in the current study. Thus,
Pearson correlations between biochar available and total
nutrient contents, pyrolysis temperature, pyrolysis type, or
feedstock choice were first determined (Table5). Most coef-
ficients were not significant. However, some exceptions were
present for predicting biochar nutrient availability based
on total nutrient content, such as for K and Cu. Predict-
ing biochar nutrient content solely on pyrolysis temperature
or production technique appears poor; predicting nutrient
availability based on feedstock choice appears somewhat
more promising.
However, in order to parse the data into something mean-
ingful for the end-user, presented below are comparisons
between total and available nutrients with respect to all bio-
char data, fast or slow pyrolysis, pyrolysis temperature, and
feedstock choice. Only data where both total and available
nutrients were presented (N, P, K, Ca, Mg, Fe, and Cu) in
previously published works are shown.
6.1 All data: eects onnutrient availability
The total versus available N, P, K, Ca, Mg, Fe, and Cu data,
for the complete dataset for each element, are presented in
FiguresS1A through S1G. The data suggest that predicting
biochar plant-available concentrations from total elemental
content is relatively poor for most elements (R2 = 0.19, 0.01,
0.35, 0.11, no fit, and 0.09 for N, P, K, Ca, Mg, and Fe,
respectively). However, predicting plant-available biochar
Cu from total Cu content had an R2 = 0.97 utilizing an expo-
nential growth model. Unfortunately, most biochar produc-
ers and end-product users are likely not as concerned about
applying plant-available Cu to soils via biochar application
as compared to other macro-element availability.
In terms of macro-element availability, most end-product
users would likely be concerned about N availability and
whether they need to add supplemental N fertilizers with
biochars to offset potential negative crop N responses (e.g.,
Borchard etal. 2014; Lentz and Ippolito 2012). For exam-
ple, in the western US, irrigated winter wheat or corn could
require 85 and 235kgN ha−1, respectively, to maximize
yields (Davis and Westfall 2014a, b). The NO3 and NH4
data in Table4, along with data shown in Figure S1A, sug-
gest that most biochars (except manures/biosolids biochars)
contain available N contents below ~ 200mgkg−1; at 200mg
of available Nkg−1 biochar, an end-user might need to apply
between 425 and 1175Mgbiocharha−1 to supply the N
Table 5 Pearson correlation coefficients between available N, P, K,
Ca, Mg, Fe, and Cu and total nutrient concentration, pyrolysis tem-
perature, pyrolysis type, and feedstock choice
Bold, italicized numbers indicate significance (p < 0.05)
Available
nutrient con-
tent
Total nutri-
ent content
Pyrolysis
temperature
Pyrolysis type Feedstock
choice
N0.267 − 0.074 0.029 0.167
P 0.110 0.135 0.130 0.275
K0.422 0.191 − 0.122 0.190
Ca 0.331 0.052 0.140 0.323
Mg 0.022 0.123 0.100 0.200
Fe 0.301 0.107 0.414 − 0.020
Cu 0.669 0.028 0.104 0.206
Biochar
1 3
demands of winter wheat or corn, respectively. Unfortu-
nately, microbial immobilization should also be accounted
for, which would likely limit N availability, as described by
Borchard etal. (2014). Furthermore, these biochar applica-
tion rates to soils would equal ~ 19% and 52% by weight,
well over the general application guidelines many biochar
researchers are considering (~ 0.5% to 1% by weight, or
112 to 224Mgha−1). If biochar costs are considered (e.g.,
$500–$1000 USD Mg−1), crop-land applications would be
economically unrealistic if it was just for an N fertilization
effect (that is not given in woody biochars anyway due to
the N being bound into the biochar matrix). Biochars would
need to contain 2000mg of available Nkg−1, or greater, to
bring application rates near the 0.5–1% application level.
According to data presented in Table4 and Figure S1A, very
few untreated biochars meet this requirement. Apart from N,
taking a closer look into varying pyrolysis type, temperature,
or feedstock choice may provide additional insight into over-
all biochar nutrient availability prediction.
There may be ways to increase the ability of biochar to
provide plant-available N, even though NO3 and NH4 con-
tent of freshly produced biochar is near-zero (e.g. Kam-
mann etal. 2015; Haider etal. 2016). Biochar has the abil-
ity to capture NO3 when co-composted (Hagemann etal.
2017a, (b); wood biochars have been shown to release up to
5000mg NO3kg−1 following co-composting when repeat-
edly extracted (Kammann etal. 2015; Haider etal. 2016;
Hagemann etal. 2017b). Biochar can also capture avail-
able N when biochar resides in soils for longer time periods
(Haider etal. 2016, 2017). In organic environments with
alternating moisture regimes, an organo-mineral coating
forms on biochar surfaces (Hagemann etal. 2017a). The
coating is enriched in functional groups that improve the
ability of biochar to capture and release nitrate (and to a
lesser extent ammonium) (Kammann etal. 2015; Hage-
mann etal. 2017a). The mechanism, however, is not yet
completely understood (Joseph etal. 2017) and deserves
further attention.
6.2 Fast pyrolysis eects onnutrient availability
The effect of fast pyrolysis on the correlation between total
and available biochar nutrients are presented in FiguresS2.
As compared to all data (Figure S1), separating data by fast
pyrolysis did not increase the predictive fit for most ele-
ments, and in some cases decreased the degree of fit. This
suggests that predicting biochar nutrient availability based
on fast pyrolysis is relatively poor. However, predicting
available Cu based on total Cu in fast pyrolysis biochars
still has a relatively good fit (R2 = 0.74; exponential growth
model). Unfortunately, as previously mentioned, most
biochar end-users likely would not be concerned with Cu
availability.
6.3 Slow pyrolysis eects onnutrient availability
The effect of slow pyrolysis on the correlation between
total and available biochar nutrients are presented in Fig-
uresS3. As compared to all data (Figure S1), separating
data by slow pyrolysis increased the predictive fit for most
elements. Furthermore, slow pyrolysis tended to fit data to
a greater degree than fast pyrolysis. This may simply be due
to the larger number of biochars created from slow pyrol-
ysis as compared to fast pyrolysis, with gaps in the data
reduced simply due to more literature information. Fitting
biochar available nutrient to total nutrient content from fast
to slow pyrolysis improved the predictive R2 function for P
(0.05–0.13), K (0.32–0.47), Ca (0.25–0.46), Mg (0.03–0.29),
and Cu (0.74–0.98). Although these fits might not be per-
fect, the data suggest that predicting slow pyrolysis biochar’s
plant-available nutrient content, based on total nutrient con-
tent, is not out of the question (e.g., K, Ca, and Cu).
