biochar for sustainable agriculture a review for sustainable agriculture – a review r. rajakumar1...

@IJAPSA-2016, All rights Reserved 73

Biochar for Sustainable Agriculture – A Review R. Rajakumar

1 and Jayasree Sankar, S

2

1 Research Scholar, 2 Professor & Head,

Department of Soil Science and Agricultural Chemistry, College of Horticulture, KAU, Thrissur

Abstract

Biochar, (commonly known agrichar) is defined as a carbon rich product derived from the

slow pyrolysis (heating with limited supply of O2) of organic materials at 250 - 700° C. It stores

carbon for long time since it is chemically and biologically more stable than the original carbon

form it comes from, making it more difficult to convert back to CO2. Greater surface area,

negative surface charge and high charge density of biochar enables greater ability to adsorb

cations and to retain and exchange nutrients with soil environment, including microorganisms

and plant roots. The special structure and high surface area of biochar helps to adsorb various

soil contaminants. It also stabilizes biomass and native SOM, which enhances soil aeration,

improves microbial activity and immobilize N which together reduces the emission of major green

house gases viz., CH4, CO2 and N2O. The role of biochar in developing a sustainable agriculture

production system is immense and so is its potential in mitigating climate change, which stands

much beyond its uses in agriculture.

Key words: Biochar; sustainable agriculture; soil properties; bioremediation; C sequestration

I. Introduction

India achieved spectacular growth in agriculture since 1966, but for meeting the increased

demand of growing population, food grain production has to increase at least 70 per cent by 2050.

High yields often come from the use of improved crop varieties, fertilizers, pest control measures and

irrigation, which have resulted in food and nutritional security. Despite high productivity, farmers

see various problems associated with our intensive agricultural systems. The present day agriculture

is challenged to fulfill with twin objectives of achieving food, fodder, fiber and fuel security as well

as sustainability with emphasis on restoring soil resources, improving water quality, mitigating

climate change and preserving soil and natural resources for long-term use. With the new emphasis

on sustainable agriculture comes a reawakening of interest in soil health. Soil health emphasizes the

integration of biological, chemical and physical measures of soil quality that affect farmers profit and

the environment. Healthy soil, an essential component of a healthy environment, is the foundation

upon which sustainable agriculture is built. For managing soil health certain organic amendments are

added. Among this potential of biochar as soil amendment in agriculture is recently recognized

though the technology still remains underutilized.

II. Biochar: production and characteristics

Biochar is the black carbon rich material derived by heating biomass (250 – 700o C) with

limited supply of oxygen. Unlike the original biomass, it contributes to long term removal of CO2

from atmosphere, since it is chemically and biologically more stable [24]. Biochar differs from

charcoal, activated carbon and other black carbon materials. The differences, however, are relatively

subtle since all products are obtained from the burning of carbon rich material. In order to

differentiate biochar from other products, list of terms used in the pyrogenic black carbon is given in

Figure 1. The Polymeric building blocks present in biomass undergo cross linking, depolymerization

and fragmentation during heating and thus the biochar retains the cell wall structure. The main

structure of biochar is stacked crystalline graphitic sheets and randomly ordered amorphous aromatic

structures. Hydrogen, oxygen, nitrogen, phosphorus and sulphur are predominantly incorporated

within the aromatic rings as heteroatoms and contribute to highly heterogeneous surface chemistry

and reactivity of biochar.

International Journal of Applied and Pure Science and Agriculture (IJAPSA)

Volume 02, Issue 09, [September- 2016] e-ISSN: 2394-5532, p-ISSN: 2394-823X

@IJAPSA-2016, All rights Reserved Page 174

Figure 1. Terms and properties of pyrogenic black carbon

A. Production of biochar

Biochar is obtained through pyrolysis of biomass: Thermochemical decomposition of

condensed substances by heating under oxygen-limited conditions. Generally, pyrolysis of biomass

or fossil hydrocarbons yields three phases: a gaseous, a liquid and a solid phase. Pyrolysis,

gasification and hydrothermal conversion are the different thermochemical conversion process used.

