CHAPTER 1

INTRODUCTION

Increase soil degradation due to intensive agricultural production differ with

time and leads to decrease in soil physical, chemical and biological properties. As a

result, a continuous amendment of the soil physical conditions is required to meet

the need of food production to support the ever growing world population.

Therefore, efficient means for accurate improvement in soil physical properties is

important considering within-field variations in soil physical properties especially

for tropical soils are important for proper management practices and precision

farming. Among different ways of improving soil physical conditions, those based

on biochar are promising because soil materials and properties have strong

correlation and can be improved through biochar application (DeLuca et al., 2006).

Good soil physical and chemical conditions can add value to farming operation if

they help improve yield, increase soil erodibility and reduce management related

problems. Researchers have reported that application of biochar on soils has

significant effect on net primary crop production, grain yield and dry matter

production (Chan et al., 2008; Chan and Xu, 2009; Major et al., 2009; Fagbenro et

al., 2015). Peake et al., (2014) and Oshunsanya and Aliku (2015) also revealed that

biochar amendment decreases bulk density, increased the field capacity (FC) and

plant available water content (PAWC) of a wide range of soil types. Brockhoff et

al., (2010) shows enhancement of soil porosity, moisture retention, aggregate

stability and saturated hydraulic conductivity after biochar application. That

increased understanding of the effect of biochar application must then lead to

improved management opportunities that could boost yield, reduce input costs, or

accurately predict the benefits that may be obtain from tiling, liming, irrigation, or

other types of field improvements. Biochar is a carbon rich solid material produced

from the heating of biomass in a closed container in an atmosphere of little or no

oxygen (Lehmann and Joseph 2009). Recently, Biochar has drafted interest world

wide as soil amendments to improve and maintain soil fertility (Lehmann et al.,

2003).

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Biochar as soil amendment has become an important topic in soil science in recent

time. Several studies are going on looking at the effects of biochar on agro-

ecosystems (Anders et al., 2013). The conversion of biochar as a carbon sink has

been proposed in the past but was not explicitly link to application on soil. As soil

amendment, biochar can greatly influence various soil properties and processes.

Many of the organic residues from agriculture, forestry and other organic systems

can be use to produce biochar and applied to agricultural soil both to sequester

carbon and to improve the production potential of crops. The origin of biochar that

has lead to a renewed focus in agriculture can be link to the discovery of terra preta

de indo soils located in the Amazon River basin.

Agricultural scientist have come to believe that soil properties could be

amended by applying biochar as an amendment (Fagbenro et al., 2015) The impact

of biochar as an amendment depends on its properties. Key properties are those

which contribute to the adsorptive properties of biochars and potentially alter soil’s

specific surface area (SA), pore size distribution (PSD), bulk density (BD), water

holding capacity (WHC), penetration resistance (PR), soil structure and soil texture.

Most soil types found in the tropics are highly weathered with high acidity,

dominance of low-activity clay minerals, low nutrient and organic matter content

especially after the vegetative cover has been removed (Babalola 2002; Fagbenro et

al., 2012b). Therefore, optimum crop production has not been possible without the

use of organic materials and inorganic fertilizers (Lombin et al., 1991; Omoti et al.,

1991). Though organic and inorganic fertilizers are use as soil inputs in other to

support increase crop production, they decompose very fast in the humid tropics so

that their benefit is often short-lived (Jekinson and Ayanaba, 1977; Bol et al., 2000).

Consequently, maintenance of soil organic matter has been a major challenge to

stake holders working in the tropics (Agboola and Fagbenro, 1985). However, there

is little or no information as regard the effect of biochar on soil erodibility.

Therefore, the objectives of this study are to assess:

(i) the effect of biochar amendment on soil erodibility

(ii) the influence of biochar on hydrological properties of an oxisol.

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CHAPTER 2

LITERATURE REVIEW

2.1 The Origin of biochar

Soils discovered in the Amazon River Basin known as Terra Preta de Indio was said to have

higher levels of charcoal, 70 times higher than the surrounding soils; they are more

productive than surrounding soils and have been around for hundreds to thousands of years

(Mann, 2002; Glaser et al., 2001, 2002; Lehmann, 2007). Terra Preta soils have been

measured with as much as 150 g/kg organic matter which is higher than the surrounding

soils (Petersen et al., 2001; Woods et al., 2000). These soils are also higher in essential

nutrients including phosphorus, calcium, sulfur and nitrogen, cation exchange capacity

(CEC) and have a more neutral pH than the typical acidic oxisol soils found around the

Terra Preta soils (Mann, 2002; Lehmann et al., 2003; Lehmann, 2007). The improved

chemical properties of the Terra Preta soils result in productive farm land where it typically

did not exist.

2.2 Definition of Biochar?

Biochar is a stable form of charcoal made from heating natural organic materials (crop and

other waste, woodchips, manure) in a high temperature and low oxygen process known as

pyrolysis. Due to its molecular configuration, biochar is chemically and biologically in a

more stable form than the original carbon form it comes from, making it more difficult to

break down. This means that in some cases it can remain stable in soil for hundreds to

thousands of years (Pessenda et al., 2001; Chmidt et al., 2002; Krull et al., 2006).

2.3 Process of biochar formation

The process of biochar formation is refer to as pyrolysis. Pyrolysis is a thermo-chemical

decomposition of organic material at elevated temperatures in the absence of oxygen (or

any halogen). Pyrolysis is a type of thermolysis, and is most commonly observed in organic

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materials exposed to high temperatures. It is one of the processes involved in charring

wood, starting at 200 to 300°C (390 to 570°F). Different pyrolysis conditions lead to

different proportions of each end product (liquid, char or gas). This means that specific

pyrolysis conditions can be tailored to each desired outcome. For example, the IEA report

(2007) stated that fast pyrolysis was of particular

interest as liquids can be stored and transported more easily and at lower cost than solid or

gaseous biomass forms. However, with regard to the use of biochar as a soil amendment

and for climate change mitigation, it is clear that slow pyrolysis would be preferable as this

maximizes the yield of char, the most stable of the pyrolysis end products. The process of

pyrolysis transforming organic materials into three different components being gas, liquid

or solid in different proportions depends upon both the feedstock and the pyrolysis

conditions used. Gases which are produced are flammable, including methane and other

hydrocarbons which can be cooled when they condense and form an oil/tar residue which

generally contains small amounts of water. The gasses (either condenses or in gaseous

form) and liquids can be upgraded and used as a fuel for combustion. The remaining solid

component after pyrolysis is charcoal; it is referred to as biochar when it is produced with

the intention of adding it to soil to improve it.

2.4 Properties of biochar

Biochars are characterized by certain morphological and chemical properties which are

borne from the physico-chemical alteration of the original feedstock as a result of pyrolytic

process. Characteristically, these properties of biochar differ since they are controlled by

factors such as type of organic material from which they are made, pyrolysis conditions (i.e.

final pyrolysis temperature or peak temperature, rate of heat application – slow or fast

pyrolysis), rate and duration of charring (Mukherjee,2011; Mukherjee et al., 2011,

Zimmerman, 2010). The impact of biochar as an amendment depends on its properties. Key

properties of biochar are the adsorptive properties that potentially alter soil’s surface area,

pore size distribution, bulk density, water-holding capacity and penetration resistance.

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2.5 Large surface area and presence of micropores

Large surface area amendment property of biochar contributes to the adsorptive properties of

soil and potentially improves pore size distribution, bulk density and consequently leading to

an increase in the soil available water needed for crop growth and development. In addition,

a strong direct relationship exists between a biochar’s surface area and the pore volume as

measured using N2 adsorption and Braunauer-Emmett-Teller (BET) modelling (Sweatman

and Quirke, 2001; Jagiello and Thommes, 2004). Jagiello and Thommes, (2004) reported

that the surface area could also be measured by using other compounds such as CO2 on

carbonaceous materials at the micrometer scale. Mukherjee and Lal, (2013) stated that

understanding and determination of the relative abundance and stability of pores of different

sizes are keys to soil ecosystem functioning. Important among these functions are aeration,

hydrology and provision of habitat for microbes while the finer pores could be involved with

molecular adsorption and transport (Atkinson et al., 2010). Differences in production

conditions, especially final combustion temperature, would result to variation in surface area

of biochars even when they are produced from the same parent biomass. Mukherjee and Lal,

(2013) stated that the relationship between the peak combustion temperature and surface

morphological parameters (i.e. surface area, pore diameter and volume) of the resulting

biochar is highly complex. Fernandes et al., (2003) stated that there may be either no simple

relationship between surface area and peak temperature, or surface area may increase with

increase in peak temperature up to a certain threshold and then decrease. Due to variations in

reports on surface area and peak temperature, Mukherjee and Lal, (2013) reported that the

mechanisms responsible for increases in surface area with an increase in peak temperature or

heating rate are not well understood. However, Mukherjee, et al., (2011) reported that

surface area increases with an increase in peak temperature of biochar production.

2.6 Adsorptive property

The adsorptive nature of biochar is related to its surface area. The adsorptive capability of

biochar is determined by its surface chemical properties and porous nature. It is an important

physical property due to its influence in the uptake and binding effect of materials from their

surroundings (Mukherjee and Lal, 2013). Schmidt and Noack, (2000) reported that biochar

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may adsorb poly aromatic compounds, poly aromatic and poly aliphatic hydrocarbons, other

toxic chemicals, metals and elements or pollutants in soils, sediments, aerosols and water

bodies.

2.7 Stability

This important physical property makes biochar a more sustainable soil amendment relative

to its original fresh biomass for agricultural purpose. The evidence of high amounts of black

carbon in the Terra Preta soils over a time suggests a high recalcitrant nature of biochar.

However, degradation of at least some components (volatile matter or labile organic matter)

of the biochar may occur (Schmidt and Noack, 2000). On the other hand, Mukherjee and Lal,

(2013) noted that the difference in sub-soil characteristics due to variations in microbial

activity and oxygen content may affect biochar oxidation and aging. Biochar can move into

sub-soil over time (Skjemstad et al., 1999) to enrich the zone. Hence, other factors

associated with its physical stability in soil include its mobility into deeper soil profile

(Mukherjee and Lal, 2013). The aggregate stability of biochar-amended soil may also

determine the susceptibility of biochars to microbial processes in subsoil. Mukherjee and

Lal, (2013) explained that these factors not only enhance the stability of soil organic matter

in the deeper profile but also improve availability of water and nutrients to crops and

decrease erosion risks.

