Biochar-induced modification of soil properties and the effect on crop production

Volume07-2019
Advances in Agricultural Science 07 (2019), 02: 59-87

Biochar-induced modification of soil properties and the effect on crop production

G. U. Chibuike Ezepue 1, 2 *, I. M. Uzoh 1, 3 and B. O. Unagwu 1

Department of Soil Science, Faculty of Agriculture, University of Nigeria, Nsukka 410001, Nigeria.
School of Agriculture and Environment, Private Bag 11222, Massey University, Palmerston North 4442, New Zealand.
Food Security and Safety (FSS) niche area, New Science Building, Faculty of Natural and Agricultural Sciences, North-West University, Mafikeng Campus, South Africa

ABSTRACT

There is high pressure on agricultural soils to produce more food to satisfy humanity due to global increase in human population. Thus, practices such as biochar addition to soils to improve crop production are increasingly being adopted, especially in the tropics where agricultural soils are, in general, highly weathered and less productive. This review aimed to explore, using existing literature, the factors that affect the agronomic effectiveness of biochar amendment, the changes in soil properties following biochar application, and the effect of such changes on crop growth. Several studies on biochar have shown that biochar application influences the physical, chemical and biological properties of soils, with most studies reporting increases in soil water holding capacity, pH and microbial activity. Changes in soil properties, following biochar application, are largely influenced by the initial properties of the soil, as well as the characteristics of the applied biochar. Typically, compared to fertile soils, less fertile soils are more positively influenced by biochar, in terms of soil modification for crop growth. Nutrient-rich biochars are also the most effective biochars on these less fertile soils. Crop growth benefits resulting from the use of biochar are generally due to the conditioning effect of biochar on soil properties, direct nutrient addition from the applied biochar and/or improvement of nutrient use efficiency, especially when combined with other amendments. Biochar application could sometimes have no effect or negative impact on the soil and this consequently affects crop growth and development. Long-term field experiments are required to improve research understanding of the mechanisms involved in the use of biochar for crop production purposes.

Keywords:  Soil fertilitySoil conditionerSoil amendmentsPlant nutrientsCrop growth


How to Cite: Chibuike, G., Uzoh, I., & Unagwu, B. (2019). Biochar-induced modification of soil properties and the effect on crop production. Advances in Agricultural Science, 7(2), 59-87. 

1. Introduction

Biochar refers to a carbonaceous material produced by heating biomass in the complete or partial absence of oxygen via a process called pyrolysis. Numerous studies have shown that biochar can improve soil fertility (Peng et al., 2011; Herath et al., 2013; Zhang et al., 2014; Zhai et al., 2015; Azlan Halmi et al., 2018; Pandit et al., 2018). It also has the capacity to sequester carbon (C); thus, it potentially contributes to climate change mitigation (Lehmann, 2007).

The addition of biochar to soils results in changes in soil chemical and physical properties such as increase in pH, cation exchange capacity (CEC), and water retention (Liang et al., 2006; Peng et al., 2011; Karhu et al., 2011; Herath et al., 2013; Martinsen et al., 2015). Biochar has also been reported to modify soil biological properties such as microbial biomass and enzyme activity (Jin, 2010; Bailey et al., 2011). The type and extent of these changes in soil properties have an impact on crop growth on biochar-amended soils (Boersma et al., 2017; Jeffery et al., 2017).

Although biochar has the potential to enhance soil properties for improved crop growth, its efficacy is affected by several factors such as the type of biochar feedstock, temperature and duration of pyrolysis, soil conditions,  crop species, and the method of application (Verheijen et al., 2010; Duku et al., 2011; Peng et al., 2011). The combination of these factors determines the effectiveness of biochar application for crop production.

Several studies have reported positive effects on crop growth after biochar application (Ezawa et al., 2002; Chen et al., 2010; Solaiman et al., 2010; Shen et al., 2016). However, there is a dearth of information on the relationship between changes in soil properties, particularly soil biological properties, after biochar addition and the subsequent effect on crop growth. Therefore, this review aimed to assist in filling this knowledge gap. The specific objectives of the review were to examine the factors that influence the efficacy of biochar for crop production, discuss changes in the physical, chemical and biological properties of soil after biochar application, and relate changes in soil properties after biochar application to crop growth, in order to improve research understanding of the mechanisms responsible for changes in crop growth and development after biochar addition to soils. To achieve these objectives, web-based search engines and databases, specifically Google Scholar and Science Direct, were used for the selection of relevant literature on biochar.

 

2.  Factors affecting the efficacy of biochar for crop production

2.1 Type of biochar feedstock

Feedstock is the biomass that is pyrolysed to form biochar. A wide range of feedstocks can be used for biochar production, including wood, plant residue (bagasse, stems, leaves, fruit pits, seed pods, nut shells, etc.), grass, green manure, animal manure, municipal wastes, industrial waste, and sewage sludge (Duku et al., 2011; International Biochar Initiative, 2015). Even though biochars are generally perceived to be high in nutrients, the type of feedstock used to produce biochar determines, to a large extent, the nutrient content of the biochar produced, which in general determines the amount of nutrients available to the crop. For instance, Domingues et al. (2017) noted that biochars derived from materials that are high in ash and nutrients (e.g. chicken manure and coffee husks) have a greater potential of liming and fertilising the soil. Conversely, biochars produced from materials with high C content and aromatic character (e.g. wood and sugarcane) are better for soil C sequestration rather than soil fertilisation.

In general, biochar produced from woody feedstock tend to possess lower amounts of ash compared to those produced from plant residue with high mineral content (Demirbas, 2004; Duku et al., 2011). Therefore, it is important to select the appropriate feedstock to suit a particular purpose of biochar application. Other factors to be considered when selecting the type of feedstock are the absence of toxins such as heavy metals (Rondon et al., 2007), as well as the cost and availability of the feedstock.

 

2.2 Pyrolysis condition of biochar feedstock

The temperature and time of biomass pyrolysis affect the physicochemical properties of biochar. Biochar produced at temperatures below 500°C promote the recovery of C and other nutrients, compared to those produced at higher temperatures (Macías and Camps Arbestain, 2010). Domingues et al. (2017) also noted that increasing the pyrolysis temperature from 350 and 450°C to 750°C decreases the CEC and hence the nutrient adsorptive capacity of nutrient-rich biochars. In addition, studies have shown that increasing the temperature and duration of pyrolysis reduces the yield and volatile matter content of biochar (Amonette and Joseph, 2009; Peng et al., 2011). Increasing the pyrolysis temperature is also known to increase the ash content of biochar (Rafiq et al., 2016). Therefore, it is critical to select the most suitable pyrolysis condition for biochar production, as this largely impacts on the effect of biochar application on soil and crops.

 

2.3 Soil conditions

Soil properties greatly influence the effectiveness of biochar application for crop production. For instance, Van Zwieten et al. (2010) compared the effect of biochar application on crops growing on two different soils (an acidic and an alkaline soil). The authors reported significant increases in plant biomass and nitrogen (N) use efficiency after biochar application on the acidic soil compared to the alkaline soil. This improvement in plant growth and performance after biochar application was attributed to better liming effect of biochar on the acidic soil compared to the alkaline soil. In addition, the significant increase in CEC of the acidic soil (which had low CEC compared to the alkaline soil prior to biochar application) after biochar application influenced crop growth on this soil. Similarly, Steiner et al. (2007) recorded increases in crop yield after biochar application on an acidic, highly weathered tropical soil near Manaus, Brazil. Haefele et al. (2011) also observed that the higher C/N ratio of a biochar amendment limited N availability and hence crop yield on a fertile soil compared to a less fertile soil. Furthermore, it has been reported that the positive effect of biochar on crop productivity is more prominent on course and medium textured soils (Jeffery et al., 2011).

After carrying out a global scale meta-analysis, Jeffery et al. (2017) concluded that biochar has no effect on crop yield in temperate regions due to the fertile and moderately-acidic state of temperate soils. This result agrees with the findings of Boersma et al. (2017) who observed that biochar had no effect on crop yield and quality parameters on a vegetable production system established on a fertile Ferrosol in Tasmania, Australia. On the other hand, Jeffery et al. (2017) noted that biochar increases crop yield (by 25%) in the tropics mainly due to increased liming and fertilisation effect on tropical soils, which are usually acidic and less fertile. The authors suggested that biochar application on temperate soils should focus on non-yield benefits of biochar, such as the mitigation of climate change through the control of greenhouse gas emission.

 

2.4 Method of biochar application

Major (2010) comprehensively described various methods of applying biochar to soil.  These methods include top dressing, uniform topsoil mixing, banding, and application to planting holes.  For any of these methods, biochar can either be applied directly or mixed with other amendments, such as manure, compost, crop residue, and seed. The biochar application method adopted will depend on the farming system and availability of labour (Duku et al., 2011). Irrespective of the method adopted, care should be taken to avoid carbon dioxide (CO2) emission beyond acceptable levels (Blackwell et al., 2009).

Where crops are already established, a top dressing (surface application) method can be used when applying biochar. It has been reported that top dressing method has the highest risk for soil loss via erosion (Major, 2009). Another method used after crop establishment is banding, which involves applying biochar below the soil surface to a depth of 0.1 m to 0.2 m (Duku et al., 2011). This method has been reported to improve the contact between the soil and biochar, as well as that between the crop and biochar (De Gryze et al., 2010). Applying biochar below the soil surface either through deep banding or direct application to planting holes reduces biochar losses due to erosion, and is the ideal method used when establishing tree crops. Uniform topsoil mixing involves broadcasting biochar across the soil before crop establishment. After broadcasting, the applied biochar is further incorporated into the soil either manually or mechanically to reduce erosion losses.

 

2.5 Plant species

The response of crops to biochar application differs among different species, and this may depend on the species’ unique characteristics such as physiology and nutrient requirement. While some crops require large amounts of nutrients and hence biochar, other may not need large amounts of biochar. Exceeding the nutrient requirement of a crop through application of large amounts of soil amendments may negatively impact on crop growth (Ericsson, 1994; McCauley et al., 2011). Thomas et al. (2013) reported variations in the biomass of two invasive weed species (Abutilon theophrasti and Prunella vulgaris) following the application of biochar on a salt-stressed soil. While biochar resulted in a significant increase in above ground biomass of P. vulgaris, no significant increase was observed for A. theophrasti. On the other hand, biochar addition resulted in the complete alleviation of salt-induced mortality in A. theophrasti, but only prolonged the survival of P. vulgaris. Other researchers have also recorded different growth responses for various crop species growing on soils amended with biochar (Siregar, 2007; Van Zwieten et al., 2010). The mechanisms responsible for these differences in crop growth have not been fully explored and this calls for more research.

