Geoderma 341 (2019) 10–17
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Geoderma
journal homepage: www.elsevier.com/locate/geoderma
Phosphorus retention and availability in three contrasting soils amended T
with rice husk and corn cob biochar at varying pyrolysis temperatures
J.O. Eduaha,b,⁎, E.K. Narteya, M.K. Abekoea, H. Breuning-Madsenb, M.N. Andersenc
a Department of Soil Science, School of Agriculture, University of Ghana, P. O. Box LG 245, Legon, Ghana
bDepartment of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350 København K, Denmark
c Department of Agroecology and Environment, Aarhus University, Denmark
A R T I C L E I N F O A B S T R A C T
Handling Editor: David Laird The reactive nature of phosphorus (P) leads to the formation of insoluble Fe, Al and Ca phosphates in highly
Keywords: weathered tropical soils, thus reducing P availability for plant uptake. Biochar with its heterogeneous surface
Corn cob biochar properties as influenced by feedstock and pyrolysis temperature can affect P retention and availability in tropical
Rice husk biochar soils. In the present study, incubation studies were conducted for 90 days to investigate the effect of corn cob and
Pyrolysis temperature rice husk biochar on P sorption and desorption in two acid (Typic Plinthustult-A & Plinthic Acrudox-B) and one
Phosphorus neutral soil (Quartzipsamment-C). The biochars were pyrolyzed at varying temperatures (300 °C, 450 °C and
Sorption 650 °C) and applied at a rate of 1% (w/w) to the soils. Phosphorus sorption data were fitted to Langmuir and
Desorption Freundlich models. Phosphorus desorption was done on the residual samples that received initial P concentra-
tions of 21.5 mg L−1, 43.0 mg L−1 and 86.0mg L−1 solution using 10mM KCl. The P sorption capacity of the two
acid soils i.e. A (395mg kg−1) and B (296mg kg−1) were more than two fold that of the neutral soil (C)
(105mg kg−1). Addition of the biochar types to soil A raised the equilibrium P concentration in solution at
decreasing pyrolysis temperature. Similar trend was observed in soil B with the exception of corn cob and rice
husk biochar at 650 °C which increased the soil's (B) P sorption capacity. In soil C, both biochar types increased P
sorption capacity with increasing pyrolysis temperatures. Phosphorus desorbability increased with increasing
initial P concentrations in the three soils. Generally, P desorbability increased in the acid soils but decreased in
the neutral soil upon biochar amendment. Decreases in P adsorption and consequently increases in P desorption
were more pronounced when the 300 °C biochar types were amended with the soils. The study thus showed that
biochar pyrolyzed at 300–450 °C could be used to reduce P sorption and increase P bioavailability especially in
acid soils. The addition of biochar to neutral or alkaline soils might increase P retention possibly in the short-
term, reducing P bioavailability.
1. Introduction 2015). The formation of calcium-P, magnesium-P compounds as well as
P adsorption and precipitation by CaCO3 occurs in alkaline and cal-
The high phosphorus (P) fixing capacity of highly weathered soils of careous soils (Eriksson et al., 2015). The amount of P uptake by plants
the tropics has restrained the development of economically sustainable in acidic and alkaline soils is much restricted due to high P fixation.
crop production (Guzman et al., 1994; Abekoe and Sahrawat, 2001). The use of biochar has been suggested to provide an integrated
Biogeochemical processes such as dissolution, complexation, adsorption approach to rectify the challenge of tropical soils infertility (Lehmann,
and precipitation determine the availability of P in soil solution for 2007). Biochar is a stable carbon rich material, which is produced
plant uptake (Gérard, 2016). These chemical processes are dependent through thermochemical reaction in oxygen limited environment
on soil properties including Al and Fe oxide type and content, the (Lehmann et al., 2006). It is highly resistant to microbial degradation
amount and type of silicate clays, ionic strength, soil solution pH, cal- and can therefore stay in soils for hundreds to thousands of years
cium carbonate content, concentration of P in solution and the presence (Lehmann et al., 2006). Feedstocks for biochar production are abundant
of competing anions (Eriksson et al., 2015; Gérard, 2016). In acid soils, and are low-cost and mainly obtained from agricultural biomass, in-
Fe and Al in solution and their oxides adsorb P through precipitation dustrial and domestic waste (Duku et al., 2011). For instance, Ghana as
and ligand exchange reactions, respectively (Schoumans and Chardon, a country generates about 363×103 and 1650×103 t of rice husk and
⁎ Corresponding author at: Department of Soil Science, School of Agriculture, University of Ghana, P. O. Box LG 245, Legon, Ghana.
E-mail address: jo.eduah@yahoo.com (J.O. Eduah).
https://doi.org/10.1016/j.geoderma.2019.01.016
Received 26 June 2018; Received in revised form 4 January 2019; Accepted 7 January 2019
Available online 18 January 2019
0016-7061/ © 2019 Elsevier B.V. All rights reserved.
J.O. Eduah et al. Geoderma 341 (2019) 10–17
corn cob biomass, respectively annually (Duku et al., 2011). These Table 1
wastes are generally disposed off by aerobic burning to pollute the Properties of studied soil types.
environment. Converting these biomasses into biochar can improve the Classificationa Typic Plinthic Quartzipsamment
biomass management and protect the environment (Dong et al., 2013). Plinthustult Acrudox
Improvement of P availability in soils upon biochar application has
been reported (Lehmann, 2007; Atkinson et al., 2010). Various me- Acronym A B C
chanisms by which biochar may directly or indirectly control the biotic Clay (%) 20.30 18.40 4.00
and abiotic components of the P dynamics have been reported (DeLuca Silt (%) 11.20 8.00 1.00
et al., 2015). Biochar contains ample amount of P and therefore can Sand (%) 68.70 64.60 95.00
directly release soluble P into soil solution to enhance P availability pH 5.03 4.73 6.63
−1
(Atkinson et al., 2010). The addition of biochar reduces soil acidity due CEC (cmol+ kg ) 15.20 12.78 3.42
Total C (g kg−1) 14.00 13.30 4.30
to its high alkalinity and consequently reduces P precipitation reactions Total N (g kg−1) 1.23 1.22 0.19
with Fe3+ and Al3+ (Wang et al., 2012). Joseph et al. (2010) also in- Total P (mg kg−1) 353.58 232.75 190.80
dicated that application of biochar to soils culminates into the pre- Exc. Ca (cmol+ kg−1) 1.27 0.32 0.40
−1
cipitation of Fe oxide on biochar surface. Other studies have on the Exc. Mg (cmol+ kg ) 0.42 0.10 0.13
Fe (g kg−1) 2.10 1.56 0.67
other hand reported that biochar decreases P availability in most al- oFed (g kg−1) 20.00 9.41 1.66
kaline soils of the tropics due to substantial release of cations including Al −1o (g kg ) 1.21 1.39 0.17
Ca2+ and Mg2+ (DeLuca et al., 2015). Biochar produced from the same Al (g kg−1d ) 3.03 2.59 0.74
feedstock at different pyrolysis temperature may have diverse physical
a
and chemical properties such as functional groups, cation exchange Soil classification based on Soil Taxonomy System; Exc. Ca: exchangeable
capacity, porosity and surface area (Liang et al., 2014), which when Ca; Exc. Mg: exchangeable Mg; Feo: oxalate extractable Fe oxides; Alo: oxalate
extractable Al oxides; Fed: dithionite citrate bicarbonate extractable Fe oxides;applied to soils may invariably alter the surface chemistry of soils and Ald: dithionite citrate bicarbonate extractable Al oxides.