2.8 Restoring/improving soil properties

Biochar has the potential capacity to restore a degraded soil when added to the soil. Biochar

mineralizes gradually over a long period of time when applied to the soil. Nutrients from

biochar are released gradually to improve the physical, chemical and biological conditions of

the soil. Mukherjee et al., (2011) reported that the impact of biochar as an amendment is a

function of its properties such as large surface area and presence of micropores. These are

key properties because they contribute to the adsorptive properties of soils and potentially

alter soil physical and hydrological properties.

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2.9 Biochar and soil properties

Interaction between biochar and soil. The application of biochar to the soil will alter the

physical and chemical properties of the soil. Verheijen et al., (2010) stated that the net effect

of biochar on the soil physical properties will depend on its interaction the physico-chemical

characteristics of the soil, the weather conditions prevalent at the particular site and the

management of its application. Biochar application can reduce the bulk density of the

different soils (Chen et al., 2011). This could bring about improvement in soil structure or

aggregation, and aeration enhancement, thus improving soil porosity. Atkinson et al., (2010)

reported that the higher the total porosity (micro- and macropores) the higher is soil physical

quality. This is because micropores are involved in molecular adsorption and transport of

water and nutrients while macropores affect aeration and drainage. Several studies have

reported that as low as 0.5% (g g−1) biochar application rate was sufficient to improve water-

holding capacity and water retention (Jones et al., 2010 and Uzoma et al., 2011). Hence, this

can be said to be good water-holding capacity amendment for sandy soils which are highly

porous due to the preponderance of macropore

2.10 Effect of biochar application on some soil physical properties

A key determinant of soil functions and processes is its physical properties, precisely and

most importantly, its texture. Hence, the addition of biochar in soils with different textures

should affect the soil hydraulic properties differently due to the fact that there is a correlation

between soil texture and soil hydraulic properties. The impacts of biochar as a soil

amendment on some soil physical and hydrological properties are briefly discussed below.

2.11 Soil surface area

Table 1 depicts a summary of results of biochar application on surface area. Soil surface

area is an intrinsic property of soil determined by the sizes of its particles. The surface

area of soils is an important physical characteristic which plays a vital role in water- and

nutrient-holding capacities, aeration and microbial activities (Van et al., 2009); hence, it

can be said to be partly controlling the essential functions of soil fertility. However, the

effectiveness of the surface area of a soil depends on its size – the larger the surface area,

the greater the soil’s water- and nutrientholding capacities. This is particularly true for

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fine-textured soils. Thus, Mukherjee and Lal, (2013) reported that agronomic

productivity improvement of biochar-amended soils may be linked to the higher surface

area of the biochar–soil mixtures. (Atkinson et al., 2010; Hammes and Schmidt, 2009;

Liang et al., 2006) explained that the high surface area of biochar provides the space for

formation of bonds and complexes with cations and anions with metals and elements of

soil on its surface, which improves the nutrient retention capacity of soil. Liang et al.,

(2006) reported that biochar incorporation can enhance specific surface area up to 4.8

times that of adjacent soils. Laird et al., (2009) also reported increases in specific surface

area of an amended clayey soil from 130 to 150 m2 g–1 when biochar derived from mixed

hardwoods was applied at rates of 0 to 20 g kg–1 in a long-term soil column incubation

study.

2.12 Porosity

Table 1 shows a summary of results of biochar application on soil porosity. This is the ratio

of the pore volume to the total volume of a representative sample of a porous medium. This

factor is said to be associated with surface area. The total porosity or pore size distribution of

biochar is a factor that can play an important role in the alteration of the properties of

biochar-amended soils. Biochars are usually characterized by the preponderance of

micropores, which may alter the pore size distribution of coarse texture soil when added.

Jones et al., (2010) reported that significant increases in mesoporosity occurred at the

expense of macropores in waste-derived biochar amended soil compared to the control.

Jones et al., (2010) further intensified that the higher the rate of biochar application the

greater its effect on porosity. Hence, biochar could be a good replacement for tillage

practices which causes short-term increase in porosity, but long-term decrease in aggregation

and ultimately lowering soil porosity.

2.13 Bulk density

Bulk density, which is defined as the mass of soil per its unit volume, has been known to

have a negative correlation with surface area. Oshunsanya, (2011) stated that well-structured

soils (fine texture) are characterized by low bulk density values between 1.0 and 1.3 g cm–3

while poorly structured (coarse texture) soils are known to have high bulk density values

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between 1.6 and 1.8 g cm–3. Hence, reports from both field and laboratory studies have

shown bulk densities to have contrasting results to surface areas of biochar-amended soils.

Laird et al., (2010), Jones et al., (2010) and Chen et al., (2011) reported that application of

biochar can decrease the bulk density of soils. Laird et al., (2010) showed in a soil column

incubation study that biochar-amended soil columns had significantly lower bulk density

than no-biochar controls. Mukherjee and Lal, (2013) reported that biochar-amended column

had a lower rate of compaction compared to the control or manure-amended soil columns

when all the columns were subjected to compaction by gravity and periodical leaching

events. They further stated that the decrease in bulk density of biochar-amended soil could

be one of the indicators of the improvement of soil structure or aggregation and aeration, and

could be soil-specific.

2.14 Aggregate stability

Results of studies showing biochar effect on soil aggregation are illustrated in Table 1.

Studies have shown biochar to respond positively to aggregation. Though Mukherjee and

Lal, (2013) reported that data on aggregate stability and penetration resistance of biochar-

amended soils are scarce, a few studies generally showed that low-temperature (220οC)

hydrochar made from spent brewer’s grains (a residue from beer brewing) responded

positively to aggregation of Albic Luvisol by significantly increasing water-stable aggregates

as compared to the control treatment. Glaser et al., (2002) have reported that the formation

of complexes of biochar with minerals, as the result of interactions between oxidized

carboxylic acid groups at the surface of biochar particles, should be responsible for the

improved soil aggregate stability (Figure 2). As a result, soil aggregates and pore size

distribution can be improved by adding organic matter from biodegradation and thus

improving soil hydraulic properties. However, other authors have reported contrasting

results. For instance, Busscher et al., (2011) reported that with or without mixing Bt and E

horizons with pecan shell (Carya illinoinensis), biochar-amended soil decreased aggregation

compared to the control, while Busscher et al., (2010) reported mixing of biochar from pecan

with switchgrass increased aggregation, but the effect was however significantly lower when

the soil was treated only with biochar without mixing with switchgrass. From this trend of

results, Mukherjee and Lal, (2013) concluded that a positive effect on soil aggregate stability

9

would require the presence of a substrate (i.e switchgrass) along with biochar as an

amendment.

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Table: 1 Total elemental composition and means of biochars from variety of feedstock

(Chan and Xu, 2009)

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2.15 Penetration resistance

Studies on the effect of biochar amendment on soil penetration resistance are illustrated in

Table 3. Penetration resistance measures the capacity of a soil in its confined state to resist

penetration by a rigid object (Ehlers et al., 1983). It is affected by moisture content. Thus, it

affects the potential for root growth and development. Briggs et al., (2012) found root

growth to be inversely related to penetration resistance. Results from literatures have shown

that the effect of biochar application on soil penetration resistance is dependent on time of

application. Busscher et al., (2011) reported that mixing Norfolk loamy sand E and E and Bt

layers with pecan shell biochar produced at a temperature of 700οC increased penetration

resistance measured after 44 days of application. Penetration resistance was, however

reduced when measured after 96 days of application. Thus, soil compaction may not be

alleviated by biochar addition over short period of time, but may be altered in the long run

due to changes in properties as a result of aging of biochar.

2.16 Hydrological properties

Several authors have reported positive response of soil hydrological properties to biochar

amendment. This may be due to the fact that soil hydrological properties such as infiltration

rate, moisture content, hydraulic conductivity, water-holding capacity and water retention are

invariably related to soil surface area, bulk density, porosity and aggregate stability

(Mukherjee and Lal, (2013). In other words, an alteration in these soil physical properties as

caused by biochar application would lead to a change in soil hydrological properties.

2.17 Water-holding capacity, water retention and moisture content

Table 4 shows the results of biochar application effect on water-holding capacity. The

amount of water in a soil is a function of its ability to hold and retain water for plant use

against the influence of gravity. Fine-textured soils would have higher moisture content

at the same tension as soils with coarse particles. This is because the ability of a soil to

retain water is a function of the micropores in the soil, which is usually lower in coarse-

textured soils. Hence, moisture required by plants to upset the evapotranspirational

demand of the atmosphere may be limiting, especially in coarse-textured soils. Thus,

application of biochar can increase water storage ability of coarse-textured soils. Several

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studies have reported alterations in water-holding capacity and water retention in soils

amended with biochar. Busscher et al., (2010) and Ehlers et al., (1983) reported that

0.5% (g g–1) biochar application rate was sufficient to improve water-holding capacity.

Application of biochar produced from black locust (Robinia pseudoacacia) was reported

to increase the available water capacity by 97%, saturation water content by 56%, but

reduced hydraulic conductivity (uzoma., 2011). This can also influence soil aeration and

temperature to a very large extent. Liard, 2010 reported that results from a long-term

column study indicated that biochar amended Clarion soil retained up to 15% more

water, with 13% and 10% more water retention at –100 KPa and –500 KPa soil matric

potential, respectively, compared to control (unamended soils). Minamikawa et al.,

(2011) showed that coal-derived humic acid substances can increase water retention,

available water capacity and aggregate stability of inherently degraded soils. Tryon,

(1948) reported that biochar application increased the available water capacity in sandy

soil, with no effect on a loamy soil, and decreased moisture content in a clayey soil.

Mukherjee, (2013) suggested that such response may be due to the hydrophobic nature of

the charcoal that caused alterations in soil pore size distribution. Tryon, (1948), therefore,

advised that because the soil moisture retention may only be improved in coarse-textured

soils, a careful choice of biochar/soil combination needs to be taken into consideration.

2.18 Biochar and soil chemical properties

Most studies of biochar as a soil amendment have focused majorly on soil nutrient status,

taking into consideration cation exchange capacity, nutrient content, pH, the carbon

sequestration potential of the amended soil, and vegetative growth and yield of crops.