6.4 Pyrolysis temperature eects onnutrient
availability
The effects of pyrolysis temperature (from < 300 °C
to > 800°C) on the correlation between total and available
biochar nutrients are presented in FiguresS4. In general,
available K, Mg, and Fe content appear to increase with
increasing pyrolysis temperature, then decrease with further
rising pyrolysis temperatures > 800°C. It also appears that,
in general, temperatures < 300 °C or > 800°C produce bio-
chars with low available nutrient content.
6.5 Specic feedstock choice eects onnutrient
availability
Based on Pearson correlations (Table5), predicting biochar
nutrient availability on feedstock choice appears somewhat
promising. The effect of feedstock choice on the correlation
between total and available biochar primary macro-nutrients
(N, P, and K) are presented in Table6, while all nutrient data
(where both total and available nutrients were reported) are
presented in FiguresS5. The discussion below focuses solely
on the predicted availability of N, P, and K in biochars cre-
ated from specific feedstocks. However, the reader is encour-
aged to visit the supplemental figures for details regarding
predicting N, P, K, Ca, Mg, Fe, and Cu availability.
6.5.1 Wood‑based feedstocks
Previous research has focused a great deal of attention on
utilizing hardwood and softwood feedstocks for biochar
creation as compared to other materials. Based on a smaller
dataset analyzed, Ippolito etal. (2015) showed that hard-
wood biochars would supply less than 0.002% of the total
Biochar
1 3
N, 2.2% of the total P, and 17% of the total K present. The
authors also showed that softwoods could supply 27% and
6% of the total P and K present, respectively. Others have
shown increases in available N, P, and K with softwood-
based biochars (Dieguez-Alonso etal. 2018). Based on the
current dataset, if producing biochars from hardwoods, K
availability can be predicted relatively well based on total
content (R2 = 0.87) as compared to N and P. If, however, one
produces biochars from softwoods, the availability of both N
and K may be predicted relatively well based on total content
(R2 = 0.68 and 0.54, respectively).
In Sect.6.1 above, it was stated that based on targeted
biochar application rates of 0.5% to 1% (by wt.), one might
need to apply at least 2000mg of available Nkg−1 to meet
some of the major crop N demands (e.g., corn). Based on
the predicted softwood N availability function (Table6), it
would require softwood total N contents to be ~ 7%. None of
the softwood biochar data collected exceeded 4.5% (Figure
S5A), and thus supplemental N fertilizers would be needed
when utilizing softwood biochars applied to high N-demand-
ing crops such as corn. Softwood biochars could likely be
co-composted in order to capture available N, as described in
Sect.6.1 above. In addition, less N-demanding crops could
potentially have N supplied by softwood biochars applied at
reasonable application rates (i.e., 0.5–1% by wt.).
Applying K fertilizers to meet crop demands depends on
soil K availability. Potassium applications could be as low
as –56kgK ha−1 (corn; Davis and Westfall 2014a) to as
high as 250kgha−1 (corn or alfalfa; University of Delaware
2019; Lissbrant etal. 2009). We can predict soil K avail-
ability well with both hardwood (R2 = 0.87) and softwood
(R2 = 0.54) biochars, with wood-based biochars averaging
1660mg K kg−1 (Table4). Using 1660 mgK kg−1 as a
starting point, a biochar application rate of between 0.8 and
7% (by wt.) would be required to meet the aforementioned
low- and high-end crop K demands. However, available K
in hardwoods and softwoods can range from 0 up to either
13,000 or 4000mgkg−1, respectively (Figure S5G). At
almost 4–10 times greater than the average K concentration
in wood-based biochars, application rates could easily be
4–10 times lower than the estimated 0.8–7% by wt. biochar
application rates needed to meet crop K demands. Utilizing
total K content in wood-based biochars could be used as a
decision-making tool for K application and could specifi-
cally make hardwood and softwood biochar land applica-
tions attractive for supplying crop K demands globally.
6.5.2 Crop waste feedstocks
The use of agricultural crop waste products for biochar cre-
ation has occurred extensively throughout the world. The
dataset created for the current study was dominated by a
variety of crops, with the three major crops globally grown
(i.e., corn, wheat, rice) utilized for predicting N, P, and K
availability. One could potentially predict P availability mar-
ginally- to-well when utilizing any one of these three bio-
chars (R2 ranged from 0.48 to 0.82). Utilizing wheat straw
biochars as a K source could be predicted fairly well based
on total K present (R2 = 0.66), while estimating N availabil-
ity from these three crop-waste biochars appears to be weak
at best (R2 = 0.02–0.41).