 

3. Modification of soil properties after biochar application

Several studies have recorded changes in soil physicochemical and biological properties following biochar application. These changes are summarised in Tables 1-3.

 

3.1 Physical modification

Generally, biochar reduces soil bulk density (Table 1). This is mainly because of the low bulk density of biochars. However, the soil type, pyrolysis conditions and quantity of biochar applied also determine the extent to which soil bulk density would be modified. The effect of biochar on the soil aggregate stability and water-related soil properties (saturated hydraulic conductivity, water content and water holding capacity) depends on the inner porous structure of the biochar (Herath et al., 2013), which varies with the temperature of pyrolysis and type of feedstock (Hina et al., 2010; Schimmelpfennig and Glaser, 2012). Higher pyrolysis temperature produces biochar with higher porosity, with an increase in the smaller diameter fractions (Downie et al., 2009). Biochar produced at lower temperature has the potential to increase aggregate formation due to its stronger interactions with soil mineral particles (Brodowski et al., 2005).

In most cases, the effect of biochar on one soil physical property directly affects other soil physical properties. For instance, Herath et al. (2013) reported that corn stover biochar added to an Alfisol significantly lowered the soil bulk density and increased the formation of macroaggregates. The modification of soil bulk density and macroaggregates further increased the soil macroporosity and hydraulic conductivity. The authors also observed that there was no effect on the bulk density of an Andisol after biochar application. There was, however, an increase in the mesoporosity of the Andisol after biochar application, and this corresponded to an increase in the soil available water capacity. These varied responses to biochar application emphasises that the modification of soil property after biochar addition varies with soil type.

The hydrophobic nature of biochar potentially decreases soil water infiltration and increases soil water repellency (Page-Dumroese et al., 2015). However, hydrophobicity in biochar tends to increase with an increase in the temperature of pyrolysis (Herath et al., 2013). When biochar is applied to soil, the extent to which it alters the soil water infiltration and repellency depends on soil texture, amount of biochar applied, and the method of application (Page-Dumroese et al., 2015). Due to its dark colour, biochar reduces the soil surface albedo, resulting in an increase in soil surface temperature (Oguntunde et al., 2008).   

 

Table 1. An overview of the effect of biochar on soil physical properties

Soil property

Effect of biochar application

Conditions

Rate of application

Type of experiment

References

Aggregate stability

Increased water stable macro-aggregates

Feedstock: corn stover; Pyrolysis temperature: 350 and 550°C; Soil type: Typic Fragiaqualf (Alfisol) and Typic Hapludand (Andisol)

10 and 11.3 Mg ha-1

Laboratory (295 days)

Herath et al. (2013)

No effect on aggregate stability

Feedstock: rice straw; Pyrolysis condition: 250 to 450°C for between 2 to 8 hours; Soil type: Typic Plinthudult (Ultisol)

1 % (w w-1)

Laboratory (11 days)

Peng et al. (2011)

Increased macro- and micro- aggregates

Feedstock: rice hulls; Pyrolysis condition: 400°C for 2 hours; Soil type: Typic Eutrudept (Inceptisol)

2.5, 5 and 10 % (w w-1)

Laboratory (168 days)

Hseu et al. (2014)

No effect on aggregate stability

Feedstock: acacia green waste; Pyrolysis condition: 550°C for 30 to 40 minutes; Soil type: Planosol developed on Permian mudstone and little Jurassic dolerite colluviums

47 Mg ha-1

Field (30 months)

Hardie et al. (2014)

Bulk density

Reduced soil bulk density

Feedstock: peanut hulls; Pyrolysis condition: 500°C for 1 hour; Soil type:  sandy loam – Typic Kandiudult (Ultisol)

25, 50, 75 and 100 % (w w-1)

Laboratory

Githinji (2014)

Reduced soil bulk density

Feedstock: corn stover; Pyrolysis temperature: 350 and 550°C; Soil type: Typic Fragiaqualf (Alfisol)

10 and 11.3 Mg ha-1

Laboratory (295 days)

Herath et al. (2013)

No effect on soil bulk density

Feedstock: corn stover; Pyrolysis temperature: 350 and 550°C; Soil type: Typic Hapludand (Andisol)

10 and 11.3 Mg ha-1

Laboratory (295 days)

Herath et al. (2013)

Reduced soil bulk density

Feedstock: wood; Soil type: Haplic Acrisol

Field

Oguntunde et al. (2008)

Reduced soil bulk density

Feedstock: mixed hard wood (oak and hickory); Pyrolysis condition: slow pyrolysis; Soil type: fine-loamy – Mesic Typic Hapludolls (Mollisol)

5, 10, and 20 g kg-1

Laboratory (500 days)

Laird et al. (2010)

Reduced soil bulk density

Feedstock: municipal green waste; Pyrolysis temperature: 450°C; Soil type: residue sand from bauxite refinery

40 and 80 Mg ha-1

Laboratory (6 weeks)

Jones et al. (2010)

Increased soil bulk density

Feedstock and pyrolysis temperature: hardwood (500°C), peanut hull (400 and 500°C), pecan shell (350 and 700°C), poultry litter (350 and 700°C), switch grass (250 and 500°C); Soil type: fine-loamy – Thermic Typic Kandiudult (Ultisol)

2 % (w w-1)

Laboratory (127 days. Bulk density was determined at the 28th and 118th day after leaching with water)

Novak et al. (2012)

Saturated hydraulic conductivity, water content and water holding capacity

Increased volumetric soil water content and saturated hydraulic conductivity

Feedstock: corn stover; Pyrolysis temperature: 350 and 550°C; Soil type: Typic Fragiaqualf (Alfisol) and Typic Hapludand (Andisol)

10 and 11.3 Mg ha-1

Laboratory (295 days)

Herath et al. (2013)

Increased saturated hydraulic conductivity

Feedstock: wood; Soil type: Haplic Acrisol

Field

Oguntunde et al. (2008)

Increased available water capacity and water content at the permanent wilting point

Feedstock: maize and beechwood; Pyrolysis condition: 750°C  for 20 ± 5 minutes (maize) and 550°C  for 15 ± 5 minutes (beechwood); Soil type: sand and loamy sand (Haplic Luvisol)

1, 2.5 and 5 % (w w-1)

Laboratory (2 weeks) and Field (6 months)

Abel et al. (2013)

Increased soil water holding capacity

Feedstock: birch; Pyrolysis condition: 400°C  for 2 to 2.5 hours; Soil type: silt loam

9 Mg ha-1

Field

Karhu et al. (2011)

Increased soil water content

Feedstock: Miscanthus giganteus; Pyrolysis temperature: 450°C; Soil type: loam and sand

25 Mg ha-1

Laboratory (1 year)

Duarte et al. (2019)

Increased soil water holding capacity

Feedstock: hardwood mix (oak, cherry and ash); Pyrolysis condition: 400°C  for 24 hours; Soil type: sandy loam

5 and 10 % (w w-1)

Laboratory (126 days)

Case et al. (2012)

Water repellency

No effect on soil water repellency

Feedstock: corn stover; Pyrolysis temperature: 350  and 550°C; Soil type: Typic Fragiaqualf (Alfisol) and Typic Hapludand (Andisol)

10 and 11.3 Mg ha-1

Laboratory (295 days)

Herath et al. (2013)

No effect on soil water repellency

Feedstock: beechwood; Pyrolysis condition: 550°C  for 15 ± 5 minutes; Soil type: loamy sand (Haplic Luvisol)

1, 2.5 and 5 % (w w-1)

Field (6 months)

Abel et al. (2013)

No significant effect on soil water repellency (surface application resulted in less water infiltration than mixing with soil)

Feedstock: mixed conifers (lodgepole pine, douglas-fir and ponderosa pine); Pyrolysis condition: short exposure at 700 to 750°C  before subsequent longer exposure at lower temperature; Soil type: sandy loam (Inceptisol)

1 and 5 Mg ha-1

Laboratory

Page-Dumroese et al. (2015)

Increased soil water repellency (surface application resulted in less water infiltration than mixing with soil)

Feedstock: mixed conifers (lodgepole pine, douglas-fir and ponderosa pine); Pyrolysis condition: short exposure at 700 to 750°C  before subsequent longer exposure at lower temperature; Soil type: silt loam (Andisol)

5 and 10 Mg ha-1

Laboratory

Page-Dumroese et al. (2015)

Albedo

Reduced soil albedo

Feedstock: wood cutoffs; Pyrolysis temperature: 350 to 400°C; Soil type: Haplic Luvisol

10, 20 and 30 Mg ha-1

Field

Usowicz et al. (2016)

Reduced soil albedo

Feedstock: wood; Soil type: Haplic Acrisol

Field

Oguntunde et al. (2008)

 

3.2 Chemical modification

Changes in soil chemical properties following biochar addition to soils are shown in Table 2. The changes in soil chemical properties are usually due to the chemical composition of the biochar applied. Several studies have reported pH increase resulting from the addition of biochar to soil, especially under acidic soil conditions (Chan et al., 2008; Peng et al., 2011; Martinsen et al., 2015). The increase in soil pH with biochar addition is mainly due to its ash content which increases with higher pyrolysis temperature and mineral/ash content of the biochar feedstock (Demirbas, 2004; Crombie et al., 2013; Rafiq et al., 2016). However, Liu and Zhang (2012) observed that biochar which had a lower pH than the amended alkaline soil resulted in a decrease in soil pH, possibly through an initial dilution of cations in biochar and a subsequent oxidation and decomposition of the added biochar within the 11-month study period.

Biochar increases the total C content of soils, which may lead to the short-term mineralisation of native organic C (positive priming), and eventually enhance soil C sequestration in the long run (Ouyang et al., 2014b; Singh and Cowie, 2014; Yin et al., 2014), hence, contributing to climate change mitigation. Biochar reduces nitrate leaching mainly via its potential to adsorb nitrates, especially when pyrolysed at a temperature of  ≥ 600oC, and also as a result of the modification of soil physical properties (Clough et al., 2013). This reduction in nitrate leaching following biochar application indicates that biochar has the potential to improve ground and surface water quality. A decrease in ammonium leaching after biochar addition to an acidic sandy soil has also been reported (Sika and Hardie, 2014). However, Sika and Hardie (2014) also observed a decrease in the amount of recoverable/exchangeable ammonium (and nitrate) on the biochar-amended leached soil, indicating a possible reduction in the amount of N available for crop growth.  The total soil N content generally increases with biochar addition (Chan et al., 2008; Prommer et al., 2014). However, both positive and negative effects (as well as no effect) of biochar on N fixation, mineralisation and immobilisation have been documented (Rondon et al., 2007; Bruun et al., 2012; Prommer et al., 2014). These discrepancies indicate that the effect of biochar on the above mentioned parameters depends on the type of feedstock (feedstock with high C/N ratio increases N immobilisation, while those with low C/N ratio promote N mineralisation), pyrolysis conditions, and rate of application.