Biochar has the potential to improve soil CEC due to the fact that it is often characterized by

high CEC values, due to its negative surface charges and its high specific surface area as was

reported for biochar produced from crop residues (Yuan et al., 2003). Furthermore, the

immediate beneficial effect of biochar application on crop productivity in tropical soils may

result from increase in availability of nitrogen, phosphorus, potassium, calcium, copper and

zinc as reported for soils amended with secondary forest biochar (Lehmann et al., 2003).

Also, poultry litter biochar may result in strong increase in soil extractable phosphorus

(Novak et al., 2009) when incorporated into the soil. In evaluating the effect of different

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biochars on soil chemical properties, Chan et al., (2007) reported that biochar produced from

poultry manure had higher electrical conductivity, nitrogen, phosphorus and pH values than

that of garden waste. However, this may be due to their effects in reducing leaching and

fixation of nutrients as moderate biochar additions are not a direct supplier of plant nutrients

in the long-term.

2.19 Effects of biochar application on Soil Organic Carbon (SOC)

Biochar application can directly or indirectly affect SOC dynamics. Indirectly, biochar could

affect net primary production and, thus, the amount of biomass that may remain in

agroecosystems. This would result to alteration in soil carbon inputs. Higher belowground

net primary production and increased root-derived carbon inputs after biochar application

may particularly result in an increase in SOC. Directly, biochar can inhibit degradation

process, and as a result increase the mean residence time (MRT) of SOC (i.e. the mean time

that a SOC-carbon atom spends in soil). As a direct consequence, biochar application would

enhance SOC stabilization processes and contribute to SOC sequestration. The MRT of

biochar-carbon is thought by some to be in the range of millennia (Glaser and Birk, 2013).

However, information on biochar longevity in soil is meagre and varies between biochars

and sites. For example, the MRTs of biochar in field experiments ranged from about 8 years

for biochar produced by burning of forest trees during slash-and-burn agricultural practices

(Nguyen, 2008) to 3,600 years for biochar produced from prunings of old mango (Mangifera

indica L.) trees (Major et al., 2010). Also, biochar longevity in soil may be affected by

differences in climatic conditions. For example, chemical and/or biological mineralization of

natural chars produced from wood during bushfires was slower under Mediterranean climate

when compared to temperate climates in Australia (McBeath et al., 2013).

2.20 Biochar application strategies

Biochar application strategies have been studied a little; the way biochar is applied to soils

can have a substantial impact on soil processes and functioning. Biochar is most commonly

incorporated into the soil. First, spread the desired amount onto the soil evenly, and then till

it in with machine or by hand. The followings are the application strategies:

i. Topsoil incorporation, ii. Depth of application, iii. Top-dressing.

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a) Top soil incorporation

This is the incorporation of biochar on soil alone or combined with organic compost /

organic manures. The homogenous mixture of biochar with organic compost/manure/slurry

is essential for top soil application (in most arable soils from 0-15/30 cm depth). Moistening

the biochar during soil application is very essential to minimize the loss of biochar from

wind and water erosion.

b) Depth application

The placement of biochar to the soil is also a very significant approach to increase the

efficiency of biochar on soil physic-chemical and biological properties. Depth application of

biochar has been described mostly as ‘deep-banded’ application (Blackwell et al., 2007).

Deep mould board ploughing essentially results in temporary ‘depth application’, although

horizontally continuously. Subsequent mouldboard ploughing and cultivation will then

further homogenize the biochar distribution through the topsoil.

c) Top-dressing

Top-dressing of biochar is the spreading of biochar (dust fraction mostly) to the soil surface

and relying on natural processes for the incorporation of the biochar into the topsoil. This

form of application is being considered mainly for those situations where mechanical

incorporation is not possible, e.g. no-till systems, forests, and pastures. An obvious drawback

is the risk of erosion by water and wind, as well as human health (inhalation) and impacts on

other ecosystem components (e.g. surface water, leaf surfaces, etc.). Both topsoil

incorporation and top-dressing can be applied with a range of frequencies, that is, a ‘one-off’

application’, every few years, or every year. For specific effects on soil, e.g. nutrient

availability (from a feedstock like poultry manure) or liming effect, a more frequent

application may be more beneficial to the soil and/or less detrimental to the environment

(nitrate leaching). The sources of materials used to produce biochar and pyrolysis technique

are the primary factors for the particle size distribution of biochar. Handling of biochar is

very difficult especially due to the particle size distribution of biochar.

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2.21 Problems of soil application

a) Wind loss: Applying of biochar to the soil is a tricky process due to wind or water

losses. The large amount of biochar is lost through wind (Figure 2) and water during

soil application for the purpose of soil carbon sequestration and crop production. The

biochar field trial in Québec, Canada in 2008, Blue Leaf Inc. faced problem during

the establishment of a biochar. Blue Leaf applied a fine grained biochar produced by

fast pyrolysis, and estimated that 2% of the material was lost loading the spreader,

3% was lost during transport, and 25% was lost during spreading, leading to a total

loss of approximately 30%. The biochar can be moistened to minimize the wind

losses, however, it will increase the weight of the biochar materials and this will

increase the transport cost. While water is usually added to biochar immediately after

exiting the pyrolysis unit in order to quench it, more water could be applied to reduce

dustiness prior to field application.

b) Minimizing wind loss:.When winds are mild, apply biochar under the good weather

conditions. The biochar dust is applied at mild rain conditions due to holding nature

of biochar on the soil surface until biochar is incorporated into the soil by tillage.

Water can be applied to the biochar for the purpose of moistening to reduce the wind

loss or it can be applied with moist manure. Different formulation can be made by

pelleting, prilling and mixing of biochar with compost or manure. Different biochar

formulations will be best suited to different application methods, and very fine

biochar may be described in certain cases, for example when applying as slurry, by

itself or mixed with manure (Blackwell et al., 2009).

c) Water erosion: Apart from wind loss, biochar can also be lost by water erosion. The

factors such as heavy rain, sloping terrain, etc exacerbate this problem. Rumpel et al.,

(2006) found that surface-deposited biochar was eroded from steep slopes in Laos;

they highlighted the need for soil incorporation especially when biochar is applied to

sloping terrain. Major et al., (2010) also observed significant losses of biochar

incorporated into particularly flat terrain, in an area where intense rainfall events

occur. Biochar can require some time for wetting soon after application, and may

float away when a thick layer of standing water pool is over the soil and moves

towards the bottom of the site’s slope.

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d) 2.22 Minimize erosion by water

Good management strategies were developed to incorporate biochar into soil especially

on sloping terrain or where intense rainfall occurs. The method used for biochar

incorporation must itself be chosen to minimize erosion losses.

2.23 Rate of biochar application

Biochar application rate in soil varies depending upon many factors including the type of

biomass used, the degree of metal contamination in the biomass, the types and proportions of

various nutrients, and also climatic and topographic factors of the land where the biochar is

applied. Experiments have found that rates between 5 to 50 t/ha (0.5 to 5 kg/m 2) have often

been used successfully. Rates around 1% by weight or less have been used successfully so

far in field crops (Major, 2013). Winsley, (2007) suggests that even low rates of biochar

application can significantly increase crop productivity. Application to soils of higher

amounts of biochar may increase the carbon credit benefit; but, in nitrogen-limiting soils, it

could fail to assist crop productivity as a high C/N ratio leads to low N availability

(Lehmann and Rondon, 2006). Chan et al., (2007) experiment shows that the case of piggery

and poultry manure biochar, the biochar works both as organic fertilizer and soil conditioner

with agronomic benefits observed at low application rate (10 t ha-1). Biochar application rates

also depend on the amount of dangerous metals present in the original biomass.

2.24 Interaction between biochar and soil

The interaction between biochar and soil . The biochar and its properties are taken under

consideration using as amendments. The properties are viz., large surface area (SA) and

presence of micropores (Mukherjee et al., 2011; Braida et al., 2003; Nguyen et al., 2004;

Rutherford et al., 2004). The impact of biochar as an amendment depends on its

properties. Key properties are those which contribute to the adsorptive properties of

biochars and potentially alter soil’s SA, pore size distribution (PSD), bulk density (BD),

water holding capacity (WHC) and penetration resistance (PR).

17

Figure 1 Biochar loses during application and transportation

18

2.25 Biochar on soil physico-chemical properties

The application of biochar to the soil will change both the soil’s physical and chemical

properties. The net effect on the soil physical properties will depend on the interaction of the

biochar with the physico-chemical characteristics of the soil, and other determinant factors

such as the weather conditions prevalent at the particular site, and the management of

biochar application (Verheijen et al., 2010). Biochar application can reduce the bulk density

(BD) of the different soils (Laird et al., 2010; Jones et al., 2010; Chen et al., 2011). About

2% (w/w) rate of biochar amendment seems enough to decrease BD of amended soils (Table

4); however, in some instances BD can increase over time due to compaction during

column leaching events (Rogovska et al., 2011). The soil BD decreased from 1.66 to 1.53

g cm−3 (Mankasingh et al., 2011), and another involving biochar amended soil columns

showed significantly lower BD compared to no-biochar controls in a column incubation

study (Laird et al., 2010). In a 3-year field study, application of biochar amendment

decreased the BD of 0 to 7.5 cm soil layer by 4.5 and 6.0% for 0.23 kg m−2 and 0.45 kg m−2

application rate, respectively (Chen et al., 2011). A decrease in soil BD from biochar

application rate of 9.4 (± 2.2%) was observed in another 2-year field study (Zhang et al.,

2012). The decrease in BD of biochar amended soil could be one of the indicators of

enhancement of soil structure or aggregation, and aeration, and could be soil-specific. The

higher the total porosity (micro- and macro-pores) the higher is soil physical quality because

micropores are involved in molecular adsorption and transport while macropores affect

aeration and hydrology (Atkinson et al., 2010). Soil hydrological properties (that is,

moisture content, WHC, water retention, hydraulic conductivity, water infiltration rate) are

invariably related to SA, porosity, BD and aggregate stability. Several studies have reported

alterations in WHC and water retention in biochar-amended soils (Laird et al., 2010; Jones et

al., 2010; Uzoma et al., 2011) with as low as 0.5% (g g−1) biochar application rate sufficient

to improve WHC (Table 2).