In pyrolysis, series of by products, biochar, bio oils and syngas (fuel gas mixture consisting of H, CO

and CO2) are derived, whereas in gasification biochar is obtained as bye product. Liquid, solid and

gas yields of pyrolysis processes at different, typical process conditions are given in the Figure 2

[42].

B. Characteristics of biochar

The properties of biochar vary substantially depending on the source of biomass, the rate at

which it is heated, the maximum temperature of heating, and the extent to which volatiles produced

during pyrolysis are separated from the biochar prior to cooling. If it is pure lignocellulosic biomass,

more better. In case of rice husk, since it contains more silica, rice husk biochar will have more

resistance to degradation. The level of aromaticity directly influences the stability of biochar in soil

environments. Other properties of biochar are particle size, porosity, surface area, charge density,

functional groups, biologically available and active compounds, and inorganic bases that are

admixed with the biochar. Pyrolysis of different organic wastes yielded biochar which was

characterized for its physical and chemical properties which revealed the dependence of biochar

properties (Table 1) with that of the biomass [10]. Jindo et al. [19] tried different pyrolysis

temperatures (400, 500, 600, 700, and 800o C) in order to optimize the physicochemical properties of

biochar as a soil amendment. Low temperature pyrolysis produced high biochar yields; in contrast,

high-temperature pyrolysis led to biochar with a high C content, large surface area and high

adsorption characteristics. Biochar obtained at 600o C leads to a high recalcitrant character, whereas

that obtained at 400o C retains volatile and easily labile compounds.

Figure 2. Liquid, solid and gas yields of different processes (%)




Table 1. Physical and chemical properties of biochar from different biological material

Properties Coconut

shell

Tapioca

stalk

Cotton

stalk

Redgram

stalk

Maize

cob

Maize

stover

Sugarcane

trash

Recovery (%) 38.75 37.85 36.16 35.76 32.26 25.28 12.46

Moisture (%) 1.42 1.41 1.41 1.40 1.40 1.38 1.31

Ash w w-1

1.16 1.22 1.23 1.25 1.27 1.31 1.39

Bulk density (Mg m-3

) 0.39 0.36 0.35 0.32 0.30 0.28 0.25

Particle density (Mg m-3

) 0.93 0.85 0.82 0.73 0.68 0.61 0.54

Pore volume (%) 58.06 57.64 57.32 56.16 55.88 54.10 53.70

pH 9.18 9.25 9.25 9.40 9.45 9.52 9.85

EC (dS m-1

) 3.08 3.04 3.32 3.00 2.85 2.64 2.50

CEC [cmol (p+) kg

-1] 16.30 16.10 15.90 15.50 13.60 13.20 12.50

TOC (g kg-1

) 76.50 74.50 74.20 73.80 70.50 40.00 38.50

Nitrogen (g kg-1

) 1.16 1.14 1.11 1.12 1.05 1.01 0.97

C:N Ratio 66.00 65.40 66.90 65.9 67.10 39.6 39.70

Sulphur (g kg-1

) 3.86 3.26 3.14 3.04 2.84 2.76 2.64

Phosphorus (g kg-1

) 1.25 1.20 1.16 1.12 1.13 1.11 1.06

Potassium (g kg-1

) 14.60 14.30 14.10 14.00 13.50 13.40 12.60

Sodium (g kg-1

) 34.50 33.20 32.50 32.20 33.00 32.50 31.30

Calcium (g kg-1

) 9.75 9.65 9.60 9.43 9.32 9.26 9.04

Magnesium (g kg-1

) 0.27 0.25 0.24 0.22 0.23 0.21 0.20

III. Effect of biochar on soil properties

Biochar, a byproduct of the pyrolysis process, is biomass-derived black carbon intended for

use as a soil amendment. As a soil amendment it is mainly used to improve soil nutrient status, C

storage and/or filtration of percolating soil water [24]. Biochar has an inherent energy value which

can be used to maximize the energy output of pyrolysis. However, research has shown that

application of biochar to soil may be more desirable as it can increase soil organic carbon (SOC),

improve the supply of nutrients to plants and therefore enhance plant growth and soil physical,

chemical, and biological properties [12, 25 & 37].