As with any fertilizer, applying P fertilizers to meet crop
demands is dependent on soil P availability. Phosphorus
applications could be as low as 9kg Pha−1 (band applica-
tion to winter wheat; Davis and Westfall 2014b) to as high
as 130kg Pha−1 (broadcast application to corn; University
of Delaware 2019). We can predict P availability fairly well
with corn, wheat, or rice-based biochars, with crop waste
averaging ~ 520mg P kg−1 (Table4). Using 520mg P kg−1
as a starting point, a biochar application rate of between
0.8% and 11% (by wt.) would be required to meet the afore-
mentioned low- and high-end crop P demands. Even though
the available P in these three crop wastes ranges from 0 to
1800mgkg−1 (Figure S5E), biochar applications to supply
Table 6 Regression analysis results of best fits (based on linear, quadratic, exponential rise to a maximum, or exponential growth equations) for
available N, P, and K based on total concentrations as a function of feedstock choice; number of observations; R2 value
Feedstock Available N = ; n; R2Available P = ; n; R2Available K = ; n; R2
Hardwoods 31.3–29.1(Total N) + 33.5(Total N)2; 74; 0.12 251(1-e(−
0.005 × Total P); 74; 0.12 − 883 + 0.50(Total K); 31; 0.87
Softwoods 44.0–126(Total N) + 57.7(Total N)2; 35; 0.68 43.8(1-e(−
0.008 × Total P); 24; 0.08 41.3 + 0.313(Total K); 23; 0.54
Corn stalks/Cobs 40.2–55.8(Total N) + 20.3(Total N)2; 9; 0.41 − 154 + 0.36(Total P); 5; 0.48 − 3910 + 0.669(Total K); 13; 0.33
Wheat straw 74.5–14.5(Total N); 11; 0.09 83.4 + 0.009(Total P); 12; 0.82 6010 + 0.042(Total K); 10; 0.66
Rice straw/Husks 3.95 + 43.8(Total N); 19; 0.02 − 103 + 0.29(Total P); 11; 0.50 No Fit
Poultry manure − 494 + 272(Total N); 17; 0.11 434 + 0.027(Total P); 22; 0.07 No Fit
Pig manure e(1.99 × Total N); 8; 0.99 − 686 + 0.043(Total P); 8; 0.27 Too few data
Cattle manure 8.30–20.6(Total N) + 16.2(Total N)2; 4; 0.99 373 + 0.008(Total P); 11; 0.22 10400(1 − e(−
0.0001 × Total K); 11; 0.07
Biosolids 857–529(Total N) + 127(Total N)2; 24; 0.36 e(0.0002 × Total P); 11; 0.28 232 + 0.048(Total K); 17; 0.21
Biochar
1 3
crop P needs would likely only be warranted for those crops
with low P requirements.
We can, however, predict wheat straw K availability
fairly well. Wheat straw available K concentrations ranged
from ~ 6000 to 30,000mgkg−1 (Figure S5H), which were
greater than those for hardwoods/softwoods. These results
should make applying wheat straw-based biochars attractive
for supplying most crop K demands globally and may solve
a problem related to waste use in certain areas of the globe.
6.5.3 Manures/biosolids feedstocks
The use of manures or biosolids feedstocks for biochar crea-
tion has also been extensively studied globally. This may
be driven by the fact that these feedstocks typically contain
greater nutrient contents as compared to other feedstocks
(e.g., Williams etal. 2017), and that pyrolyzing these materi-
als represents a sound form of hygienization. Biochars made
from these feedstocks have been shown to release available
N (Liu etal. 2014; Sigua etal. 2016) in contrast to woody
biochars. In the current study, N availability based on total
biochar N content was predicted very well when utilizing
either pig or cattle manure (R2 = 0.99 and 0.99, respectively),
but not with poultry or biosolids biochars. This suggests to
biochar producers that, if they wanted to create a biochar
that would act as an N fertilizer, that they either have to
blend it with organic N-rich fertilizer materials (e.g. liq-
uid manures, biogas digestate, vinasse, etc.) and use it as a
carrier in low doses in the root zone (Schmidt etal. 2017)
where 0.8–2Mgha−1 may suffice, or utilize either pig or
cattle manure as a feedstock which might be also promis-
ing. As outlined in Sect.6.1 above, based on a somewhat
realistic biochar application rate (0.5–1.0% by wt.), one
might need to apply at least 2000mg of available Nkg−1
to meet some of the major crop N demands (e.g., corn).
Based on the predictive N functions in Table6, pig or cat-
tle manure would need to contain 3.8% or 11.7% total N,
respectively. This total N content may be potentially feasible
in pig manure (Figure S5C) if the material were sufficiently
dried to concentrate total N (swine manures typically have
low dry matter contents of 15–20%; e.g., McFarland etal.
2012). However, reaching 11.7% total N in cattle manure
is likely nearly impossible given total N content ranges in
the material and the relatively high dry matter content pre-
sent (50–80%, e.g., McFarland etal. 2012). This leaves pig
manure as the only biochar feedstock in the current study to
have the potential to sufficiently supply N for crop growth
without mixing the biochar with organic fertilizer materials,
or use it in their treatment (e.g. composting; see: Godlewska
etal. 2017; meta-study: Zhao etal. 2020).
It may be somewhat surprising that the prediction of
available N from poultry manure and biosolids biochars
was relatively low given that these feedstocks may contain
greater initial N contents as compared to other biochar feed-
stocks (Figure S5C). However, the lack of prediction may
simply be due to pyrolysis itself. Clough etal. (2013) noted
that manures and biosolids pyrolysis can result in increas-
ing aromatic and heterocyclic N structures within biochars,
which are more difficult to degrade (i.e., recalcitrant).
It is also surprising to note that predicting either P or K
availability was, at best, marginal with manures or biosolids-
based biochars. Again, this may simply be due to pyrolysis
itself. Biochars derived from manures and biosolids contain
greater ash content (Table1). As previously mentioned, this
ash contains oxides, hydroxides, carbonates, as well as sili-
cate phases (Novak etal. 2019a), that can form recalcitrant
associations with K. Manure and biosolids derived biochars
also contain greater Ca concentrations as compared to other
biochars (Table1), which, in combination with elevated
alkalinity, pH, and aromatic C has been shown to reduce P
solubility (Ngatia etal. 2017). This may also be the reason
for lack of P fit for other biochars above (Wang etal. 2013).
Finally, the information presented above may lend itself
for creating biochars from a combined variety of feed-
stocks. For example, mixing pig manure with agricultural
crop wastes and hardwood or softwood, then pyrolyzing
the combined materials, might effectively supply N, P, and
K, respectively. Other researchers have followed a similar
approach, albeit post biochar creation. Novak etal. (2014)
blended manure biochar containing excessive P, with
a nutrient poor biochar to achieve an end-product with a
more balanced nutrient content. Sigua etal. (2016) utilized
a 50:50 mix of softwood biochar with poultry manure bio-
char, observing a 670% and 830% increase in soil P and K,
respectively. The promise of mixing feedstocks for balancing
nutrient availability in biochars could be potentially realized
based on the data presented in the current manuscript.
7 Conclusions
Understanding the influences that pyrolysis type, pyrolysis
temperature, and initial feedstocks have on final biochar
properties can help researchers and practitioners create bio-
chars to meet agricultural environmental demands. Based
on ~ 5400 published articles and over 50,000 individual
observations, this project makes inferences to further our
understanding of biochar physicochemical properties from
the broad to specific and minute perspective. As compared
to fast pyrolysis, slow pyrolysis leads to biochars contain-
ing greater SSA, CCE, ash content, available Fe and NO3
concentrations.