19

Table. 2.2 Impact of biochar on water holding capacity

20

2.26 Effect of biochar on soil microorganisms

Studies have shown higher microbial biomass but yet lower microbial activity in

biocharamended soil than the neighbouring soils (Thies JE, Rillig, 2009). However, most

studies have focused on biochar interaction with mycorrhizal fungi (Thies JE, Rillig, 2009).

Specifically, biochar has been reported to have symbiotic relationship with the mycorrhizal

system. According to Warnock, (2007), the four mechanisms by which biochar could

improve mycorrhizal abundance (40%) and functioning are listed as follows: i. Alteration of

soil physico-chemical properties, ii. Indirect effects on mycorrhizae through effects on other

soil microbes, iii. Plant-fungus signalling interference, and iv. Detoxification of

allelochemicals on biochar. Lehmann and Rondon, (2006) noted 50% to 72% increase in soil

biological nitrogen fixation through biochar application. Saito and Marumoto, (2002) have

hypothesized both bacteria and fungi to be better protected from grazers or competitors by

exploring pore habitats in biochars. This is because biochar provides microbial habitat and

refugia for microbes where they are also protected from unfavourable conditions.

The current knowledge about soil microbes is mostly based on the experimental evidence,

biochar has symbiotic relationship with the mycorrhizal system. The four mechanisms iby

which bichar could improve mycorrhizal abundance (40%) and functioning are given by

Warnock et al., (2007). The mechanisms are: i. Alteration of soil physic-chemical

properties, ii. Indirect effects on mycorrhizae through effects on other soil microbes, iii.

Plant-fungus signaling interference, and iv. Detoxification of allelochemicals on biochar.

There are 50 to 72% increases of soil biological nitrogen fixation (BNF) through biochar

application (Lehman and Rondon, 2006). Biochar has positive effects on soil biology. It

provides microbial habitat and refugia for microbes where they are protected from

grazing. Both bacteria and fungi are hypothesized to be better protected from grazers or

competitors by exploring pore habitats in biochars (Ogawa, 1994; Ezawa et al., 2002; Saito

and Marumoto, 2002; Thies and Rillig, 2009). Earthworms have been shown to prefer some

soils amended with biochar to those soils alone. However, this is not true of all biochars,

particularly at high application rates (Verheijen et al., 2010).

21

2.27 Biochar and Soil carbon sequestration

The principle of using biochar for carbon (C) sequestration is related to the role of soils in

the C-cycle. Biochar produced and added to the soil, in conjunction with bioenergy

generation, can result in carbon sequestration (Lehmann, 2007). The stable form of organic

carbon present in the biochar has significant effect on carbon sequestration and improves the

soil condition. In photosynthesis, it converts light energy into the chemical energy of sugars

and other organic compounds. This process consists of a series of chemical reactions that

require carbon dioxide (CO2) and water (H2O) and store chemical energy in the form of

sugar. The products of photosynthesis include carbohydrates in the form of sugars and

starches as well as water and oxygen. The following equation summarizes photosynthesis:

6CO2 + 6H2O 6(CH2O) + 6O2

Organic biomass from decaying plant species or remnants of agriculture can be converted

into a charcoal or biochar that can prevent global climate change by displacing fossil fuel use

by sequestering carbon into soil carbon pools and by dramatically reducing emissions of

nitrous oxides, a more potent greenhouse gas than carbon dioxide” (International Biochar

Initiative [IBI], 2010). Biochar slows down the decaying and mineralization of the biological

carbon cycle to establish a carbon sink and a net carbon withdrawal from the atmosphere of

20%, as seen in Figure 4. Additionally, calculations have shown that putting this biochar

back into the soil can reduce emissions by 12 to 84% of current values; a positive form of

sequestration that “offers the chance to turn bio-energy into a carbon negative industry”

(Lehmann, 2007). International Biochar Initiative (IBI) has already developed a model to

predict the carbon removing potential of sustainable biochar utilizing system. Figure 5 shows

the results of this preliminary model and gives a sense of what is possible counting only the

impacts of biochar buried in soil; and without considering the displacement of energy from

fossil fuels, we can conservatively offset one quarter of a gigaton of carbon annually by

2030. Optimistically, we could achieve one gigaton of offsets annually before 2050. It has

been well documented that biochar amendment to crop lands enhances crop

productivity through improving soil quality (Asai et al., 2009; Major et al., 2010; Sohi et

al., 2010; Zwieten et al., 2010; Gaskin et al., 2010; Haefele et al., 2011). The calculated

biochar affects intensity (BEI) values for soil quality and crop productivity as well as GHGs

22

emission. While there was positive effect in increasing soil pH (H2O), SOC, total N and

decreasing soil bulk density were observed in both rice cycles;1 the BEI (%) was observed

less than 5% for pH (H2O), and less than 10% for soil bulk density, −1.7 to 22.5% for total

N, and 9.3 to 56% for soil organic carbon in both cycles (Zhanga et al., 2012).

2.28 Mitigation of greenhouse gas emissions

Every year, the amount of carbon dioxide in the atmosphere increased day by day and by the

year 2020, the world will produce 33.8 billion metric tons up from 29.7 billion metric tons in

2007 (Projected U.S. GHG emissions meeting recently proposed goals (EPA, 2010). In

recent years the use of surplus organic matter or biomass to create biochar has yielded

promising results in the reduction of CO2. Biochar is a carbon rich charcoal that is formed by

the pyrolysis (thermal decomposition) of organic biomass. There are other environmental

benefits that can be achieved by application of biochar in soils which will reduce emission of

non-CO2 green house gases (GHGs) by soil. N2O and CO2 gases are 23 and 298 times more

potent than carbon dioxide as green house gases in the atmosphere (Srinivasarao et al.,

2013). Biochar is reported to reduce N2O emission that could be due to inhibition of either

stage of nitrification and/or inhibition of denitrification, or promotion of the reduction of

N2O; and these impacts could occur simultaneously in a soil (Berglund et al., 2004; DeLuca

et al., 2006).

2.29 Effect of biochar on crop yield

The forms of biochar viz., dust, fine particles, coarse grain and the method of soil

application viz., surface application, top dressing, drilling are the two main issues. These

are all the important aspects to study the effect of biochar on soil health as well as crop

productivity. Hill et al., (2007) clearly explained that even small quantities of biochar added

to seed coatings may in some cases be sufficient for a beneficial effect. Effect of biochar on

the different growing environments in rice viz., i) a double-cropped irrigated lowland, ii) a

monocropped rain-fed upland, and iii) a monocropped rain-fed lowland are evaluated by

Haefele, (2008) and the grain yield variation between the sites was identified. Initially, the

effect will be nonsignificant but significant improvement was shown in last three seasons.

Lehmann et al., (2003) reported increasing crop yields with increasing biochar applications

23

of up to 140 t C ha-1 on highly weathered soils in the humid tropics, and Rondon et al. (2007)

found that the biomass growth of beans rose with biochar applications up to 60 t C ha-1.

Scientists have reported that application of biochar on soil has significant effect on net

primary crop production, grain yield and dry matter production (Chan et al., 2008; Chan and

Xu, 2009; Major et al., 2009; Spokas et al., 2009). Purakayastha, (2010) clearly explained

that application of biochar prepared from wheat straw (1.9 t/ha) along with recommended

doses of NPK at 180:80:80 kg ha-1 significantly increased the yield of maize in Inceptisol of

IARI farm and this treatment was superior to either crop residue incorporation or 30 crop

ressidue burning. Table 8 clearly shows the summary of experiments of biochar on crop

yield.

2.30 Liming effect

Biochar can be said to be acidic or alkaline in nature depending on the temperature of the

materials used during pyrolysis. Li et al., (2013)explained that the acid functional group

concentration in biochars produced from the biomass of rice, valley oak (Quercus lobata Ne´

e), etc decreased with increasing peak pyrolysis temperature as more fused aromatic ring

structures were produced and more volatile matter was lost. The effectiveness of both types

will depend on the pH of the soil to be amended. Biederman and Harpole, (2013) State that

the alkaline biochars produced at higher pyrolysis temperature are more effective in

supporting increases in biomass by improved growth conditions than acidic biochars

presumably through increases in soil alkalinity. Blackwell et al., (2009) stated that the

moderation in aluminium toxicity may be the reason why biochar application has positive

effects on productivity in tropical and irrigated systems on highly weathered and acid soils

with low-activity clays. This is because the reduction of aluminium and iron concentrations

in the soil solution will enhance the availability of previously bound phosphorus to plants,

and plant roots would be able to explore even acid soils to absorb nutrients and water more

effectively. The moderation in Al toxicity may be the reason why biochar application has

particularly positive effects on productivity in tropical and irrigated systems on highly

weathered and acid soils with low-activity clays (Blackwell et al., 2009). The greatest

positive crop yield response to biochar was seen in acidic and neutral pH soils (Jeffery et al.,

2011; Liu et al., 2013). The reasons for yield increases on acid soils following application of

24

bark charcoal produced from Acacia mangium Wild. Without co-application of fertilizer

were increases in soil pH and alleviation of Al and possibly Mn toxicity (Yamato et al.,

2006). The alkaline biochars produced at higher pyrolysis temperature are more effective in

supporting increases in biomass by improved growth conditions than acidic biochars

presumably through increases in soil alkalinity (Biederman and Harpole, 2013).

25

26

CHAPTER THREE

MATERIALS AND METHODS

3.0 Study area.

The experiment was carried out at the Bowen University Teaching and Research Farm of the Faculty of Agriculture and Forestry, Iwo, Osun state, Nigeria (longitude 7° 38' 0"N, latitude 4° 11' 0.1"E) from 2012 to 2016. The site is located in a forest savannah transition zone. The soil is an Oxisol (Aubert and Tavenier; FAO/UNESCO, 1997).