Biochar is believed to benefit crop production through three primary mechanisms viz. direct

modification of soil chemistry through its intrinsic elemental and compositional make up (e.g.

availability of nutrients and light organic molecules and decrease in soil acidity); providing

chemically active surfaces that modify the dynamics of soil nutrients or otherwise catalyse useful soil

reactions (e.g. increasing the cation exchange capacity of the soil) and modifying physical character

of the soil in a way that benefits root growth and/or nutrient and water retention and acquisition (e.g.

reduction of soil bulk density, creation of stable macro- aggregates, improved tilth, provision of

shelter for microorganisms) [39].

A. Effects of biochar on soil physical properties

Soil structure

The incorporation of biochar into soil can alter soil physical properties such as structure, pore

size distribution and density with logical implications in soil aeration, water holding capacity, plant

growth and soil workability. Sohi et al. [39] proposed an analogy between the impact of biochar

addition and the observed increase in soil water repellency as a result of fire. Rearrangement of

amphiphilic molecules by heat from a fire, as proposed by Doerr et al. [9], might not affect the soil,

but could affect biochar itself during pyrolysis. In addition, the soil hydrology may be affected by

partial or total blockage of soil pores by the smallest particle size fraction of biochar, thereby

decreasing water infiltration rates. Liu et al. [27] reported that, when 40 t ha-1

biochar is applied, the

soil water stable aggregate (>0.25 mm) in the 0-15 cm soil layer had a remarkable increase than other

treatments, especially the macro aggregate with particle size larger than >2 mm and also suggested




that biochar incorporation into upland red soil will increase crop productivity and improve soil

structure.

Soil density

Biochar has a bulk density much lower than that of mineral soils; therefore, the application of

biochar can reduce the overall bulk density of the soil [4]. Tensile strength of the hard setting soil

under investigation also decreased with increasing rate of biochar application. Jein and Wang [18]

reported that application of 5 per cent biochar decreased the bulk density (1.08 Mg m-3

) from 1.42

Mg m-3

(Control).

Surface area

Biochar specific surface area, being generally higher than sand and comparable to/or higher

than clay, it will cause a net increase in the total soil specific surface when added as an amendment.

There is evidence that suggests that biochar application into soil may increase the overall net soil

surface area [4] and consequently, may improve soil water retention and soil aeration. The direct

effect is related to the large inner surface area of biochar. An increased soil specific surface area and

physical conditions may also benefit native microbial communities.

Porosity

Biochar has a very porous nature and thus its application to soil will improve soil aeration.

Jein and Wang [18] reported an increase in porosity from 41.24 per cent (control) to 52.43 per cent in

treatment where biochar is applied at the rate of 5 per cent. Improved aeration will be partly due to

increase in macro porosity with resulting higher air filled porosity and improved supply of oxygen to

soil under a wide range of soil water conditions. However, the extent of changes will depend on the

porosity characteristics of different biochar types and application rates. Pore size distribution of

biochar depends on anatomical structure of parent feedstock and process conditions of pyrolysis,

such as charring temperature and activation.

Soil water

The influence of biochar on soil physical properties will affect soils response to water,

aggregation, workability, shrink-swell dynamics, permeability and soil water retention. This change

may be due to physical changes in the soil whereby small particles of char block soil pores and

reduce water infiltration rates. Glaser et al. [12] found that Amazonian char rich anthrosols had field

water retention capacity of 18 per cent, which is higher than surrounding soil that had no char. The

hydrophobic polyaromatic backbone reduces the entry of water into the aggregate pores leading to an

increased aggregate stability and water availability.

