ABSTRACT
Three field experiments each in two cropping seasons were conducted at the National Root Crops Research Institute (NRCRI), Umudike in southeastern Nigeria, between 2016 and 2017. The objectives of the study were to determine the effect of sett size and spacing on the growth and yield of Yandu white yam (Dioscorea rotundata) cultivar; to determine the effect of stake height and NPK fertilizer levels on Yandu white yam (Dioscorea rotundata) cultivar and to determine the effect of stake height and NPK (15:15:15) fertilizer on growth and yield of trifoliate yam (Dioscorea dumentorum). The three experiments were each laid out as factorial in randomized complete block design (RCBD). For each experiment, replication was thrice. Results showed that the wider spacing of 1x1m increased vine length at 3MAP in 2017 while the closer spacings of 1 x 0.25m and 1 x 0.5m increased leaf area index, tuber weight and tuber yield of the Yandu white yam cultivar mini-setts on average. The smaller 35 and 45g setts increased vine length while the larger 55 and 65g setts increased photosynthetic efficiency. The smaller 35g sett had the highest tuber yield (12.9t/ha), although the larger 55g setts gave similar results (13.1t/ha). Stakes of 2m or 3m height enhanced Yandu white yam cultivar vine length, leaf area index, photosynthetic efficiency and tuber weight on average. As mean across two seasons, staking did not significantly affect tuber yield, despite the higher yield with no staking in 2017. NPK fertilizer application did not significantly influence vine length, leaf area index, photosynthetic efficiency, tuber weight and tuber yield, but application of 200kg/ha NPK increased number of tubers per plant in 2017. NPK fertilizer did not influence trifoliate yam leaf area index, photosynthetic efficiency and tuber weight but application of a higher fertilizer rate of 450 or 600kg/ha increased vine length at 3 MAP in 2017 while 300kg/ha NPK increased number of tubers per plant in 2016. On average, application of the lower NPK fertilizer of 150kg/ha produced optimum tuber yield. The use of 1m stake increased trifoliate yam vine length but staking had no effect on leaf area index, photosynthetic efficiency, number of tubers per plant, tuber weight and tuber yield.
TABLE OF CONTENTS
Title Page
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of contents vii
List of Tables xiii
List of appendices xvi
Abstract xvii
CHAPTER 1: INTRODUCTION
CHAPTER 2: LITERATURE REVIEW
2.1 Effect of Sett Size on Yam 5
2.2 Effect of Plant Spacing on Yam 6
2.3 Effect of
NPK Fertilizer on Yam 8
2.4 Effect of Staking on Yam 9
CHAPTER 3: MATERIALS AND METHODS
3.1 Location of Study Area 11
3.2 Planting Materials 11
3.3 Experiment 1: Effect of Sett-Size and
Spacing on the Growth and Yield of
Yandu White Yam (Dioscorea rotundata) Cultivar 11
3.3.1 Field preparation and soil sampling 11
3.3.2 Experimental design, treatments and
treatment allocation 12
3.3.3 Planting and field maintenance 13
3.3.4 Records of agronomic measurements 13
3.3.5 Statistical model and analysis 15
3.4 Experiment
2: Effect of Stake Lengths and NPK Fertilizer Levels on
Yandu White Yam (Dioscorea rotundata) Cultivar 16
3.4.1 Field preparation and soil sampling 16
3.4.2 Experimental design, treatments and
treatment allocation 16
3.4.3 Planting and field maintenance 17
3.4.4 Records of agronomic measurements 17
3.4.5 Statistical model and analysis 18
3.5 Experiment
3: Effect of Stake Length and NPK (15:15:15) Fertilizer on
Growth and Yield of Trifoliate Yam (Dioscorea
dumentorum) 19
3.5.1 Field preparation and soil sampling 19
3.5.2 Experimental design, treatments and
treatment allocation 19
3.5.3 Planting and field maintenance 20
3.5.4 Records of agronomic measurements 20
3.5.5 Statistical model and analysis 20
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Soil and Meteorological Data 22
4.1.1 Experiment 1: Effect of sett-size and
