Agriculture Reference
In-Depth Information
18
Tropical Root Crops
Debbie Rees, Andrew Westby, Keith Tomlins, Quirien van Oirschot,
Muhammad U. A. Cheema, Eric Cornelius and Muhammad Amjad
INTRODUCTION
Root and tuber crops provide the dietary base for 500-700
million people in the world. FAO statistics indicate that
root and tuber crops are particularly important in the
tropical countries of the world (Lancaster & Coursey
1984). Cassava (
Manihot esculenta
Crantz), sweet potato
(
Ipomoea batatas
(L.) Lam) and yam (
Dioscorea
spp.) are
the major tropical root crops grown in developing countries
and will be the main focus of this chapter. They play a vital
role in the food security and economies of many countries,
and their importance to poor people makes them key
targets for making an impact on poverty world-wide. There
is, however, a wide range of lesser known root and tuber
crops, many of which are of key importance to populations
in specific regions. Some of these crops are listed in
Table 18.1. Organisations such as the Global Facilitation
Unit for Underutilized Species (www.underutilized-species.
org) and the International Centre for Underutilised Crops
(www.icuc-iwmi.org) work to maintain genetic diversity
and therefore to preserve these crops.
World production data estimates for 2005 (FAOSTAT
2006) for the major root crops are shown in Table 18.2. Some
of the main points to note are the importance of cassava,
particularly in Sub-Saharan Africa (54% of world produc-
tion), China's dominance of sweet potato production (83%
of world production) and the importance of yam in Africa
(97% of world production), particularly in Nigeria (68% of
world production). The figures may even underestimate
the importance of cassava; Cock (1985) estimated that
cassava was a staple food crop for 500 million people in 24
countries. In the Democratic Republic of Congo, the
Republic of Congo, Central African Republic, Mozambique
and Angola cassava provides over one third of the calories in
the diet (FAO 1990). Cassava takes on an importance of its
own in times of civil unrest and war when it remains available
while other crops have to be abandoned.
Root crops have become so important in tropical
developing countries because of their agronomic advantages
and limited requirement for inputs. For example, cassava
gives a high yield of carbohydrates even on poor soils, has
good tolerance to drought, is relatively resistant to pest
infestation and disease and can be stored in the ground until
required. Sweet potato produces the highest quantity of
energy per hectare per day of any of the major tropical crops
(194 MJ/ha/day compared to 149 for rice, 145 for maize and
101 for sorghum) (Woolfe 1992). Yams need more
agricultural inputs than the other root crops (for example, in
terms of labour requirements; 45 working days/tonne of
yam, in comparison to 21 for cassava, 121 for maize and
145 for rice). Nevertheless yams are an important source of
household income and they have great cultural significance,
especially in West Africa (Coursey 1967).
These crops also have a role in world trade and in
developed countries. The international trade in fresh
cassava is small but growing with the movement of
populations from Latin America, the Caribbean and Africa
