ABSTRACT
Two field experiments were conducted to study the responses of five white yam cultivars to three harvesting dates during June 2016 and June 2017 cropping seasons in a tropical ultisol of south eastern Nigeria. The experiment was a 5 x 3 factorial arrangement laid out in a randomized complete block design (R C B D) with five replications. Treatments comprised all possible combinations of five white yam cultivars (Adaka, Ame, Amula, Hembamkwase, and Yandu) and three harvest dates (8, 16, and 24 weeks after planting). Cultivar did not significantly (P ≥ 0.05) affect percent establishment, vine length, total leaf area, tuber bulking, number of tubers per plant, tuber weight and tuber yield, but Hembamkwase had thicker vines than Amula and Adaka. Increasing the harvesting date from 8weeks after planting to 24weeks after planting increased significantly (P ≤ 0.05) tuber bulking, number of tubers per plant, tuber weight and tuber yield. Tuber yield at 24 weeks after planting, which produced the highest yield was higher than the yield at 8 and 24 weeks after planting by 356% and 136%, respectively on average. Based on this results, early planting is recommended to ensure the crop goes through a growing season of about 8 to 10 months that would allow for ample vegetative growth and the manifestation of the full genetic potentials of the cultivars.
TABLE OF
CONTENTS
Title Page i
Certification ii
Declaration iii
Dedication iv
Acknowledgement v
Table of
contents vi
List of
tables’ ix
Abstract x
CHAPTER 1: INTRODUCTION
1.1 Objective of the study 1
CHAPTER 2: LITERATURE REVIEW
2.1 Effect
of cultivars on yam 3
2.2 Effect
of harvest dates on Yam
3
CHAPTER 3: MATERIALS AND METHODS
3.1 Study
location
9
3.2 Planting
materials
9
3.3 Field
preparation
9
3.4 Soil
sampling
10
3.4.1 Particle
size
10
3.4.2 Soil
pH
10
3.4.3 Organic
carbon
11
3.4.4 Available phosphorus
11
3.4.5 Total Nitrogen
11
3.4.6 Potassium
11
3.5 Experimental
design, treatment and treatment allocation 11
3.6 Planting
and field maintenance
12
3.7 Data
collection
12
3.8 Statistical
model and analysis
12
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Soil Meteorological
Data 14
4.2 Crop
growth
14
4.6 Tuber bulking rate
21
4.7 Yield and yield components 22
CHAPTER 5: CONCLUSIONS AND
RECOMMENDATIONS
5.1 Conclusion
28
5.2 Recommendation
28
References
30
LIST OF TABLES
Table
Title Page
4.1 Soil
physic-chemical properties of the experimental site in 2016 and 2017
cropping seasons
15
4.2 Agro-meteorological
data of the experimental site in 2016 and 2017 cropping
seasons 16
4.3 Percent
establishment (at 1 month after planting) of five white yam cultivars in
2016 and 2017
cropping seasons
17
4.4 Vine girth and vine
length (cm) of five white yam cultivars in 2016 2017
cropping seasons
19
4.5 Number of
leaves/plant and total leaf area (cm2) of five white yam cultivars
at 4 and 8 WAP
in 2016 and 2017 cropping seasons 20
4.6 Effect of white
yam cultivar and harvesting date on tuber bulking rate (g/week)
in 2016 and 2017
cropping seasons
21
4.7 Effect of white
yam cultivar and harvesting date on number of tubers/plant in
2016 and 2017
cropping seasons
23
4.8 Effect of white
yam cultivar and harvesting date on tuber weight (kg/plant) in
2016 and 2017
cropping seasons
24
4.9 Effect of white
yam cultivar and harvesting date on tuber yield in 2016 and
2017 cropping
seasons
25
CHAPTER 1
INTRODUCTION
Yam (Dioscorea spp) is an important crop for food, medicine, income and
socio-cultural events. They are leading source of calories for over 300 million
people in the tropics and subtropics (Degras, 1993). The crop is grown in
Africa, Asia, parts of South America, as well as the Carribbean and the South
Pacific islands. In West Africa, about 48 million tons of yams are produced
annually on 4 million hectares of arable land (Degras, 1993). Out of the more
than 600 species, only 10 species are generally cultivated as food. D. alata, D. rotundata, D. cayenensis, D.
bulbifera, D. esculenta, D. opposite japonica, D. mummularia, D. pentaphylla,
D. transversa and D. trifida (Lebot,
2009). D. rotundata and D. cayenensis (together also referred to
as D. cayenensis rotundata complex)
are indigenous to Africa, and represent most global yam production. Food yams
are believed to have originated in the tropical areas of three separate
continents namely, Africa, South East Asia and South America (Orkwor, 1998). It
plays an important role in diet, economic welfare and socio-cultural traditions
of people in Africa, the Caribbean and Pacific countries.
In most yam producing countries, the production of yams has been on
the increase with respect to food security and nutritional diversification,
provision of employment and incomes, as well as alleviation of rural poverty (Baud
ion and Lutaladio, 1998). Orkwor and Ekanayake (1998) reported that, in
Nigeria, yams could constitute up to 32% of gross income derived from annual
cropping. The yam tuber is a good source of energy mainly from the carbohydrate
content since it is low in fat and protein. Yams are processed into various food
forms in Nigeria and the forms include pounded yam, boiled yam, roasted or
fried yam slices, yam chips, and yam flour.
One of the major constraints responsible for low productivity of
some tuber crops is the lack of knowledge of suitable time of harvest especially
with the introduction of new cultivars (Anioke, 1996) The time of harvesting
yam is not usually considered critical when the crop is planted early, as
harvesting in the traditional system is normally scheduled at 8 or more months
after planting. In a cropping sequence in which yam is followed by another rain
fed crop without an intervening fallow, the time of harvesting should be
necessarily adjusted to accommodate the following crop during the conventional
growing season. Besides, some farmers may not plant yam early in the cropping
season while those who plant the crop early, harvest early during the period of
milking at about 5 or 6 months after planting. In white yam, tuber initiation
occurs at about 8 to 10 weeks after sprouting (Okezie et al., 1981) while in cassava CIAT, (1973) reported that the
number of roots with capacity to thicken (storage roots) is fixed within the
first 3 months and that increases in root dry matter produced rapidly up to 8
months after planting and thereafter slowly for the rest of the rest of the growth
period. If the yam tubers are immature, they tend to be very watery and have a
poor waste taste and if they are left in the ground for too long, they are
exposed to factors which can cause deterioration in quality (Lebot, 2009).
There is very limited research information on the yield of white yam
cultivars harvested at different growth periods. Hence, this study was
undertaken to evaluate the response of some white yam cultivars to different
harvesting dates.
1.1
RESEARCH OBJECTIVES
The objectives of this study were to:
1. determine the effect
of harvest date on yield components of white yam
2. evaluate some white
yam cultivars for growth and yield
3. examine the effect
of three harvest dates and five cultivars on the yield components of white yam.
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