3.1 Experimental materials

Plant residue, saw dust biochar, Gliricidia biochar and mineral fertilizer

3.2 Experimental design and layout

A randomized complete block design (RCBD) was adopted with eight treatments replicated three times and each replicate occupy a 4m x 4m field area. The experiment began in 2012, but samples were collected in February, 2016 at a depth of 0-15 cm, and 15-30 cm. Treatments implored include:

(1) Control C

(2) 22.5 kg N ha-1 (mineral fertilizer) MF

(3) Residue (maize stuble) R

(4) 22.5 kg N ha-1 (mineral fertilizer) + residue MF+R

(5) 2.5t C ha-1 (saw dust biochar) SDB

(6) 2.5t C ha-1 (saw dust biochar) + 22.5 kg N ha-1 mineral fertilizer SDB + MF

(7) 2.5t C ha-1 (Gliricidia biochar) GB

(8) 2.5t C ha-1 (Gliricidia biochar) + 22.5 kg N ha-1 mineral fertilizer GB + MF

Analysis of gliricidia sepium and sawdust biochar are presented in Table: 3.1

27

MF GB+MF C

GB SDB MF

MF+R C R

SDB GB MF+R

R MF SDB

GB+MF R SDB+MF

SDB+MF MF+R GB

C SDB+MF GB+MF

Figure 3.1: The experimental layout of the field showing randomization of treatments

Legends C = Control, MF = 22.5 kg N ha-1Mineral fertilizer, R = Residue,MF+R = 22.5 kg N ha-1Mineral fertilizer + Residue,SDB = 2.5t C ha-1 Saw dust biochar,2.5t C ha-1 SDB + MF = Saw dust biochar + 22.5 kg N ha-1Mineral fertilizer,GB = 2.5t C ha-1 Gliricidia biochar,GB + MF = 2.5t C ha-1 Gliricidia biochar + 22.5 kg N ha-1Mineral fertilizer.

28

3.3 Land preparation

The site was cleared with hoe and cutlass and the residue left on site to decompose after

which it was mechanically ploughed and later harrowed by a tractor.

3.4 Treatment application

Application of treatment was done manually with hoe. The treatments were broadcasted

on the surface of the soil after which it was incorporated within 0-30 cm depth manually.

29

Table: 3.1 Selected proximate properties of gliricidia sepium and Sawdust

Property  Gliricidi

a  Sawdus

tpH(H2O, 1:1) 8.5 8.1pH(CaCl2) 8.3 7.8NO3

-N(g/kg) 1.0 1.7Organic carbon(g/kg) 892.8 908.7Total N(g/kg) 10.3 11.3HA(g/kg) 92.2 80.9CEC(Cmol/kg) 45.38 106.38Ash(g/kg) 37.2 38.9Total P(g/kg) 2.8 3.8C:N ratio   86.7   80.4

30

Figure.3.1 Saw dust before pyrolysis

Figure.3.2 Saw dust after pyrolysis

31

3.5 Soil sampling and analysis

Soil samples at 0-15 cm and 15-30 cm depths were collected. Two undisturbed soil cores (5 cm × 5 cm in diameter) were collected per replicate to determine bulk density, total porosity, volumetric moisture content and hydraulic conductivity, erodibility factor (K), C:N ratio and field capacity. Composite samples from each replicate were used to determine soil Ph, SOC and particle size distribution.

3.5.1 Particle size distribution

Particle size distribution of the soil samples (< 2 mm) was determined using hydrometer

method as described by Gee (2002). Air dried (2 mm) sieved soil weighing 50g was

measured into a dispersing cup. 200 ml of distilled water was added after which about 20

ml of 0.5 N sodium hexametaphosphate (calgon) was added and allowed the soil to soak

for about 15 minutes. The suspension was mechanically shaken for between 10-20

minutes. The suspension was later transferred from the cup into the glass cylinder through

the 0.2mm sieve to separate the fine sand. The fine sand was collected into a petri dish

and oven dry. The remaining suspension was top to the 1000 ml mark with distilled water

in the cylinder. The top of the cylinder was covered with hand and the suspension shaken

end to end 50 times. The cylinder was left undisturbed and after about 40 seconds the first

reading on the hydrometer was taken. The temperature was also recorded. The second

reading was taken after two hours and the temperature was also recorded. The percentages

of sand, silt and clay were determined from the readings obtained. The textural class of

the soils was determined by using a textural triangle (USDA, 2013).

3.5.2 Saturated hydraulic conductivity (SHC)

Saturated hydraulic conductivity was determined using the constant head method as

described by Klute (1986). A flask of water was inverted above the core containing water

in other to maintain constant head of water after the samples had been saturated for 72

hours. The quantity of water (Q) drained in every 5 min was measured until equilibrium

(constant through of water) is reached.

32

Darcy’s equation was employed as presented in

Equation (1):

Ks = QH ................ (1) At (H+h)

Where, Q = quantity of water discharged at equilibrium (cm3), H = length of soil core

(cm), t = time taken to reach equilibrium (mins), h = head of water above the soil

core (cm), Ks = saturated hydraulic conductivity (cm mins-1), A = cross sectional area of

the soil core (cm2).

3.5.3 Bulk density

Core samples taken from the depth of 0-15 cm and 15-30 cm were used to determine bulk

density using core method (Grossman and Reinsch, 2002). Bulk density was estimated by

dividing the oven dry mass of the soil at 105 °C by the volume of the soil as:

pb ⁼ Ms ………………………………………………….. (2)Vb

Where, Ms = mass of the oven dry soil (g), Vb ⁼ volume of the core sampler (cm3), pb ⁼

bulk density (g cm-3).

3.5.4 Total porosity

Total porosity was estimated from bulk density values by the use of a formula.

TP ⁼ [1- (eb / es)] x 100 ………………………………………… (3)

Where, TP ⁼ total porosity, eb bulk density and e⁼ s particle density (2.65 g cm⁼ -3).

33

3.5.5 Erodibility factor

Erodibility factor (K) was estimated from the universal soil loss equation (USLE):

K (MghMJ-1mm) = 2.8x10-7 M1.14 (12-a) + 4.3x10-3 (b-2) + 3.3x10-3 (c-3)

Where, M = Particle size parameter (%silt + %very fine sand) x (100 - %clay)a = % soil organic matterb = soil structure code (1-granular, 2-fine granular, 3-medium or coarse granular, 4-blocky, 5- platy or massive)c = Profile permeability class factor; 1-rapid, 2-moderate to rapid, 3-moderate, 4-slow to moderate, 5-slow, 6-very slow (Lal and Elliot., 1994; Lal, 1998).

3.5 C:N ratio

The C:N ratio was estimated from the equation bellow as describe by bouyoucus, (1935).

C:N ratio =% sand+ %silt

% clay

3.5.7 Field capacity

The soil field capacity was determined using the tension table. Core samples were

saturated for 24hrs after which they are placed inside the tension table for 48 hrs at

suction of 30 cm (0.03 bar). A differential pressure is established between the top and

bottom of the table.

FC = Wt of soil at tension table – Ovs x BD

Ovs

Where Wt = Mass of soil from the tension table BD = Bulk density Ovs = Oven dry soil

34

3.5.8 Soil pH

Procedure:

Twenty (20) g of air dry (2 mm sieved) soil sample was weighed into a 50 ml beaker. 20

ml of distilled water was added and shaken for two minutes. The electrode of already

calibrated pH meter was inserted into the suspension and the reading on the pH-meter was

taken. The result was expressed as “Soil pH measure in water”.

3.5.9 Organic carbon

Procedure: soil organic carbon was determine by the Walkley-Black wet oxidation

method (Allison, 1965) and later converted to soil organic matter (SOM) by multiplying

with the factor 1.724.

Air-dry 0.5 mm sieved soil sample was weight and transferred into 250 ml conical flash.

Then, 10 ml of 1 N K2Cr2O7 solution was pipette into each flask. The flask was swirled

gently until soil and reagent was thoroughly mixed, 20 ml of concentrated H2SO4 was

added and mixed vigorously for 1 minute and then allowed to stand for 30 minutes. The

solution was diluted using 200 ml of distilled water, three (3) drops of ortho-

phenothroline indicator were added, and the resulting suspension was titrated with 0.5 N

ferrous ammonium sulphate solutions. Near end point, the solution took a greenish cast

and then changes to dark green. At this point, the ferrous ammonium sulphate was added

drop wise until the colour changed sharply from blue to maroon. Thereafter, a blank

titration was made in the same manner as above without soil to standardize the

dichromate.

Calculation

% C = Volume of dichromate used × (B – T) × 0.003 × 1.33 × 100 …………..(4)

Sample weight

35

Where B = Volume of blank, T = Volume of titre, 0.003 = oxidizable fraction of carbon, 1.33 = constant, Organic C (g/kg) = % C × 10.

3.6 Data analysis

Data was subjected to analysis of variance (ANOVA) using generalized linear model (GLM) procedure of the SAS 9.3 version. Correlation analysis was also computed.

36

CHAPTER FOUR

RESULTS AND DISCUSSIONS

4.1: Soil physical and chemical properties

The surface soil of the site was sandy loam with bulk density value of 1.68 g cm -3 at 0-15

cm depth indicating a coarse textured soil (Table 4.1). The site is characterized with low

value of saturated hydraulic conductivity of 4.46 cm hr -1 at 0-15 cm depth. The SOC

recorded was low (1.23gkg-1) and the pH of the experimental site was generally acidic (pH

5.6).

4.2: Effect of biochar application on particle size distribution

Table 4.2 presents the effect of biochar application on soil particle size distribution.

Biochar application did not have a significant (P<0.05) effect on particle size distribution.

Though, it was observed that the quantity of coarse sand decreased in the order of

Control>Mineral fertilizer>Residue>Mineral fertilizer + Residue>Sawdust biochar +

Mineral fertilizer >Gliricidia biochar>Sawdust biochar> Gliricidia biochar + Mineral

fertilizer. Also, the entire treatments recorded a loamy sand texture except for residue

which recorded a sandy loam soil texture. Clay content was also higher than that of silt for

all amended soils except soils treated with residue. Higher clay content could be ascribed

to the beneficial effect of incorporating biochar with the soil.