Uzoma et al. [43] reported that the lower bulk density and porous nature of added biochar

increased water use efficiency consequent to improvement in field capacity and hydraulic

conductivity. The result of this study also indicates that application of cow manure biochar to sandy

soil is not only beneficial for crop growth but it also significantly improved the physico-chemical

properties of the coarse soil. Increase in water holding capacity of both sandy and silt loam soil due

to the application of biochar was also reported by Granatstein et al. [13] (Figure 3).

B. Effects of biochar on soil chemical properties

Biochar is a high surface area, highly porous and variable charge organic material which has

the potential to increase cation exchange capacity, surface sorption capacity and base saturation

when added to soil. The broad array of beneficial properties associated with biochar addition to soil

may function alone or in combination in order to influence nutrient transformations. Application of

biochar alters the soil chemical properties viz. pH, total and available nutrients, cation exchange

capacity, amount of exchangeable cations, base saturation and also decreased the content of

exchangeable Al3+

.




pH

In the context of nutrient availability, the impact of biochar addition on pH may be important.

Southavong et al. [40] observed that the pH of the soil was significantly increased when biochar was

applied. This was further confirmed by the work of Nigussie et al. [30] who reported that the highest

mean value of pH was observed in soils treated with 10 t ha-1

biochar, while the lowest values was

recorded at the control (0 t ha-1

). The increase in soil pH due to application of biochar was generally

dominated by carbonates of alkali and alkaline earth metals. Another reason for the increase in soil

pH consequent to application of biochar could be because of high surface area and porous nature of

biochar that increases the CEC of the soil. Results of the study conducted by Chang et al. [4]

revealed that the increase in pH as a result of biochar application also reduced the exchangeable

acidity and toxicity of Al3+

in acid soils.

CEC

Biochar has a greater ability than other soil organic matter to adsorb cations due to its greater

surface area, negative surface charge and greater charge density. This makes it potentially more

capable of retaining nutrients and providing these to growing plants. The CEC of freshly produced

biochar is relatively low and only aged biochar shows high cation retention. Peng et al. [33] reported

that amending with one per cent biochar increased CEC by 3.9 – 17.3 per cent. Granatstein et al. [13]

studied the effect of biochar on soil of different texture and concluded that in both sandy and silt

loam soil the CEC gets increased with increased rate of biochar (Figure 4).

Nutrient retention and availability

Higher nutrient availability for plants is the result of both direct nutrient addition by biochar

and greater nutrient retention. Long term benefits of nutrient availability include a greater

stabilization of organic matter, concurrent slower nutrient release from added organic matter and

better retention of cations due to a greater CEC [25]. Lehmann and Rondon [23] reported that,

applied biochar helps the soil to retain nutrients which remain available to plants for long time thus

increasing the plant growth and yield. From soil leaching studies Elangovan [10] found that the

nutrient concentration in soil leachate gets reduced in the order of PO43-

> NH4+

> NO3-

> K+,

whereas the residual surface and subsurface soil got accumulated with high OC, available N, P and K

which proves that the biochar have improved the retention of nutrients in soil. Similar results were

also found by Dainy [7] (Table 3).

Figure 3. Water holding capacity as influenced by biochar application




Figure 4. Effect of biochar on CEC of soil

In acid soils, soluble inorganic P is fixed by aluminium and iron and becomes unavailable to

plants. Amending soil with biochar increased total phosphorus, available phosphorus, inorganic

phosphorus fractions and organic phosphorus. This was possible mainly because the biochar

increased soil pH and reduced exchangeable acidity. The amendment also effectively fixes

aluminium and iron instead of phosphorus, thus rendering phosphorus available for a longer period

[6].

Table 3. Sorption and desorption of nutrients by biochar

Nutrients Sorption (%) Desorption (%)

NH4+ 100.00 32.35

PO43-

90.70 75.65

K+ 92.00 45.14

Ca2+

87.00 46.00

Mg2+

86.15 23.45

SO42-

91.82 74.38

Fe2+

99.67 36.80

Mn2+

100.00 30.20

Zn2+

99.12 26.75

Cu2+

99.12 26.72

C. Effects of biochar on soil biological properties

The soil biota is vital to the functioning of soils and provides many essential ecosystem

services. Understanding the interaction between biochar and soil biota is therefore vital. It is mainly

through promoting arbuscular mycorrhizal fungi. Kolb et al. [22] demonstrated that, biochar caused a

significant increase in microbial efficiency as a measure of units of CO2 released per microbial

biomass carbon in the soil. Biochar addition to soil increased N fixation by both free living and

symbiotic diazotrophs and led to 30 – 40 per cent increase in bean yield with biochar additions upto

50 g kg-1

[37].

