ABSTRACT
Field experiments were conducted at the Teaching and Research Farm of Michael Okpara University of Agriculture, Umudike (MOUAU) and the Research Farm of the National Root Crop Research Institute, (NRCRI) both in Umudike, Ikwuano Local Government Area of Abia State in the 2012 and 2014 respectively on the effects of percentage leaf defoliation and NPK 15:15:15 fertilizer application on the growth and yield parameters of cassava (Manihot esculenta (L.) Crantz) TMS 419 sourced from the National Root Crop Research Institute, (NRCRI). The experiments were laid out in a factorial experiment fitted into a randomized complete block design (RCBD). The first experiment was laid out as a 4 by 3 factorial scheme with three (3) replications and twelve (12) treatment combinations, that gave a sum total of thirty-six (36) plots in all while the repeat experiment was laid out as a 2 by 3 factorial scheme with three (3) replications and six (6) treatment combinations, that gave a sum total of eighteen (18) plots. Two months after planting (2MAP), defoliation and the application of NPK 15:15:15 fertilizer were carried out simultaneously using the different rates of treatments which were 0%, 25%, 50%, 75% and 100% for defoliation and 0kg/ha, 150kg/ha, 200kg/ha, 300kg/ha and 400kg/ha for fertilizer applied. The results showed that significant defoliation effect was observed on plant height (5%) in both experiments at 50%, 75% and 100%, fertilizer applied was only significant in the second experiment with 400kg/ha fertilizer applied being more significant. Also, significant defoliation effect (5%) were observed in the number of leaves, number of branches, and likewise significant fertilizer effect (5%) were observed in the number of branches at 300kg/ha, number of leaves at 150kg/ha to 300kg/ha with interaction, leaf area, fresh stem weights at 300kg/ha to 400kg/ha, and the stem dry weights at 200kg/ha to 300kg/ha, these significant effects shown by the fertilizer applied, implied that the fertilizer at the different rates of treatments compensated for the effects of defoliation which were as a result of the distortion of the photosynthetic capacity of the leaves being defoliated. Although with defoliation, NPK fertilizer applied and the interaction showed no significant effect on the yield parameters, but there were some reasonable percentage yield from the results obtained with 200kg/ha to 400kg/ha fertilizer applied, while the plots with all levels of defoliation and zero NPK applied yielded lowly, which implied that the NPK applied was effective, although not significant but showed that, there existed a source-sink relationship. It therefore showed that farmers can still achieve reasonable yield regardless of the degree of defoliation considering the fact that there must be an alternate source of nutrients such as the NPK 15:15:15 fertilizer used in the experiment ranging from 200kg/ha to 400kg/ha, and for the farmers with livestock farming inclusive. This is of great importance to them, owing to the fact that they can defoliate cassava leaves at 25% and 50% level of defoliation for their animal’s feed production and yet have some reasonable yield available for consumption at harvest.