therefore affect P availability and retention in soils. For instance, under
the same pyrolysis temperature of 400 °C, the surface area and porosity obtained from Soil Research Institute of the Council for Scientific and
of poultry litter manure was much higher than wheat straw biochar Industrial Research (CSIR), Ghana. The CC and RH feedstocks charred
(Sun et al., 2011). Even though much work has been conducted on P at 300 °C, 450 °C and 650 °C are herein after designated as CC3, CC4,
sorption and availability in soils using P sorption characteristics CC6, RH3, RH4 and RH6, respectively. The biochars were finely ground
(Abekoe and Tiessen, 1998; McDowell and Condron, 2001), very lim- to< 1mm using mortar and pestle, dried at 105 °C and stored in air-
ited work has been done on P adsorption characteristics of biochar-soil tight bags for characterization and incubation studies.
complex at varying pyrolysis temperatures. Studies using different
biochar types on soils are required to evaluate the reactivity and
sorption characteristics of biochar-soil complex vis-à-vis soil P avail- 2.2. Soil and biochar analyses
ability after biochar application.
The objectives of the study were to find out (1) the effect of corn cob Soil samples were air dried, ground and sieved to< 2mm for suc-
biochar and rice husk biochar produced at different pyrolysis tem- cessive analyses. The particle size distribution was done using hydro-
peratures on P sorption on soils, and (2) the effect of the biochar types meter method of Bouyoucos (Day, 1965). The pH of soils and biochar
on P desorption on soils. types were measured in deionized water at the ratio of 1:2.5 w/w after
shaking for 1 h (Gaskin et al., 2008). Cation exchange capacity (CEC)
2. Materials and methods and exchangeable bases (Ca and Mg) were measured by modified NH4-
acetate compulsory displacement method (Gaskin et al., 2008). A LECO
2.1. Soil and biochar TIUMAC CNS analyzer was used to measure total C and N. Total P, base
cations (Ca, Mg, Na, K), Al and Fe were determined using inductively
Three soils of varying pH were sampled at a depth of 20 cm from coupled plasma optical emission spectrometry (ICP-OES). Briefly, the
different agro-ecological zones in Ghana. Soil A (A) which is sandy clay 0.5 g of crushed biochar and blanks in triplicates were digested in 3.5%
loam (Table 1) was collected from a Moist Semi-Deciduous Forest HF and H2O2. The ICP-OES elemental quantification was carried out by
(06°8.6′N; 0°54.144′W) with a mean annual temperature of about 32 °C using a Perkin Elmer Optima 5300DV instrument (Waltham, USA).
and a mean annual rainfall between 800 and 1200mm (Dickson and Reactive crystalline and amorphous Fe and Al oxides were determined
Benneh, 1995). In accordance with Soil Taxonomy System (Soil Survey by dithionite citrate bicarbonate (DCB) and oxalate extractions as de-
Staff, 2010) and World Reference Base (WRB, 1998), the soil is classi- scribed respectively, by Mehra and Jackson (1960) and Schwertmann
fied as Typic Plinthustult and Gleyi-Plinthic Acrisol, respectively (1964). The functional groups on the biochar types were examined
(Dwomo and Dedzoe, 2010). Soil B (B) also sandy clay loam was col- using photoacoustic spectroscopy (PAS)-FTIR. Briefly, the spectra were
lected from the Evergreen High Rain Forest (05°13′N; 02°38′W) with a recorded using a Nicolet 6700 (Thermo Scientific, USA) spectrometer
mean annual temperature and rainfall of 30 °C and 2000mm, respec- equipped with a PA-301 photoacoustic detector (Gasera Ltd., Finland).
tively. It is classified as Plinthic Acrudox (Dwomo and Dedzoe, 2010) For each sample, 128 scans in the mid-infrared region between 4000
−1 −1
according to Soil Taxonomy System (Soil Survey Staff, 2010) and as and 500 cm at a resolution of 4 cm were recorded and averaged.
Plinthic Ferralsol (Dwomo and Dedzoe, 2010) based on World Re-
ference Base (WRB, 1998). Soil C (C) was sampled from the Coastal 2.3. Incubation experiment
Savannah (05°47′N; 00°53′E) located on sand pit and is of low fertility
(Awadzi et al., 2008). According to Soil Taxonomy (Soil Survey Staff, An incubation study was done to find out the effect of biochar types
2010), the soil is classified as a Quartzipsamment (Dwomo and Dedzoe, at the various pyrolysis temperatures on P sorption and desorption in
2010). It is located in a dry equatorial climatic zone with a mean annual the three soils. The biochar types were mixed with soil at a rate of 1%
rainfall below 900mm and a mean annual temperature of 28 °C (30.4 t ha−1) in small pots of 5 cm diameter and 7 cm height. Soils
(Dickson and Benneh, 1995). without (control) and with biochar types were incubated at 70% field
Two biochar types at three different pyrolysis temperatures (300 °C, capacity at room temperature (28 °C) for 90 days in the dark. Each
450 °C and 650 °C) produced using Nabertherm furnace from corn cob treatment was replicated thrice. After the 90 days of incubation, the
(Zea mays) (CC) and rice husk feedstock (Oryza sativa) (RH) were soils (control) and soil-biochar mixtures were air-dried (70 °C) and
11
J.O. Eduah et al. Geoderma 341 (2019) 10–17
stored for P sorption studies. The biochar amended soils after the 90- Qc is the calculated values, Qe is experimental values and n is the
day incubation period were analyzed for pH, organic carbon, CEC, total number of observations. Shapiro-Wilk test was used to test for the
P, exchangeable Ca, DCB and oxalate extractable Fe and Al according to normality of soil-biochar mixture and desorption data before subjecting
their respective methods described earlier. it to one-way ANOVA test at a significance level of 1%. The variations
among the mean values were done using Tukey test.