Pyrolysis temperature influences biochar stability, with
temperatures > 500°C generally leading to longer-term
half-lives (> 1000years). This, in combination with greater
pyrolysis temperatures promoting more stable C structures,
Biochar
1 3
greater SSA, and potential improvements in soil aeration,
percolation, infiltration, and overall structure, potentially
suggests that greater pyrolysis temperatures may lead to
long-term soil improvements and C storage.
Perhaps the most important influence on final biochar
properties is feedstock choice. Wood-based feedstocks typi-
cally led to biochars containing the greatest SSA as com-
pared to other feedstocks; this, in combination with pyroly-
sis temperature could greatly influence soil improvements.
Crop-, grass-, and manures/biosolids-based feedstocks
led to biochars containing elevated CECs as compared to
wood-based biochars, which could affect nutrient sorption
following land application. Based on the complete dataset
collected, it appears possible to predict some plant-available
biochar nutrients simply from total nutrient analysis. The
collected data showed that we could reasonably predict (1)
available N from softwood, corn, pig manure, and cattle
manure biochars; (2) available P from corn, wheat, and rice
straw/husk biochars; and (3) available K from hardwood,
softwood, and wheat-derived biochars. This latter informa-
tion could be useful when creating designer biochars for spe-
cific nutrient applications, simply by blending several feed-
stocks together. Based on this information, future research
should test whether the available nutrient predictive func-
tions, in combination with created mixed feedstock biochars,
would hold true when placed within nutrient-poor soils.
Acknowledgements This work was partially supported by the USDA/
NIFA Interagency Climate Change Grant Proposal number 2014-
02114 [Project number 6657-12130-002-08I, Accession number
1003011] under the Multi-Partner Call on Agricultural Greenhouse
Gas Research of the FACCE-Joint Program Initiative. The German
BLE and FACCE-JPI funded the German participants of the “Design-
erChar4Food” (D4F) project (CK: Project No. 2814ERA01A; NW-M:
Project No. 2814ERA02A), the Spanish colleagues (JME and TFM)
were funded by FACCE-CSA no 276610/MIT04-DESIGN-UPVASC
and IT-932-16, MLC thanks the Spanish Ministry of Science, Inno-
vation and Universities, project #RTI2018-099417-B-I00, cofinanced
with EU FEDER funds and US colleagues (JN, JI and KS) were funded
by The USDA-National Institute of Food and Agriculture (Project #
2014-35615-21971), USDA-ARS CHARnet and GRACENet programs
– D4F greatly stimulated discussions. Any opinions, findings, or rec-
ommendation expressed in this publication are those of the authors
and do not necessarily reflect the view of the USDA. This work was
also partially supported by the National Natural Science Foundation
of China under a Grant number of 41501339, 21677119, 21277115,
41301551, 21407123, Jiangsu Province Science Foundation for Youths
under a grant number of BK20140468, sponsored by Qing Lan Project.
Funding Open access funding provided by Natural Resources Institute
Finland (LUKE).
Open Access This article is licensed under a Creative Commons Attri-
bution 4.0 International License, which permits use, sharing, adapta-
tion, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons licence, and indicate if changes
were made. The images or other third party material in this article are
included in the article’s Creative Commons licence, unless indicated
otherwise in a credit line to the material. If material is not included in
the article’s Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will
need to obtain permission directly from the copyright holder. To view a
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References
Ahmad M, Lee SS, Dou XM, Mohan D, Sung JK, Yang JE, Ok YS
(2012) Effects of pyrolysis temperature on soybean stover- and
peanut shell-derived biochar properties and TCE adsorption in
water. Bioresour Technol 118:536–544
Ahmad M, Lee SS, Lim JE, Lee SE, Cho JS, Moon DH, Hashimoto Y,
Ok YS (2014) Speciation and phytoavailability of lead and anti-
mony in a small arms range soil amended with mussel shell, cow
bone and biochar: EXAFS spectroscopy and chemical extrac-
tions. Chemosphere 95:433–441
Ajayi AE, Horn R (2016) Modification of chemical and hydrophysical
properties of two texturally differentiated soils due to varying
magnitudes of added biochar. Soil Till Res 164:34–44
Amoah-Antwi C, Kwiatkowska-Malina J, Thornton SF, Fenton O,
Malina G, Szara E (2020) Restoration of soil quality using bio-
char and brown coal waste: a review. Sci Tot Environ 722:137852
Antal MJ, Grønli M (2003) The art, science, and technology of char-
coal production. Ind Eng Chem Res 42:1619–1640
aqion (2019) pH of common acids and bases. https ://www.aqion .de/
site/191. Accessed 27 July 2020
Asadullah M, Zhang S, Li C-Z (2010) Evaluation of structural features
of chars from pyrolysis of biomass of different particle sizes. Fuel
Process Technol 91:877–881
Blum CS, Lehmann J, Solomon D, Caires EF, Alleoni LRF (2013)
Sulfur forms in organic substrates affecting S mineralization in
soil. Geoderma 200–201:156–164
Bolan NS, Kunhikrishnan A, Choppala G, Thangarajan R, Chung J
(2012) Stabilization of carbon in composts and biochars in rela-
tion to carbon sequestration and soil fertility. Sci Tot Environ
424:264–270
Borchard N, Siemens J, Ladd B, Möller A, Amelung W (2014) Appli-
cation of biochars to sandy and silty soil failed to increase
maize yield under common agricultural practice. Soil Till Res
144:184–194
Borchard N, Schirrmann M, Cayuela M, Kammann C, Wrage-Mönnig
N, Estavillo JM, Fuertes-Mendizabal T, Sigua G, Spokas K,
Ippolito JA, Novak J (2018) Biochar, soil and land use interac-
tions that reduce nitrate leaching and N2O emissions: a meta-
analysis. Sci Tot Environ 651:2354–2364
Brewer CE, Hu Y-Y, Schmidt-Rohr K, Loynachan TE, Laird DA,
Brown RC (2012) Extent of pyrolysis impacts on fast pyrolysis
biochar properties. J Environ Qual 41:1115–1122
Briggs C, Breiner JM, Graham RC (2012) Physical and chemical prop-
erties of Pinus ponderosa charcoal: implications for soil modifi-
cation. Soil Sci 177:263–268
Cantrell KB, Martin JH (2012) Stochastic state-space temperature
regulation of biochar production. Part II: application to manure
processing via pyrolysis. J Sci Food Agric 92:490–495
Cantrell KB, Hunt PG, Uchimiya M, Novak JM, Ro KS (2012) Impact
of pyrolysis temperature and manure source on physicochemi-
cal characteristics of biochar. Bioresource Technol 107:419–428
Cao X, Harris W (2010) Properties of dairy-manure-derived biochar
pertinent to its potential use in remediation. Bioresour Technol
101:5222–5228
Biochar
1 3
Cao XF, Sun SN, Sun RC (2017) Application of biochar-based catalysts
in biomass upgrading: a review. RCS Adv 7:48793–48805
Carpenter DL, Bain RL, Davis RE, Dutta A, Feik CJ, Gaston KR,
Jablonski W, Phillips SD, Nimlos MR (2010) Pilot-scale gasi-
fication of corn stover, switchgrass, wheat straw, and wood: 1.