4.3.: Effects of biochar application on saturated hydraulic conductivity

Table 4.3: Presents the effect of biochar application on saturated hydraulic conductivity of

the field. Statistically, there was a significant difference among the treatments indicating

application of biochar may have improve horizontal movement of water at saturation with

increase in the rate of

biochar application for both soil depth (0-15 cm and 15-30 cm) at (P<0.05). Similarly,

increase in saturated hydraulic have been reported by Jones et al., (2010)

37

4.4.: Effects of biochar application on Total porosity

Table 4.3 presents the effect of biochar on total porosity after 5 years of application. Soil

treated with gliricidia biochar (GB) was significantly (P<0.05) higher (43.58%) than other

treatments at both 0-15 cm and 15-30 cm. Figure 1: presents the effect of the interaction

between gliricidia biochar and soil in which gliricidia biochar soil amendment contributes

to a change in the status of total porosity was estimated to be 43.4 % at A (0-15 cm) depth

on average basis. The corresponding change made by gliricidia biochar at depth B (15-

30cm) was 43.6%. Similarly, Figure 2: present the distribution of pore volume within the

0-15 cm and 15-30 cm soil depths (horizons) due to contribution of gliricidia biochar

addition to the soil. The pore volume for 0-15 cm and 15-30 cm depth was estimated to be

43% and 44% respectively on average basis. This effect indicates that gliricidia biochar

amendment contributes more to total pore volume in the aforementioned two depths than

any other form of biochar. Jones et al., (2010) reported that biochars are usually

characterized by the preponderance of micropores, which may alter the pore size

distribution of coarse texture soil when added.

4.5.: Effects of biochar application on soil chemical properties

Table 4.4 presents the effect of biochar application on soil chemical properties. There was

no significant difference in soil pH among the treatments. However, pH increases in the

order. Mineral fertilizer<Control<Mineral fertilizer + Residue<Sawdust biochar + Mineral

fertilizer<Gliricidia biochar<Gliricidia biochar + Mineral fertilizer. Increase in pH might

be due to the contribution from biochar. Gliricidia and sawdust biochars are alkaline

materials in nature. For example gliricidia biochar has a pH value of 6.03. Therefore,

addition of biochar could reduce soil acidity.

Sawdust biochar + Mineral fertilizer plot was significantly (P<0.05) higher in soil organic

carbon (SOC) than any other treatments at both 0-15 cm and 15-30 cm soil depths. This

could be attributed to inherent higher carbon content of sawdust biochar as reflected in the

proximate analysis of SDB. Figure 3 reveals the contribution of SDB + MF to soil organic

carbon. SDB + MF contributed 2.5% of total soil organic carbon present within 0-15 cm

38

depth. Corresponding contribution of SDB + MF to total soil organic carbon within 15-30

cm soil depth is 1.5%. This indicates that SDB + MF contributed more to total soil

organic carbon at 0-15 cm than 15-30cm soil depth.

4.6.: Effects of biochar application on soil bulk density

Table 4.2 presents the effect of biochar amendment on soil bulk density. Soil bulk density

was significant among treatments. However, decrease in bulk density was observed in the

following order Gliricidia biochar + Mineral fertilizer<Sawdust biochar <Gliricidia

biochar< Sawdust biochar + Mineral fertilizer < Mineral fertilizer + Residue< Residue <

Mineral fertilizer <Control. The decrease may be assoccciated with contribution of

biochar amendment on soil. This is in line with the work of other researchers that reported

decrease in soil bulk density due to biochar application. Mukherjee and Lal, (2013), Chen

et al., (2011) all reported low bulk density with biochar amendment. They further stated

that the decrease in bulk density of biochar-amended soil could be one of the indicators of

the improvement of soil structure or aggregation and aeration, and could be soil-specific.

4.7.: Effects of biochar application on field capacity

Table 4.3 presents the effect of biochar amendment on field capacity. The values of field

capacity increase among the treatments. Residue and gliricidia biochar were highly

significant and significant respectively. Soil amendment with residue (R) was highly

significant (P<0.05) in field capacity than any other treatments at both 0-15 cm and 15-30

cm soil depths. This could be attributed to inherent mulching effect of residue. Figure 5

presents the effect of the interaction between residue and soil in which residue amendment

contributes to a change in the status of field capacity was estimated to be 0.25. % at A (0-

15 cm) and 0.12 % at B (15-30 cm) soil depth on average basis. Similarly, figure 6

presents the Contribution of residue amendment on field capacity distribution within soil

depth A (0-15 cm) and B (15-30cm). It is hereby observed that the residue amendment

contributes to highest field capacity at 0-15 cm depth than 15-30 cm. The corresponding

change in field capacity made by gliricidia biochar at depth A (0-15 cm) was estimated at

> 0.16% and <0.15% for soil depth 15-30 cm. Figure 7 presents the effect of interaction

between gliricidia biochar and the soil in which amendment with gliricidia biochar

39

contribute to change in status of field capacity was estimated to be >0.16 % at depth A (0-

15 cm) on the average basis. Less than 0.15% was estimated for at depth B (15-30cm) on

the average basis. Figure 8 presents the Contribution of gliricidia biochar amendment on

field capacity distribution within soil depth A (0-15 cm) and B (15-30cm) respectively. It

is observed that the residue amendment contributes to highest field capacity at 0-15 cm

depth than 15-30 cm. Busscher et al., (2010) and Ehlers et al., (1983) also reported an

increase in moisture retain after natural gravity which is an indication of biochars ability

to increase water storage of coarse-textured soils.

4.8.: Effects of biochar application on soil erodibility

Table 4.5 presents the effect of biochar amendment on soil erodibility. The effect of soil

amendment on erodibility increases in the order

GB+MF>GB>SDB>R>SDB+MF>MF+R>C. Significant (<0.05) difference were only

observed in plot amended with residue, gliricidia biochar, sawdust and gliricidia biochar

combine with mineral fertilizer. Erodibility factor (K) decreases among the treatments;

indicating that soils amended with gliricidia biochar, residue, sawdust biochar and

gliricidia biochar combine with mineral fertilizer in combination or alone could help

reduce the soil susceptibility to erosion forces. However, the C:N ratio was not

significant among the treatments with biochar and in combine form with mineral fertilizer

though incresase in the order.

4.9: Correlation analysis between treatments and soil erodibility

Table 4.6: presents correlation analysis between treatments and erodibility. Result

indicates that soil amendment with gliricidia biochar + mineral fertilizer (GB+MF)

contribute to a significant positive correlation (r = 0.88; p < 0.05) between GB+MF and

erodibility. It implies that an increase in GB+MF brings about an increase in soil

resistance to erosion. GB+MF treatments brings about decrease in soil susceptibility to

erosion.

40

Table 4.1: Initial soil chemical and physical properties of the study site

Table 4.2: Effects of biochar application on soil physical properties

41

Soil parameter 0 – 15 cm

pH (H2O 1:1) 5.6

Organic carbon (g kg-1) 1.23

Particle size (gkg-1)

Sand 830

Silt 57

Clay 113

Texture Sandy Loam

Saturated hydraulic conductivity (cm hr-1) 4.46

Bulk density (g cm-3) 1.68

Treatment BD (gcm-3) Particle size distribution (g/kg) Texture    Sand Silt Clay  C 1.64c 820a 60a 120a SLMF 1.63c 837a 63a 103a SLR 1.49a 803a 80a 117a LSMF+R 1.62c 823a 70a 107a SLSDB 1.46ab 830a 53a 117a SLSDB+MF 1.51a 830a 53a 117a SLGB 1.45ab 827a 63a 110a SLGB+MF 1.49a 830a 53a 117a SL

Means with same letter(s) in the same column are not significantly different

Legends

C: Control (bare soil)MR: Mineral fertilizerR: ResidueMF + R: Mineral fertilizer combine with ResidueSDB: Sawdust biocharSDB + MF: Sawdust biochar combine with Mineral fertilizerGB: Gliricidia biocharGB + MF: Gliricidia biochar combine with Mineral fertilizerSL: Sandy loamLS: Loamy sand

Table 4.3: Effects of biochar application on soil hydrological properties

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Treatment

SHC (cmhr-1) TP (%) FC (%)

    0-15 cm 15-30 cm 0-15 cm 15-30 cm 0-15 cm 15-30 cmC 3.80ab 5.32a 35.01b 35.32bc 0.11b 0.11a

MF 3.53a 4.80ab 39.60a 39.50b 0.11a 0.11aR 5.63ab 5.41b 41.63ab 41.20ab 0.13ab 0.11a

MF+R 4.69ab 5.77b 41.37a 41.43ab 0.11ab 0.12abSDB 7.52ab 11.36a 43.63a 43.67ab 0.15ab 0.16a

SDB+MF 6.36b 6.36a 43.23bc 43.07bc 0.14b 0.15abGB 7.07ab 8.71a 43.40ab 43.58ab 0.15ab 0.15a

GB+MF 9.88ab 12.14a 43.90a 43.90a 0.17ab 0.16abMeans with same letter(s) in the same column are not significantly different

Legends

C: Control (bare soil)MR: Mineral fertilizerR: ResidueMF + R: Mineral fertilizer combine with ResidueSDB: Sawdust biocharSDB + MF: Sawdust biochar combine with Mineral fertilizerGB: Gliricidia biocharGB + MF: Gliricidia biochar combine with Mineral fertilizer

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Table 4.4: Effects of biochar application on soil chemical properties

Treatment pH SOC (%)

   0-15 cm 15-30 cm 0-15 cm 15-30 cmC 5.6ab 5.5a 1.3ab 1.2a

MF 5.3a 5.8ab 1.2b 1.2abR 5.7ab 5.9a 1.9bc 1.8ab

MF+R 5.5ab 5.7a 1.5b 2.0bcSDB 6.0ab 5.9a 3.3b 2.8bc

SDB+MF 6.0ab 5.7a 1.9ab 2.5abGB 6.0ab 6.1b 3.1bc 2.9ab

GB+MF 6.1ab 6.0a 2.8bc 2.5b Means with same letter(S) in the same column are not

significantly different

Legends

C: Control (bare soil)MR: Mineral fertilizerR: ResidueMF + R: Mineral fertilizer combine with ResidueSDB: Sawdust biocharSDB + MF: Sawdust biochar combine with Mineral fertilizerGB: Gliricidia biocharGB + MF: Gliricidia biochar combine with Mineral fertilizer

44

Table 4.5: Effects of biochar application on soil erodibility

Treatment C:N Erodibility factor (K)C 7.13a 0.41c

MF 6.72a 0.40c

R 7.55ab 0.38c

MF+R 8.35c 0.38c

SDB 7.55ab 0.32bc

SDB+MF 7.55ab 0.26b

GB 8.10c 0.20ab

GB+MF 7.33a 0.12a

Means with same letter(s) in the same column are not significantly different

Legends

C: Control (bare soil)MR: Mineral fertilizerR: ResidueMF + R: Mineral fertilizer combine with ResidueSDB: Sawdust biocharSDB + MF: Sawdust biochar combine with Mineral fertilizerGB: Gliricidia biocharGB + MF: Gliricidia biochar combine with Mineral fertilizer