2.4. P sorption of soils and soil-biochar mixtures
n
RMSE 1= ∑ (Qc − Q )2n i e=1 (5)
Phosphorus sorption isotherms were determined on each soil and
soil-biochar mixture. Orthophosphate stock solution containing
200mg L−1 was prepared from KH2PO4 salt of Analar grade. Thirty 3. Results and discussion
(30) mL of 0.01M KCl solution containing 0 (blank), 10.1, 21.5, 32.3,
43.0, 64.5 and 86.0 mg P L−1 were added to centrifuge tubes containing 3.1. Properties of the studied soils, biochar types and the soil-biochar
2 g of sample (soil or soil-biochar mixture). The suspensions in the mixtures
centrifuge tubes were shaken on an end-to-end shaker at 120 rpm for
24 h at 28 °C. The suspension was then centrifuged (3500 rpm, 15min) Table 1 shows the physical and chemical properties of the soils used
and the resulting supernatant filtered through a 0.45 μm filter paper. for the study. Soils A, B and C were acidic (pH=5.03), very acidic
The filtrate was analyzed for equilibrium pH and P by the colorimetric (pH=4.73) and neutral (pH=6.63), respectively. Soils A and B are
molybdenum-blue method (John, 1970). The initial aqueous P con- highly weathered and contain 1:1 clay minerals (low activity clays).
centration Ci (mg L−1) and equilibrium P concentration Ce (mg L−1) The organic carbon (OC) content of the soils was low (< 15 g kg−1),
were measured and the P adsorbed (qt) was calculated from the mass which is typical of soils of the humid tropics. The low activity clays
balance equation as follows (Eq. (1)): coupled with the low organic matter content of these soils may have
(Ci − Ce)V contributed to the low cation exchange capacity (CEC) of the soils. Theqt =
M (1) two acid soils (A and B) had almost the same non-crystalline (oxalate
extractable) contents. The crystalline (DCB) Fe contents in soil A was
where V is the volume of the aqueous solution (L) and M is the dry twice more than that of soil B. Comparably, the non-crystalline and
weight in grams of soils and soil-biochar mixtures (adsorbent). crystalline Fe and Al oxides of the acid soils were higher than that of
The sorption data were fitted to Langmuir (Eq. (2)) and Freundlich soil C, probably due to the more advanced weathering stage of the
equations (Eq. (3)): former soils. This implies a higher P sorption capacity of the acid soils
bQmaxCe than the neutral soil. The low to modest content of Fe and Al oxides inqt = 1 + bCe (2) soil C coupled with its low clay content of 4% depicts restrained P
adsorption capacity (Borggaard et al., 2004).
q K Ce1t = f n (3) The chemical composition of corn cob and rice husk biochar types at
−1 the three different temperatures are shown in Table 2. The pH, total P,where b and Kf indicate the Langmuir binding energy (L mg ) and the
(1−n) n −1 C and Si contents and concentration of the basic cations (Ca, Mg, K andFreundlich affinity coefficient (mg L g ), respectively, Qmax is
−1 Na) and acidic cations (Fe and Al) increased with increasing pyrolysisthe Langmuir maximum sorption capacity (mg kg ), and 1 / n is the temperature. Cation exchange capacity (CEC) and total N, however,
Freundlich linearity constant. decreased with increasing pyrolysis temperature. Biochar produced
from corn cob and rice husk at 650 °C had extremely high pH (>9.0)
2.5. P desorption of soils and soil-biochar mixtures and could serve as liming agent to ameliorate acid soils of the tropics.
The biochar types had a higher CEC as compared to a typical clay mi-
Desorption studies were done using the residual samples, which neral (Sohi et al., 2010), such as the studied soil types. Therefore, corn
received initial P concentration of 21.5mg L−1, 43.0mg L−1 and cob and rice husk amendments in the studied soils is likely to increase
86.0 mg L−1. After filtering the supernatant from the previous sorption soil CEC. The high CEC of biochar is a result of oxidative reactions of
experiment, the centrifuge tube plus the wet sample was weighed and a acid functional groups located on the edges of biochar aromatic C sheet
total of 20mL of 0.01M KCl solution was added to the sample in the (Agrafioti et al., 2013). The decrease in CEC with increasing pyrolysis
centrifuge tube on a weighing balance. The suspension was then shaken temperature can be attributed to the reduction in the eCOOH and eOH
for 3 h and centrifuged at 3500 rpm for 10min at room temperature.
The supernatant was filtered through a 0.45 μm filter paper into a clean Table 2
plastic bottle and a suitable aliquot taken for P analysis. The P carried Properties of corn cob biochar and rice husk biochar produced at 300 °C, 450 °C
over between desorption steps was determined from the weight of the and 650 °C.
entrapped solution that remained after decanting the supernatant so-
lution. The extraction was repeated for three successive times and P Biochar Corn cob Rice husk
released into the supernatant at each extraction period was then mea- Temperature 300 °C 450 °C 650 °C 300 °C 450 °C 650 °C
sured (John, 1970). The percentage of P desorbed was calculated as P
desorbability (Eq. (4)), where P desorbed is calculated as P adsorbed Acronym CC3 CC4 CC6 RH3 RH4 RH6
minus P remaining on the soil surface. pH (H2O) 8.90 9.23 10.30 7.11 7.40 9.50
−1
P desorbed (mg kg−1) Total C (g kg ) 729.80 743.10 780.72 415.80 419.80 425.51
P desorbability (%) = 1 × 100 Total N (g kg
−1) 29.31 21.20 19.11 17.72 13.3 12.10
P adsorbed (mg kg− ) (4) Total P (g kg−1) 1.54 1.60 1.94 1.19 1.32 1.52
Ca (g kg−1) 3.32 3.88 4.19 2.07 2.56 3.29
Mg (g kg−1) 2.43 3.21 3.43 0.91 1.01 1.27
2.6. Statistical analysis K (g kg−1) 1.54 1.56 1.94 0.19 1.12 1.52
Na (g kg−1) 24.71 26.31 30.80 5.34 6.36 8.19
A generalized linear model function in R studio (3.4.0) was used to CEC (cmol+ kg
−1) 38.02 37.82 30.10 49.40 42.72 38.00
generate a linear model for Langmuir and Freundlich equations. Si (g kg
−1) 13.94 14.01 14.44 138.53 169.2 194.49
Al (g kg−1) 0.57 0.67 1.10 1.26 1.53 1.88
Selection of the best fit model to sorption data was based on the com- Fe (g kg−1) 0.62 0.70 0.95 1.25 1.50 1.66
puted residual mean square error (RMSE) as described in Eq. (5), where
12
J.O. Eduah et al. Geoderma 341 (2019) 10–17
biochar was assigned to the aromatic CeH out of plane bend, indicating
the presence of adjacent aromatic hydrogen. The stretching vibration of
silicates was at peaks 800 cm−1 and 1100 cm−1 (Bourke et al., 2007).
