ABSTRACT
Incubation studies and field trial were carried out at the Michael Okpara University of Agriculture, Umudike to evaluate the effect of biochar rates on some soil chemical properties, yield and nutrient content of sweet potato (Ipomoea batatas) in an Ultisol of Umudike, southeastern Nigeria. The incubation study was aimed at determining the rate of nutrient release as well as the rate of acid neutralization by biochar and NPK (15:15:15) fertilizer. The treatments comprised of control (0 t/ha), biochar at 2.5t/ha, 5t/ha, 7.5t/ha and 10t/ha and NPK (15:15:15) fertilizer at 400kg/ha with the equivalent rates of biochar at 3.3g, 6.6g, 10g and 13.3g respectively and NPK (15:15:15) fertilizer at 0.53g. These were replicated four times in Randomized Complete Block Design (RCBD). The second experiment which was the field experiment was carried out to investigate the effect of treatments on the root tuber yield of sweet potato in t/ha of the rates mentioned above. Sweet potato variety UmuSpo1 was the test crop. Analysis of the nutrient content of sweet potato was also carried out after harvest to test for the nitrogen, phosphorus and potassium contents of the harvested sweet potato root tubers. From the incubation study, biochar rates significantly (p<0.05) increased soil pH from 4.87 to 13.92 and as the rates were increasing, pH increased with time following these pattern 10t/ha>7.5t/ha > 5t/ha > 2.5t/ha> and 400kg/ha having these values 13.92>13.50>10.21>7.85>5.49>4.53 respectively. The application rate of 2.5t/ha of biochar reduced soil exchangeable acidity at 4weeks of incubation from 1.92cmol/kg to 0.62cmol/kg. At 12weeks of the incubation study, 10t/ha of biochar gave an increase in the level of soil exchangeable potassium from 0.13cmol/kg to 0.83cmol/kg. Results from the field study showed that 400kg/ha of NPK (15:15:15) fertilizer gave the highest value for vine length at 16WAP (150.4cm) over the control 117.2cm. Biochar at 5t/ha gave the highest number of leaves per plant (235.6) at 12WAP and this was significantly (p<0.05) different from control and 7.5t/ha of biochar gave the highest value of stem girth (0.45cm) at 16WAP. Results on yield of sweet potato root tubers showed that biochar at 5t/ha produced the highest saleable sweet potato root weight (7.84t/ha), 7.5t/ha of biochar produced the least non-saleable sweet potato root weight (0.21t/ha) and 5t/ha of biochar gave the highest total root weight (8.11t/ha). 7.5t/ha of biochar recorded the highest percentage saleable root number (87.20) and also the least non-saleable root number (13.70). What this implies is that, there would be no need applying beyond 5t/ha of biochar in the study area in order to obtain optimum yield. Also in terms of non-saleable root yield, 7.5t/ha is better as it is not economical for non-saleable root yield to be in abundance. For the nutrient contents of sweet potato root tubers, 2.5t/ha of biochar gave the highest nitrogen content (0.947%), while 10t/ha of biochar gave the highest phosphorus and potassium contents (0.532% and 0.984%) respectively. Conclusively, therefore biochar at the rates of 5t/ha, 7.5t/ha and 10t/ha is ideal for improving yield and nutrient contents of sweet potato production in the study area.
TABLE OF CONTENTS
Certification i
Dedication ii
Declaration iii
Acknowledgements iv
Table of contents vii
List of Tables xi
Abstract xii
CHAPTER 1:
INTRODUCTION
1.1
Objectives 3
CHAPTER 2: LITERATURE
REVIEW
2.1 Unique Characteristics of Ultisols of the
Humid Tropics 4
2.2 Biochar 5
2.2.1
Biochar feed stocks and pyrolysis 7
2.2.2 Elemental composition of biochar 7
2.3.3 Characteristics of biochar 8
2.2.4 Effect of biochar on soil properties 9
2.2.5 Effect of biochar on crop growth 10
2.2.6 Effects of biochar on crop nutrient content 11
2.2.7 Adverse effect of biochar application on
soil 11
2.3 NPK Fertilizer and its Effect on Growth
of Crops 12
2.3.1 Nitrogen 12
2.3.2 Phosphorous 13
2.3.3 Potassium 14
2.4 NPK (15:15:15) 15
2.4.1
Advantages of NPK (15:15:15) 15
2.4.2 Functions of NPK 16
2.4.3 Effect of NPK on nutrient content 17
2.4.4 Adverse effect of NPK on soils and water
bodies 17
2.4.5 Adverse effect of NPK on crop growth 18
2.5 Sweet Potato 19
2.5.1 Nutrient requirements of sweet potato 22
2.5.2 Importance of potassium in sweet potato
production 22
CHAPTER 3:
MATERIALS AND METHODS
3.1
Description of experimental site 24
3.2 Soil Sampling and Soil Preparation 24
3.2.1 pH determination 24
3.2.2 Particle
size analysis 25
3.2.3 Organic