45

Table 4.6: Correlation matrix for soil erodibility, treatments and soil properties

  C MF R MF+R SDB SDB+MF GB GB+MF1 -0.14 0.32 0.44 -0.22 -0.31 0.34 -0.21

1 -0.43 0.15 -0.57 -0.049 -0.087 0.88*

1 0.63 0.094 0.12 0.075 -0.60

1 -0.68 0.16 -0.44 -0.23

1 -0.36 0.61 -0.18

  0.49 0.20 0.74

1 -0.39 -0.39

1 0.18

1

Legends

C: Control (bare soil)MR: Mineral fertilizerR: ResidueMF + R: Mineral fertilizer combine with ResidueSDB: Sawdust biocharSDB + MF: Sawdust biochar combine with Mineral fertilizerGB: Gliricidia biocharGB + MF: Gliricidia biochar combine with Mineral fertilizer

46

Figure 4.1 Effect of interaction between gliricidia biochar (GB) and soil on total porosity at soil depth A (0-15 cm) and B (15-30cm)

FA = Soil depthA = 0-15 cmB = 15-30 cm

47

Figure 4.2 Contribution of gliricidia biochar (GB) amendment on distribution of total porosity within soil depth

A (0-15 cm) and B (15-30cm)FA = Soil depthA = 0-15 cmB = 15-30 cm

48

Figure 4.3 Effect of interaction between SDB + MF and soil on SOC at soil depth A (0-15 cm) and B (15-30cm)

FA = Soil depthA = 0-15 cmB = 15-30 cmSDB+MF = Sawdust biochar combined with mineral fertilizerSOC = Soil organic carbon

49

Figure 4.4 Contribution of SDB+MF amendment on SOC distribution within soil depth A (0-15 cm) and B (15-30cm)

FA = Soil depthA = 0-15 cmB = 15-30 cm

SDB+MF = Sawdust biochar combined with mineral fertilizer SOC = Soil organic carbon

50

Figure 4.5 Effect of interaction between residue and soil on field capacity at soil depth A (0-15 cm) and B (15-30cm

FA = Soil depthA = 0-15 cmB = 15-30 cm

51

Figure 4.6 Contribution of residue amendment on SOC distribution within soil depth A (0-15 cm) and B (15-30cm)

FA = Soil depthA = 0-15 cmB = 15-30 cmSOC = Soil organic carbon

52

Figure 4.7 Effect of interaction between gliricidia biochar (GB) and soil on field capacity at soil depth A (0-15 cm) and B (15-30cm

FA = Soil depthA = 0-15 cmB = 15-30 cm

53

Figure 4.8 Contribution of gliricidia biochar (GB) amendment on field capacity distribution within soil depth A (0-15 cm) and B (15-30cm)

FA = Soil depthA = 0-15 cmB = 15-30 cm

54

CHAPTER 5

SUMMARY AND CONCLUSIONS

Addition of biochar was found to influence soil physical properties such as bulk density,

total porosity and field capacity. Specifically, gliricidia biochar significantly improved

bulk density, total porosity and field capacity than any other treatments. In terms of soil

erodibility, gliricidia biochar applied at the rate of 2.5t C ha-1 or sawdust biochar at 2.5t C

ha-1 significantly reduced vulnerability of soil to water erosion. This implies that gliricidia

or sawdust biochar could improve soil aggregates against the impact of raindrops.

Similarly, hydrological properties were improved when combineed with baseline

fertilizers. Saturated hydraulic conductivity and field capacity were significantly higher

than plots without biochar application. This is an indication that both gliricidia and

sawdust biochar treated plots had higher water retention capacity for growing crops

especially during the dry spell. Therefore, farmers should be encorraged to embrace the

use of gliricidia biochar or sawdust biochar in order to reduce the vulnerability of oxisol to

water erossion especially in a sloping farmland.

55

REFERENCES

Agboola, A. A., and J. A. Fagbenro. 1985. Soil organic matter and it management in the humid tropics with particular reference to Nigeria. In proceedings of the international Society of Soil Science (Commission IV and VI) Conference, eds. R. A. Sobolu and E. J. Udo. 215-33. University of Ibadan, Nigeria, July 21-27.

Anders E, Watzinger A, Rempt F, Kitzler B, Wimmer B, Zehetner F. 2013. Biochar affects the structure rather than the total biomass of microbial communities in temperate soils. Agricultural Food Science; 22:404-423.

Atkinson CJ, Fitzgerald JD, Hipps NA. 2010. Potential mechanisms for achieving agricultural benefits from biochar application to temperate soils: a review. Plant and Soil analysis. 337:1–18.

Babalola, O. 2002. Nigerian agriculture: Basis for hope, hurdles against hope for tomorrow. 2000/2001 University Lectures, University of Ibadan, Nigeria.

Biederman LA, Harpole WS. 2013. Biochar and its effects on plant productivity and nutrient cycling: a meta-analysis. GCB Bioenergy; 5:202–14.

Blackwell P, Riethmuller G, Collins M. 2009. Biochar application to soil (Chapter 12). In: Lehmann J, Joseph S. (eds.) Biochar for Environmental Management: Science and Technology. London, UK: Earthscan. p. 207.

Bol, R. A., W. Amelung, C. Friedrich, and N. Ostle. 2000. Tracing dung-derived carbon in temperate grassland using 13C natural abundance measurements. Soil Biology and Biochemistry 32:1337-1343.

Briggs C, Breiner JM, Graham RC. 2012. Physical and chemical properties of pinus ponderosa charcoal: implications for soil modification. Soil Science ; 177:263–8.

Brockhoff SR, Christians NE, Killorn RJ, Horton R, Davis DD, 2010. Physical and mineral-nutrition properties of sand-based turf grass root zones amended with biochar. Agronomy Journal 102: 1627-1631.

Busscher WJ, Novak JM, Ahmedna M. 2011. Physical effect of organic matter amendment of a southeastern us coastal loamy sand. Soil Science; 176:661–7.

Busscher WJ, Novak JM, Evans DE, Watts DW, Niandou MAS, Ahmedna M. 2010. Influence of pecan biochar on physical properties of a norfolk loamy sand. Soil Science ; 175:10–4.

Chan KY, Van Zwieten L, Meszaros I, Downie A, Joseph S. 2007. Assessing the agronomic values of contrasting char materials on an Australian hard setting soil. Paper presented in International Agrichar Initiative (IAI) Conference, Terrigal, New South Wales, Australia.

56

Chan KY, Xu Z (2009). Biochar: nutrient properties and their enhancement. In: Biochar for environmental management (J. Lehmann and S. Joseph eds.), Science and Technology, Earthscan, London. pp. 67-84.

Chan Y, Van Zwieten L, Meszaros I, Downie A, Joseph S. 2008. Using poultry litter biochars as soil amendments. Australian Journal Soil Research;46:437–44.

Chen H-X, Du Z-L, Guo W, Zhang Q-Z. 2011. Effects of biochar amendment on cropland soil bulk density, cation exchange capacity, and particulate organic matter content in the North China plain. Yingyong Shengtai Xuebao; 22:2930–4.

Chmidt MWI, Skjemstad JO, Jager C. 2002. Carbon isotope geochemistry and nanomorphology of soil black carbon: Black chernozemic soils in central Europe originate from ancient biomass burning, Global Biogeochemical Cycles 16:1123

DeLuca TH, Mackenzie MD, Gundale MJ, Holben WE .2006. Wildfire produced charcoal directly influences nitrogen cycling in forest ecosystems. Soil Science Society of America. 70:448-453.

Ehlers W, Popke V, Hesse F, Bohm W. 1983. Penetration resistance and root growth of oats in tilled and untilled loam soil. Soil Tillage Research ; 3:261–75.

Fagbenro J A, Oshunsanya S O, Oyeleye B A. 2015. Effects of gliricidia biochar and inorganic fertilizer on moringa plant grown in an oxisol. Communication in Soil Science and Plant Analysis. 46(5):619-626.

Fagbenro J. A., B. T. Salami, S. O. Oshunsanya, and E. A. Aduayi. 2012. The potential and promise of biochar for sustainable soil productivity and crop production. Environtropica Journal 8:90-111.

Fernandes MB, Skjemstad JO, Johnson BB, Wells JD, Brooks P. 2003. Characterization of carbonaceous combustion residues. In: Morphological, elemental and spectroscopic features. Chemosphere; 51:785–95.

Gee, G.W.D. (2002). Particle size analysis. In: Dane JH, Topp GC (eds.) Methods of soil analysis. Part 4, Physical Methods, SSSA, Incorporated, Madison, pp. 255-294.

Glaser B, Birk JJ. 2013. State of the scientific knowledge on properties and genesis of Anthropogenic Dark Earths in Central Amazonia (terra preta de I´ndio). Geochim Cosmochim Ac ; 82:39–51.

Glaser B, Haumaier L, Guggenberge G, Zech W. 2001. The ‘Terra Preta’phenomenon: a model for sustainable agriculture in the humid tropics. Naturwissenschaften 88:37-41.

Glaser B, Lehmann J, Zech W. 2002. Ameliorating physical and chemical propertiesof highly weathered soils in the tropics with charcoal – A review. Biol. Fertil. Soils 35:219-230.

57

Grossman, R.B. and Reinsch, T.G. (2002). Bulk density and linear extensibility: Core method. In: J. H. Dane and G. C. Topp (eds.) Methods of soil analysis. Part 4, Physical Methods, SSSA, Incorporated, Madison, pp. 208-228.

Hammes K, Schmidt, M. Changes in biochar in soil. In: Lehmann J, Joseph S. (eds.). 2009. Biochar for Environmental Management: Science and Technology. London, UK: Earthscan. pp. 169–182.

Hill RA, Harris A, Stewart A, Bolstridge N, McLean KL, Blakeley R. 2007. Charcoal and selected beneficial microorganisms: plant trials and SEM observations. In: International Agrichar Conference; Terrigal May. NSW Australia:.

Jagiello J, Thommes M. 2004. Comparison of DFT characterization methods based on N2, Ar, CO2, and H2 adsorption applied to carbons with various pore size distributions. Carbon; 42:1227–32.