The peak at 875 cm−1 corresponds to the content of carbonate in the
biochar types (Brewer et al., 2009).
One percent (1%) corresponding to approximately 30.4 t ha−1
amendment of the biochar types to the soils resulted in a> 0.5 unit
increases in pH (Table 3) similar to that reported for addition of non-
woody biochar types at rates between 15 and 30 t ha−1 to soils else-
where (Soinne et al., 2014). The predominant increase in pH for par-
ticularly the RH6 and CC6 amended soils is a reflection of a higher
increase in exchangeable Ca in the amended soils (Table 3) which could
be due to the inherently high pH and Ca contents of the biochar types
(Table 2). Wang et al. (2014) also reported increases in exchangeable
Ca and Mg after biochar addition to some tropical soils. The more
significant (p < 0.05) effect of the CC6 and RH6 on the soils' ex-
changeable Ca may be attributed to Ca enrichment at high temperatures
of 600 °C (Table 2).
Upon addition of the biochar types, there was generally significant
increases in OC contents only in the A soil. This increase was from
14.01 g kg−1 to between 17.72 and 21.51 g kg−1. The CEC of the three
amended soils increased significantly (p < 0.05), particularly at low
pyrolysis temperatures i.e. CC3 and RH3, obviously due to the increases
in solution pH which would facilitate more deprotonation of organic
acids and kaolinite present in the soils. Total P of all the three biochar
amended soils increased significantly (p < 0.05) due to the inherently
high P of the biochar types.
It is worthy of note that the acid soil A which had significant
(p < 0.05) increases in organic carbon contents upon amendment also
had increases in the oxalate extractable Fe (Feo) with concomitant de-
creases in DCB extractable Fe (Fed) (Table 3). Increases in organic
carbon levels may be controlling crystallinity of Fe in soil A within the
90 day incubation period. It is also note-worthy that upon addition of
biochar to the acid soils, Fed decreased from that of the un-amended
soils. This decrease in the Fed content of the acid soils may lead to
decreases in P adsorption. Apart from Alo which increased marginally in
soil C, there were no changes in oxalate and DCB extractable Fe and Al
in the neutral soil C probably due to the soil's low clay content (4%)
Fig. 1. Photoacoustic spectroscopy-FTIR analysis of (a) rice husk biochar which reduced its reactivity with biochar.
charred at 300 °C (RH3), 450 °C (RH4) and 650 °C (RH6); (b) corn cob biochar
charred at 300 °C (CC3), 450 °C (CC4) and 650 °C (CC6). 3.2. Effect of biochar types on P sorption of soils
groups at 650 °C (Fig. 1). Zheng et al. (2013) reported that the en- Table 4 lists the Langmuir and Freundlich adsorption parameters
richment of base cations and P with increasing pyrolysis temperature is together with the RMSE and equilibrium pH of the solution after the
due to their high vaporization energy. For instance, K and P are lost at sorption studies. Langmuir and Freundlich models effectively fitted the
temperatures above 800 °C, whiles Mg and Ca at temperatures above P adsorption data of the soils and soil-biochar mixtures. Considering the
1200 °C and 1300 °C, respectively (Knicker, 2007). The particularly RMSE values of the two models, Langmuir model had a better fit in the
high level of Si in the rice husk biochar type confirms the element as a three soils without biochar amendment. However, upon biochar ap-
nutrient in rice. This is consistent with the high intensity peak of SiO2 in plication, P adsorption in soils A and B were better fitted to Langmuir
the PAS-FTIR analysis. Silica is an important constituent of plant phy- model whereas soil C amended with biochar fitted better to Freundlich
toliths as it safeguards the plant from biochemical degradation of model. Most of the sorption curves fitted better with the Langmuir
carbon (Parr, 2006). The high C content at 650 °C can be explained by model, expressing P adsorption to soil surface with homogenous sorp-
increased carbonization and probable dehydration and disappearance tion sites. Similar results were described in Jiang et al. (2015) and
of volatile H and Oe carbon compounds as a result of structural de- Bornø et al. (2018) for P adsorption on soils and biochar amended soils.
gradation (Antal and Gronli, 2003). This is corroborated by the loss of Phosphorus adsorption increased with increasing initial P con-
CH2 functional groups at higher temperatures as evident in the PAS- centration (Fig. 2). This observation is consistent with other studies
FTIR spectra of all the biochar types (Fig. 1). The peak at about (Abekoe and Sahrawat, 2001; Bornø et al., 2018). The Langmuir sorp-
3400 cm−1 indicates the presence of OeH stretching and strong hy- tion maximum (Qmax) of soil A (395mg kg
−1) and soil B
−1
drogen bonding (Chun et al., 2004). The carboxylic C stretch was (296mg kg ) was relatively higher than that of soil C (106mg kg
−1).
around 1720 cm−1 and 1396 cm−1 (Bourke et al., 2007; Brewer et al., The relatively high P sorption capacity of the former is due to the high
2009). Adsorption at 2925 cm−1 suggested the presence of aliphatic content of amorphous and crystalline Fe and Al oxides providing more
eCH2 groups which disappeared at 650 °C (Chun et al., 2004). The adsorptive sites for P (Jiang et al., 2015). Soil A with relatively higher
decrease in peaks 2925 cm−1, 3400 cm−1, 1396 cm−1 and 1720 cm−1 content of Fe and Al oxides and clay than soils B and C showed much
at 650 °C suggests the decrease in polar functional groups at high decrease in P availability. The high sand content of soil C may have
temperature (Brewer et al., 2009). The peak at 3050 cm−1 of rice husk culminated into its low P sorption capacity.