The addition of biochar to soils is known to increase phosphorus (P) availability due to the high concentration of P in biochar ash content (Parvage et al., 2013; Zhai et al., 2015). This increase in P availability is influenced by the sorption capacity of the soil. After biochar application, P availability could be greater in soils with lower sorption capacities e.g. alkaline soils compared to acidic soils (Zhai et al., 2015). However, Chintala et al. (2014) reported that biochar addition decreased P availability (increased P sorption) in an alkaline soil and conversely increased P availability in an acidic soil, while Soinne et al. (2014) reported that biochar addition had no effect on the P sorption affinity of  acidic soils. These studies, therefore, suggest that the effect of biochar on P availability is interdependent on properties of the biochar and soil.

The CEC of most soils (especially acidic soils) increases with the addition of biochar (Masulili et al., 2010; Martinsen et al., 2015; Rabileh et al., 2015). This modification of soil CEC is usually accompanied by an increase in the base-forming cations (due to the ash content and other properties of the feedstock) and a decrease in the acid-forming cations. Changes in soil CEC and cation concentrations greatly impact on the availability (and toxicity) of nutrients for crop growth. For instance, Rabileh et al. (2015) reported a reduction in aluminium (Al) toxicity due to Al precipitation (as hydroxides) and chelation after biochar addition to an acidic Ultisol.

 

Table 2. An overview of the effect of biochar on soil chemical properties

Soil property

Effect of biochar application

Conditions

Rate of application

Type of experiment

References

pH

Increased soil pH

Feedstock: rice straw; Pyrolysis condition: 250 to 450°C for between 2 to 8 hours; Soil type: Typic Plinthudult (Ultisol)

1 % (w w-1)

Laboratory (11 days)

Peng et al. (2011)

Increased soil pH

Feedstock: cacao shell, oil palm shell and rice husk; Pyrolysis condition: 250  to 350°C for 1 to 3.5 hours; Soil type: a wide range of acidic tropical soils

0.1, 0.3, 1, 3, 10 and 30 % (w w-1)

Laboratory

Martinsen et al. (2015)

Decreased soil pH

Feedstock: Chinese pine and locust; Pyrolysis condition: 600°C for 2 hours; Soil type: alkaline soils of loess origin

4, 8 and 16 g kg-1

Laboratory (11 months)

Liu and Zhang (2012)

Increased soil pH

Feedstock: poultry litter; Pyrolysis condition: 450°C (inactivated) and 550°C (activated using high temperature steam); Soil type: Alfisol

10, 25 and 50 Mg ha-1

Glasshouse

Chan et al. (2008)

Increased soil pH

Feedstock: wood; Soil type: from Voltaian sandstone (Haplic Acrisol)

Field

Oguntunde et al. (2004)

Carbon

Increased soil (total) organic carbon

Feedstock: greenwaste (mixture of grass clippings, cotton trash and plant prunings); Pyrolysis condition: 450°C; Soil type: Alfisol

10, 50 and 100 Mg ha-1

Glasshouse

Chan et al. (2007)

Increased soil total carbon

Feedstock: poultry litter; Pyrolysis condition: 450°C (inactivated) and 550°C (activated using high temperature steam); Soil type: Alfisol

10, 25 and 50 Mg ha-1

Glasshouse

Chan et al. (2008)

Rapidly increased soil carbon mineralisation within the first 15 days before subsequent reductions (with stably low values recorded with time); increased soil (total) organic carbon and dissolved organic carbon

Feedstock: fresh dairy manure and pine tree woodchip; Pyrolysis condition: 300, 500 and 700°C for 1 hour; Soil type: forest loamy soil

5 % (w w-1)

Laboratory (180 days)

Ouyang et al. (2014b)

Decreased soil labile carbon and increased (total) organic carbon

Feedstock: rice straw; Pyrolysis condition: 250 and 350°C for 2 hours; Soil type: Ferrosol

50 g oven-dried soil + 0.52 g of biochar (250oC); 50 g oven-dried soil + 0.34 g of biochar (350oC)

Laboratory (112 days)

Yin et al. (2014)

Increased total carbon content

Feedstock: Miscanthus giganteus; Pyrolysis temperature: 450°C; Soil type: loam and sand

25 Mg ha-1

Laboratory (1 year)

Duarte et al. (2019)

Increased total organic carbon and carbon/nitrogen ratio; no effect on dissolved organic carbon

Feedstock: wheat straw; Pyrolysis temperature: 450°C; Soil type: Black Chernozem

20 Mg ha-1

Laboratory (15 months)

Hu et al. (2014)

Increased mineralisation of native total organic carbon (positive priming) with a subsequent decrease with time

Feedstock: Eucalyptus saligna wood, E. saligna leaves, poultry manure (made up of manure and rice hulls) and cow manure; Pyrolysis condition: 400 and 550°C for 40 minutes (with and without steam activation); Soil type: Vertisol

8.17 Mg ha-1

Laboratory (5 years)

Singh and Cowie (2014)

Nitrogen

Increased soil total nitrogen

Feedstock: poultry litter; Pyrolysis condition: 450°C (inactivated) and 550°C (activated using high temperature steam); Soil type: Alfisol

10, 25 and 50 Mg ha-1

Glasshouse

Chan et al. (2008)

Increased total nitrogen and gross nitrification rates; reduced nitrate, total dissolved nitrogen and organic nitrogen cycling rates (i.e. reduced protein production and consumption); no effect on rate of gross nitrogen mineralisation and ammonium immobilisation

Feedstock: beech wood; Pyrolysis condition: 500°C for 2 hours; Soil type: calcareous Chernozem

72 Mg ha-1

Field (14 months)

Prommer et al. (2014)

Increased biological nitrogen fixation

Feedstock: logs of rainbow eucalyptus; Pyrolysis condition: 350°C for 1 hour; Soil type: clay loam (Typic Haplustox)

30 and 60 g kg-1

Glasshouse

Rondon et al. (2007)

Decreased nitrogen derived from biological nitrogen fixation

Feedstock: logs of rainbow eucalyptus; Pyrolysis condition: 350°C for 1 hour; Soil type: clay loam (Typic Haplustox)

90 g kg-1

Glasshouse

Rondon et al. (2007)

Reduced mineral nitrogen (ammonia and nitrate)

Feedstock: prosopis biomass; Soil type: sandy clay loam (Vertic Ustropept)

1, 2, 3, 4 and 5 % (w w-1)

Laboratory (90 days)

Shenbagavalli and Mahimairaja (2012)

Decreased net nitrogen mineralisation

Feedstock: Jarrah wood (Eucalyptus marginata); Pyrolysis condition: 600°C for 24 hours; Soil type: Grey Orthic Tenosol

5 and 25 Mg ha-1

Glasshouse (10 weeks)

Dempster et al. (2012)

Decreased leaching of ammonium and nitrate

Feedstock: pine wood; Pyrolysis condition: slow pyrolysis at 450°C; Soil type: acidic sandy soil (Haplic Stagnosol)

0.5, 2.5 and 10 % (w w-1)

Laboratory (6 weeks)

Sika and Hardie (2014)

Reduced nitrate leaching

Feedstock: bagasse and biosolids; Pyrolysis temperature: 600°C; Soil type: heavy clay

3 % (w w-1) for bagasse and 1 % (w w-1) for biosolids

Outdoor lysimeter (15 months)

Chen et al. (2010)

No effect on nitrate and ammonium

Feedstock: Blue mallee (Eucalyptus polybractea R. Baker); Pyrolysis condition: 550°C for 30 minutes; Soil type: deep red earth (Ferrosol)

10 Mg ha-1

Field (12 months)

Boersma et al. (2017)

Increased nitrogen immobilisation

Feedstock: wheat straw; Pyrolysis condition: 525°C (fast pyrolysis); Soil type: sandy loam

38 g of dry soil mixed with 2 g of biochar

Laboratory (65 days)

Bruun et al. (2012)

Increased net nitrogen mineralisation

Feedstock: wheat straw; Pyrolysis condition: 525°C (slow pyrolysis); Soil type: sandy loam

38 g of dry soil mixed with 2 g of biochar

Laboratory (65 days)

Bruun et al. (2012)

Phosphorus

Increased (Olsen) phosphorus availability as influenced by lower phosphorus sorption capacity

Feedstock: maize straw; Pyrolysis condition: 400°C for 1.5 hours; Soil type: Ferralic Cambisol (slightly acidic) and Haplic Luvisol (alkaline)

2, 4 and 8 % (w w-1)

Laboratory (42 days)

Zhai et al. (2015)

Increased water-soluble phosphorus

Feedstock: wheat residue; Soil type: silt loam, clay loam and loam

0.5 and 1% (w w-1)

Laboratory (16 hours)

Parvage et al. (2013)

Decreased water-soluble phosphorus

Feedstock: wheat residue; Soil type: silt loam, clay loam and loam

2 and 4% (w w-1)

Laboratory (16 hours)

Parvage et al. (2013)

Increased plant available phosphorus

Feedstock: Eupatorium adenophorum; Pyrolysis temperature: 600 to 700°C; Soil type: moderately acidic Dystrochrept (Inceptisol)

0.5 and 2.0 % (w w-1)

Glasshouse (50 days)

Pandit et al. (2018)

No effect on phosphorus sorption affinity

Feedstock: chips of Norway spruce and Scots pine; Pyrolysis condition: 550 to 600°C for 10 to 15 minutes; Soil type: silty clay loam (Endogleyic Stagnosol) and clay (Cutanic Vertic Luvisol)

15 and 30 Mg ha-1

Laboratory (3 weeks)

Soinne et al. (2014)

Reduced phosphorus sorption affinity

Feedstock: chips of Norway spruce and Scots pine; Pyrolysis condition: 550 to 600°C for 10 to 15 minutes; Soil type: sand (Endogleyic Umbrisol)

15 and 30 Mg ha-1

Laboratory (3 weeks)

Soinne et al. (2014)

Increased phosphorus sorption

Feedstock: wheat straw; Pyrolysis temperature: 350 to 550°C; Soil type: acidic sandy loam (Inceptisol)

10, 50 and 100 g kg-1

Laboratory

Xu et al. (2014)

Decreased phosphorus sorption

Feedstock: wheat straw; Pyrolysis temperature: 350 to 550°C; Soil type: alkaline loam to silt loam (Alfisol)