Jekinson, D. S., and A. Ayanaba. 1977. Decomposition of carbon -14 labeled plant material under tropical conditions. Soil Science Society of America 41:912-915.

Jones BEH, Haynes RJ, Phillips IR. 2010. Effect of amendment of bauxite processing sand with organic materials on its chemical, physical and microbial properties. Journal of Environmental Management ; 91:2281–8.

Klute, A. (1986). Water retention: Laboratory methods: Methods of soil analysis, Part1. Klute A. (ed.). 2nd edition. Agronomy Monograph 9. ASA and SSSA, Madison, WI, pp. 635-662.

Krull ES, Swanston CW, Skjemstad JO, McGowan JA. 2006. Importance of charcoal in determining the age and chemistry of organic carbon in surface soils. Journal of Geophysical. Research. P. 111

Laird DA, Fleming P, Davis DD, Horton R, Wang BQ, Karlen DL. 2010. Impact of biochar amendments on the quality of a typical midwestern agricultural soil. Geoderma; 158: 443–449.

Lehmann J (2007). Bio-energy in the black. Frontiers in Ecology and the Environment 5.

Lehmann J, da Silva JP, Steiner C, Nehls T, Zech W, Glaser B. 2003. Nutrient availability and leaching in an archaeological anthrosol and a ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant Soil ; 249:343–57.

Lehmann J, da Silva JP, Steiner C, Nehls T, Zech W, Glaser B. 2003. Nutrient Availability and leaching in archaeological anthrosol and ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant Soil; 249:343-57.

Lehmann J, Joseph S. 2009. Biochar for Environmental Management: Science and Technology. Earth scan, London.

Lehmann J, Joseph S. 2009. Biochar for environmental Management: Science and Technology. London: Earth scan;

58

Lehmann J, Kern D, German L, McCann J, Martins G, Moreira A. 2003. Soil fertility and production potential. In: Amazonian Dark Earths: Origin, Properties, Management (eds. Lehmann, J., Kern, D.C., Glaser, B., and Woods W.I) Kluwer Academic Publishers, Netherlands, pp. 105-124.

Lehmann J, Pereia da Silva Jr J, Steiner C, Nehls T, Zech W, Glaser B. 2003. Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant Soil 249:343-357.

Lehmann J, Rillig MC, Thies J, Masiello CA, Hockaday WC, Crowley D. 2011. Biochar effects on soil biota: A review. Soil Biology. Biochemistry. 43:1812-1836.

Lehmann J, Rondon M. 2006. Biochar soil management on highly weathered soils in the humid tropics. In: Biological Approaches to Sustainable Soil Systems (N. Uphoff et al., eds), Boca Raton, FL: CRC Press. pp. 517-530.

Lehmann J. 2007. A handful of carbon. Nature 447:143-144.

Li X, Shen Q, Zhang D, Mei X, Ran W, Xu Y, et al. 2013. Functional groups determine biochar properties (pH and EC) as studied by two-dimensional 13C NMR correlation spectroscopy.

Liang B, Lehmann J, Solomon D, Kinyangi J, Grossman J, O’Neill B, et al., 2006. Black carbon increases cation exchange capacity in soils. Soil science Society; American Journal; 70:1719–30.

Lombin, L. G., J. A. Adepetu, and K. A. Ayoade. 1991. Complimentary use of organic and inorganic fertilizers in arable crop production. In proceedings of first nation seminar on organic fertilizer in Nigerian agriculture: Present and future, eds. G. Lombin, K. B. Adeoye, V. O. Chude, J. M. A. Torunana, O. O. Agbede, G. L. C. Nwaka, J. A. I. Omueti and S. O. Olayiwola 146-62. Kaduna, Nigeria.

Major J, Rondon M, Molina D, Riha SJ, Lehmann J. 2010. Maize yield and nutrition after 4 years of doing biochar application to a Colombian savanna oxisol. Plant Soil 333:117-128.

Major J, Rondon M, Molina D, Riha SJ, Lehmann J. 2013. Maize yield and nutrition after 4 years of doing biochar application to a Colombian savanna oxisol. Plant Soil; 333:117–28.

Major J, Steiner C, Downie A, Lehmann J (2009). Biochar effects on nutrient leaching. In: Biochar for environmental management(J. Lehmann and S. Joseph eds.), Science and Technology. Earthscan, London. pp. 271-287.

Major J. 2013. Practical aspects of biochar application to tree crops. IBI Technical Bulletin#102, International Biochar Initiative

Mann CC. 2002. The real dirt on rainforest fertility. Science 297: 920923.

McBeath AV, Smernik RJ, Krull ES. A 2013demonstration of the high variability of chars produced from wood in bushfires. Org Geochemistry ; 55:38–44.

59

Minamikawa K, Hayakawa A, Nishimura S, Akiyama H, Yagi K. 2011. Comparison of indirect nitrous oxide emission through lysimeter drainage between an andosol upland field and a fluvisol paddy field. Soil Science Plant Nutr ; 57:843–54.

Mukherjee A, Lal R. 2013. Biochar impacts on soil physical properties and greenhouse gas emissions. Agronomy; 3: 313–39.

Mukherjee A, Zimmerman AR, Harris WG. 2011. Surface chemistry variations among a series of laboratory-produced biochars. Geoderma; 163:247–55.

Mukherjee A. 2011. Physical and Chemical Properties of a Range of Laboratory-produced Fresh and Aged Biochars [thesis]. Gainesville, FL, USA: University of Florida.

Nguyen BT, Lehmann J, Kinyangi J, Smernik R, Riha SJ, Engelhard MH. 2008. Long-term black carbon dynamics in cultivated soil. Biogeochemistry; 89:295–308.

Novak JM, Busscher WJ, Laird DA, Ahmedna M, Watts DW, Niandou MAS. 2009. Impact of biochar amendment on fertility of a Southeastern coastal plain soil. Soil Science ; 174:105– 12.

Omoti, U., C. R. Obatolu, and J. A. Fagbenro. 1991. Complimentary use of organic and inorganic fertilizers in arable crop production. In proceedings of first nation seminar on organic fertilizer in Nigerian agriculture: Present and future, eds. G. Lombin, K. B. Adeoye, V. O. Chude, J. M. A. Torunana, O. O. Agbede, G. L. C. Nwaka, J. A. I. Omueti and S. O. Olayiwola 163-76. Kaduna, Nigeria.

Oshunsanya SO. 2011. Soil Physics. 1st ed. Nigeria: Dabank Publishers; 166 p.

Oshunsanya, S. O and Aliku, O. 2016. Biochar technology for sustainable organic farming. In: Organic farming book- A promising way of food production , edited by Peter Konvalina, Intech (Science, Technology and medicine open access publishers), pp 111-129

Peake LR, Reid BJ, Tang X, 2014. Quantifying the influence of biochar on the physical and hydrological properties of dissimilar soils. Geoderma 235-236: 182-190.

Pessenda LCR, Gouveia SEM, Aravena R. 2001. Radiocarbon dating of total soil organic matter and humin fraction and its comparison with 14C ages of fossil charcoal. Radiocarbon 43:595-601.

Petersen JB, Neves EG, Heckenberger MJ. 2001. Gift from the past: Terra preta and prehistoric Amerindian occupation in Amazonia. In Unknown Amazonia. Ed. C. McEwan. pp. 86-105. British Museum, London, UK.

Rondon M, Lehmann J, Ramirez J, Hurtado M. 2007. Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with biochar additions. Biological Fertility. Soils: 43:688–708.

Saito M, Marumoto, T. 2002. Inoculation with arbuscular mycorrhizal fungi: the status quo in Japan and the future prospects. Plant Soil: 244:273–9.

60

Schmidt MWI, Noack AG. 200. Black carbon in soils and sediments: analysis, distribution, implications, and current challenges. Global Biogeochemical Cycles. 14: 777–93.

Skjemstad JO, Taylor JA, Janik LJ, Marvanek SP. 1999. Soil organic carbon dynamics under long-term sugarcane monoculture. Australian Journal of Soil Research; 37: 151–64.

Soil Survey Division Staff. Soil Survey Manual. Washington, D.C.: USDA-NRCS; 1993.

Sweatman MB, Quirke N. 2001. Characterization of porous materials by gas adsorption: Comparison of nitrogen at 77 k and carbon dioxide at 298 k for activated carbon. Langmuir ; 17:5011–20.

Thies JE, Rillig M. 2009. Characteristics of biochar: biological properties. In: Lehmann J, Joseph S. (eds.) Biochar for Environmental Management: Science and Technology. London: Earthscan. pp. 85–105.

Tryon EH. 1948. Effect of charcoal on certain physical, chemical, and biological properties of forest soils. Ecological Monograph ; 18:81–115.

USDA, (2013). Soil water characteristic estimates by texture and organic matter for hydrologic solutions. hppt://hydrolab.arsusda.gov/SPAW/Index.htm.

Uzoma KC, Inoue M, Andry H, Zahoor A, Nishihara E. 2011. Influence of biochar application on sandy soil hydraulic properties and nutrient retention. Journal of Food Agricultural Environment; 9:1137–1143.

Van Zwieten L, Singh B, Joseph S, Kimber S, Cowie A, Yin Chan K. 2009. Biochar and emissions of non-CO2 greenhouse gases from soil. In: Lehmann J, Joseph S. (eds.) Biochar for Environmental Management. VA, USA: Earthscan: London Sterling.

Verheijen F, Jeffery S, Bastos AC, Van der Velde M, Diafas I. 2010. Biochar Application to Soils: A Critical Scientific Review of Effects on Soil Properties, Processes and Functions. JRC Scientific Technical reports; 1-166.

Warnock DD, Lehmann J, Kuyper TW, Rillig MC. 2007. Mycorrhizal responses to biochar in soil—concepts and mechanisms. Plant Soil: 300:9–20.

Woods W, McCann JM, Meyer DW. 2000. Amazonian dark earth analysis: State of knowledge and directions for future research. In Papers and Proceedings of Geography Conferences, 23 Eds. F.A. School master and J. Clark. pp. 114-121.

Yuan JH, Xu RK, Zhang H. 2011. The forms of alkalis in the biochar produced from crop residues at different temperatures. Biores Technol ; 102:3488–97.

Zimmerman AR. 2010. Abiotic and microbial oxidation of laboratory-produced black carbon (biochar). Environ Science Technology; 44:1295–301

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