carbon determination 25
3.2.4 Available phosphorus 25
3.2.5 Total nitrogen 25
3.2.6
Exchangeable cations 25
3.2.7 Exchangeable acidity 26
3.3
Treatments 26
3.4
Biochar Production 27
3.4.1
Biochar chemical analysis 27
3.5 Incubation
Studies 28
3.6 Experimental
Design and Field Layout 29
3.7
Collection of Vine Cuttings 29
3.8
Soil Parameters 29
3.9
Plant Parameters 29
3.10
Treatment Application 29
3.11
Cultural Practice 30
3.12
Records at Harvest 30
3.12.1 Total
root weight 30
3.12.2 Total
root number 30
3.12.3 Weight
of saleable roots 30
3.12.4 Weight
of non-saleable roots 30
3.12.5
Number of saleable (marketable) root 30
3.12.6
Number of non-saleable unmarketable roots 31
3.13 Nutrient Content of Sweet potato 31
3.14
Statistical Analysis 31
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Physical and Chemical Properties of the
Soil before Experimentation 32
4.2 Chemical Properties of Biochar 35
4.3 Incubation Study 36
4.3.1 Effect of treatments on soil pH 36
4.3.2 Effect of treatments on the soil
exchangeable acidity 38
4.3.3 Effect of treatments application on
exchangeable K 40
4.4 Growth Parameter of Sweet potato 42
4.4.1 Effect of treatments on vine length (cm) of
sweet potato 42
4.4.2 Effect of treatments on number of
leaves/plant of sweet potato 44
4.4.3 Effect of treatments on stem girth (cm) of
sweet potato 46
4.5 Effect of Treatments on the Total Root
Weight of Sweet potato at
Harvest (t/ha) 48
4.5.1 Effect of treatments on total number of root
sweet potato after harvest 48
4.5.2 Effect of treatments on saleable sweet potato
root weight at harvest (t/ha) 49
4.5.3 Effect of treatments of non-saleable root
weight of sweet potato at
harvest (t/ha) 49
4.5.4 Effect of treatments on number of saleable
roots of sweet potato 50
4.5.5 Effect of treatments of the number of
non-saleable root of sweet potato 50
4.5.6 Effect of treatments on percentage number of
saleable roots of
sweet potato 50
4.5.7 Effect of treatments on percentage number of
non-saleable root of
sweet potato after harvest 51
4.6 Effect of Treatments on Some Chemical
Properties after Harvest 54
4.6.1 Soil pH (water) 54
4.6.2 Soil organic carbon 54
4.6.3 Soil total nitrogen (%) 55
4.6.4 Soil available phosphorus 55
4.7 Effect of Treatments Exchangeable Cations
(Ca, Mg, K and Na) after Harvest 57
4.8
Effect of Treatments on Soil
Exchangeable Acidity, Effective Cation Exchange
Capacity (ECEC) and Base Saturation after
Harvest 58
4.8.1 Soil exchangeable acidity 58
4.8.2 Effective cation exchange capacity of the
soil (ECEC) 58
4.8.3 Percentage base saturation 59
4.9 Effect of Treatments on N, P and K
Content of Sweet Potato Root after Harvest 60
4.9.1 Effect of treatments on the nitrogen content
of sweet potato root tubers
after harvest 60
4.9.2 Effect of treatments on phosphorus content
of sweet potato root tubers
after harvest 60
4.9.3 Effect of treatments on potassium content of
sweet potato root tubers
after harvest 61
CHAPTER 5: CONCLUSION AND RECOMMENDATION
5.1
Conclusion 63
5.2 Recommendations 64
Reference
LIST OF TABLES
4.1 Physical
and chemical properties of soil before experimentation 34
4.2 Chemical composition of biochar 35
4.3 Effect of treatments application on vine
length of sweet potato in the field 43
4.4 Effect of treatments on number of leaves
of sweet potato in the field 45
4.5 Effect of treatments on stem girth (cm)
in the field 47
4.6 Effect of treatments on the yield of
sweet potato at harvest 52
4.7 Effect of treatments on some yield
parameter of sweet potato (t/ha) 53
4.8
Effects of biochar and NPK
(15:15:15) on soil pH, organic carbon total
nitrogen and available phosphorus 56
4.9
Effect of treatments on exchangeable
cations (cmol/kg) after harvest 57
4.10 Effects of biochar and NPK (15:15:15) fertilizer
on soil exchangeable
acidity, cation exchange capacity and base saturation after harvest 59
4.11 Effect of treatments on N, P and K content
of sweet potato
62
LIST OF FIGURES
4.1: Effects of treatments on
soil pH (H20) at 24Hrs, 4Wks, 8Wks,
12Wks and 16Wks of
incubation
37
4.2: Effects of treatments on
soil exchangeable acidity (cmol/kg)
at 24Hrs, 4Wks,
8Wks, 12Wks and 16WKs of incubation 39
4.3: Effects of treatments on
soil exchangeable potassium (cmol/kg) at
24Hrs, 4Wks,
8Wks, 12Wks and 16WKs of incubation 41
CHAPTER 1
INTRODUCTION
Ultisols are commonly known as red clay
soils. They are typically quite acidic, often having a pH of less than 5. The
red and yellow colors result from the accumulation of iron oxide (rust), which
is highly insoluble in water (WRB, 2015).