Incorporating corn cob and rice husk biochar into soil A increased P
13
J.O. Eduah et al. Geoderma 341 (2019) 10–17
Table 3
Chemical properties of soils and soil-biochar mixtures.
Soil Treatment pH Organic C CEC Exc. Ca Total P Feo Fed Alo Ald
H2O g kg−1 cmol+ kg−1 cmol+ kg−1 mg kg−1 mg kg−1 mg kg−1 mg kg−1 mg kg−1
A Control 5.03 14.01aa 15.20a 1.27a 353.60a 2.10a 20.00d 1.21b 3.02ab
CC3 6.03 21.51d 22.27c 1.50bcd 428.81b 2.77c 14.32a 1.65c 2.55ab
CC4 6.43 20.10cd 19.20b 1.58de 482.80cd 2.66c 14.95a 1.27b 3.10ab
CC6 6.43 19.20bc 19.49bc 1.65e 505.82d 2.54b 17.70c 1.12b 3.47b
RH3 5.73 18.72bc 20.07bc 1.41b 413.60b 2.65bc 16.81b 1.08b 2.55ab
RH4 6.07 18.91bc 20.27bc 1.44bc 470.50c 2.71c 17.44bc 1.10b 3.44b
RH6 6.23 17.72b 17.89ab 1.53cd 460.61c 2.55b 17.07bc 0.78a 3.49b
B Control 4.73 13.30a 13.00a 0.32a 232.71a 1.56ab 9.41c 1.39b 2.59b
CC3 5.30 17.30c 18.18c 0.46cd 301.00b 1.68ab 5.79a 0.93a 2.71b
CC4 5.47 15.53abc 18.13c 0.47cd 330.90bc 1.68ab 6.09ab 1.31b 2.31ab
CC6 5.47 15.11ab 16.09b 0.48d 408.20d 1.51a 6.45ab 1.18ab 2.98b
RH3 5.17 16.50bc 16.31b 0.35b 304.02b 1.66ab 6.45ab 1.21ab 1.54a
RH4 5.30 14.91ab 16.14b 0.36b 347.00c 1.72b 6.99b 1.24ab 2.39ab
RH6 5.23 14.30ab 13.66a 0.45c 325.41bc 1.68ab 7.09b 1.19ab 2.34ab
C Control 6.63 4.31a 3.50a 0.40a 190.22a 0.67a 1.66ab 0.17a 0.74a
CC3 7.10 4.50a 7.74d 0.46ab 249.40bc 0.76abc 1.83ab 0.29bc 0.78a
CC4 7.33 5.30ab 6.83cd 0.64bc 230.81abc 0.78bc 1.72ab 0.26b 0.94ab
CC6 7.47 5.02ab 6.87cd 0.76c 270.30c 0.80bc 1.87b 0.27bc 0.97ab
RH3 6.63 6.01b 7.54d 0.49ab 209.80ab 0.86c 1.61a 0.33d 0.95ab
RH4 6.77 5.20ab 5.11b 0.73c 222.51ab 0.71ab 1.83ab 0.32cd 0.91a
RH6 7.20 4.62a 5.90bc 0.72c 270.30c 0.72ab 1.90b 0.29bc 1.23b
a Values of the same letter within a column are significantly the same at 1% level of significance based on Tukey's test.
bioavailability with decreasing pyrolysis temperature. The 395mg kg−1 Fitzsimmons (2016) proposed that maximum P availability is observed
Qmax of soil A decreased to between 262mg kg−1 and 366mg kg−1 at pH range of 5.5 to 7.2 in an aquatic system. The addition of the two
and between 279mg kg−1 and 367mg kg−1 respectively in corn cob biochar types raised the equilibrium pH of soil A (4.92) to a range of
and rice husk treatments. Similarly, both biochar amendments to soil B 5.79 to 5.99 and soil B (4.61) to a range of 5.71 to 6.02 (Table 4) which
decreased P sorption capacity with the exception of biochar types were within the suitable range. Such pH range might have led to the
produced at 650 °C. The result of the present study is consistent with precipitation of polymeric Fe and Al oxides (Gérard, 2016), thereby
those of Morales et al. (2013) who found that biochar reduces P fixing increasing P availability.
capacity of degraded acidic tropical soils. Similarly, Cui et al. (2011) Corn cob and rice husk biochar pyrolyzed at 300 °C were lower in P
also found a decrease in P adsorption onto ferrihydrite when amended adsorption when amended to the two acid soils than their counterparts
with straw biochar. The equilibrium pH value of the P solution is of pyrolyzed at 450 °C and 650 °C. Therefore, biochar produced at 300 °C
much importance regarding the process of adsorption, the form of P in can be considered as better amendment in acid soils for more P bioa-
solution as well as the surface charge of the soil and or soil-biochar vailability for plant uptake. The comparatively lower P adsorption onto
mixture and hence its adsorption capacity for P. Cerozi and the 300 °C biochar types could be attributed to the lower Al and Fe
Table 4
Phosphorus adsorption parameters from Langmuir and Freundlich equations, equilibrium pH and root mean square error (RMSE) of soils and biochar amended soils.
Soil Treatment Langmuir Freundlich Langmuir Freundlich Equilibrium pHc
Qmax (mg kg−1)a,b b (Lmg−1)a,b Kf (mg kg−1)a,b (1 / n)a,b RMSE RMSE
A Control 395 0.04 42 0.48 20 29 4.92
CC3 262 0.06 42 0.39 19 27 5.99
CC4 314 0.08 56 0.38 26 35 5.82
CC6 366 0.10 79 0.36 31 42 5.83
RH3 279 0.05 35 0.44 23 29 5.83
RH4 347 0.06 50 0.43 21 29 5.79
RH6 367 0.09 71 0.38 19 32 5.80
B Control 296 0.16 84 0.30 17 24 4.61
CC3 187 0.19 64 0.25 16 14 6.00
CC4 249 0.05 36 0.41 28 33 6.02
CC6 310 0.48 136 0.21 21 28 5.91
RH3 193 0.29 43 0.42 24 36 5.73
RH4 286 0.09 56 0.37 18 24 5.71
RH6 307 0.08 57 0.37 21 30 5.74
C Control 105 0.09 29 0.28 12 14 6.50
CC3 122 0.20 47 0.22 14 14 6.53
CC4 162 0.31 67 0.22 18 15 7.40
CC6 180 0.39 83 0.20 17 16 7.61
RH3 148 0.21 54 0.24 17 12 6.58
RH4 182 0.33 77 0.21 14 12 7.32
RH6 203 0.43 89 0.16 14 11 7.71
a Derived sorption parameters using non-linear least squares function nls in R studio v.3.4.2.
b Derived sorption parameters for each models for each treatment for the individual soil types were all significant p < 0.01.
c Supernatant pH after the sorption experiment.
