The sweet potato, native to tropical America, was brought back to Spain by Christopher Columbus in 1492 then introduced to African lands by the Portuguese. Today it is the third most important crop in seven eastern and central African countries, and fourth in 6 southern African countries. The highest consumer of sweet potato per capita is an ACP country, the Solomon Islands in the South Pacific .
Despite its appearance, the sweet potato is classified as a storage root unlike the potato which is a tuber. It is a trailing or climbing plant; its tubers, of varying colour (white to red through yellow and violet) depending on the variety, are rich in starch and sugar.
The sweet potato is cultivated in tropical and sub-tropical regions, but it is known as a highly tolerant crop as it tolerates high temperatures, poor soils, and floods, not forgetting its resistance to disease and pests. However, the sweet potato needs abundant sunshine and exposure to temperatures below 13°C for several days or 3°C for one day damage it. A perennial plant which is often treated like an annual, as a rule it does not incur many production costs, although it does require some work, particularly weeding in the early stages of development and gentle, and therefore labour-intensive, harvesting.
More often the sweet potato is associated with mixed productions thanks to its short cycle; its leaves can serve as a primary culture for soil coverage, countering erosion and enabling slower cultures to develop. Harvesting is a delicate manual task as any injury when pulling out causes skin damage; this allows fungus to colonise. In terms of conservation, it is more delicate than the potato, which has implications on its international commercialisation and explains its high level of autoconsumption: it must be conserved in a cool, dry environment.
Its consumption is threefold: human food, animal feed and the production of alcohol and starch. The sweet potato has a well defined place in African food security as a substitute food in the lean season. To a large extent it is valued for its tubers which are boiled, fried or roasted in an oven. But its leaves are also edible - unlike those of the potato which are toxic - and are rich in proteins, vitamins and various minerals. They can be eaten like spinach when they are not used as animal feed.
Finally, composed of simple starches as well as complex carbohydrates, the tubers can be used in the production of alcohol or starch which can make syrup if mixed with sugar. But overall, the potential of sweet potato remains largely unknown.
On a global level, producers of sweet potatoes are often poor. This food is strategic because it can enable them to combat shortages and provide coverage in the event of natural disasters.
According to the FAO, 115 countries produced 106,569,572 tons of sweet potato in 2010. However supply remains very concentrated, 82.3% of global production being in Asia. With 81,175,660 tons, China produces by far the largest part and possesses a little less than half the global acreage dedicated to the sweet potato (cf. infra Cultivated acreages 2009 table. Far behind, Indonesia is the 2nd Asian producing country and the 4th in the world with more than 2 million tonnes (Mt) of production. For example, in the Papua province in Indonesia, 90% of dishes contain sweet potato; it is also the staple food for pigs.
Far behind but ranked the second continent in the world, Africa contributes up to 14% of global production with more than 14.2 Mt. Contrary to the main producing countries which have seen their offer decline over the years, such as China, Indonesia, Brazil and the Philippines, some African countries have increased their production. Today, the most important is Uganda with a harvest that increased from around 2 million in 1999 to 2.83 Mt in 2010. The sweet potato is its 3rd most important agricultural product in terms of volume after the plantain and the cassava.
Nigeria (2.83 Mt) and Tanzania (1.4 Mt) follow, which, with Uganda, represent half the African supply. This expansion in production in Africa is explained by an increased demand linked to a strong demographic growth.
A minor player in the global sweet potato arena, Latin America produced 1.97 Mt in 2010, i.e. a little more that 2% of global supply: Brazil holds first place on the continent, followed by Cuba and Argentina. As for the United States, they produce relatively little (around 1,0 Mt in 2010) but are the leading global exporter. In Europe only Spain, Portugal and Italy produce sweet potatoes, albeit in very limited quantities on a global scale.
Table 1: World production of sweet potatoes (tons)
|| 1,400,000 |
|| 920,000 |
|Latin America, including:
|| 384,700 |
|North America, including:
|| 1,081,590 |
|Oceania, including :
|Papua New Guinea
Source : FAOSTAT, Février 2012
The sweet potato is still considered an exotic product in most countries throughout the world, particularly in western countries; it is still little known, not only because of difficulties relating to its commercialisation and conservation, but also due to limited investments that are made into it. The sweet potato is therefore above all autoconsumed in producing countries. Nonetheless, with globalisation and the impact of diasporas on consumption models, traded volumes have jumped the last few years, increasing by more than 54% between 2004 and 2009.
In 2009, of the 102 323 748 t of sweet potatoes produced throughout the world, only 188 794 t, barely 0.18%, were to be found on the global market. Less than 80 countries export it and only 13 of them represent 90% of global exports.