Parametric study and comparison with literature. J Ind Eng Chem
Res 49:1859–1871
Cayuela ML, Jeffery S, van Zwieten L (2015) The molar H: corg ratio
of biochar is a key factor in mitigating N2O emissions from soil.
Agric Ecosyst Environ 202:135–138
Cha JS, Park SH, Jung SC, Ryu C, Jeon JK, Shin MC, Park YK
(2016) Production and utilization of biochar: a review. J Indust
Engineer Chem Res 40:1–15
Chang Y-M, Tsai W-T, Li M-H (2015) Chemical characterization of
char derived from slow pyrolysis of microalgal residue. J Anal
Appl Pyrol 111:88–93
Cheah S, Malone SC, Feik CJ (2014) Speciation of sulfur in bio-
char produced from pyrolysis and gasification of oak and corn
stover. Environ Sci Technol 48:8474–8480
Chen B, Zhou D, Zhu L (2008) Transitional adsorption and partition
of nonpolar and polar aromatic contaminants by biochars of
pine needles with different pyrolytic temperatures. Environ Sci
Technol 42:5137–5143
Chen H, Lin G, Wang X, Chen Y, Liu Y, Yang H, Shao J (2016)
Physicochemical properties and hygroscopicity of tobacco
stem biochar pyrolyzed at different temperatures. J Renew
Sustain Energy 8:013112
Clough TJ, Condron LM, Kammann C, Müller C (2013) A review
of biochar and soil nitrogen dynamics. Agronomy 3:275–293
Cui L, Yin C, Chen T, Quan J, Ippolito JA, Gan H, Xiao B, Pan M,
Lui B, Yan J, Ding C, Hussain Q, Umer M (2019) Remediation
of organic halogen- contaminated wetland soil using biochar.
Sci Tot Environ 696:134087
Davis JG, Westfall DG (2014a) Fertilizing corn. Colorado State
Extension Factsheet 0.538. https ://exten sion.colos tate.edu/
topic -areas /agric ultur e/ferti lizin g-corn-0-538/. Accessed 27
July 2020
Davis JG, Westfall DG (2014b) Fertilizing winter wheat. Colorado
State Extension Factsheet 0.544. https ://exten sion.colos tate.
edu/topic -areas /agric ultur e/ferti lizin g-winte r-wheat -0-544/.
Accessed 27 July 2020
de Mendonça FG, da Cunha IT, Soares RR, Tristão JC, Lago RM
(2017) Tuning the surface properties of biochar by thermal
treatment. Bioresour Technol 246:28–33
Dieguez-Alonso A, Funke A, Anca-Couce A, Rombolà AG, Ojeda G,
Bachmann J, Behrendt F (2018) Towards biochar and hydro-
char engineering—influence of process conditions on surface
physical and chemical properties, thermal stability, nutrient
availability, toxicity and wettability. Energies 11:496
Domingues RR, Trugilho PF, Silva CA, de Melo ICNA, Melo LCA,
Magriotis ZM, Sánchez-Monedero MA (2017) Properties of
biochar derived from wood and high-nutrient biomasses with
the aim of agronomic and environmental benefits. PLoS One
12:e0176884
Downie A, Crosky A, Munroe P (2009) Physical properties of bio-
char. In: Lehmann J, Joseph S (eds) Biochar for environmental
management: science, technology and implementation, 1st edn.
Routledge, New York, pp 227–249
Fuertes-Mendizábal T, Huérfano X, Vega-Mas I, Torralbo F, Menén-
dez S, Ippolito JA, Kammann C, Wrage-Mönnig N, Cayuela
ML, Borchard N, Spokas K, Novak J, González-Moro MB,
González-Murua C, Estavillo JM (2019) Biochar reduces the
efficiency of nitrification inhibitor 3,4-dimethypyrazole phos-
phate (DMPP) mitigating N2O emissions. Sci Reports. https ://
www.natur e.com/artic les/s4159 8-019-38697 -2.pdf. Accessed
27 July 2020
Funke A, Ziegler F (2010) Hydrothermal carbonization of biomass:
a summary and discussion of chemical mechanisms for process
engineering. Biofuels Bioprod Biorefin 4:160–177
Godlewska P, Schmidt HP, Ok YS, Oleszczuk P (2017) Biochar for
composting improvement and contaminants reduction. A review.
Bioresour Technol 246:193–202
Gondek K, Mierzwa-Hersztek M (2016) Effect of low-temperature bio-
char derived from pig manure and poultry litter on mobile and
organic matter-bound forms of Cu, Cd, Pb and Zn in sandy soil.