spacing on the growth and yield of
yandu white yam (Dioscorea rotundata) cultivar 25
4.1.2 Crop growth characteristics 25
4.1.3 Yield and yield components 31
4.1.4 Discussion 37
4.2 Experiment 2: Response of White Yam (Dioscorea rotundata) to Stake
Length
and NPK Fertilizer Levels 39
4.2.1 Results 39
4.2.2 Effect on crop growth characteristics 39
4.2.3 Effect on yield and yield components 46
4.2.4 Discussion 51
4.3 Experiment 3: Response of Growth and
Yield of Trifoliate Yam
(Dioscorea
dumentorum) to Different Stake Length and
Inorganic Fertilizer in the Ultisol of
South-eastern Nigeria 53
4.3.1 Results 53
4.3.2 Crop growth characteristics 53
4.3.3 Yield and yield components 59
4.3.4 Discussion 64
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS 66
References 68
Appendices 75
LIST OF TABLES
Table Page
4.1 Physico-chemical properties of soil at
study site 23
4.2 Meteorological data of National Root
Crops Research Institute Umudike
during
the period of study 24
4.3 Effect of plant spacing on vine length
(cm) of yandu white yam cultivar
at
different sampling dates 26
4.4 Effect of sett-weight on vine length (cm)
of yandu white yam cultivar
at different sampling dates 27
4.5 Effect of plant spacing on leaf area
index of yandu white yam cultivar
at
different sampling dates 28
4.6 Effect of sett weight on leaf area index
of yandu white yam cultivar at
different
sampling dates 29
4.7 Effect of sett-size and spacing on
photosynthetic efficiency (mj/m) of
yandu
white yam cultivar in 2016 and 2017 30
4.8 Effect of sett-size and spacing on the
number of tubers per plant of yandu
white
yam cultivar in 2016 and 2017 32
4.9 Effect of sett-size and spacing on the
number of tuber weight (kg) of yandu
white
yam cultivar in 2016 and 2017 33
4.10 Effect of sett-size and spacing on tuber
yield (t/ha) of yandu white yam
cultivar
in 2016 and 2017 34
4.11 Effect of sett-size and spacing on the mean
tuber yield (t/ha) of yandu white
yam
cultivar (2016 and 2017) 36
4.12 Effect of stake height on vine length (cm)
of yandu white yam cultivar
at
different sampling dates 40
4.13 Effect of
NPK fertilizer on vine length (cm) of yandu white yam cultivar
at
different sampling dates 41
4.14 Effect of stake heights on leaf area index
of yandu white yam cultivar
at
different sampling dates 42
4.15 Effect of NPK fertilizer on leaf area index
of yandu white yam cultivar
at
different sampling dates 43
4.16 Effect of NPK fertilizer and stake heights
on photosynthetic efficiency (mj/m)
of
yandu white yam cultivar in 2016 and 2017 45
4.17 Effect of NPK fertilizer and stake height
on number of tubers per plant
of yandu white yam cultivar in 2016 and 2017 47
4.18 Effect of NPK fertilizer and stake height
on tuber weight (kg) of yandu
white
yam cultivar in 2016 and 2017 48
4.19 Effect of NPK fertilizer and stake height
on tuber yield (t/ha) of yandu
white
yam cultivar in 2016 and 2017 49
4.20 Effect of NPK fertilizer and stake height
on mean tuber yield (t/ha) of
yandu
white yam cultivar (2016 and 2017) 50
4.21 Effect of NPK fertilizer on vine length
(cm) of trifoliate yam ona-ohuru at
different
sampling dates 54
4.22 Effect of stake height on vine length (cm)
of trifoliate yam cultivar ona-ohuru
at
different sampling dates 55
4.23 Effect of NPK fertilizer on leaf area index
of trifoliate yam cultivar ona-ohuru
at
different sampling dates 56
4.24 Effect of stake height on leaf area index
of trifoliate yam cultivar ona-ohuru
at
different sampling dates 57
4.25 Effect of NPK fertilizer and stake height
on photosynthetic efficiency (mj/m)
of trifoliate yam
ona-ohuru in 2016 and 2017 58
4.26 Effect of NPK fertilizer and stake height
on number of tubers per plant of
trifoliate yam ona-ohuru in 2016 and 2017 60
4.27 Effect of NPK fertilizer and stake height
on tuber weight (kg) of trifoliate
yam
cultivar ona-ohuru 61
4.28 Effect of NPK fertilizer and stake height
on the tuber yield (t/ha) of trifoliate
yam