Table 2: World exports of sweet potatoes in 2009
| United States
|| 11,779 |
|| 9,056 |
|| 7,185 |
|| 2,618 |
Source : ITC 2011
It should be noted that 50% of global supply is destined for human consumption, 30% for animal feed (a demand rising sharply), with the remainder being used for seed and other agricultural aspects. Even though the United States represents less than 1% of global production and only exports 7.6% (67 194 t in 2009) of its national production (which is very modest compared with giants like China), it is the leading global exporter providing a third of available supplies on the international market. By way of comparison, China exports roughly 26 000 t, a fraction of the 76 Mt produced.
Since the 1980s, production in the United States has not varied much but consumption per capita has fallen, allowing for exports and in particular for purchases by the American Department of Agriculture (USDA) for its policy of international food aid . Between 2005 and 2009, American exports more than doubled in value reaching $ 51.4 million. The main part of demand for the North American sweet potato comes from Europe (which hardly knew this vegetable ten years ago), particularly the United Kingdom whose global imports increased from 7.5 Mt in 2005 to 20.4 Mt in 2009. Ireland has become particularly partial to it.
The European market discovered the sweet potato, no doubt under the influence of its diaspora, and the United States seized the opportunities which opened up to it in this emerging market. Something that Africa barely did, if at all.
The main customer of the American sweet potato is Canada (33 600 t), followed by the United Kingdom (27 000 t) and the Netherlands (3 600 t); its competitors on the European market are Israel, Egypt and South Africa. Both investments in research & development as well as quality standards benefit the American vegetable making competition difficult.
ACP countries hardly export at all. In 2010, only 14 461 t were exported, i.e. barely 8% of world volumes, from the Dominican Republic (8 247 t), Saint Vincent and the Grenadines (1 621 t) and from Jamaica (1 135 t). From the African continent, only South Africa (2 603 t), Ghana (419 t), Rwanda (167 t), Cameroon (69 t) and Madagascar (68 t) operate on the global market albeit with extremely low volumes.
Even though the sweet potato is easy to cultivate, it does not prove to be cost-effective in the African context. Labour costs are high, yields remain poor, while post-harvest losses and low purchase prices penalise production and deter investment. In Africa, sweet potato cultivation is primarily destined for family autoconsumption. The urban population still consumes this product relatively little.
Just like in South America, 90% of African production is destined for human consumption, unlike to China which uses 40% of its available harvest of sweet potatoes for animal feed which is in increased demand because the Chinese are eating more and more animal protein. In Africa, unlike to Asia, the sweet potato is minimally processed, apart from producing flour. However this processing would enable post-harvest losses to be reduced and generally resolve problems relating to conserving the product.
As for South Africa, it is self-sufficient: over the last ten years, its average consumption has amounted to 47 766 tonnes a year whilst its lowest production over the same 10-year period was 47 935 t in 2006 (a year of adverse weather conditions and a rise in production costs) and its highest was 62 688 t in 2009. Its exports vary according to its production levels. Its main market is Europe (Netherlands, United Kingdom, Portugal, France and Belgium) but it also dispatches volumes to the rest of Africa. Only 2 tonnes were destined for Singapore in 2009.
It should be noted that while South African sweet potatoes enter onto European and Canadian markets without paying any import duty, a duty of 45% is imposed in Korea, 40% in Portugal (2009) and Thailand, 12.8% on the Japanese market, 6% in the United States and 10% in Albania.
Aside from a fall of 3% in 2009, global imports increased from 2006 to 2010, from 156 988 t to some 245 000 t, an increase of 56% in 4 years. Of the 122 importing countries, 17 represent 90% of total purchases on the global market.
The biggest importer is currently European, the United Kingdom, with more than 39 000 t (of which 27 659 t from the United States, 4 179 t from Israel and 2 931 t from Honduras). Canada is in second place, almost exclusively supplied by its neighbour the United States, the leading global exporter. It should be noted that the United States also import, particularly from the Dominican Republic for 7 300 t and China for 2 800 t.
Then other European countries which have become partial to sweet potatoes follow, like Albania which imported 15 740 t almost entirely from Slovakia, Italy, the Netherlands and France. In Asia, Japan ranks fourth amongst importers, followed by Thailand, Singapore and Malaysia.
The importance of Europe as a destination for global exports is also explained by the fact that it is the highest paying market in the world. This has been particularly noted by South Africa which prefers to sell its sweet potatoes there to the detriment of supplying other neighbouring African markets, or even Asian .
Table 3: World imports of sweet potatoes in 2009
|Hong Kong (China)
Source : ITC 2011
Little more than 3 500 t were destined for ACP countries in 2010, i.e. less than 1.5% of global imports, highlighting once more the importance of autoconsumption of this staple food for rural populations but also the lack of stimulation in urban markets which are often inclined to import foodstuffs even if they are produced in their country. In Africa, importers remain modest with Botswana on top (around 600 t), Angola (one hundred or so tonnes), South Africa (some 60 t) and Zimbabwe (around 50 t).
The level of South African imports is strongly linked to variations in its own production. The largest purchases on the global market date back to 2008 when 310 t were imported from African countries, particularly Ghana, Gabon, and Nigeria but also from China, to meet the fall in production from 50 598 to 48 531 tonnes from 2007 to 2008.