Soil Use Manage 32:357–367
Guo J, Chen B (2014) Insights on the molecular mechanism for the
recalcitrance of biochars: interactive effects of carbon and sili-
con components. Environ Sci Technol 48:9103–9112
Guo J, Lua AC (1998) Characterization of chars pyrolyzed from oil
palm stones for the preparation of activated carbons. J Anal
Appl Pyrol 46:113–125
Hagemann N, Joseph S, Schmidt H-P, Kammann CI, Harter J,
Borch T, Young RB, Varga K, Taherymoosavi S, Elliott
KW, McKenna A, Albu M, Mayrhofer C, Obst M, Conte P,
Dieguez-Alonso A, Orsetti S, Subdiaga E, Behrens S, Kappler
A (2017a) Organic coating on biochar explains its nutrient
retention and stimulation of soil fertility. Nat Commun 8:1089
Hagemann N, Kammann CI, Schmidt H-P, Kappler A, Behrens S
(2017b) Nitrate capture and slow release in biochar amended
compost and soil. PLoS One 12:e0171214
Haider G, Steffens D, Müller C, Kammann CI (2016) Standard
extraction methods may underestimate nitrate stocks captured
by field aged biochar. J Environ Qual 45:1196–1204
Haider G, Steffens D, Moser G, Müller C, Kammann CI (2017)
Biochar reduced nitrate leaching and improved soil moisture
content without yield improvements in a four-year field study.
Agric Ecosyst Environ 237:80–94
Hass A, Gonzalaz JM, Lima IM, Godwin HW, Halvorson JJ, Boyer
DG (2012) Chicken manure biochar as liming and nutrient
source for acid Appalachian soil. J Environ Qual 41:1096–1106
International Biochar Initiative (IBI) (2015) Standardized product
definition and product testing guidelines for biochar that is
used in soil. https ://bioch ar-inter natio nal.org/wp-conte nt/
uploa ds/2020/06/IBI_Bioch ar_Stand ards_V2.1_Final 2.pdf.
Accessed 27 July 2020
Ippolito JA, Strawn DG, Scheckel KG, Novak JM, Ahmedna M,
Niandou MAS (2012) Macroscopic and Molecular Investi-
gations of Copper Sorption by a Steam-Activated Biochar. J
Environ Qual 41:1150–1156
Ippolito JA, Spokas KA, Novak JM, Lentz RD, Cantrell KB (2015)
Biochar elemental composition and factors influencing nutrient
retention. In: Lehmann J, Joseph S (eds) Biochar for environ-
mental management: science, technology and implementation,
2nd edn. Routledge, New York, pp 137–161
Ippolito JA, Berry CM, Strawn DG, Novak JM, Levine J, Harley A
(2017) Biochars reduce mine land soil bioavailable metals. J
Environ Qual 46:411–419
Jeffery S, Verheijen FGA, Kammann C, Abalos D (2016) Biochar
effects on methane emissions from soils: a meta-analysis. Soil
Biol Biochem 101:251–258
Joseph S, Kammann CI, Shepherd JG, Conte P, Schmidt H-P, Hage-
mann N, Rich AM, Marjo CE, Allen J, Munroe P, Mitchell
DRG, Donne S, Spokas K, Graber ER (2017) Microstructural
and associated chemical changes during the composting of a
high temperature biochar: mechanisms for nitrate, phosphate
and other nutrient retention and release. Sci Total Environ
618:1210–1223
Kammann C, Linsel S, Gößling J, Koyro H-W (2011) Influence of
biochar on drought tolerance of Chenopodium quinoa Willd and
on soil–plant relations. Plant Soil 345:195–210
Biochar
1 3
Kammann CI, Schmidt H-P, Messerschmidt N, Linsel S, Steffens D,
Müller C, Koyro H-W, Conte P, Joseph S (2015) Plant growth
improvement mediated by nitrate capture in co-composted bio-
char. Sci Reports 5:11080
Kim KH, Kim J-Y, Cho T-S, Choi JW (2012) Influence of pyrolysis
temperature on physicochemical properties of biochar obtained
from the fast pyrolysis of pitch pine (Pinus rigida). Bioresour
Technol 118:158–162
Kinney TJ, Masiello CA, Dugan B, Hockaday WC, Dean MR, Zyg-
ourakis K, Barnes RT (2012) Hydrologic properties of biochars
produced at different temperatures. Biomass Bioenergy 41:34–43
Kloss S, Zehetner F, Dellantonio A, Hamid R, Ottner F, Liedtke V,
Schwanninger M, Gerzabek MH, Soja G (2012) Characterization
of slow pyrolysis biochars: effects of feedstocks and pyrolysis
temperature on biochar properties. J Environ Qual 41:990–1000
Knicker H (2007) How does fire affect the nature and stability of soil
organic nitrogen and carbon? A review. Biogeochem 85:91–118
Knudsen JN, Jensen PA, Dam-Johansen K (2004) Transformation and
release to the gas phase of Cl, K, and S during combustion of
annual biomass. Energy Fuels 18:1385–1399
Kuzyakov Y, Bogomolova I, Glaser B (2014) Biochar stability in
soil: decomposition during eight years and transformation as
assessed by compound-specific 14C analysis. Soil Biology Bio-
chem 70:229–236
Laird DA, Novak JM, Collins HP, Ippolito JA, Karlen DL, Lentz RD,
Sistani KR, Spokas K, Van Pelt RS (2017) Multi-year and multi-
location soil quality and crop biomass yield responses to hard-
wood fast pyrolysis biochar. Geoderma 289:46–53
Lehmann J (2007) Bio-energy in the black. Fronti Ecol Environ
5:381–387
Lehmann J, Joseph S (2009) Biochar for environmental management:
an introduction. In: Lehmann J, Joseph S (eds) Biochar for envi-
ronmental management: science, technology and implementa-
tion, 1st edn. Routledge, New York, pp 1–12
Lehmann J, Pereira da Silva J, Steiner C, Nehls T, Zech W, Glaser B
(2003) Nutrient availability and leaching in an archaeological
Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer,
manure and charcoal amendments. Plant Soil 249:343–357
Lehmann J, Rillig MC, Thies J, Masiello CA, Hockaday WC, Crowley
D (2011) Biochar effects on soil biota—a review. Soil Biology
Biochem 43:1812–1836
Lentz RD, Ippolito JA (2012) Biochar and manure affect calcareous
soil and corn silage nutrient concentrations and uptake. J Environ
Qual 41:1033–1043
Lentz RD, Ippolito JA, Lehrsch GA (2019) Biochar, manure, and saw-
dust alter long-term water retention dynamics in degraded soil.