Also biochar addition to soil alters soil microbial population and shift functional groups in

soil organic compounds. The structure of biochar provides a refuge for small beneficial soil

organisms, such as symbiotic mycorrhizal fungi which can penetrate deeply in to the pore space of

biochar, where sporulation goes on with less competition from saprophytes [38]. Yamato et al. [44]

stated that increase in the root amount and colonization rate of arbuscular mycorrhizal fungi were




observed on maize after biochar application. A more rapid cycling of nutrients in soil organic matter

and microbial biomass as well as better colonization of roots by arbuscular mycorrhizal fungi will

improve nutrient availability and crop yields by retention of nutrients against leaching in highly

weathered soils of the humid tropics that have little CEC and a better access of the plants to fixed P

due to inoculation by mycorrhizae.

Enzyme activity

Mineralization of soil organic matter (SOM) is an important microbial mediated process by

which carbon, nitrogen, and other nutrients are converted from organic forms into inorganic forms.

Soil microbes must produce soil enzymes to catalyze the breakdown of soil organic matter and to

make readily-usable dissolved compounds for growth and metabolism. Demise et al. [8] studied the

effect of biochar on soil enzyme activities and found that both urease and β – glucosidase enzyme

activity got increased with the application of biochar when compared to control (Figure 5). Higher

enzyme activity could be due to the higher microbial biomass in the biochar treatments that released

more urease enzyme than the other treatments.

Figure 5. Effect of biochar on soil enzyme activity

IV. Effect of biochar on crop productivity

For increasing any agricultural crop production, use of organic manures along with inorganic

fertilizers is well established, thus revealing the complimentary effect of manures and fertilizers in

improving the growth, yield and yield attributes. Yield increase with biochar application has been

documented in controlled environment as well as in the field [11]. Asai et al. [1] studied the effect of

biochar application on grain yield of upland rice (Oryza sativa L.) in northern Laos. With an

application rate of 4 t ha-1

they found double the increase in yield.

Revell [35] reported that addition of biochar had no significant impact on pepper yield in

either silt loam or sandy loam soil. However, N often increased yield in both soils at biochar

application rates of 2.5 per cent and below, especially in the sandy loam. This shows the importance

of adding N source with biochar, as biochar is not inherently rich in N (much of the N in the feed

material is lost during pyrolysis). Summary of experiments assessing the impact of biochar addition

on crop yield is furnished hereunder in the Table 4.

Table 4. Impact of biochar addition on crop yield

Crop Soil Biochar

(t ha-1

)

Fertilizer rate

(kg ha-1

)

Yield

increase (%) Reference

Wheat Ultisol 10

1.25g nutricote per

250g soil (Nutricote -

15.2:4.7:8.9 % NPK)

250 [46]

Radish Alfisol 100 N(100) 266 [4]

Rice Inceptisol 30 Nil 294 [31]




Maize Degraded

soils 15 N(180),P(36), K(50)

14, 32 in 1st

& 2nd

year [17]

Groundnut Alfisol 15 N(10), P(10), K(45) 55 [21]

Rapeseed Alfisol 40 N(90), P(52.5),

K(107)

36.02

[27] Sweet

potato Alfisol 40 53.77

V. Biochar and climate change

Impact on soil carbon sequestration

Biochar production and utilization systems differ from most biomass energy systems because

the technology is carbon negative and it removes net carbon dioxide from the atmosphere and store it

as stable soil carbon sinks in the terrestrial ecosystem [26]. The ways in which biochar reduce the

CO2 emission are achieved by reducing the requirement for fertilizer while increasing soil microbial

life which results in more carbon storage in soil. Biochar may persist in soil for millennia because it

is very resistant to microbial decomposition and mineralization and leads to a net sequestration of

CO2. It is one of the best technological solutions to reducing CO2 levels emphasizing that biochar has

the potential to sequester almost 400 billion tonnes of carbon by 2100 and to lower atmospheric CO2

concentrations by 37 parts per million [34].