Table 4: Index of wholesale U.S. price ($ / ton)
Source : US Dept. of labor, Bureau of Labor Statistics
Prices for fresh sweet potatoes respond to the law of supply and demand, as no price regulation mechanism exists and there is no international organisation that records their movements such as there is for cocoa, coffee and sugar, etc.
Prices can be monitored by referring in particular to the PPI (Production Price Index) in the United States which is based on wholesale trade prices. Since 2004, the PPI has fallen below $ 125 per tonne when it had been around the $ 80 mark between 1996 and 2002. 2003 remains an exceptional year as it was marked by a rise in prices following damage and losses caused by insects and pests.
In South Africa prices have been relatively steady throughout the period from 2000 to 2009, albeit with some significant fluctuations which are entirely down to market fundamentals. From 2005 prices rose continuously and steadily, from around 1200 rands per tonne reaching 2400 in 2009/10.
The sweet potato price index monitored in Africa for Ethiopia, Kenya or Uganda shows that between 2007 and 2009 prices increased, especially in Uganda where it almost tripled in 2 years.
CHALLENGES AND ISSUES
As in the majority of industries, most ACP countries, particularly in Africa, are not competitive at the industry or logistics level, nor in their research & development. To encourage the cultivation of the sweet potato, rural development and working conditions for women and farmers must be supported. And yet, more and more benefits are being discovered in the sweet potato by research and study.
If we compare a few producing countries, China has average yields of 21.5 t/ha and Indonesia 11.2t/ha, while Uganda is at 4.5t/ha, Nigeria at 2.9t/ha and Tanzania at 2t/ha. The potential of the sweet potato is underestimated and its use is often limited to a substitute food in ACP countries.
Table 5. Productivity of sweet potato
||Dry matter (kg / ha / day)
||Energy contribution (kcal thousands / ha / day)|
Source : Ewell & Kirby, 1990
The sweet potato has an often little known advantage in terms of productivity: comparing its dry matter and energy values with other agricultural products it has the highest values. Furthermore its protein content exceeds that of many other products.
• Nutritional Value
The sweet potato is rich in vitamin A, B and C and potassium. But in sub-Saharan Africa it is estimated that 32% of the population suffers from vitamin A deficiency which can lead, amongst others illnesses, to blindness. The sweet potato can therefore be a high value-added food staple particularly for children and pregnant women who are more often exposed to deficiencies.
• Research and development
The International Potato Centre (Centro Internacional de la Papa, CIP) in Lima, Peru, maintains the largest bank of sweet potato genes in the world; it includes thousands of wild, traditional and improved varieties. Research carried out at the beginning of the 20th century has shown that more than 100 industrial products could be produced from the sweet potato. But to date its implementation is still to be developed.
By way of example, large industrial groups like Toyota or Cargill & Dow are only at the planning stage of the industrial applications of research into the sweet potato, in particular the production of lactic or polylactic acid used in the manufacture of biodegradable plastics.
Studies have also shown that the sweet potato provides 2 to 3 times more carbohydrates than maize and could be an important source in the production of bioethanol. Carbohydrate levels in sweet potatoes are close to those of the sugar cane. It should also be noted that the sweet potato requires a lot less pesticide and fertiliser than maize. There are some who are seriously considering producing sweet potatoes for bioethanol on condition that there is enough for human and animal food.
A programme for improving the sweet potato has been implemented, crossing varieties obtained from the CIP and selected local varieties. In France, CIRAD has identified a hybrid, since called “Africa” by producers for whom it has been a great success; it is sold on urban African markets. It boasts a shorter production cycle of 12 to 16 weeks, a better yield with many roots and a very high resistance to disease (leaf and stem scab), a post-harvest shelf life of 4 weeks, a good appearance and very good taste which pleases consumers. Its high provitamin A content makes it all the more interesting.
"Les richesses du sol- Les plantes à racines et tubercules en Afrique : une contribution au développement des technologies de récolte et d’après-récolte", 2000, édité par A.Bell, O. Mück & B. Schuler
South Africa Department of Agriculture, forestry & fisheries, A profile of the South African sweet potato market value chain 2010
Les tubercules tropicaux comestibles et leur conservation, 1- La patate douce, Fruitrop n°11, Février 1995
Sweet potato in Ugandan Food Systems : Enhancing Food Security and Alleviating Poverty, CIP Program Report 1997-1998, G.J. Scott, J. Otieno, S.B. Ferris, A.K. Muganga, and L. Maldonado
« La production biologique de la patate douce », Cultures horticoles, janvier 2005, Katherine L. Adam, spécialiste en agriculture du NCAT
https://research.cip.cgiar.org/confluence/display/cipqnl/Sweetpotato, Q&N Lab (Quality and Nutrition Labratory), Centro Internacional de la Papa