Acid, sandy Ultisols, which are common in
the humid rainforest zone of southeastern Nigeria, are inherently infertile,
especially under the intensive cultivation that has been occasioned by
reduction in fallow periods following high population pressure and
industrialization (Udoh, 2018). The usual approach of maintaining fertility has
simply been the application of recommended doses of inorganic fertilizers. Inorganic
fertilizers when applied on acid sandy Ultisols, under a high rainfall regime
like that of southeastern Nigeria, the nutrients supplied are easily lost
through leaching, surface runoff or soil erosion (Udoh, 2018). Indeed high
dependence on inorganic fertilizers in the humid zones of the tropics is
becoming less preferable and uneconomical, including the need for frequent
applications in order to sustain fertility. Organic fertilizers on the other
hand improve soil CEC, nutrient stock, soil structure, base saturation and bulk
density. However, applications of large doses of manures could cause
environmental hazards, stream and river pollution and soil acidification (Munoz
et al., 2003).
Biochar is a term used to designate a carbon-rich product obtained when
a biomass (such as wood, crop residue, etc.) is heated in a closed container
with little or no available oxygen (Lehmann and Joseph, 2009a). When added to
soil, biochar has been reported to increase available nutrients and prevent
their leaching, stimulate activity of agriculturally important soil
microorganisms, act as effective carbon sink for several hundred years,
sequester atmospheric CO2 in soil, suppress emissions of other
greenhouse gases, and mitigate offsets from agrochemicals (Thies and Rillig,
2009).
A fertilizer is any material of natural or
synthetic origin (other than liming materials) that is applied to soil or to
plant tissues to supply one or more plant nutrients essential to the growth of
plants (Heinrich, 2000). According to "Summary of State Fertilizer
Laws" (EPA, 2013), NPK fertilizers are three-component fertilizers
providing nitrogen, phosphorus, and potassium. NPK classification describes the
amount of nitrogen, phosphorus, and potassium in a fertilizer. The three main
macronutrients which are contained in fertilizers are important in the
following ways: Nitrogen (N) is important for leaf growth, phosphorus (P) for
development of roots, flowers, seeds, fruit and potassium (K) is important for
strong stem growth, translocation of water in plants, promotion of flowering
and fruiting (Dittmar et al., 2009).
These macro-nutrients are required in larger quantities and are present in
plant tissue in quantities from 0.15% to 6.0% on a dry matter (DM) (0%
moisture) basis (Mills and Jones, 1996).
Ipomoea batatas
(L) Lam), commonly known as sweet potato belongs to the family Convolvulaceae. It is an important root
vegetable which is large, starchy, and sweet tasting (Purseglove, 1972; Woolfe, 1992). Ipomoea
batatas has played an important role as energy and phytochemical source in
human nutrition and animal feeding. The plant has significant
medicinal importance and various parts of the plant are used in traditional
medicine. (FNB and Anno, 1980), besides simple starches, sweet potatoes are
rich in complex carbohydrates, dietary fiber,
iron, and vitamin content such as beta-carotene (a pro-vitamin A carotenoid),
vitamin B2, vitamin C, and vitamin E (Antia et al., 2006). The tuber is an excellent source of flavonoids,
phenolic compounds such as beta-carotene which converts to vitamin A once
consumed.
There are a number of papers which report
positive effects of biochar addition on crop growth and development (Asai et al., 2009; van et al., 2010; Coomer et al.,
2012; Zhang et al., 2012; Carter et al., 2013; Saxena et al., 2013; Vinh et al., 2014). Some reports have also illustrated negative (Lehmann
et al., 2013; Chan et al., 2008) or no response of crops to
biochar (Branndstaka et al., 2010;
Borsari 2011; Lal et al., 2013). Some
reports emphasized that the effect was positive when biochar and mineral
fertilizers were used, with mineral fertilizers having greater positive effect
(Alburquerque et al., 2014). However,
more studies are required to understand the difference in the performance of
plants when biochar rates and NPK (15:15:15) fertilizers are used.
The objective of this study therefore was
to determine the effect of biochar rates on soil chemical properties, growth
and yield of Sweet potato.
1.1
THE SPECIFIC OBJECTIVES OF THIS STUDY WERE TO;
·
Determine the effect of
biochar and NPK (15:15:15) fertilizer on the soil pH, soil acidity and rate of
potassium release with time from incubation study.
·
Determine the effects of
biochar and NPK (15:15:15) on yield attributes of sweet potato.
·
Determine the effects of
biochar and NPK (15:15:15) fertilizer on some soil chemical properties at
harvest
·
Determine the effects of
biochar and NPK (15:15:15) fertilizer on nutrient content of sweet potato.
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