Soil Sci Soc Am J 83:1491–1501
Lian F, Huang F, Chen W, Xing B, Zhu L (2011) Sorption of apolar and
polar organic contaminants by waste tire rubber and its chars in
single-and bi-solute systems. Environ Pollut 159:850–857
Liang B, Lehmann J, Solomon D, Kinyangi J, Grossman J, O’neill B,
Skjemstad J, Thies J, Luizao F, Petersen J (2006) Black carbon
increases cation exchange capacity in soils. Soil Sci Soc Am J
70:1719–1730
Lin Q, Xu X, Wang L, Chen Q, Fang J, Shen X, Lou L, Tian G (2017)
The speciation, leachability and bioaccessibility of Cu and Zn in
animal manure-derived biochar: effect of feedstock and pyrolysis
temperature. Front Environ Sci Eng 11:5
Lissbrant S, Berg WK, Volanec J, Brouder S, Joern B, Cunningham
S, Johnson K (2009) Phosphorus and potassium fertilization of
alfalfa. Purdue University Extension Bulletin AY-331-W
Liu X, Zhang A, Ji C, Joseph S, Bian R, Li L, Pan G, Paz-Ferreiro J
(2013) Biochar’s effect on crop productivity and the dependence
on experimental conditions-a meta-analysis of literature data.
Plant Soil 373:583–594
Liu Y, Liu Y, Ding Y, Zheng J, Zhou T, Pan G, Crowley D, Li L,
Zheng J, Zhang X, Yu X, Wang J (2014) Abundance, composi-
tion and activity of ammonia oxidizer and denitrifier communi-
ties in metal polluted rice paddies from south China. PLoS One
9:e102000
Lu J, Li J, Li Y, Chen B, Bao Z (2012) Use of rice straw biochar
simultaneously as the sustained release carrier of herbicides and
soil amendment for their reduced leaching. J Agric Food Chem
60:6463–6470
Luo L, Xu C, Chen Z, Zhang S (2015) Properties of biomass-derived
biochars: combined effects of operating conditions and biomass
types. Bioresour Technol 192:83–89
McFarland ML, Provin TL, Feagley SE (2012) Managing crop nutri-
ents through soil, manure and effluent testing. Texas A&M
AgriLife Extension Bulletin E-536
Nelissen V, Rütting T, Huygens D, Staelens J, Ruysschaert G, Boeckx
P (2012) Maize biochars accelerate short-term soil nitrogen
dynamics in a loamy sand soil. Soil Biology Biochem 55:20–27
Ngatia L, Hsieh Y, Nemours D, Fu R, Taylor R (2017) Potential phos-
phorus eutrophication mitigation strategy: biochar carbon com-
position, thermal stability and pH influence phosphorus sorption.
Chemosphere 180:201–211
Nguyen TTN, Xu CY, Tahmasbian I, Che RX, Xu ZH, Zhou XH, Wal-
lace HM, Bai SH (2017) Effects of biochar on soil available inor-
ganic nitrogen: a review and meta-analysis. Geoderma 288:79–96
Novak JM, Lima I, Xing B, Gaskin JW, Steiner C, Das KC, Ahmedna
M, Rehrah D, Watts DW, Busscher WJ, Schomberg H (2009)
Characterization of designer biochar produced at different tem-
peratures and their effects on a loamy sand. Ann Environ Sci
3:195–206
Novak JM, Cantrell KB, Watts DW, Busscher WJ, Johnson MG (2014)
Designing relevant biochars as soil amendments using lignocel-
lulosic-based and manure-based feedstocks. J Soils Sediments
14:330–343
Novak JM, Ippolito JA, Lentz RD, Spokas KA, Bolster CH, Sistani K,
Trippe KM, Johnson MG (2016) Soil health, crop productivity,
microbial transport, and mine spoil response to biochars. Bioen-
ergy Res 9:454–464
Novak J, Ippolito JA, Watts DW, Sigua GC, Ducey TF, Johnson MG
(2019a) Biochar compost blends facilitates switchgrass growth
in mine soils by reducing Cd and Zn bioavailability. Biochar
1:97–114
Novak JM, Sigua GC, Ducey TF, Watts DW, Stone KC (2019b)
Designer biochars impact on corn grain yields, biomass pro-
duction, and fertility properties of a highly-weathered Ultisol.
Environments 6:64
Pariyar P, Kumari K, Jain MK, Jadhao PS (2020) Evaluation of change
in biochar properties derived from different feedstock and pyroly-
sis temperature for environmental and agricultural application.
Sci Total Environ 713:136433
Qambrani NA, Rahman MM, Won S, Shim S, Ra C (2017) Biochar
properties and eco-friendly applications for climate change miti-
gation, waste management, and wastewater treatment: a review.
Renew Sustain Energy Rev 79:255–273
Sager M (2012) Levels of sulfur as an essential nutrient element in the
soil-crop-foods system in Austria. Agriculture 2:1–11
Schimmelpfennig S, Glaser B (2012) One step forward toward char-
acterization: some important material properties to distinguish
biochars. J Environ Qual 41:1001–1013
Schmidt H-P, Pandit BH, Cornelissen G, Kammann C (2017) Bio-
char-based fertilization with liquid nutrient enrichment: 21
field trials covering 13 crop species in Nepal. Land Degrad Dev
28:2324–2342
Schmidt H-P, Anca-Couce A, Hagemann N, Werner C, Gerten D,
Lucht W, Kammann C (2019) Pyrogenic carbon capture & stor-
age (PyCCS). GCB Bioenergy 11:573–591
Biochar
1 3
Sigua GC, Novak JM, Watts DW (2016) Ameliorating soil chemical
properties of a hard setting subsoil layer in Coastal Plain USA
with different designer biochars. Chemosphere 142:168–175
Sigua GC, Novak JM, Watts DW, Ippolito JA, Ducey TF, Johnson
MG, Spokas KA (2019) Phytostabilization of Zn and Cd in mine
soil using corn in combination with manure-based biochar and
compost. Environments 6:69
Sistani KR, Novak JM (2006) Trace metal accumulation, movement
and remediation in soils receiving animal manure. In: Prasad
MN, Sajwan KS, Naidu R (eds) Trace elements in the environ-
ment, biogeochemistry, biotechnology, and bioremediation. CRC
Press, Boca Raton, pp 689–706
Smith P, Adams J, Beerling DJ, Beringer T, Calvin KV, Fuss S,
Griscom B, Hagemann N, Kammann C, Kraxner F, Minx JC,
Popp A, Renforth P, Vicente JLV, Keesstra S (2019) Impacts of
land-based greenhouse gas removal options on ecosystem ser-
vices and the United Nations Sustainable Development Goals.