14
J.O. Eduah et al. Geoderma 341 (2019) 10–17
Fig. 2. P sorption curves in three soil types amended with corn cob biochar (CC3, CC4, CC6) or rice husk biochar (RH3, RH4, RH6) in comparison with control soils
(soils without biochar amendment). Soil A and B were fitted to Langmuir model and Soil C was fitted to Freundlich model. The sorption curves parameters were
obtained from non-linear least squares regression method in R studio 3.4.2.
contents of these materials as depicted in Table 2. At lower tempera- biochar-soil mixture could therefore be the mechanism underlying the
tures e.g. 300 °C, labile organic C would be more than at 450 °C and increase in P sorption in the neutral soil. It is clear from the study that it
650 °C. This higher labile organic C content would inhibit P adsorption is not advisable to add biochar to neutral soils since it could reduce P
in the soil and thus in part account for the lower P adsorption when the availability for plant uptake.
biochar types at 300 °C were amended to the acid soils. This assertion is
corroborated by Schneider and Haderlein (2016) who suggested that
labile organic C from low temperature pyrolysis biochar inhibit P 3.3. Effect of biochar types on P desorption of soils
sorption in Fe and Al oxides dominated soils of the tropics. Such a
competitive reaction has been reported between P and several low Phosphorus desorbability was used to describe the amount of P
molecular weight organic acids and anions (Gerke et al., 2000). Com- desorbed from soils and soil-biochar mixtures as shown in Fig. 3.
paratively, corn cob biochar was more effective in increasing P avail- Phosphorus desorbability of all the treatments showed that increasing
ability in soils A and B than rice husk biochar. For instance, CC3 de- initial P concentration from 21.5 mg L
−1 to 86.0 mg L−1 resulted in an
creased P sorption capacity of soil A and B respectively by 33.7% and increase in P desorbability. This was in line with those of Cui et al.
36.8% whereas RH3 did similarly by 29.4% and 34.8%. The relatively (2011) who observed an increase in P released from ferrihydrite when
−1 −1
lower P adsorption by the soils upon amendment with the corn cob initial P concentration was increased from 1mg L to 200mg L .
biochar types is as a result of the lower Al and Fe and higher P contents Phosphorus adsorption mechanism on clay minerals involves basically
of the biochar type (Table 2). monodentate and bidentate reactions (Jaisi et al., 2010). At low initial P
−1
Unlike the decrease in P sorption in soil A and B amended with concentration of< 50mg L , bidentate mechanism of P adsorption
biochar, soil C (Quartzipsamment) showed increase in P sorption with dominates whereas monodentate reaction occurs when the initial P
increasing pyrolysis temperature (Table 4). The addition of corn cob concentration is> 50mg L
−1 (Antelo et al., 2010). This obviously ex-
biochar and rice husk biochar increased the Qmax of soil C from plains the low amount of P desorbed from the adsorbents at initial P
−1 −1 −1105mg kg to a range of 112mg kg−1 to 180mg kg−1 and concentrations of 21.5mg L and 43.0 mg L as compared to
−1 −1 −1148mg kg to 203mg kg respectively. This was in agreement with 86.0 mg L . The substantial amount of P released from the treatments
that of Zhai et al. (2014) who reported an increase in P sorption at at all the three P loadings namely 21.5, 43.0 and 86.0 mg L
−1 implies
increasing pyrolysis temperature in a slightly alkaline soil when maize high P bioavailability for plant uptake. However, the sandy texture of
residue biochar produced at different pyrolysis temperature was added. the neutral soil (soil C) could result in high leaching potential of P in-
Most of the P are fixed by added alkaline and alkaline earth metals in ducing eutrophication in ground water.
char (DeLuca et al., 2015; Xu et al., 2014). Corn cob and rice husk The study showed significant (p < 0.01) variation among the
biochar have higher inherent Ca and Mg content than Fe and Al treatments for each of the initial P concentration levels. Generally, corn
(Table 2). The equilibrium pH observed in the Quartzipsamment after cob and rice husk biochar amendment significantly (p < 0.01) in-
adsorption was between 6.50 and 7.71, a range within which most Fe creased P released in the acid soils (soil A and B). However, there was a
and Al would be precipitating or polymerizing out of solution. The ash significant (p < 0.01) decrease in P desorption in soil C. The increase
in the biochar contains high levels of basic cations as shown in Table 2. in P desorbability was more sensitive to biochar type charred at 300 °C
There could therefore be biochar surface complexation between the Ca and 450 °C in the two acid soils. Similar results for higher P desorption
and Mg in the ash and the H PO − that will be prevalent in soil solution from an Oxisol amended with wheat straw biochar produced at 350 °C2 4
at these pH ranges. The formation of CaeP and MgeP precipitate on the than 700 °C was observed by Xu et al. (2014). Acid functional groups
such as carboxylic and phenolic groups on organic material can cause P
15
J.O. Eduah et al. Geoderma 341 (2019) 10–17
Fig. 3. Effect of initial P concentration (21.5 mg P L−1, 43.0 mg P L−1 and 86.0mg P L−1) on P desorption in the soils types amended with corn cob biochar (CC3,
CC4, CC6) or rice husk biochar (RH3, RH4, RH6) as compared to un-amended control soils (A, B or C). Error bars depict standard error. One-way ANOVA was
performed on P desorbability for each initial P concentrations with p values showing significant difference at 1%.