Impacts on soil N2O and CH4 emission

Biochar amended soils have shown 50 to 80 per cent reduction in N2O emission and reduced

runoff of phosphorus into surface waters and leaching of nitrogen into groundwater. Field

experimentation with biochar in Columbia showed 80 per cent suppression of N2O emission and

considerable amount of CH4 emission reduction [34]. Biochar application resulted 50 and 80 per cent

reduction in N2O emission in soybean plantations and grassland system [36]. Since biochar in soil

may modify the moisture regime and physical location of water within the soil matrix, it may

mitigate the enhanced emission of N2O that may occur in no-till systems.

Methane emission from agricultural soils, mainly from paddy fields, account for 12 per cent

of the global CH4 emission from all sources. Some studies have suggested that addition of biochar

may partially suppress CH4 emission. Recent studies have indicated that biochar reduces N2O

emissions and increases CH4 uptake from soil [36]. Biochar addition also significantly suppressed

ambient CH4 oxidation at all levels compared to unamended soil.

VI. Role in soil bioremediation

Remediation of heavy metals

Pollutants may exert toxic effect to ecosystem if they move through soils and transfer to

crops/biota or leach into groundwater. Biochar has been evidenced to act as an efficient sorbent of

various contaminants, organic and inorganic, because of its huge surface area and special structure.

Many reports provided sound data on the potential effectiveness of biochar in removing heavy metal

from aqueous solution and soils. The mechanism of heavy metal removal with biochar amendment

might be attributed to electrostatic interactions, precipitation and other reactions. With the

incorporation of biochar, there arises more negative charge on soil surface due to the decreasing zeta

potential and increasing CEC. Therefore, the electrostatic attraction between heavy metals with

positive charge and soil will be enhanced. In relation to precipitation, the markedly increased soil pH

arising from biochar amendment may lead to decreased mobilization of heavy metal. Some of the

research studies with respect to the heavy metal remediation using biochar are given in the Table 5.

Table 5. Effect of biochar on heavy metal concentration in soil, plant and water

Pollutant Study Results Reference

Cd, Zn Soil sediments 300 times reduction in Cd and

45 times in Zn [2]




Cd, Pb Bioavailability in

rapeseed crop

10 % biochar led to a reduction

of 71 %, 92 % for Cd & Pb [15]

Pb, Ni,

Cd

Removal from

aqueous solutions

Significant amount of sorption

ranging from 57 to 97 % [16]

Remediation of organic pollutants

The various research reports in recent years have revealed that biochar have the ability to

remove organic pollutants from soil, water and sediments, and thus lowering their bioavailability and

preventing toxic substances transferring from environment to plant and further to organisms

including human. Results showed that 2 – 14 per cent sulfamethoxazole was found to transport

through soils with biochar amendment versus 60 per cent in the leachate of soils without biochar

amendment [45]. Oleszczuk et al. [32] reported that the freely dissolved concentration of PAH in

sewage sludge can significantly decrease, in the presence of biochar, to the extent of 0 – 57 per cent

depending on the added amount of biochar.

Remediation of pesticide residue

The effect of biochar on remediation of heavy metals and organic pollutants proposed a cost-

effective and environmental friendly tool to manage polluted environment. However, pesticide is

added to soil or other environmental compartments deliberately to control pest and disease in

agriculture. The increased sorption and decreased dissipation of pesticides in the presence of biochar

may lower the risk of environmental contamination and human exposure from the perspective of

ecosystem and human health. Furthermore, the decreased bioavailability and plant uptake may

increase crop yield and reduce pesticide residues in crops from agricultural perspective. Encouraging

results concerning retention of both organic and inorganic pollutants on biochar surfaces have been

found in many studies and are summarized in Table 6.