TABLE
OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents vi
List of Tables viii
Abstract ix
CHAPTER
1: INTRODUCTION
1.1
Background of the Study 1
1.2
Objectives of the Study 3
CHAPTER
2: LITERATURE REVIEW
2.1 Botany 4
2.1.1 Taxonomy
of cassava 4
2.1.2 Cassava
morphology 4
2.2 Environmental
Requirement of Cassava 4
2.3 Defoliation in Cassava and its Effects 6
2.4 Defoliation in other Crops and its Effects 7
2.4.1 Effects of defoliation in vegetables 7
2.4.2 Effect of defoliation in grasses 9
2.4.3 Effect of defoliation in tree crop 11
2.4.4 Effect of defoliation in flower 11
2.4.5 Effect of defoliation in legumes 12
2.4.6 Effects of defoliation in root crops 13
2.5 Fertilizer Application in Cassava and its
Effects 14
2.6 Fertilizer Application in Other Crops and
its Effects 16
2.6.1 Effect of fertilizer application in vegetables 16
2.6.2 Effect of fertilizer application in grasses 18
2.6.3 Effect of fertilizer application in flower 21
2.6.4 Effect of fertilizer application in legumes 21
2.6.5 Effect of fertilizer application in root crops 22
CHAPTER
3: MATERIALS AND METHODS
3.1 Experimental
Site/Location 24
3.2 Land Preparation 24
3.3 Source of Materials 25
3.4 Experimental Design and Treatments 25
3.5 Agronomic Practices 26
3.6 Data Collection 27
3.7 Data Analysis 28
CHAPTER
4: RESULTS AND DISCUSSION 28
4.1 Soil
Properties and Meteorological Data of the Experimental Sites 29
4.5 The Mean Effects of Defoliation and npk
Fertilizer Application on the Vegetative Traits of Cassava 33
4.5.3 Effect of npk fertilizer application and
defoliation on the plant height 35
4.5.6 Effect of npk fertilizer application and
defoliation on the number of
branches 38
4.5.8: Effect of npk fertilizer application and
defoliation on the number of leaves
per plant 40
4.5.10: Effect of npk fertilizer application and defoliation on the leaf
area 42
4.6 The
Mean Effects of Defoliation and npk Fertilizer Application on
the Dry Matter Content of Cassava 43
4.6.2 Effect of npk fertilizer application and
defoliation on the fresh stem
Weight 44
4.6.5 Effect of npk fertilizer application and
defoliation on the stem dry weight 47
4.7 Tables
for the Mean Effects of Defoliation and npk Fertilizer
Application on the Final Harvest of Cassava` 48
4.7.3 Effect of npk fertilizer application and
defoliation on the number of tubers 50
4.7.6 Effect of npk fertilizer application and
defoliation on the weight of
the tubers 53
4.8 Discussion
CHAPTER 5: CONCLUSION AND
RECOMMENDATIONS 58
5.1 Conclusion 58
5.2 Recommendations 59
References
Appendix I 69
Appendix II 73
LIST
OF TABLES
4.2 Soil Physico-Chemical Properties of the First and
the Repeat
Experimental Sites before Treatments Application 30
4.3 Meteorological Data of the Experimental
Site in 2012 31
4.4 Meteorological
Data of the Experimental Site in 2014 32
4.5.1 First experiment: mean effects of
defoliation and NPK fertilizer
application on the height (cm) per plant (4map) 33
4.5.2 Repeat experiment: mean effects of
defoliation and NPK fertilizer
application on the height (cm) per plant (4map) 34
4.5.4 First experiment: mean effects of
defoliation and NPK fertilizer
application on the number of branches per plant (4map) 36
4.5.5 Repeat experiment: mean effects of
defoliation and NPK fertilizer
application
on the number of branches per plant (4map) 37
4.5.7 First experiment: mean effects of
defoliation and NPK fertilizer
application on the number of leaves per plant (4map) 39
4.5.9 Repeat experiment: mean effects of
defoliation and NPK fertilizer
application on the leaf area (cm²) per plant (4map) 41
4.6.1 First experiment: mean effects of
defoliation and NPK fertilizer
application on the fresh stem weight (g) per plant
(4map) 43
4.6.3 First experiment: mean effects of
defoliation and NPK fertilizer
application on the stem dry weight (g) per plant
(4map) 45
4.6.4 Repeat experiment: mean effects of
defoliation and NPK fertilizer
application
on the stem dry weight (g) per plant (4map) 46
4.7.1 First experiment: mean effects of
defoliation and NPK fertilizer
application on the number of tubers of cassava 48
4.7.2 Repeat experiment: mean effects of
defoliation and NPK fertilizer
application on the number of tubers of cassava 49
4.7.4 First experiment: mean effects of
defoliation and NPK fertilizer
application
on the weight of fresh tubers of cassava (ton/ha) 51
4.7.5 Repeat experiment: mean effects of
defoliation and NPK fertilizer
application
on the weight of fresh tubers of cassava (ton/ha) 41
CHAPTER
1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Cassava, Manihot
esculenta (L.) Crantz belongs to
the class Dicotyledoneae, family, Euphorbiaceae and it is known to be a
perennial woody shrub, grown annually, reaching
2 to 4m in height and the root consisting of the bark and the fleshy starchy
parenchyma which is the edible part of agricultural importance both for human
consumption and industrial uses (Lebot, 2009).