removal from clay minerals through ligand exchange and or enhanced 4. Conclusion
ligand dissociation of oxides and hydroxides of Fe and Al (Kirk et al.,
1999). Correspondingly, the ample amount of acid functional groups on The study showed that the properties of corn cob biochar and rice
the low pyrolysis temperature biochar i.e. 300 °C and 450 °C, may ex- husk biochar were influenced by the pyrolysis temperature and there-
plain the high P release. Biochar produced at high temperatures, fore differently affected the P dynamics in the soils. In the acid soils (A
especially at 650 °C, seems to decrease the amount of P desorbed in acid and B), both biochar types effectively decreased P sorption capacity
soils most predominantly at the 86.0 mg L−1 loading. The removal of with increasing pyrolysis temperature. Contrasting results were ob-
OH groups at high pyrolysis temperature (650 °C) leads to the switch served in biochar amended soil C. It is obvious that the effect of biochar
over of FeeP and AleP outer sphere complex to an inner sphere com- on P sorption was sensitive to the type of feedstock, pyrolysis tem-
plex reaction which eventually affects the amount of P desorbed using perature and equilibrium pH. However, P desorption was less affected
neutral salts such as KCl and CaCl2 (Frost et al., 2012). Biochar addi- by the feedstock type but rather was more dependent on pyrolysis
tions decreased P desorbability in soil C. This was obviously seen in the temperature, pH and initial P concentration. Phosphorus desorption in
increase in binding energy (b) of soil C after the two biochar applica- soil A and B increased after the application of all biochar types but
tions, from 0.09 Lmg−1 to a range of 0.20 to 0.39 Lmg−1 and 0.21 to decreased in soil C. The study thus suggested that P availability and
0.43 Lmg−1 for corn cob biochar and rice husk biochar respectively retention in tropical soils are influenced by biochar addition and that
(Table 4). The small amount of P released in the neutral soil could be biochar produced at low temperatures (300 °C and 450 °C) can be
ascribed to increasing binding energy as a result of increasing equili- considered as appropriate amendments in acid soils to make P more
brium pH (pH > 7) upon biochar incorporation. available for plant uptake. However, biochar application to neutral or
16
J.O. Eduah et al. Geoderma 341 (2019) 10–17
alkaline soils can be considered as inappropriate P management prac- (PO4)2(OH)·(H2O). J. Therm. Anal. Calorim. 107, 905–909.
tice since it increases P adsorption and lowers P desorbability. Gaskin, J., Steiner, C., Harris, K., Das, K., Bibens, B., 2008. Effect of low-temperature
pyrolysis conditions on biochar for agricultural use. Trans. ASABE 51 (6),
2061–2069.
Acknowledgment Gérard, F., 2016. Clay minerals, iron/aluminum oxides, and their contribution to phos-
phate sorption in soils. A myth revisited. Geoderma 262, 213–226.
The authors thank Danida (Ministry of Foreign A airs of Denmark) Gerke, J., Beibner, L., Romer, W., 2000. The quantitative effect of chemical phosphateff mobilization by carboxylate anions on P uptake by single root. The basic concept and
for providing financial assistance to the project “Green Cohesive determination of soil parameters. J. Plant Nutr. Soil Sci. 163, 207–212.
Agricultural Resource Management, WEBSOC”, DFC project no: 13- Guzman, G., Alcantara, E., Baron, V., Torrent, J., 1994. Phytoavailability of phosphate
01AU. They would like to acknowledge Professor Ole. K. Borggaard for adsorbed on ferrihydrite, hematite and goethite. Plant Soil 159, 219–225.
Jaisi, D.P., Blake, R.E., Kukkadapu, R.K., 2010. Fractionation of oxygen isotopes in
his supervision during the research stay of Joseph Osafo Eduah at phosphate during its interactions with iron oxides. Geochim. Cosmochim. Acta 74,
University of Copenhagen, Denmark. 1309–1319.
Jiang, J., Yuan, M., Renkou, X., Bish, D.L., 2015. Mobilization of phosphate in variable-
charge soils amended with biochars derived from crop straws. Soil Tillage Res. 146,
References 139–147.
John, M.K., 1970. Colorimetric determination of phosphorus in soil and plant materials
Abekoe, M.K., Sahrawat, K.L., 2001. Phosphorus retention and extractability in soils of with ascorbic acid. Soil Sci. 109 (4), 214–220.
the humid zones in West Africa. Geoderma 102, 175–187. Joseph, S., Graber, E.R., Chia, C., Munroe, P., Donne, S., Thomas, T., Nielsen, S., Marjo,
Abekoe, M.K., Tiessen, H., 1998. Phosphorus forms, lateritic nodules and soil properties C., Rutlidge, H., Pan, G.X., Li, L., Taylor, P., Rawal, A., Hook, J., 2010. Shifting
along a hillslope in northern Ghana. Catena 33, 1–15. paradigms: development of high-efficiency biochar fertilizers based on nano-struc-
Agra oti, E., Bouras, G., Kalderis, D., Diamadopoulos, E., 2013. Biochar production by tures and soluble components. Carbon Manag. 4, 323–343.fi
sewage sludge pyrolysis. J. Anal. Appl. Pyrolysis 101, 72–78. Kirk, G.J.D., Santos, E.E., Santos, M.B., 1999. Phosphate solubilization by organic anion
Antal, M.J., Gronli, M., 2003. The art, science, and technology of charcoal production. excretion from rice growing in aerobic soils: rates of excretion and decomposition,
Ind. Eng. Chem. Res. 42, 1619–1640. effects of rhizosphere pH and effects on phosphate solubility and uptake. New Phytol.
Antelo, J., Fiol, S., Pérez, C., Mariño, S., Arce, F., Gondar, D., López, R., 2010. Analysis of J. 142, 185–200.
phosphate adsorption onto ferrihydrite using the CD-MUSIC model. J. Colloid Knicker, H., 2007. How does fire affect the nature and stability of soil organic nitrogen
Interface Sci. 347, 112–119. and carbon? A review. Biogeochemistry 85, 91–118.
Atkinson, C.J., Fitzgerald, J.D., Hipps, N.A., 2010. Potential mechanisms for achieving Lehmann, J., 2007. Bio-energy in the Black. Front. Ecol. Environ. 5, 381–387.
agricultural bene ts from biochar application to temperate soils: a review. Plant Soil Lehmann, J., Gaunt, J., Rondon, M., 2006. Biochar sequestration in terrestrial ecosystem-fi
337, 1–18. a review. Mitig. Adapt. Strateg. Glob. Chang. 11, 403–427.
Awadzi, T.W., Ahiahor, E., Breuning-Madsen, H., 2008. The soil-land use system in a sand Liang, Y., Cao, X., Zhao, L., Xu, X., Harris, W., 2014. Phosphorus release from dairy
spit area in the semi-arid coastal savannah region of Ghana-development, sustain- manure, the manure-derived biochar, and their amended soil: effects of phosphorus
ability and threat. West Afr J. App. Ecol. 13, 181–194. nature and soil property. J. Environ. Qual. 43, 1504–1509.