10, 50 and 100 g kg-1

Laboratory

Xu et al. (2014)

Increased phosphorus sorption (decreased phosphorus availability)

Feedstock: corn stover, switch grass and Ponderosa pine wood residue; Pyrolysis condition: 650°C for 18 minutes; Soil type: calcareous fine-loam (Eutrudepts)

40 g kg-1

Laboratory (30 days)

Chintala et al. (2014)

Decreased phosphorus sorption (increased phosphorus availability)

Feedstock: corn stover, switch grass and Ponderosa pine wood residue; Pyrolysis condition: 650°C for 18 minutes; Soil type: acidic clay (Aridic Ustorthents)

40 g kg-1

Laboratory (30 days)

Chintala et al. (2014)

Cation exchange capacity (CEC), exchangeable cations and other nutrients

Increased CEC and exchangeable base cations (calcium, magnesium and potassium)

Feedstock: cacao shell, oil palm shell and rice husk; Pyrolysis condition: 250  to 350°C for 1 to 3.5 hours; Soil type: a wide range of acidic tropical soils

0.1, 0.3, 1, 3, 10 and 30 % (w w-1)

Laboratory

Martinsen et al. (2015)

Increased CEC

Type of biochar: black carbon from archaeological sites; Soil type: Anthrosols developed from Oxisols, Utisols and Spodosols

Not applicable

Field

Liang et al. (2006)

No effect on CEC; increase in Mehlich 1 extractable calcium, potassium and manganese; decrease in exchangeable acidity, sulphur and zinc

Feedstock: pecan shells; Pyrolysis condition: 700°C for 1hour; Soil type: loamy sand – Thermic Typic Kandiudults (Utisol)

0.5, 1 and 2 % (w w-1)

Laboratory (67 days)

Novak et al. (2009)

Increased CEC and percentage base saturation

Feedstock: wood of white lead tree; Pyrolysis temperature: 700°C; Soil type: Typic Paleudults

2.5 and 5 % (w w-1)

Laboratory (105 days)

Jien and Wang (2013)

Increased plant available potassium

Feedstock: Eupatorium adenophorum; Pyrolysis temperature: 600 to 700°C; Soil type: moderately acidic Dystrochrept (Inceptisol)

0.5 and 2.0 % (w w-1)

Glasshouse (50 days)

Pandit et al. (2018)

Increased CEC and exchangeable bases (calcium, magnesium, potassium and sodium)

Feedstock: maize stalk; Pyrolysis temperature: 500°C; Soil type: Nitisol

5 and 10 Mg ha-1

Pot experiment

Nigussie et al. (2012)

Increased CEC and exchangeable bases (calcium, magnesium, potassium and sodium); decreased exchangeable aluminium (and manganese in soil solution)

Feedstock: oil palm empty fruit bunch; Pyrolysis temperature: 300 to 350°C; Soil type: Typic Paleudult (Ultisol)

5, 10 and 20 Mg ha-1

Glasshouse (50 days)

Rabileh et al. (2015)

Increased CEC and exchangeable calcium and potassium; decreased exchangeable aluminium and iron

Feedstock: rice husk; Pyrolysis temperature: 600°C; Soil type: acid sulphate soil

10 Mg ha-1

Glasshouse (30 days)

Masulili et al. (2010)

 

3.3 Biological modification

The effect of biochar on soil organisms has been receiving attention in recent years (Table 3), though the emphasis has been on microbial properties. Biochar increases the soil microbial community and biomass (Zhang et al., 2014; Demisie and Zhang, 2015; Xu et al., 2016) mainly by providing favourable habitat and labile C needed by the microbes. However, biochar may also negatively affect microbial biomass, especially when applied at high concentrations (Zhang et al., 2014; Demisie and Zhang, 2015), though this negative effect varies with soil properties. Typically, it is expected that high concentrations of biochar on a fertile soil would be detrimental to soil microbes.  The application of biochar with low pH could also have negative effects on soil bacterial abundance, since bacterial abundance increases with increases in soil pH (Lehmann et al., 2011; Lehmann et al., 2015). It is important to note that volatile compounds (such as benzene) found in biochar also have the potential to decrease soil microbial biomass (Girvan et al., 2005; Dempster et al., 2012).

Increase in microbial biomass leads to an increase in microbial activities e.g. soil respiration (Kolb et al., 2009; Smith et al., 2010; Xu et al., 2016). No effect on soil respiration after biochar addition has also been reported, especially in field experiments (Lu et al., 2014; Liu et al., 2016), and this is probably because the added C from biochar is protected or bound by soil aggregates and mineral particles. This is not usually the case in most laboratory and glasshouse experiments, where the C is easily accessible to the microorganisms. The controlled environmental condition in laboratory and glasshouse experiments could also promote the activities of soil microorganisms in biochar-amended soils.

Biochar exerts both positive and negative effects on soil enzyme activity depending on the type of soil and biochar applied (Table 3). The increase in enzyme activity after biochar addition is mainly attributed to the increase in microbial activity, due to the introduction of a labile C source from the biochar (Bailey et al., 2011; Ouyang et al., 2014a). Zhai et al. (2015) noted that the reduction in phosphosmonoesterase activity following biochar addition was due to the large amount of inorganic P (60 mg P kg-1 as KH2PO4) added to the soil. Variations in environmental conditions such as moisture content (which increases microbial activities) also influence how the soil enzymes respond to biochar addition (Niemi et al., 2015).

The effect of biochar on mycorrhizal association  was summarised by Warnock et al. (2007). The authors noted that biochar influences mycorrhizal abundance and activity via four mechanisms namely: (i) modification of soil nutrient availability through the alteration of the physicochemical properties of soil; (ii) alteration of the activities of other soil microorganisms which indirectly affects mycorrhizae; (iii) interference with the plant fungus signalling dynamics or detoxification of allelochemicals; and (iv) provision of refugia from soil predators. One or more of these mechanisms contribute to the increase in mycorrhizal colonisation reported in several studies (Ezawa et al., 2002; Yamato et al., 2006; Solaiman et al., 2010; LeCroy et al., 2013; Shen et al., 2016). Negative effects (e.g. decrease in hyphal growth) and absence of any effect (e.g. no colonisation) following biochar addition have also been documented (Rondon et al., 2007; Shen et al., 2016). High P content interferes with mycorrhizal associations (Schubert and Hayman, 1986; Liu et al., 2000). Therefore, both soil type and biochar feedstock determine the effect of biochar on mycorrhizae.

Studies on the effect of biochar on soil fauna have focused more on earthworms and less on other soil fauna. Earthworms ingest biochar when feeding and burrowing through the soil. However, the role of the ingested biochar in earthworm system is not well understood. Lehmann et al. (2011) noted that the ingested biochar may grind up organic matter in the earthworm’s gizzard, or more microorganisms and microbial metabolites may be ingested alongside the biochar, since microbes are more abundant on biochar surfaces. In general, soil fauna (earthworms) respond to biochar application in different ways (positive, negative, and neutral–no effect) depending on the type of feedstock and soil.

 