Annu Rev Environ Resour 44:255–286
Sohi S, Lopez-Capel E, Krull E, Bol R (2009) Biochar, climate change
and soil: a review to guide future research. CSIRO Land Water
Sci Rep 5:17–31
Spokas KA (2010) Review of the stability of biochar in soils: predict-
ability of O: C molar ratios. Carbon Manag 1:289–303
Tripathi M, Sahu JN, Ganesan P (2016) Effect of process parameters
on production of biochar from biomass waste through pyrolysis:
a review. Renew Sustain Energy Rev 55:467–481
Tsai W-T, Liu S-C, Chen H-R, Chang Y-M, Tsai Y-L (2012) Textural
and chemical properties of swine-manure-derived biochar per-
tinent to its potential use as a soil amendment. Chemosphere
89:198–203
University of Delaware, College of Agriculture and Natural Resources
Soil Testing Program (2019) Grain corn. https ://www.udel.edu/
conte nt/dam/udelI mages /canr/pdfs/exten sion/facts heets /AGR-
Grain -Corn.pdf. Accessed 27 July 2020
Wang Y, Hu Y, Zhao X, Wang S, Xing G (2013) Comparisons of bio-
char properties from wood material and crop residues at different
temperatures and residence times. Energy Fuels 27:5890–5899
Wang J, Xiong Z, Kuzyakov Y (2016) Biochar stability in soil: meta-
analysis of decomposition and priming effects. Global Change
Biol Bioenergy 8:512–523
Weber K, Quicker P (2018) Properties of biochar. Fuel 217:240–261
Werner C, Schmidt H-P, Gerten D, Lucht W, Kammann C (2018) Bio-
geochemical potential of biomass pyrolysis systems for limiting
global warming to 1.5°C. Environ Res Lett 13:044036
Williams CL, Westover TL, Emerson RM, Tumuluru JS, Li C (2016)
Sources of biomass feedstock variability and the potential impact
on biofuels production. Bioenergy Res 9:1–14
Williams CL, Emerson RM, Tumuluru JS (2017) Biomass compo-
sitional analysis for conversion to renewable fuels and chemi-
cals. In: Tumuluru JS (ed) Biomasss volume estimation and
valorization for energy. IntechOpen Limited, London. https ://
doi.org/10.5772/65777
Wolf M, Lehndorff E, Wiesenberg GLB, Stockhausen M, Schward L,
Amelung W (2013) Towards reconstruction of past fire regimes
from geochemical analysis of charcoal. Organic Geochem
55:11–21
Woolf D, Lehmann J, Cowie A, Cayuela ML, Whitman T, Sohi S
(2018) Biochar for climate change mitigation. In: Lal R, Stew-
art BA (eds) Navigating from science to evidence-based policy.
Advances in Soil Science, Soils and Climate. CRC Press. ISBN
9781498783651. http://www.css.corne ll.edu/facul ty/lehma nn/
publ/Woolf %20et%20al%20201 8%20Bio char%20for %20Cli
mate%20Cha nge%20Mit igati on.pdf. Accessed 27 July 2020
Zhang H, Chen C, Gray EM, Boyd SE (2017a) Effect of feedstock and
pyrolysis temperature on properties of biochar governing end use
efficacy. Biomass Bioenergy 105:136–146
Zhang H, Voroney RP, Price GW (2017b) Effects of temperature and
activation on biochar chemical properties and their impact on
ammonium, nitrate, and phosphate Sorption. J Environ Qual
46:889–896
Zhao Y, Zhao L, Mei Y, Li F, Cao X (2018) Release of nutrients and
heavy metals from biochar-amended soil under environmentally
relevant conditions. Environ Sci Pollut Res 25:2517–2527
Zhao S, Schmidt S, Qin W, Li J, Li G, Zhang W (2020) Towards the
circular nitrogen economy—a global meta-analysis of compost-
ing technologies reveals much potential for mitigating nitrogen
losses. Sci Total Environ 704:135401
Aliations
JamesA.Ippolito1 · LiqiangCui1,2· ClaudiaKammann3· NicoleWrage‑Mönnig4· JoseM.Estavillo5·
TeresaFuertes‑Mendizabal5· MariaLuzCayuela6· GilbertSigua7· JeNovak7· KurtSpokas8· NilsBorchard9
James A. Ippolito
Jim.Ippolito@colostate.edu
1 Department ofSoil andCrop Sciences, Colorado State
University, FortCollins80523, USA
2 School ofEnvironmental Science andEngineering,
Yancheng Institute ofTechnology, 9 Yingbin Avenue,
Yancheng224051, China
3 Department ofApplied Ecology, Geisenheim University,
Von-Lade-Straße 1, 65366Geisenheim, Germany
4 Faculty ofAgricultural andEnvironmental Sciences,
Grassland andFodder Sciences, University ofRostock,
Justus-von-Liebig-Weg 6, 18059Rostock, Germany
5 Department ofPlant Biology andEcology, University
oftheBasque Country (UPV/EHU), Apdo. 644,
48080Bilbao, Spain
6 Department ofSoil andWater Conservation andWaste
Management, CEBAS-CSIC, Campus Universitario de
Espinardo, 30100Murcia, Spain
7 United States Department ofAgriculture, Agriculture
Research Service, Coastal Plains Research Center, 2611 West
Lucas Street, Florence, SC29501, USA
8 United States Department ofAgriculture, Agriculture
Research Service, Soil andWater Management Research
Unit, University ofMinnesota, 439 Borlaug Hall, 1991
Buford Circle, St.Paul, MN29501, USA
9 Natural Resources Institute Finland (Luke),
Latokartanonkaari 9, 00790Helsinki, Finland