Borggaard, O.K., Szilas, C., Gimsing, A.L., Rasmussen, L.H., 2004. Estimation of soil McDowell, R.W., Condron, L., 2001. Influence of soil constituents on soil phosphorus
phosphate adsorption capacity by means of pedotransfer function. Geoderma 118, sorption and desorption. Commun. Soil Sci. Plant Anal. 32, 2531–2547.
55–61. Mehra, O.P., Jackson, M.L., 1960. Iron oxide removal from soils and clays by dithionite-
Bornø, M.L., Muller-Stover, D.S., Lui, F., 2018. Contrasting e ects of biochar on phos- citrate system buffered with sodium bicarbonate. Clay Clay Miner. 7, 317–327.ff
phorus dynamics and bioavailability in di erent soil types. Sci. Total Environ. 627, Morales, M.M., Comerford, N., Guerrini, I.A., Falcao, N.P.S., Reeves, J.B., 2013. Sorptionff
963–974. and desorption of phosphate on biochar and biochar-soil mixtures. Soil Use Manag.
Bourke, J., Manley-Harris, M., Fushimi, C., Dowaki, K., Nunoura, T., Antal, M.J., 2007. Do 29, 306–314.
all carbonized charcoals have the same chemical structure? A model of the chemical Parr, J.F., 2006. Effect of fire on phytolith coloration. Geoarcheology 21, 171–185.
structure of carbonized charcoal. Ind. Eng. Chem. Res. 46, 5954–5967. Schneider, F., Haderlein, S.B., 2016. Potential effects of biochar on the availability of
Brewer, C.E., Schmidt-Rohr, K., Satrio, J.A., Brown, R.C., 2009. Characterization of bio- phosphorus mechanistic insights. Geoderma 277, 83–90.
char from fast pyrolysis and gasi cation systems. Environ. Prog. Sustain. Energy 28, Schoumans, O.F., Chardon, W.J., 2015. Phosphate saturation degree and accumulation offi
386–396. phosphate in various soil types in Netherlands. Geoderma 237–238, 325–335.
Cerozi, B.D.S., Fitzsimmons, K., 2016. The e ect of pH on phosphorus availability and Schwertmann, U., 1964. Differenzierung der Eisenoxide des bodens Dutch extraction mitff
speciation in an aquaponics nutrient solution. Bioresour. Technol. 778–781. Ammoniumoxalate-Losung. Z. Pflanzenernahr. Dung. Bodenkd. 105, 194–202.
Chun, Y., Sheng, G.Y., Chiou, C.T., Xing, B.S., 2004. Compositions and sorptive properties Sohi, S.P., Krull, E., Lopez-Capel, E., Bol, R., 2010. Chapter 2–a review of biochar and its
of crop residue-derived chars. Environ. Sci. Technol. 38, 4649–4655. use and function in soil. Adv. Agron. 105, 47–82.
Cui, H.J., Wang, M.K., Fu, M.L., Ci, E., 2011. Enhancing phosphorus availability in Soil Survey Staff, 2010. Keys to Soil Taxonomy, 11th ed. USDA Natural Resources
phosphorus-fertilized zones by reducing phosphate adsorbed on ferrihydrite using Conservation Service, Washington, DC.
rice straw-derived biochar. J. Soils Sediments. 11, 1135–1141. Soinne, H., Hovi, J., Tammeorg, P., Turtola, E., 2014. Effect of biochar on phosphorus
Day, P.R., 1965. Particle fractionation and particle-size analysis. In: Black, C.A. (Ed.), sorption and soil clay aggregate stability. Geoderma 219–220, 162–167.
Methods of Soil Analysis. Agronomy, vol. 9. pp. 545–567. Sun, K., Ro, K., Guo, M.X., Novak, J., Mashayekhi, H., et al., 2011. Sorption of bisphenol
DeLuca, T.H., Gundale, M.J., MacKenzie, M.D., Jones, D.L., 2015. Biochar e ects on soil A, 17a-ethinyl estradiol and phenanthrene on thermally and hydrothermally pro-ff
nutrient transformations. In: Lehmann, J., Joseph, S. (Eds.), Biochar for duced biochars. Bioresour. Technol. 102, 5757–5763.
Environmental Management: Science, Technology and Implementation. Taylor and Wang, T., Camps-Arbestain, M., Hedley, M., Bishop, P., 2012. Predicting phosphorus
Francis, London, pp. 421–454. bioavailability from high-ash biochars. Environ. Pollut. 357, 173–187.
Dickson, K.B., Benneh, G., 1995. A New Geography of Ghana, 3rd ed. Longman, Essex. Wang, T., Camps-Arbestain, M., Hedley, M., 2014. The fate of phosphorus of ash-rich
Dong, X., Ma, L.Q., Zhu, Y., Li, Y., Gu, B., 2013. Mechanistic investigation of mercury biochars in a soil-plant system. Plant Soil 375, 61–74.
sorption by Brazilian pepper biochars of di erent pyrolysis temperatures based on X- WRB, 1998. World Reference Base for Soil Resources. World Resources Report. No. 84.ff
ray photoelectron spectroscopy and flow calorimetry. Environ. Sci. Technol. 47, FAO, Rome.
12156–12164. Xu, G., Sun, J., Shao, H., Chang, S.X., 2014. Biochar had effects on phosphorus sorption
Duku, M.H., Gu, S., Hagan, E.B., 2011. Biochar production potential in Ghana-a review. and desorption in three soils with differing acidity. Ecol. Eng. 62, 54–60.
Renew. Sust. Energ. Rev. 15, 3539–3551. Zhai, L., CaiJi, Z., Liu, J., Wang, H., Ren, T., Gai, X., Xi, B., Liu, H., 2014. Short-term
Dwomo, O., Dedzoe, C.D., 2010. Oxisol (ferralsol) development in two agro-ecological effects of maize residue biochar on phosphorus availability in two soils with different
zones of Ghana: a preliminary evaluation of some pro les. J. Sci. Technol. 30 (2), phosphorus sorption capacities. Biol. Fertil. Soils 51, 113–122.fi
11–28. Zheng, H.Z., Deng, X., Zhao, J., Luo, Y., Novak, J., Herbert, S., Xing, B., 2013.
Eriksson, A.K., Gustafsson, J.P., Hesterberg, D., 2015. Phosphorus speciation of clay Characteristics and nutrient values of biochars produced from giant reed at different
fractions from long-term fertility experiments in Sweden. Geoderma 241–242, 68–74. temperatures. Bioresour. Technol. 130, 463–471.
Frost, R., Palmer, S., Pogson, R., 2012. Thermal stability of crandallite CaAl3
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