Table 3. An overview of the effect of biochar on soil biological properties
Soil property Effect of biochar application Conditions Rate of application Type of experiment References
Microbial biomass and diversity Increased bacterial and archaeal nitrifiers (soil ammonium oxidiser population) Feedstock: beech wood; Pyrolysis condition: 500°C for 2 hours; Soil type: calcareous Chernozem 72 Mg ha-1 Field (14 months) Prommer et al. (2014)
Decreased microbial biomass carbon; no effect on microbial biomass nitrogen Feedstock: Jarrah wood (Eucalyptus marginata); Pyrolysis condition: 600°C for 24 hours; Soil type: Grey Orthic Tenosol 5 and 25 Mg ha-1 Glasshouse (10 weeks) Dempster et al. (2012)
Increased microbial biomass phosphorus as influenced by lower phosphorus sorption capacity Feedstock: maize straw; Pyrolysis condition: 400°C for 1.5 hours; Soil type: Ferralic Cambisol (slightly acidic) and Haplic Luvisol (alkaline) 2, 4 and 8 % (w w-1) Laboratory (42 days) Zhai et al. (2015)
Increased microbial biomass carbon and nitrogen (but decreased microbial biomass nitrogen at higher rates); increased microbial biomass carbon and nitrogen ratio Feedstock: corn cob; Pyrolysis condition: 360°C for 24 hours; Soil type: sandy loam (Fluvic Cambisol) 4.5 and 9 Mg ha-1 Field (4 years) Zhang et al. (2014)
Increased microbial biomass carbon and nitrogen; changed bacterial community structure and increased bacterial diversity Feedstock: corn straw; Pyrolysis condition: 500°C for 1.5 hours; Soil type: Fluvo-aquic soil 40, 80 and 160 Mg ha-1 Glasshouse (5 months) Xu et al. (2016)
Increased bacterial diversity Feedstock: mixture of peanut shell and wheat straw; Pyrolysis condition: 500°C for 30-40 minutes; Soil type: sand 5 and 10 % (w w-1) Field (3 months) Wong et al. (2019)
Increased microbial communities and biomass carbon and nitrogen at lower rates of application Feedstock: oak wood and bamboo; Pyrolysis condition: 600°C for 2 hours; Soil type: clay loam (Typic Plinthustults) 0.5, 1 and 2 % (w w-1) Laboratory (16 weeks, with samplings at different intervals) Demisie and Zhang (2015)
Increased microbial biomass carbon and nitrogen; decreased microbial biomass carbon and nitrogen ratio; increased bacterial and fungal gene abundance Feedstock: palm kernel shell; Pyrolysis condition: slow pyrolysis at 400°C; Soil type: sandy loam (Udults Ultisol) 20 Mg ha-1 Field (75 days) Azlan Halmi et al. (2018)
Soil respiration Increased soil basal respiration, substrate induced respiration and metabolic quotient (ratio of soil basal respiration and microbial biomass carbon) Feedstock: corn straw; Pyrolysis condition: 500°C for 1.5 hours; Soil type: Fluvo-aquic soil 40, 80 and 160 Mg ha-1 Glasshouse (5 months) Xu et al. (2016)
Increased soil basal respiration, substrate induced respiration and metabolic quotient (ratio of soil basal respiration and substrate induced respiration) Feedstock: mixture of bull manure, dairy manure and pine shavings; Pyrolysis temperature: 500°C; Soil type: clay loam (Alfisol), sandy loam (Spodosol), loamy sand (Entisol) and silt loam (Mollisol) 1, 2.5, 5 and 10 % (w w-1) Laboratory (3 months, with sampling at different intervals) Kolb et al. (2009)
Increased soil respiration Feedstock: switch grass; Pyrolysis condition: 500°C for 2 hours; Soil type: silt loam (mesic Xeric Haplocambids and mesic Typic Haploxerolls) 11.2, 22.4 and 44.8 Mg ha-1 Laboratory (49 days, with sampling at different intervals) Smith et al. (2010)
No effect on soil respiration Feedstock and pyrolysis condition: maize stalk pyrolysed at 350-500°C for 1 hour, rice straw and maize stalk pyrolysed at 550-650°C for 1 hour; Soil type: Hydro agric stagnic Anthrosol, Calcaric entic fluvent, Typic orchrept and Typic hapludult 20 and 40 Mg ha-1 Field Liu et al. (2016)
Increased soil organic carbon-derived soil respiration; decreased rhizosphere-derived soil respiration; no effect on total soil respiration Feedstock: mixed pruned wood from fruit trees, especially peach and grape vine; Pyrolysis temperature: 500°C; Soil type: Haplic Calcisol 10 Mg ha-1 Field (~ 2 years, with sampling at 20 days interval) Ventura et al. (2014)
No effect on soil respiration Feedstock: maize cob; Pyrolysis condition: 360°C for 24 hours; Soil type: loam (Fluvic Cambisol) 4.5 and 9 Mg ha-1 Field (3 months, with sampling at 3 days interval) Lu et al. (2014)
Soil enzyme activity Reduced acid and alkaline phosphomonoesterase activity Feedstock: maize straw; Pyrolysis condition: 400°C for 1.5 hours; Soil type: Ferralic Cambisol (slightly acidic) and Haplic Luvisol (alkaline) 2, 4 and 8 % (w w-1) Laboratory (42 days) Zhai et al. (2015)
Increased β-glucosidase, urease and phosphodiesterase activity Feedstock: palm kernel shell; Pyrolysis condition: slow pyrolysis at 400°C; Soil type: sandy loam (Udults Ultisol) 20 Mg ha-1 Field (75 days) Azlan Halmi et al. (2018)
Increased urease activity; reduced β- and acid- glucosidase activity Feedstock: oak wood and bamboo; Pyrolysis condition: 600°C for 2 hours; Soil type: clay loam (Typic Plinthustults) 0.5, 1 and 2 % (w w-1) Laboratory (16 weeks, with samplings at different intervals) Demisie and Zhang (2015)
Increased soil enzyme activity (polyphenol oxidase, dehydrogenase, peroxidise, β-glucosidase and catalase), especially within the first 80 days Feedstock: Dairy manure and woodchip; Pyrolysis condition: 300, 500 and 700°C for 1 hour; Soil type: loam 5 % (w w-1) Pot experiment (180 days, with sampling at different intervals) Ouyang et al. (2014a)
Increased β-glucosidase, leucine-aminopeptidase and lipase activity; inconsistency in β-N-acetylglucosaminidase activity Feedstock: switch grass; Pyrolysis condition: 500°C for 2 hours; Soil type: silt loam (Pachic Ultic Haploxeroll) 2 % (w w-1) Laboratory  (7 days) Bailey et al. (2011)
Decreased β-glucosidase and lipase activity; no effect on leucine-aminopeptidase activity; inconsistency in β-N-acetylglucosaminidase activity Feedstock: switch grass; Pyrolysis condition: 500°C for 2 hours; Soil type: sand (Xeric Torripsamment) 2 % (w w-1) Laboratory  (7 days) Bailey et al. (2011)
Increased β-N-acetylglucosaminidase activity; decreased leucine-aminopeptidase activity; inconsistency in β-glucosidase activity Feedstock: switch grass; Pyrolysis condition: 500°C for 2 hours; Soil type: sandy loam (Xeric Haplocambid) 2 % (w w-1) Laboratory  (7 days) Bailey et al. (2011)
No negative effect on arylsulfatase activity Feedstock: birch wood; Pyrolysis temperature: 500°C; Soil type: sandy loam (Typic Hapludalf) 10, 20, 40, 50 and 100 Mg ha-1 Field (2 years) Sun et al. (2014)
Slightly decreased leucine and alanine aminopeptidase activity Feedstock: spruce chips; Pyrolysis condition: 400-450°C for 10-15 minutes; Soil type: sandy till 1 % (w w-1) Mesocosm Niemi et al. (2015)
Slightly increased β-N-acetylglucosaminidase and phosphomonoesterase activity Feedstock: spruce chips; Pyrolysis condition: 400-450°C for 10-15 minutes; Soil type: medium fine sand 1 % (w w-1) Mesocosm Niemi et al. (2015)
Mycorrhizae Increased colonisation which induced mycorrhizal parasitism (reduced above-ground biomass) at high amounts of mineral nitrogen in soil Feedstock: apple wood sawdust; Pyrolysis condition: ~ 400°C for ~ 250 minutes; Soil type: mixture of sand and organic potting media (1:1); Plant: sorghum; Type of mycorrhiza: arbuscular mycorrhizal fungus 17.6 Mg ha-1 Glasshouse LeCroy et al. (2013)
Increased hyphal length in “hyphal zone” of soil with high phosphorus concentration (i.e. phosphorus-rich soil patch) which resulted in increased plant growth and phosphorus uptake. This was especially true for biochar pyrolysed at lower temperature Feedstock: pine wood chips; Pyrolysis temperature: 450 and 550°C; Soil type: Andosol; Plant: Lotus pedunculatus; Type of mycorrhiza: arbuscular mycorrhizal fungi 10 Mg ha-1 Glasshouse (32 weeks) Shen et al. (2016)
Slightly decreased hyphal length in “hyphal zone” of soil with high phosphorus concentration (i.e. phosphorus-rich soil patch) Feedstock: willow wood chip; Pyrolysis temperature: 550°C; Soil type: Andosol; Plant: Lotus pedunculatus; Type of mycorrhiza: arbuscular mycorrhizal fungi 10 Mg ha-1 Glasshouse (32 weeks) Shen et al. (2016)
Increased root colonisation (in the presence of mineral fertiliser) which improved plant yield Feedstock: oil mallee Eucalyptus; Soil type: sandy clay loam; Plant: wheat; Type of mycorrhiza: arbuscular mycorrhizal fungi 1.5, 3 and 6 Mg ha-1 Field Solaiman et al. (2010)
Increased root colonisation and length (in the presence of mineral fertiliser) which resulted to improved plant growth and phosphorus nutrition Feedstock: oil mallee Eucalyptus; Soil type: sandy clay loam; Plant: subterranean clover; Type of mycorrhiza: arbuscular mycorrhizal fungi 1.5, 3 and 6 Mg ha-1 Glasshouse (6 weeks) Solaiman et al. (2010)
Increased mycorrhizal colonisation, especially in the ground (verses unground) treatment, which resulted in increased plant growth Feedstock: rice hull; Pyrolysis condition: 380°C for 8 hours; Soil type: Pale Humult; Plant: Dwarf marigold; Type of mycorrhiza: arbuscular mycorrhiza fungi 1 volume (180 ml) of biochar mixed with 2 volumes (360 ml) of soil Glasshouse (6 weeks) Ezawa et al. (2002)
Increased mycorrhiza formation which promoted plant growth Feedstock: rice husk; Soil type: forest top soil; Plant: Shorea smithiana; Type of mycorrhiza: ectomycorrhiza 1 + 15, 2 + 15, 3 + 15, 4 + 15, 5 + 15 L m-2 (biochar + soil) Pot experiment – nursery (9.5 months) Mori and Marjenah (1994)
Increased mycorrhiza formation which promoted plant growth Feedstock: rice husk; Soil type: degraded forest soil; Plant: Shorea smithiana; Type of mycorrhiza: ectomycorrhiza 300 cm3 of biochar mixed with 1 L of top soil. The mixture was placed in a hole of about 25 cm in depth and diameter Field (8 month) Mori and Marjenah (1994)
No effect on spore number and root colonisation Feedstock: logs of Eucalyptus deglupta; Pyrolysis condition: 350°C for 1 hour; Soil type: acidic clay loam (Typic Haplustox – Oxisol); Plant: common beans; Type of mycorrhiza: arbuscular mycorrhiza fungi 30, 60 and 90 g kg-1 Glasshouse (75 days) Rondon et al. (2007)
Increased root quantity and colonisation rate Feedstock: bark of Acacia mangium; Pyrolysis temperature: 260-360°C; Soil type: acidic soil; Plant: maize; Type of mycorrhiza: arbuscular mycorrhiza fungi 10 L m-2 Field (3 months) Yamato et al. (2006)
Soil fauna No effect on the feeding rates of soil fauna (mainly collembolans and enchytraeids, and to some extent, earthworms) Feedstock: corn stover; Pyrolysis condition: 600°C for 30 minutes; Soil type: silt loam (mesic Aeric Endoaquepts and mesic Oxyaquic Hapludalfs) 3, 12 and 30 Mg ha-1 (applied 3 years before current study) with additional 1 Mg ha-1 applied annually for 3 years Field Domene et al. (2014)
Reduced feeding activity of soil fauna Feedstock: gasifier pine (Pinus pinaster + Pinus radiate) chip; Pyrolysis condition: 600-900°C for 10 seconds; Soil type: calcareous Fluventic haploxerept 12 and 50 Mg ha-1 Field (24 months, with sampling at 3 intervals) Marks et al. (2016)
No effect on earthworm biomass and assimilation of biochar-carbon Feedstock: Miscanthus x giganteus; Pyrolysis condition: ~ 600°C; Soil type: stagnic Luvisol with a silty texture 30 Mg ha-1 Laboratory (37 days) Bamminger et al. (2014)
No effect of biochar on earthworm (no interaction). However both biochar and earthworm additively increased the total vegetative and grain biomass of rice Feedstock: logs of Eucalyptus  deglupta; Pyrolysis condition: 350°C for 1 hour; Soil type: volcanic-ash clayey soil (Inceptisol) 25.5 g kg-1 Glasshouse (3 months) Noguera et al. (2010)
Biochar was not a nutrient source for earthworms Feedstock: native charcoal from a slash-and-burn field; Soil type: Oxisol 3:2 w w-1 mixture of charcoal and soil Microcosm (2 weeks) Topoliantz and Ponge (2003)
Earthworm preferred the biochar-amended soil compared to the control soil (differed with soil type) Feedstock: paper mill waste; Pyrolysis temperature: 550°C; Soil type: Ferrosol (acidic) and Calcarosol (alkaline) 10 Mg ha-1 Glasshouse (48 hours) Van Zwieten et al. (2010)
Earthworm mortality and weight loss (differed with type of feedstock) Feedstock: pine chip and poultry litter; Pyrolysis condition: 400°C for 0.5 hour; Soil type: artificial soil (mixture of sand, kaolin and sphagnum peat moss) 22.5, 45, 68 and 90 Mg ha-1 Mesocosm (28 days) Liesch et al. (2014)
Increased earthworm density and nematode number; decreased the amount of amoebic protozoae; no effect on number of ciliate and flagellate protozoae. The data were not statistically analysed. Feedstock: hard wood waste; Pyrolysis condition: fast pyrolysis; Soil type: clay loam 3.9 Mg ha-1 Field (18 months) Husk and Major (2010)
Altered the propagation and population dynamics of enchytraeid (Cognettia sphagnetorum) due to a destabilisation in body size distribution Feedstock: birch wood; Soil type: organic soil (humus layer of a forest soil) 2.4 Mg ha-1 Microcosm (14 weeks) Nieminen and Haimi (2010)