Cassava known as a
root crop is a staple food crop, contributing about 15% of the dietary energy
intake of most Nigerians on daily basis, forming an essential part of the diet
of about 500 million people and provides a suitable means of livelihood for
millions of farmers, processors and traders (Lancaster
and Brooks 1993; Onyenwoke and Simonyan,
2014)
In a bit to increase the yield
potential of the cassava crop, the crop had been reported to respond to good
soil fertility and adequate fertilizer application (Howeler, 1996; Fermont
et al., 2010; Chaisri et al., 2013; Mathias and Kabambe, 2015).
As much as cassava crop has the
natural ability to thrive better in an unfavourable condition (Boansi, 2017),
excessive amount of rainfall has been reported to effectively affect the
lifespan of added fertilizer to the soil, the retention capacity and the availability
to the crops and consequently may affect the tuber formation and quality
(Duluora, 2012; FAO, 2013). Nitrogen, Phosphorus and Potassium
are the three major nutrients in a fertilizer that are most important for
cassava tuber formation (Odedina et al.,
2015), and explained that chemical fertilizers usually have 10-20 times higher
concentrations of these nutrients (Howeler, 2014).
The importance of cassava cannot be overemphasized;
its greatest staple utility rest in Africa (Onwueme, 2002). About 90% of
cassava produced is used locally for food (it could be processed into over 50
food forms; gari, lafun, bread, flakes, flour etc (Denton et al., 2004). It can also be used for animal feed, and bio fuel,
industrial and pharmaceutical uses (Akpan et al., 2004; Chandel
et al., 2007; Tillman et al., 2009).
Defoliation is a widespread loss of leaves or
stripping of leaves on a plant, it is just all about leaf removal which could
be positive or negative; it could be for human or animal feed production. Page et al., (1980) found out that experimental defoliation of cassava
caused a significant reduction in the tuber yield and delayed the natural leaf
regeneration which occurred during the rainy seasons, following a dry season
during which cassava plants were normally defoliated (Toye-Afolabi, 1982).
Defoliation by Zonocerus variegatus
(Elegant Grasshoppers) led to high yield
losses page et al., (1980) as damages
to cassava have increased in recent time and threaten the livelihood of many
poor subsistence farmers.
Furthermore, Lockard et al. (1985) and Phengvichith et al. (2006), had tested the
effects of leaf harvesting at different level of frequencies on storage root
yields and thus reported a decrease in storage root yields as the harvesting
frequency increases regardless of the variety used. In communities where cassava
is grown in many African countries, the leaves are harvested for human and
livestock consumption. Cows, sheep and goats also routinely eat up the cassava
leaves in the farmer’s plots.
More so, diseases like cassava mosaic and
bacterial blight etc reduce the size of the leaves, thereby reducing the
photosynthetic leaf areas. African farmers recognize pests and diseases as
important cassava production constraints (Ndunguru et al., 2005) and many of these pests and diseases which pose
serious damage to the crop, affect the final yield (Lozano, 1975; Mtunda et al., 2003). The effects of these leaf
removal and distortion of the photosynthetic activities on the tuberisation and
yields of the crop have not been assessed; hence the overall aim of this study
was to examine the effects of NPK fertilizer application and leaf area
manipulation on the growth and yield of cassava.
1.2 OBJECTIVES OF THE STUDY
The specific objectives of this study were to:
i.
determine the effects of
defoliation on the performance (growth and root yield) of cassava;
ii.
evaluate the effects of
NPK fertilizer application on the crop;
iii. establish
if there is any interaction between the NPK fertilizer application and
defoliation on the growth and yield of the crop.
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