ABSTRACT
Soil acidity has remained a major yield limiting factor for crop production worldwide, and in Umudike Southeastern Nigeria, where the soils are characterized by high acidity and low nutrient status, Incubation studies, field experiment and laboratory analysis were carried out to investigate the effects of biochar on soil acidity, pH-buffering capacity and nutrient status in an Ultisol planted to cucumber in Umudike, Southeastern Nigeria. The treatments were 0 tonne per hectare biochar, 1 tonne per hectare biochar, 3 tonnes per hectare biochar, 5 tonnes per hectare biochar, 1 tonne biochar + 400kg NPK (15:15:15) per hectare, 3 tonnes biochar + 400kg NPK (15:15:15) per hectare, 5 tonnes biochar + 400kg NPK (15:15:15) per hectare and 400 kg NPK (15:15:15) per hectare. The treatments were replicated 3 times. The incubation studies were carried out to investigate the effect of the treatments on soil pH and Exchangeable acidity of the soil under study over a period of four weeks, using the equivalent of the treatments used in the field experiment, 0g biochar, 1.6g biochar, 5g biochar, 8g of biochar, 1.6g biochar + 0.6g NPK(15:15:15), 5g biochar +0.6g NPK(15:15:15), 8g biochar +1.6g of NPK(15:15:15) and 0.6g of NPK(15:15:15). Each of the treatments was added to 50g of soil in plastic containers of equal size and basal diameter and replicated three times. The soil used for the incubation studies was strongly acidic, having a pH (H2O) of 4.38 and exchangeable acidity of 1.84. The soil pH (H2O) and Exchangeable acidity were determined on the incubated samples at weekly interval for 4 weeks, using standard laboratory procedures. The effect of the treatments on the pH-buffering capacity of the soil during incubation was also determined using standard procedures. Results obtained showed that 5 tonnes per hectare biochar significantly (P<0.05) increased soil pH from 4.38 to 8.1, 8.64, 8.20 and 8.42 from week 1 to week 4 of incubation respectively, while Exchangeable acidity was reduced from 1.84 to 0.34, 0.61, 0.56 and 0.37 from week 1 to week 4 respectively throughout the incubation period. The pH-buffering capacity of the incubated soil was also increased by 96%, 97%, 87% and 92% from week 1 to week 4 respectively. The field experiment was laid out in a randomized complete block design and conducted at Michael Okpara University of Agriculture Eastern Farm. The soil used for the experiment was strongly acidic, having a pH (H2O) of 4.50 and exchangeable acidity of 1.44 cmolkg-1. The variety of cucumber planted was “Market More” and the result obtained from the field experiment indicated a significant (P<0.05) increase in the number of leaves and vine length of cucumber by 3 tonnes biochar + 400 kg NPK (15:15:15) per hectare over other treatments. It could therefore be inferred that the application of biochar as soil amendment can viably ameliorate soil acidity, increase soil pH-buffering capacity, enhance nutrient status and invariably improve cucumber growth in the soils of the study area.
TABLE
OF CONTENTS
Title page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents vi
List of Tables x
List of Figures xi
List of Plates xii
Abstract xiii
CHAPTER 1: INTRODUCTION 1
CHAPTER
2: LITERATURE REVIEW 5
2.1 Soil
Acidity 5
2.1.1
Effect of soil acidity on soil
nutrients 6
2.2 Biochar 6
2.3 Pyrolysis 7
2.3.1 Methods
of pyrolysis 7
2.4 Feedstock
9
2.5 Biochar
Application Methods 10
2.5.1 Top
soil application 11
2.5.2 Depth
application 11
2.5.3 Top
dressing 11
2.6 Biochar
Quality 11
2.6.1 Characteristics
of biochar 12
2.6.2 Physical
structure of biochar 13
2.6.3 Particle
size distribution of biochar 14
2.6.4 pH
of biochar 14
2.6.5 Ash
content of biochar 15
2.6.6 Ion
exchange capacities of biochar 15
2.6.7 Biochar
nutrient content 16
2.6.8 Physicochemical properties of biochar 17
2.7 Effect
of Biochar on Soil pH Buffering Capacity 18
2.8
Effect of Biochar on Soil Properties 19
2.8.1 Effect of biochar on soil chemical properties 19
2.8.2 Effect of
biochar on soil
structure 20
