THE EFFECT OF SOIL FERTILITY ON GROWTH AND YIELD OF
DIOSCOREA ROTUNDATA VARIETIES GROWN IN SOUTH EAST AGRO-ECOLOGICAL ZONE.
NJOGO IFEOMA E.
EBSU/2007/41808
A PROJECT SEMINAR/PROPOSAL SUBMITTED TO THE
DEPARTMENT OF CROP PRODUCTION AND LANDSCAPE MANAGEMENT, FACULTY OF AGRICULTURE
AND NATURAL RESOURCES MANAGEMENT, EBONYI STATE UNIVERSITY ABAKALIKI.
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
AWARD OF BACHELOR’S DEGREE IN AGRICULTURE (B.AGRIC)
CO-ORDINATOR: DR. ANIEKWE N.L.
SUPERVISOR: DR. H.O. OSELEBE
NOVEMBER, 2012
CHAPTER
ONE
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| fertile Soil |
INTRODUCTION
Dioscorea
rotundata
Prior(white yam) originated in Africa. It is grown in West Africa, including
countries such as Ivory Coast and Nigeria. It is widely spread and is one of
the major staple foods in many tropical countries (Omonigbo and Ikenemomeh,
2000). Dioscorea rotundata is the
most widely grown and preferred yam species. Their vines are cylindrical and thorny
and they twin anticlockwise (from right to left). The leaves are heart shaped,
while the tubers are thin, fresh and vary from cream to white colour. Dioscorea
rotundata is grown and cultivated for its energy rich tuber. It gives more calories
per unit of land area than most crops and matures within 7(seven) months. On soils
of average fertility, between 20 and 30 tonnes per hectare of tubers can be
obtained, and up to 55 tonnes per hectare on fertile soils, it also stores very
well. It is adaptable to fairly fertile soils and is suitable for intercropping
with grain legumes such as cowpeas, soybeans and a variety of leafy vegetables.
A well drained, rich, loamy soil is most favorable for growth of Dioscorea rotundata
with a warm, humid climate.
A
large number of white yam cultivars exist with differences in their production
and post-harvest characteristics. However, they have quite demanding labour
and maintenance requirements, such as hilling the soil around each plant to
form mounds, to ensure a pulverized soil favourable for tuber development.
Storage of tubers occurs after harvest in barns or heaps covered with grass.
In
Nigeria Dioscorea rotundata are
processed into various food forms. This includes pounded yam, boiled yam,
roasted or grilled yam, fried yam slices and yam balls, mashed yam, yam chips
and flakes. Another method of consumption is to leave the raw yam pieces to dry
in the sun., These are then milled to create a brown powder known in Nigeria as
elubo. The powder can be mixed with boiling water to create a thick starchy
paste, which is the favourite for the Yoruba where the reconstituted food is
known as “amala”. Yam is an excellent
source of carbohydrate, energy and some minerals (Ward low et al, 2002). Yams
are also sources of steroids and alkaloids-chemicals that are extremely active
physiologically in vertebrate animals. The most important yam steroid is
diosegenin that is used in the production of birth control pills. Alkaloids
from yams have been used to fill fish and to poison darts arrows for hunting.
Some yams are poisonous to humans because of their high alkaloid content, and
their tubers must be boiled before eating to remove the toxins (Degras et al,
1993). It is also used as raw material for industrial products such as starch
and alcohol (Bradshaw 2010).
The
major problems facing yam production inlude high labour requirement, low yield
per hectare compared to crops such as cassava or sweet potato, relatively large
amount of planting material required and long growing season. By far the most
critical of these problems is labor requirement, which exceeds that of other
comparable crops. For these reasons and problem of storage of harvested yams,
the cost of yam production is high making the crop to slowly lose ground to
cassava. It has been estimated that the cost per 1,000 calories of yam is four
(4) times greater than those of cassava (reference). But, despite these high
cost, the nutritional value of yam is sufficiently high to justify further work
into its general improvement.
The
supply and availability of fertilizer to boost yam production in Nigeria have
inadequate. In addition there were reports that yams grown with fertilizer
application were more susceptible to pathological deterioration during storage
than those grown without fertilizer (reference). In survey of yam storage
practices carried out in southeast Nigeria, it was reported that yam tubers
grown with organic manure had longer shelf life than those treated with
chemical fertilizer in the field. It also reported that rotting incidence
during storage appeared less where no fertilizer or organic manure was applied
evidently due to high native fertility of the soil (Orkwor and Ugwu, 2006).
Moreover, there are indications that our soils are becoming marginal and many
smallholder farmers may not have the fund to purchase the fertilizers for
application in their farms.
Objective of the
Study
The
objective of this study was therefore to
a)
study
the morphological characteristics of the Dioscorea
rotundata varieties used in the study
b)
determine
the effect of soil fertility on growth characteristics of Dioscorea rotundata varieties grown in southeast agro-ecological
zone.
c)
determine
the effect of soil fertility on yield of
Dioscorea rotundata varieties studied
d)
identify
possible incidence of pests and diseases on the yam varieties in the field
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