cultivar ona-ohuru in 2016 and 2017 62
4.29 Effect of NPK fertilizer and stake height
on mean tuber yield of trifoliate yam
cultivar
ona-ohuru in 2016 and 2017 63
LIST OF APPENDICES
Appendix Page
1: Analysis of
variance for the mean yield of yandu white yam
cultivar in 2016 and 2017 75
2: Analysis of
variance for tuber number per plant of yandu white yam
cultivar in 2016 76
3: Analysis of
variance for tuber number per plant of yandu white yam
cultivar in 2017 77
4: Analysis of
variance for tuber weight (kg) per plant of yandu white
yam cultivar in 2016 78
5: Analysis of
variance for tuber weight (kg) per plant of yandu white
yam cultivar in 2017 79
6: Analysis of
variance for tuber yield (t/ha) of yandu
white yam
cultivar in 2016 80
7: Analysis of
variance for tuber yield (t/ha) of yandu
white yam
cultivar in 2017 81
8: Analysis of
variance for tuber mean yield of yandu
white yam
cultivar in 2016 and 2017 82
9: Analysis of
variance for tuber number per plant of
yandu white yam
cultivar in 2016 83
10: Analysis of
variance for tuber number per plant of
yandu white yam
cultivar in 2017 84
11: Analysis of
variance for tuber weight (kg) per plant
of yandu white yam
cultivar in 2016 85
12: Analysis of
variance for tuber weight (kg) per plant
of yandu white yam
cultivar in 2017 86
13: Analysis of
variance for tuber yield (t/ha) of yandu white yam
cultivar in 2016 87
14: Analysis of
variance for tuber yield (t/ha) of yandu
white yam
cultivar in 2017 88
15: Analysis of
variance for mean yield of trifoliate yam
ona-ohuru in
2016 and 2017 89
16: Analysis of
variance for number of tuber of trifoliate yam
ona-ohuru in 2016 90
17: Analysis of variance
for number of tuber of trifoliate yam
ona-ohuru in 2017 91
18: Analysis of
variance for tuber weight (kg) of
trifoliate yam
ona-ohuru in 2016 92
19: Analysis of
variance for tuber weight (kg) of
trifoliate yam
ona-ohuru in 2017 93
20: Analysis of
variance for tuber yield (t/ha) of
trifoliate yam
ona-ohuru in 2016 94
21: Analysis of
variance for tuber yield (t/ha) of
trifoliate yam
ona-ohuru in 2017 95
CHAPTER 1
INTRODUCTION
Yam (Dioscorea species) is an important tuber crop belongs to the family
Dioscoreaceae. The species of economic importance are Dioscorea rotundata, Dioscorea alata, Dioscorea cayenensis, Dioscorea
dumetorum, Dioscorea bulbifera and Dioscorea
esculenta (Aighewi, 2014). The most widely cultivated species in West
Africa is Dioscorea rotundata, which
is also referred to as white yam or white guinea yam. Yam is the most important
food and income source for millions of producers, processors and consumers in
West Africa. In 2012, world production of yam was estimated at 58.7 million
tons, with West Africa producing more than 92% (FAOSTAT, 2014). Both Nigeria
and Ghana are reported to have produced about 66% of the world's yam supply. In
West Africa, the five major yam producing countries are Benin, Cote d'lvoire,
Ghana, Nigeria and Togo; accounting for 93% of world production. Nigeria alone
is reported to account for 68% of global production (36 million tons on 3
million hectares). Yam plays an important role in the provision of cash and
dietary carbohydrate to millions of people.
Besides, being a major source
of carbonhydratre, the crop also contributes to protein in the diet, ranking
third as the most important source of supply (Ekanayake and Asiedu, 2003; IITA,
2013). Yam stores better than most other tropical root and tuber crops because
the tubers have an prolonged period of dormancy during which physiological
activities are greatly reduced. Yam therefore, serves as an important food
security crop, with 31.8% of the population in Nigeria and 26.2 % in Ghana
depending on yams for food and income security. Yam tuber is normally prepared
for consumption in a variety of ways which include boiling, frying, baking,
processing into flour or “amala”, processing into pounded yam and processing
into pottage (Orkwor and Ekanayake, 1998).