4. Implications for crop growth

Most studies have reported an improvement in crop growth upon the addition of biochar to soil (Chan et al., 2007; Chen et al., 2010; Solaiman et al., 2010; Peng et al., 2011; Rabileh et al., 2015; She et al., 2018). The positive effect biochar additions have on crop growth is most likely due to the conditioning effect of biochar, i.e. its ability to modify soil properties. For instance, Chen et al. (2010) reported an increase in yield and sugar content of sugarcane due to an increase in soil moisture content after the addition of bagasse biochar on a heavy clay soil. Similarly, She et al. (2018) reported that biochar increased tomato growth under salt-stress conditions, through the adsorption of sodium ions, release of nutrients (potassium, calcium and magnesium) into soil solution, and increase in available water content of the salt-stressed soil. Increases in soil pH and CEC after biochar addition to soil have been shown to enhance crop growth, especially on acidic soils (Peng et al., 2011; Rabileh et al., 2015). Improved mycorrhizal colonisation after biochar addition has also been reported to increase crop growth (Mori and Marjenah, 1994; Ezawa et al., 2002; Shen et al., 2016).

Although biochar application to soil can increase crop growth, it could also affect crops negatively, especially when applied in high concentrations as reported by Rondon et al. (2007) The authors attributed this negative effect to the toxic levels of volatile compounds and heavy metals that are present in some biochars. These toxic substances can hinder seed germination and crop development, though these effects are crop specific (Gascó et al., 2016). Horel et al. (2019) also noted that high concentrations of biochar could negatively impact on soil microbes through the suppression of biological N fixation. These observed negative effects suggest that microcosm experiments are crucial to determine the threshold for biochar application before its use in large-scale field trials.

Due to the nutrient content of biochar, it could also serve as a fertiliser (i.e. directly contribute nutrients to crops). In fact, Pandit et al. (2018) observed that biochar improved maize biomass production mainly through the alleviation of nutrient stress (i.e. the increase in plant available potassium–K and P) and not through soil conditioning effects, such as the alleviation of salt and water stress. Due to biochar recalcitrance, however, nutrients may not be readily available in some biochars (Peng et al., 2011; Enders et al., 2012). Therefore, biochar may be combined with other soil amendments. Studies where biochar was combined with other soil amendments, such as N fertiliser, have reported increases in crop growth due to higher N use efficiency compared to when only biochar was applied to the soil (Oguntunde et al., 2004; Chan et al., 2007; 2008; Peng et al., 2011). However, the effect of such combinations could also vary with the type of soil and biochar (Van Zwieten et al., 2010).

It is important to exercise caution when combining biochar with other amendments because combinations of biochar with fertiliser could induce mycorrhizal parasitism which negatively affects crop growth, especially with high N fertiliser rates (LeCroy et al., 2013). Interestingly, Bonanomi et al. (2017) reported that combining biochar with organic amendments which have low N content (low quality litter) could result in antagonistic effect on crops (though a major limitation in this study was the use of only one crop–lettuce). The authors proposed a short-term N immobilisation to be a likely reason for this antagonistic effect. These conflicting observations regarding the contribution of N from other amendments suggests that further research is needed on the mechanisms underlying the combination of biochar with other amendments, and the effect of this combination on crops.

 

5. Conclusion

The feedstock and pyrolysis condition used in producing biochar are the main contributors to the characteristics of biochar. These inherent factors, together with other external factors, such as soil type and application method, determine the efficacy of biochar application. In most cases, biochar acts as a soil conditioner by modifying the physical, chemical and biological properties of a soil, especially its water holding capacity, pH, CEC, and mycorrhizal colonisation. This conditioning effect, the direct addition of nutrients from biochar, and its ability to improve nutrient use efficiency when combined with other soil amendments, lead to improved crop growth and yield. Conducting microcosm experiments before large-scale/field experiments will minimise the uncertainties associated with the application of biochar to soil for crop production purposes.

Further investigation into the mechanisms controlling the interaction between biochar and other soil amendments will create better understanding of the agronomic effect of biochar application. More research is also needed on the reason for the varying responses of different crops to biochar. Finally, the interaction between biochar and soil fauna also requires further research, especially for other groups of soil fauna such as arthropods, as most research to date have focused on earthworms.

 

References

Abel, S., Peters, A., Trinks, S., Schonsky, H., Facklam, M. & Wessolek, G. (2013). Impact of biochar and hydrochar addition on water retention and water repellency of sandy soil. Geoderma 202–203: 183-191.

Amonette, J. & Joseph, S. (2009).Characteristics of biochar – Micro-chemical properties. In Biochar for Environmental Management: Science and Technology, 33-52 (Eds J. Lehmann and S. Joseph). London, UK: Earthscan.

Azlan Halmi, M., Hasenan, S., Simarani, K. & Abdullah, R. (2018). Linking soil microbial properties with plant performance in acidic tropical soil amended with biochar. Agronomy 8(11): 255; https://doi.org/10.3390/agronomy8110255.

Bailey, V. L., Fansler, S. J., Smith, J. L. & Bolton Jr, H. (2011). Reconciling apparent variability in effects of biochar amendment on soil enzyme activities by assay optimization. Soil Biology and Biochemistry 43(2): 296-301.

Bamminger, C., Zaiser, N., Zinsser, P., Lamers, M., Kammann, C. & Marhan, S. (2014). Effects of biochar, earthworms, and litter addition on soil microbial activity and abundance in a temperate agricultural soil. Biology and Fertility of Soils 50(8): 1189-1200.

Blackwell, P., Riethmuller, G. & Collins, M. (2009).Biochar application to soil. In Biochar for Environmental Management: Science and Technology, 207-226 (Eds J. Lehmann and S. Joseph). London, UK: Earthscan.

Boersma, M., Wrobel-Tobiszewska, A., Murphy, L. & Eyles, A. (2017). Impact of biochar application on the productivity of a temperate vegetable cropping system. New Zealand Journal of Crop and Horticultural Science 45(4): 277-288.

Bonanomi, G., Ippolito, F., Cesarano, G., Nanni, B., Lombardi, N., Rita, A., Saracino, A. & Scala, F. (2017). Biochar as plant growth promoter: Better off alone or mixed with organic amendments? Frontiers in Plant Science 8(1570).

Brodowski, S., Amelung, W., Haumaier, L., Abetz, C. & Zech, W. (2005). Morphological and chemical properties of black carbon in physical soil fractions as revealed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Geoderma 128(1–2): 116-129.

Bruun, E. W., Ambus, P., Egsgaard, H. & Hauggaard-Nielsen, H. (2012). Effects of slow and fast pyrolysis biochar on soil C and N turnover dynamics. Soil Biology and Biochemistry 46: 73-79.

Case, S. D. C., McNamara, N. P., Reay, D. S. & Whitaker, J. (2012). The effect of biochar addition on N2O and CO2 emissions from a sandy loam soil – The role of soil aeration. Soil Biology and Biochemistry 51: 125-134.

Chan, K. Y., Van Zwieten, L., Meszaros, I., Downie, A. & Joseph, S. (2007). Agronomic values of greenwaste biochar as a soil amendment. Soil Research 45(8): 629-634.

Chan, K. Y., Van Zwieten, L., Meszaros, I., Downie, A. & Joseph, S. (2008). Using poultry litter biochars as soil amendments. Soil Research 46(5): 437-444.

Chen, Y., Shinogi, Y. & Taira, M. (2010). Influence of biochar use on sugarcane growth, soil parameters, and groundwater quality. Soil Research 48(7): 526-530.

Chintala, R., Schumacher, T. E., McDonald, L. M., Clay, D. E., Malo, D. D., Papiernik, S. K., Clay, S. A. & Julson, J. L. (2014). Phosphorus sorption and availability from biochars and soil/biochar mixtures. CLEAN – Soil, Air, Water 42(5): 626-634.

Clough, T., Condron, L., Kammann, C. & Müller, C. (2013). A review of biochar and soil nitrogen dynamics. Agronomy 3(2): 275-293.

Crombie, K., Mašek, O., Sohi, S. P., Brownsort, P. & Cross, A. (2013). The effect of pyrolysis conditions on biochar stability as determined by three methods. GCB Bioenergy 5(2): 122-131.

De Gryze, S., Cullen, M. & Durschinger, L. (2010). Evaluation of the Opportunities for Generating Carbon Offsets from Soil  Sequestration of Biochar. An issues paper commissioned by the Climate Action Reserve. San Francisco, CA: Terra Global Capital LLC.

Demirbas, A. (2004). Effects of temperature and particle size on bio-char yield from pyrolysis of agricultural residues. Journal of Analytical and Applied Pyrolysis 72(2): 243-248.

Demisie, W. & Zhang, M. (2015). Effect of biochar application on microbial biomass and enzymatic activities in degraded red soil. African Journal of Agricultural Research 10(8): 755-766.

Dempster, D. N., Gleeson, D. B., Solaiman, Z. M., Jones, D. L. & Murphy, D. V. (2012). Decreased soil microbial biomass and nitrogen mineralisation with Eucalyptus biochar addition to a coarse textured soil. Plant and Soil 354(1): 311-324.

Domene, X., Mattana, S., Hanley, K., Enders, A. & Lehmann, J. (2014). Medium-term effects of corn biochar addition on soil biota activities and functions in a temperate soil cropped to corn. Soil Biology and Biochemistry 72: 152-162.

Domingues, R. R., Trugilho, P. F., Silva, C. A., de Melo, I. C. N. A., Melo, L. C. A., Magriotis, Z. M. & Sánchez-Monedero, M. A. (2017). Properties of biochar derived from wood and high nutrient biomasses with the aim of agronomic and environmental benefits. PLoS ONE 12(5): e0176884.