2.8.3 Effect of biochar on soil microbial community 21
2.9 Biochar
and Soil Nutrient Transformation 21
2.9.1 Nitrogen
fixation 21
2.9.2 Nitrogen
mineralization 22
2.9.3 Nitrogen immobilization 22
2.9.4 Denitrifiaction 23
2.9.5 Phosphorus
availability 23
2.10
Effect of Biochar on Soil Nutrient
Leaching 24
2.11 Effect
of Biochar on Crop Productivity 25
2.12 Economic
Implication of Biochar Use 27
2.13 Cucumber 27
2.13.1 Agronomic requirement of cucumber 28
CHAPTER
3:
MATERIALS
AND METHODS 30
3.1 Description
of Experimental Site 30
3.2 Soil
Sampling 30
3.3
Field Experiment 31
3.4 Treatments 32
3.5 Biochar
Production 33
3.6 Biochar
Application 35
3.7 Growth Data Collection 36
3.8 Incubation
Studies 37
3.9
pH- Buffering Capacity of
Biochar 38
3.10 Statistical
Design 38
CHAPTER
4: RESULTS AND DISCUSSION 39
4.1 Initial Soil Analysis 39
4.2 Biochar Analysis 42
4.3 Effect of the Treatments on pH and Exchangeable
Acidity During
Incubation 45
4.4 Effect of the Treatments on pH Buffering Capacity
of the Soil During
Incubation 52
4.5 Effect
of the Treatments on Soil Properties after Application 54
4.6 Effect
of the Treatments on Soil pH during the Field Experiment 54
4.6.1 Effect of the treatments on the other
chemical properties of the soil 55
4.7 Correlation
Matrix for Soil Properties 60
4.8 Effect of the Treatments on Growth of
Cucumber 63
CHAPTER
5: CONCLUSION AND RECOMMENDATION 66
References 68
Appendix 88
LIST OF TABLES
Page
2.1 Processes contributing to increased
levels of hydrogen (H+) ions in
Soil
solution, thereby resulting in increasingly acidic conditions. 5
4.1
Physical and chemical
properties of the soil used for the field experiment 41
4.2 Some properties of the biochar used
for the experiment 43
4.3 Physical
and chemical properties of the soil before treatment application
during the
incubation studies. 44
4.4
Effect of the treatments on soil pH buffering capacity during Incubation 56
4.5 Effect
of treatment on soil properties at 4Weeks after treatment
application 60
4.6 Effect of treatment on soil properties
at 8 Weeks after treatment
application 61
4.7 Effect of treatment on soil properties
at 12 weeks after treatment application
62
4.8
Correlation matrix for soil properties 65
4.9
Effect of the treatments on number of leaves produced by Cucumber
67
4.10
Effect of the treatments on vine length produced by cucumber 68
LIST OF FIGURES
Page
3.1 Field
Layout 33
4.1 Effect
of treatments on soil pH at week 1,2,3 and 4 of incubation 50
4.2 Effect of treatments on
exchangeable acidity (cmol/kg) at week
1,2,3 and 4 of incubation 51
LIST OF PLATES
Page
3.1 Local
Biochar Drum during Biochar Production 34
3.2 Biochar After Production 34
3.3 Biochar
Application 35
3.4 Cucumber
at 6 weeks five days after planting. 36
CHAPTER 1
INTRODUCTION
Soil acidity is a major factor
that limits yield in crop production worldwide and acid soils account for about
4 billion hectares of the total world land area (Von and Mutert, 1997). This is
30% of the total world land area and 58% of land suitable for agriculture,
inhabited by 73% of the world’s population. As a result of extensive weathering
and leaching, most soils found in South and North America, Asia and Africa, are
acidic (Muindi et al., 2016). Soil
acidity is linked with toxicity of hydrogen (H), aluminium (Al), iron (Fe) and
manganese (Mn) especially to plant roots and corresponding deficiencies of
plant available phosphorus (P), molybdenum (Mo), calcium (Ca), magnesium (Mg)
and potassium (K) (Giller and Wilson 1991; Jorge and Arranda 1997; Muindi,
2016) which negatively affects the fertility and productivity of the soil
(Muindi et al., 2016).
Soils found in southeastern Nigeria which
are characterized by high acidity and low rate of exchangeable cations cannot
support optimal crop production without the use of soil amendment. The
application of biochar, has been proven to change soil pH to a more neutral pH,
especially in acidic soils (Fowles, 2007). The changes in CEC and pH create a
suitable environment for growing crops in an area that cannot support optimal
crop production.