Table 6. Effect of biochar on agrochemical concentration in soil

Contaminant Result Reference

Pentachlorophenol Levels in extractable liquid decreased to

0.17 from 4.53 mg L-1

[28]

Atrazine Significant sorption of atrazine on biochar

surfaces; effective immobilization in soil [3]

Simazine Significant sorption with 100 t ha

-1 biochar

- 97 per cent simazine sorbed in 24 hours [20]

Glyphosate Leaching of glyphosate reduced [14]

VII. Application and limitations

Application rate

Recommended application rate for any soil amendment must be based on extensive field

testing. As of now, field data is insufficient to make general recommendations on biochar application

rates in tune with soil types and crops. In general, biochar materials can differ widely in their

characteristics (e.g. pH, ash content) which in turn influences application rate. Several studies have

reported positive effects of biochar application at the rate 5-50 tonnes per hectare on crop yields,

with appropriate nutrient management. Though this is a large range, when several rates are used, the

plots with the higher biochar application rate showed better results [4][5]. Most biochar materials are

not substitutes for fertilizer. So adding biochar without necessary amounts of nitrogen (N) and other

nutrients cannot be expected to provide improvements on crop yield.

Application methods

Biochar should ideally be applied near the soil surface in the root zone, where the bulk of

nutrient cycling and uptake by plants take place. Certain systems may benefit from the application of

biochar in layers below the root zone, for example during landscaping for C sequestration or if using




biochar for moisture management. Similarly, if biochar were to be applied to soil solely for C

sequestration purposes, placement deeper in the soil would be desirable since microbial activity that

can degrade biochar carbon is reduced. The likelihood of wind and water erosion losses of biochar is

reduced when it is thoroughly incorporated into soil [29]. The different application methods are as

follows

Broadcasting

Traditional banding

Mixing biochar with other solid amendments

Mixing biochar with liquid manures

Targeted biochar applications in precision agriculture

Frequency of application

Due to its recalcitrance nature, single application of biochar can provide beneficial effects

over several growing seasons in the field [41]. Therefore, biochar does not need to be applied with

each crop, as is usually the case for manures, compost, and synthetic fertilizers. Depending on the

target application rate, the availability of the biochar supply, and the soil management system,

biochar amendments can be applied in increments. However, it is believed that beneficial effects of

applying biochar to soil improve with time, and this may need to be taken into consideration when

splitting applications over time.

Limitations in using biochar

If biochar is not properly made, it can pollute soils with compounds, such as PAHs

(polycyclic aromatic hydrocarbons), dioxins (toxic heterocyclic hydrocarbons), furans (cyclic

flammable liquid compounds), heavy metals (metals or metalloids that present environmental

problems), etc. and also poses threat to ecosystem, being carcinogenic. This would include the levels

of arsenic, cadmium, lead, chromium, manganese, mercury, nickel, vanadium, etc. There might be

other sources of pollution, which would depend on the substrate that was used to make the biochar. It

is important to use pure lignocellulosic biomass, without plastic or rubber contaminants.

VIII. Conclusion

Biochar has very promising potential for the further development of sustainable agriculture

production systems. Also, biochar production provides a great potential for worldwide climate

change mitigation that goes beyond its uses in agricultural production alone. It also makes soil

cleaner and healthier through decontamination effect. Promotes better CO2 absorption through

improved crop stand and helps in C sequestration.

IX. Future line of work

Low cost biochar pyrolysis equipments

Municipal solid waste disposal through biochar production

Standardization of biochar based nutrient fortification and nutrient releasing pattern

Optimization of biochar application for different agricultural crops

Long term carbon sequestration potential of biochar in different ecosystem

Acid soil reclamation capability of biochar

Biochar induced microbial dynamics and its role in nutrient availability

Biochar induced systemic resistance in plant disease and pest control

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