Downie, A., Crosky, A. & Munroe, P. (2009).Physical properties of biochar. In Biochar for Environmental Management: Science and Technology, 227-249 (Eds J. Lehmann and S. Joseph). London: Earthscan.

Duarte, S. d. J., Glaser, B. & Cerri, C. E. P. (2019). Effect of biochar particle size on physical, hydrological and chemical properties of loamy and sandy tropical soils. Agronomy 9(4): 165; doi:110.3390/agronomy9040165.

Duku, M. H., Gu, S. & Hagan, E. B. (2011). Biochar production potential in Ghana—A review. Renewable and Sustainable Energy Reviews 15(8): 3539-3551.

Enders, A., Hanley, K., Whitman, T., Joseph, S. & Lehmann, J. (2012). Characterization of biochars to evaluate recalcitrance and agronomic performance. Bioresource Technology 114: 644-653.

Ericsson, T. (1994). Nutrient dynamics and requirements of forest crops. New Zealand Journal of Forestry Science 24(2/3): 133-168.

Ezawa, T., Yamamoto, K. & Yoshida, S. (2002). Enhancement of the effectiveness of indigenous arbuscular mycorrhizal fungi by inorganic soil amendments. Soil Science and Plant Nutrition 48(6): 897-900.

Gascó, G., Cely, P., Paz-Ferreiro, J., Plaza, C. & Méndez, A. (2016). Relation between biochar properties and effects on seed germination and plant development. Biological Agriculture & Horticulture 32(4): 237-247.

Girvan, M. S., Campbell, C. D., Killham, K., Prosser, J. I. & Glover, L. A. (2005). Bacterial diversity promotes community stability and functional resilience after perturbation. Environ Microbiol 7(3): 301-313.

Githinji, L. (2014). Effect of biochar application rate on soil physical and hydraulic properties of a sandy loam. Archives of Agronomy and Soil Science 60(4): 457-470.

Haefele, S. M., Konboon, Y., Wongboon, W., Amarante, S., Maarifat, A. A., Pfeiffer, E. M. & Knoblauch, C. (2011). Effects and fate of biochar from rice residues in rice-based systems. Field Crops Research 121(3): 430-440.

Hardie, M., Clothier, B., Bound, S., Oliver, G. & Close, D. (2014). Does biochar influence soil physical properties and soil water availability? Plant and Soil 376(1): 347-361.

Herath, H. M. S. K., Camps-Arbestain, M. & Hedley, M. (2013). Effect of biochar on soil physical properties in two contrasting soils: An Alfisol and an Andisol. Geoderma 209–210: 188-197.

Hina, K., Bishop, P., Arbestain, M. C., Calvelo-Pereira, R., Maciá-Agulló, J. A., Hindmarsh, J., Hanly, J. A., Macías, F. & Hedley, M. J. (2010). Producing biochars with enhanced surface activity through alkaline pretreatment of feedstocks. Soil Research 48(7): 606-617.

Horel, Á., Gelybó, G., Potyó, I., Pokovai, K. & Bakacsi, Z. (2019). Soil nutrient dynamics and nitrogen fixation rate changes over plant growth in temperate soil. Agronomy 9(4): 179; doi: 110.3390/agronomy9040179.

Hseu, Z. Y., Jien, S. H., Chien, W. H. & Liou, R. C. (2014). Impacts of biochar on physical properties and erosion potential of a mudstone slopeland soil. ScientificWorldJournal 2014: 602197.

Hu, Y.-L., Wu, F.-P., Zeng, D.-H. & Chang, S. X. (2014). Wheat straw and its biochar had contrasting effects on soil C and N cycling two growing seasons after addition to a Black Chernozemic soil planted to barley. Biology and Fertility of Soils 50(8): 1291-1299.

Husk, B. & Major, J. (2010). Commercial Scale Agricultural Biochar Field Trial in Québec, Canada Over Two Years: Effects of Biochar on Soil Fertility, Biology and Crop Productivity and Quality. Québec, Canada.

International Biochar Initiative (2015).Feedstocks. An electronic article by International Biochar Initiative. Available online at http://www.biochar-international.org/technology/feedstocks (Accessed  on 08/07/2015).

Jeffery, S., Abalos, D., Prodana, M., Bastos, A. C., van Groenigen, J. W., Hungate, B. A. & Verheijen, F. (2017). Biochar boosts tropical but not temperate crop yields. Environmental Research Letters 12(5): 053001.

Jeffery, S., Verheijen, F. G. A., van der Velde, M. & Bastos, A. C. (2011). A quantitative review of the effects of biochar application to soils on crop productivity using meta-analysis. Agriculture, Ecosystems & Environment 144(1): 175-187.

Jien, S.-H. & Wang, C.-S. (2013). Effects of biochar on soil properties and erosion potential in a highly weathered soil. Catena 110: 225-233.

Jin, H. (2010).Characterization of microbial life colonizing biochar and biochar amended soils. A PhD Dissertation. Cornell University. Ithaca, NY.

Jones, B. E. H., Haynes, R. J. & Phillips, I. R. (2010). Effect of amendment of bauxite processing sand with organic materials on its chemical, physical and microbial properties. Journal of Environmental Management 91(11): 2281-2288.

Karhu, K., Mattila, T., Bergström, I. & Regina, K. (2011). Biochar addition to agricultural soil increased CH4 uptake and water holding capacity – Results from a short-term pilot field study. Agriculture, Ecosystems & Environment 140(1–2): 309-313.

Kolb, S. E., Fermanich, K. J. & Dornbush, M. E. (2009). Effect of charcoal quantity on microbial biomass and activity in temperate soils. Soil Science Society of America Journal 73(4): 1173-1181.

Laird, D. A., Fleming, P., Davis, D. D., Horton, R., Wang, B. & Karlen, D. L. (2010). Impact of biochar amendments on the quality of a typical Midwestern agricultural soil. Geoderma 158(3–4): 443-449.

LeCroy, C., Masiello, C. A., Rudgers, J. A., Hockaday, W. C. & Silberg, J. J. (2013). Nitrogen, biochar, and mycorrhizae: Alteration of the symbiosis and oxidation of the char surface. Soil Biology and Biochemistry 58: 248-254.

Lehmann, J. (2007). Bio-energy in the black. Frontiers in Ecology and the Environment 5(7): 381-387.

Lehmann, J., Kuzyakov, Y., Pan, G. & Ok, Y. S. (2015). Biochars and the plant-soil interface. Plant and Soil 395(1): 1-5.

Lehmann, J., Rillig, M. C., Thies, J., Masiello, C. A., Hockaday, W. C. & Crowley, D. (2011). Biochar effects on soil biota – A review. Soil Biology and Biochemistry 43(9): 1812-1836.

Liang, B., Lehmann, J., Solomon, D., Kinyangi, J., Grossman, J., O’Neill, B., Skjemstad, J. O., Thies, J., Luizão, F. J., Petersen, J. & Neves, E. G. (2006). Black carbon increases cation exchange capacity in soils. Soil Science Society of America Journal 70(5): 1719-1730.

Liesch, A. M., Weyers, S. L., Gaskin, J. W. & Das, K. C. (2014). Impact of two different biochars on earthworm growth and survival. Annals of Environmental Science 4: 1-9.

Liu, A., Hamel, C., Hamilton, R. I. & Smith, D. L. (2000). Mycorrhizae formation and nutrient uptake of new corn (Zea mays L.) hybrids with extreme canopy and leaf architecture as influenced by soil N and P levels. Plant and Soil 221(2): 157-166.

Liu, X.-H. & Zhang, X.-C. (2012). Effect of biochar on pH of alkaline soils in the loess plateau: results from incubation experiments. International Journal of Agriculture & Biology 14: 745-750.

Liu, X., Zheng, J., Zhang, D., Cheng, K., Zhou, H., Zhang, A., Li, L., Joseph, S., Smith, P., Crowley, D., Kuzyakov, Y. & Pan, G. (2016). Biochar has no effect on soil respiration across Chinese agricultural soils. Science of The Total Environment 554–555: 259-265.

Lu, N., Liu, X.-R., Du, Z.-L., Wang, Y.-D. & Zhang, Q.-Z. (2014). Effect of biochar on soil respiration in the maize growing season after 5 years of consecutive application. Soil Research 52(5): 505-512.

Macías, F. & Camps Arbestain, M. (2010). Soil carbon sequestration in a changing global environment. Mitigation and Adaptation Strategies for Global Change 15(6): 511-529.

Major, J. (2009).A Guide to Conducting Biochar Trials. Version 1.1. International Biochar Initiative.

Major, J. (2010).Guidelines on Practical Aspects of Biochar Application to Field Soil in Various Soil Management Systems. Version 1.0. International Biochar Initiative.

Marks, E. A. N., Mattana, S., Alcañiz, J. M., Pérez-Herrero, E. & Domene, X. (2016). Gasifier biochar effects on nutrient availability, organic matter mineralization, and soil fauna activity in a multi-year Mediterranean trial. Agriculture, Ecosystems & Environment 215: 30-39.

Martinsen, V., Alling, V., Nurida, N. L., Mulder, J., Hale, S. E., Ritz, C., Rutherford, D. W., Heikens, A., Breedveld, G. D. & Cornelissen, G. (2015). pH effects of the addition of three biochars to acidic Indonesian mineral soils. Soil Science and Plant Nutrition 61(5): 821-834.

Masulili, A., Utomo, W. H. & MS, S. (2010). Rice husk biochar for rice based cropping system in acid soil 1. The characteristics of rice husk biochar and its influence on the properties of acid sulfate soils and rice growth in West Kalimantan, Indonesia. Journal of Agricultural Science 2(1): 39-47.

McCauley, A., Jones, C. & Jacobsen, J. (2011).Plant nutrient functions and deficiency and toxicity symptoms. In Nutrient Management Module 9. MSU ExtensionBozeman: Montana State University.

Mori, S. & Marjenah (1994). Effect of charcoaled rice husks on the growth of Dipterocarpaceae seedlings in East Kalimantan with special reference to ectomycorrhiza formation. Journal of the Japanese Forestry Society 76(5): 462-464.

Niemi, R. M., Heiskanen, I. & Saarnio, S. (2015). Weak impacts of biochar amendment on soil enzyme activities in mesocosms in bare or Phleum pratense soil. Boreal Environment Research 20: 324-334.

Nieminen, J. K. & Haimi, J. (2010). Body size and population dynamics of enchytraeids with different disturbance histories and nutrient dynamics. Basic and Applied Ecology 11(7): 638-644.