The use of biochar, as soil amendment to
mitigate man-induced climate change, as well as to improve soil productivity
was proposed as a new approach (McHenry, 2009).
However, the usage of charred materials as soil amendment is not a new
concept. In the Amazon River Basin, there are areas that have remained
productive for thousands of years due to charcoal accumulation that
significantly increased the carbon’s stability against microbial decay (Steiner
et al., 2007). The Amazonian Dark
Earth now serves as a guide to create a carbon sink in soils as well as hold
the possibility to reduce the amount of fertilizer farmers need to apply to
fields.
Presently, application of biochar to soils
is attaining universal attention due to the potential of it improving fertility
in acidic soils by enhancing soil properties such as pH,
cation-exchange-capacity and water-holding-capacity (Smebye, 2014) as well as soil
nutrient retention capacity and sustaining carbon storage, thereby reducing the
emission of greenhouse gas (Downie et al.,
2009; Abukari, 2014). As such, biochar can concurrently act in both soil
modification, improving soil physical condition and as carbon sequestration
medium, giving a high prospect that could help decrease atmospheric carbondioxide
in the near future (Amonette and Joseph, 2009).
Biochar is therefore seen as a simple approach, yet a very powerful tool
to combat soil acidity challenge by significantly increasing soil cation
exchange capacity (Yuan et al.,
2011b) thereby, increasing the pH buffering capacity of acidic soils (Xu et al., 2012). Biochar contains ample
amounts of oxygen-containing functional groups which supply negative surface
charge of biochar (Yuan et al., 2011a;
Xu et al., 2012). The
oxygen-containing functional group is regarded as the main mechanism in biochar
that increases the pH buffering capacity of acid soils treated with biochar (Xu
et al., 2012). Furthermore, biochar
is known to have the capability of reducing soil compaction, improving soil physical
condition, enhancing plant nutrient uptake from the soil and decreasing
emission of nitrous oxide (Lehmann et al., 2005; Lehmann 2007; Kannan et al., 2012). Biochar has the potential
to increase the availability of plant nutrients (Lehmann et al., 2008);
through increasing cation exchange capacity (CEC), improving soil pH, or
immediate nutrient contributions from the biochar itself. According to Mbagwu
and Piccolo (1997) the potential mechanism for improved nutrient retention and
supply due to biochar modification is the increase of cation exchange capacity
up to 50% as compared to unamended soils. Biochar has a greater capacity to
absorb and retain cations than other forms of soil organic amendment owing to
its greater surface area, and the negative surface charge that is found on
biochar (Liang et al., 2006;
Abukari, 2014).
Cucumber (Cucumis sativus L.) is an important vegetable, thought to be one of
the oldest vegetables with historical records dating as far back as 5000 years
(Wehner and Guner, 2004). The crop is cultivated mainly for its fruits and
eaten fresh (salad). The fruit is rich in nutrients and vitamins such vitamin
E, K, C, A among others; minerals such as magnesium, potassium, zinc, calcium
and phosphorus as well as phyto-nutrients like Carotene-B, Xanthein-B and
Lutein (Vimale et al., 1999; Nwofia et al., 2015). The nutritional
composition of cucumber fruit per 100g edible portion is as follows:
carbohydrate, protein, total fat and dietary fibre at 3, 1, 0.5, and 1 percent
respectively (USDA, National Data Base, 2014).
The crop requires fertile soils as
infertile soils affect the quality of the fruit resulting in bitter and
misshapen fruits (Eifediyi and Remison, 2010). As a short gestation crop,
cucumber requires instant release of nutrient in the field which inorganic
fertilizer can supply better than organic fertilizer (Marjan, 2005). However, under
intensive agriculture, the use of inorganic fertilizer has not been helpful because
of the high cost, associated reduction in the crop yields, nutrient imbalance,
soil degradation and acidity (Kang and Juo, 1980; Obi and Ebo, 1995; Eifediyi
and Remison, 2010).
Therefore, this study’s overall objective
was to examine the influence of biochar on some soil physicochemical properties
and neutralization of acidity on ultisols of Umudike, Southeastern Nigeria.
The objectives were:
i.
To evaluate the acid
neutralizing effect of biochar on the soil in a controlled environment.
ii.
To evaluate the
pH-buffering capacity of biochar on an ultisol in Umudike, Southeastern
Nigeria.
iii.
To determine the effect
of biochar on soil chemical properties.
iv.
To determine the effect
of biochar on the growth of cucumber.
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