Like other yams, trifoliate
yams (Dioscorea dumentorum) is an
important food crop in Nigeria and is grown by poor resource farmers who
intercrop it with maize, vegetables, cassava, okra and cowpea. It features
prominently in the diet and farming systems in south eastern agro-ecological
zone of Nigeria, especially Abia State. Onyekwere et al., (2012) reported that trifoliate yam is high in protein,
minerals and vitamins contents and is superior to other commonly consumed yams.
Research has shown that it has crude protein contents of 11.07%, fibre content
of 2.06% and total carotenoid content of 217.73µg/100g, and is a good source of
carbohydrate like other yam varieties. It is also recommended for diabetics
(Ezeocha et al., 2010). Presently,
the cultivation of this medicinal yam has been on the decrease as a result of
factors like soil fertility decline.
In traditional systems, most
farmers do not apply fertilizer to yam, but the crop is planted immediately
after a fallow so that it benefits from the organic matter accumulated during
the fallow period. Because of their high nutrient demands, yams are planted as
the first crop on cleared land or after fallow periods (Ekanayake and Asiedu,
2003). However, the degradation of soils has been aggravated by continuous
cropping and shortened fallow period due to high population density that has
put considerable pressure on farmlands in Nigeria. This has necessitated
fertilization which needs to be used rationally in order to avoid negative
ecological impact and undesirable effects on the sustainability of agricultural
production systems. In order to determine the amount of fertilizer to be
applied to crops, it is important to develop recommendation programmes. Irizarry et al (2015) reported that yams respond well to fertilizer
application under varying agronomic conditions. Consequently, they extract
large quantities of nutrients from the soil. For example, a yam yield of 29
t/ha removed 133kg N, 10kg P and 85 kg K from the soil (Sobulo, 1972). Where
there is need for fertilizer application, NPK (15:15:15) compound fertilizer is
recommended at the rate of 400-500 kg/ha applied at 8-12 WAP in bands on both
sides of the ridges for single and double rows plantings (Eke-Okoro et al, 2006). However, Okpara et aI, (2014) have shown that fertilizer
needs of yam may depend on the technology used to generate planting materials
and plant population density, among other factors.
Most yam genotypes, in most
production environments, yield better when the vines are provided with support
than when they are not (Ekanayake and Asiedu, 2003). Staking appears to perform
functions such as increase in light interception of the leaf canopy and
increase in ventilation around the leaves. Ventilation is particularly
important in humid environments where high humidity in the canopy can increase
the incidence of fungal leaf diseases, especially anthracnose. Staking also
facilitates weeding, especially with thorny varieties (King and Risimeri,
1992). Obiazi (1995) reported that the average Nigerian farmer spends 60
person-days per ha in procuring and installing stakes. The reliance of yam
genotypes on staking may be due to their strength of apical dominance and the
tendency to branch. Those that are slow to initiate branches may develop well
on tall stakes, where the vital early growth of the vine is uninterrupted.
Those with less apical dominance and greater branchiness may be less assisted
by staking. The system of staking depends on local conditions and available
materials. A typical method is to provide one vertical stake per stand.
Frequently, where stakes are less available, one stake may be provided for 2-6
stands. The benefit of very tall stakes appears to depend on the yield
potential of individual plants (Okigbo, 1973). The agro ecology in which yam is
cultivated is also important in terms of staking requirements of the crop as
well as the availability of staking materials. In a humid climate like south
eastern Nigeria, where clouds can greatly limit the number of hours of
sunshine, staking improves photosynthesis of plants, prevents foliar diseases
and allows the cultivation of interim crops (Ekanayake and Asiedu, 2003).
However, the staking height may depend on the species or cultivars, the
planting materials and the environment.
The objectives of this study therefore, were:
1. To
examine the effect of sett-size and spacing on Yandu white yam (Dioscorea rotundata)cultivar in the ultisol
of south eastern Nigeria.
2. To
evaluate the effect of stake height and NPK (15:15:15) fertilizer on growth and
yield of Yandu white yam (Dioscorea
rotundata) cultivar in an ultisol of south eastern Nigeria.
3. To determine the
effect of stake height and NPK (15:15:15) fertilizer on the growth and yield of
trifoliate yam (Dioscorea dumentorum)
in the ultisol of south eastern Nigeria
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