Nigussie, A., Kissi, E., Misganaw, M. & Ambaw, G. (2012). Effect of biochar application on soil properties and nutrient uptake of lettuces (Lactuca sativa) grown in chromium polluted soils. American-Eurasian Journal of Agricultural & Environmental Sciences 12(3): 369-376.

Noguera, D., Rondón, M., Laossi, K.-R., Hoyos, V., Lavelle, P., Cruz de Carvalho, M. H. & Barot, S. (2010). Contrasted effect of biochar and earthworms on rice growth and resource allocation in different soils. Soil Biology and Biochemistry 42(7): 1017-1027.

Novak, J. M., Busscher, W. J., Laird, D. L., Ahmedna, M., Watts, D. W. & Niandou, M. A. S. (2009). Impact of biochar amendment on fertility of a southeastern coastal plain soil. Soil Science 174(2): 105-112.

Novak, J. M., Busscher, W. J., Watts, D. W., Amonette, J. E., Ippolito, J. A., Lima, I. M., Gaskin, J., Das, K. C., Steiner, C., Ahmedna, M., Rehrah, D. & Schomberg, H. (2012). Biochars impact on soil-moisture storage in an Ultisol and two Aridisols. Soil Science 177(5): 310-320.

Oguntunde, P. G., Abiodun, B. J., Ajayi, A. E. & van de Giesen, N. (2008). Effects of charcoal production on soil physical properties in Ghana. Journal of Plant Nutrition and Soil Science 171(4): 591-596.

Oguntunde, P. G., Fosu, M., Ajayi, A. E. & van de Giesen, N. (2004). Effects of charcoal production on maize yield, chemical properties and texture of soil. Biology and Fertility of Soils 39(4): 295-299.

Ouyang, L., Tang, Q., Yu, L. & Zhang, R. (2014a). Effects of amendment of different biochars on soil enzyme activities related to carbon mineralisation. Soil Research 52(7): 706-716.

Ouyang, L., Yu, L. & Zhang, R. (2014b). Effects of amendment of different biochars on soil carbon mineralisation and sequestration. Soil Research 52(1): 46-54.

Page-Dumroese, D. S., Robichaud, P. R., Brown, R. E. & Tirocke, J. M. (2015). Water repellency of two forest soils after biochar addition. Transactions of the ASABE 58(2): 335-342.

Pandit, N. R., Mulder, J., Hale, S. E., Martinsen, V., Schmidt, H. P. & Cornelissen, G. (2018). Biochar improves maize growth by alleviation of nutrient stress in a moderately acidic low-input Nepalese soil. Science of The Total Environment 625: 1380-1389.

Parvage, M. M., Ulén, B., Eriksson, J., Strock, J. & Kirchmann, H. (2013). Phosphorus availability in soils amended with wheat residue char. Biology and Fertility of Soils 49(2): 245-250.

Peng, X., Ye, L. L., Wang, C. H., Zhou, H. & Sun, B. (2011). Temperature- and duration-dependent rice straw-derived biochar: Characteristics and its effects on soil properties of an Ultisol in southern China. Soil and Tillage Research 112(2): 159-166.

Prommer, J., Wanek, W., Hofhansl, F., Trojan, D., Offre, P., Urich, T., Schleper, C., Sassmann, S., Kitzler, B., Soja, G. & Hood-Nowotny, R. C. (2014). Biochar decelerates soil organic nitrogen cycling but stimulates soil nitrification in a temperate arable field trial. PLoS ONE 9(1): e86388. doi:86310.81371/journal.pone.0086388.

Rabileh, M. A., Shamshuddin, J., Panhwar, Q. A., Rosenani, A. B. & Anuar, A. R. (2015). Effects of biochar and/or dolomitic limestone application on the properties of Ultisol cropped to maize under glasshouse conditions. Canadian Journal of Soil Science 95(1): 37-47.

Rafiq, M. K., Bachmann, R. T., Rafiq, M. T., Shang, Z., Joseph, S. & Long, R. (2016). Influence of pyrolysis temperature on physico-chemical properties of corn stover (Zea mays L.) biochar and feasibility for carbon capture and energy balance. PLoS ONE 11(6): e0156894.

Rondon, M. A., Lehmann, J., Ramírez, J. & Hurtado, M. (2007). Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions. Biology and Fertility of Soils 43(6): 699-708.

Schimmelpfennig, S. & Glaser, B. (2012). One step forward toward characterization: some important material properties to distinguish biochars. Journal of Environmental Quality 41(4): 1001-1013.

Schubert, A. & Hayman, D. S. (1986). Plant growth responses to vesicular-arbuscular mycorrhiza. XVI. Effectiveness of different endophytes at different levels of soil phosphate. The New Phytologist 103(1): 79-90.

She, D., Sun, X., Gamareldawla, A. H. D., Nazar, E. A., Hu, W., Edith, K. & Yu, S. e. (2018). Benefits of soil biochar amendments to tomato growth under saline water irrigation. Scientific Reports 8(1): 14743.

Shen, Q., Hedley, M., Camps Arbestain, M. & Kirschbaum, M. U. F. (2016). Can biochar increase the bioavailability of phosphorus? Journal of Soil Science and Plant Nutrition 16: 268-286.

Shenbagavalli, S. & Mahimairaja, S. (2012). Characterization and effect of biochar on nitrogen and carbon dynamics in soil. International Journal of Advanced Biological Research 2(2): 249-255.

Sika, M. P. & Hardie, A. G. (2014). Effect of pine wood biochar on ammonium nitrate leaching and availability in a South African sandy soil. European Journal of Soil Science 65: 113-119.

Singh, B. P. & Cowie, A. L. (2014). Long-term influence of biochar on native organic carbon mineralisation in a low-carbon clayey soil. Scientific Reports 4 3687 DOI:3610.1038/srep03687.

Siregar, C. A. (2007). Effect of charcoal application on the early growth stage of Acacia mangium and Michelia montana. Indonesian Journal of Forestry Research 4(1): 19-30.

Smith, J. L., Collins, H. P. & Bailey, V. L. (2010). The effect of young biochar on soil respiration. Soil Biology and Biochemistry 42(12): 2345-2347.

Soinne, H., Hovi, J., Tammeorg, P. & Turtola, E. (2014). Effect of biochar on phosphorus sorption and clay soil aggregate stability. Geoderma 219–220: 162-167.

Solaiman, Z. M., Blackwell, P., Abbott, L. K. & Storer, P. (2010). Direct and residual effect of biochar application on mycorrhizal root colonisation, growth and nutrition of wheat. Soil Research 48(7): 546-554.

Steiner, C., Teixeira, W. G., Lehmann, J., Nehls, T., de Macêdo, J. L. V., Blum, W. E. H. & Zech, W. (2007). Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil. Plant and Soil 291(1): 275-290.

Sun, Z., Bruun, E. W., Arthur, E., de Jonge, L. W., Moldrup, P., Hauggaard-Nielsen, H. & Elsgaard, L. (2014). Effect of biochar on aerobic processes, enzyme activity, and crop yields in two sandy loam soils. Biology and Fertility of Soils 50(7): 1087-1097.

Thomas, S. C., Frye, S., Gale, N., Garmon, M., Launchbury, R., Machado, N., Melamed, S., Murray, J., Petroff, A. & Winsborough, C. (2013). Biochar mitigates negative effects of salt additions on two herbaceous plant species. Journal of Environmental Management 129: 62-68.

Topoliantz, S. & Ponge, J.-F. (2003). Burrowing activity of the geophagous earthworm Pontoscolex corethrurus (Oligochaeta: Glossoscolecidae) in the presence of charcoal. Applied Soil Ecology 23(3): 267-271.

Usowicz, B., Lipiec, J., Łukowski, M., Marczewski, W. & Usowicz, J. (2016). The effect of biochar application on thermal properties and albedo of loess soil under grassland and fallow. Soil and Tillage Research 164: 45-51.

Van Zwieten, L., Kimber, S., Morris, S., Chan, K. Y., Downie, A., Rust, J., Joseph, S. & Cowie, A. (2010). Effects of biochar from slow pyrolysis of papermill waste on agronomic performance and soil fertility. Plant and Soil 327(1): 235-246.

Ventura, M., Zhang, C., Baldi, E., Fornasier, F., Sorrenti, G., Panzacchi, P. & Tonon, G. (2014). Effect of biochar addition on soil respiration partitioning and root dynamics in an apple orchard. European Journal of Soil Science 65(1): 186-195.

Verheijen, F., Jeffery, S., Bastos, A. C., van der Velde, M. & Diafas, I. (2010).Biochar application to soils: A critical scientific review of effects on soil properties, processes and functions. In JRC Scientific and Technical ReportsLuxembourg: Office for Official Publications of the European Communities.

Warnock, D. D., Lehmann, J., Kuyper, T. W. & Rillig, M. C. (2007). Mycorrhizal responses to biochar in soil – concepts and mechanisms. Plant and Soil 300(1): 9-20.

Wong, J. T. F., Chen, X., Deng, W., Chai, Y., Ng, C. W. W. & Wong, M. H. (2019). Effects of biochar on bacterial communities in a newly established landfill cover topsoil. Journal of Environmental Management 236: 667-673.

Xu, G., Sun, J., Shao, H. & Chang, S. X. (2014). Biochar had effects on phosphorus sorption and desorption in three soils with differing acidity. Ecological Engineering 62: 54-60.

Xu, N., Tan, G., Wang, H. & Gai, X. (2016). Effect of biochar additions to soil on nitrogen leaching, microbial biomass and bacterial community structure. European Journal of Soil Biology 74: 1-8.

Yamato, M., Okimori, Y., Wibowo, I. F., Anshori, S. & Ogawa, M. (2006). Effects of the application of charred bark of Acacia mangium on the yield of maize, cowpea and peanut, and soil chemical properties in South Sumatra, Indonesia. Soil Science & Plant Nutrition 52(4): 489-495.

Yin, Y.-f., He, X.-h., Gao, R., Ma, H.-l. & Yang, Y.-s. (2014). Effects of rice straw and its biochar addition on soil labile carbon and soil organic carbon. Journal of Integrative Agriculture 13(3): 491-498.

Zhai, L., CaiJi, Z., Liu, J., Wang, H., Ren, T., Gai, X., Xi, B. & Liu, H. (2015). Short-term effects of maize residue biochar on phosphorus availability in two soils with different phosphorus sorption capacities. Biology and Fertility of Soils 51(1): 113-122.

Zhang, Q.-z., Dijkstra, F. A., Liu, X.-r., Wang, Y.-d., Huang, J. & Lu, N. (2014). Effects of biochar on soil microbial biomass after four years of consecutive application in the North China Plain. PLoS ONE 9(7): e102062.

 

 

Menu