INTERNATIONAL POTATO CENTER: WORLD SWEETPOTATO ATLAS
CHINA
HISTORY AND OVERVIEW
When times are good, pigs eat sweetpotato. When times are not so good, we all eat sweetpotato.
--Danying Yi
Sweetpotato, Ipomoea batatas, was widely grown in tropical America when Columbus took several roots with him on his return to Spain from his first voyage in 1492, eighty years before the potato reached Europe (Purseglove 1968, p. 81). From Europe, sweetpotato was carried, initially by Portuguese mariners, to ports throughout Africa and Asia, and had apparently entered China by the 1560s. Sweetpotato cultivation is noted in the Dalifuzhi (Dali Prefecture Gazetteer) written by Li Yuanyang in 1563 and in the Yunnan Tongzhi (Yunnan Gazetteer) written in 1574 (Gitomer 1987, p. 1).
However, this dispersal, the "batata line," was not the only means by which sweetpotato was introduced to the Asia Pacific region. A separate "camote line" (from the Nahuatl word comotli ) was transferred directly from Mexico via Spanish galleons to the Philippines (Zhang et. al. 2004, p. 116). From the Philippines, sweetpotato could well have been introduced to China via the coastal Fujian province, as supported by a document dating around 1650, Minxiaoji (Fujian Remembrances) by Zhou Lianggong. A more colorful account of a transfer via the Philippines was provided by Lu Binglin, who wrote that sweetpotatoes were introduced after a typhoon in 1594 when the provincial inspector general, named Jin, presented sweetpotato as a famine relief crop. To honor Inspector General Jin, people called the crop jinshu ("golden potatoes"), although the term might have simply conveyed the sentiment that growing sweetpotato is like growing gold (Gitomer 1987, p. 1). Another term for sweetpotato in the south is fan shui ("foreign potato"), again suggesting recent arrival via foreigners (Danying Yi, personal communication).
Although sweetpotato cultivation is derived mostly from these relatively recent introductions, sweetpotato has been present in the Asian Oceanic region for centuries, as indicated for example by carbonized roots found in northern New Zealand dating back approximately 1,000 years (Yen 1982, cited in Zhang et. al. 2004, p. 116). Whether the transfer from tropical America occurred via natural dispersal or by human voyagers has remained a point of speculation for several decades (Purseglove 1968, pp. 79-81). Research by Zhang et. al. (2004) compared genetic associations among seventy-five sweetpotato landraces drawn from the Asia Pacific region, as well as Andean America (Peru and Ecuador) and Mesoamerica (Mexico). That research demonstrated a relatively weak association between sweetpotatoes from the Asia Pacific region and those of Andean America, suggesting a transfer from Mesoamerica prior to introductions via European exploration.
Another variety of sweetpotato, locally called ganshu, has been cultivated on a limited scale in southern China since well before the European dispersal. It is characterized by one large tuberous root and numerous secondary roots, while varieties introduced via Europe have no obvious large root (Gitomer 1987, p. 2). It is possible that sweetpotato cultivation in southern China persisted for several centuries as a marginal crop and remained locally confined due to the physical isolation of the region, before Europeans introduced the crop more widely via the Chinese coast.
Whatever the circumstances and routes of the sweetpotato's introduction and subsequent travels, over the past several centuries the crop has become vital to the food security of China. Production in China has remained stable over the past few decades due to higher average yields compensating for a reduction in cultivated area. The sweetpotato crop of China accounts for an estimated 82 percent of total world production (FAOSTAT), although the role of sweetpotato has undergone a dramatic shift with economic developments and policy reforms since the late 1970s. As personal incomes in China have increased, sweetpotato and course grains, such as maize and barley, are being replaced as a source of direct human nutrition by higher consumption of wheat in the north and rice in the south. Roughly half of the sweetpotato crop of China was utilized as a food staple in the 1970s, a proportion which had declined to less than 15 percent by the end of the 1990s, as most of the crop was being utilized for animal feed (primarily for pigs) and industrial purposes (Huang et. al. 2003).
Assuming that China sustains rapid economic growth (even if less rapid than the pace of the early twenty-first century), higher incomes will place greater demands on food production, especially in the form of animal feed for meat and other animal products. The share of total staple crop production used for animal feed is projected to increase from approximately 25 percent in the mid 1990s to 45 percent by 2020 (Huang et. al. 1999, cited in Huang et. al. 2003, p. 1). The prospects of the sweetpotato crop depend largely on economic and technological developments.
- For a chart of China's sweetpotato production over the past several decades, please see Production Charts.
GEOGRAPHY AND PRODUCTION ZONES
Although China's immense size and ecological diversity challenge any attempt at general description, for the sake of sweetpotato cultivation, the country can be divided into five regions, or agroecological zones. With seasonal variations, sweetpotato can be grown widely in China, wherever frost-free conditions persist for at least four months, rainfall is well distributed (or irrigation is readily available), sunshine is abundant (Purseglove 1968, p. 82), and day to night temperature differences are fairly high (Gitomer 1987). Those regions are briefly described below (Wang et. al. 1984, cited in Gitomer 1987, unless cited otherwise).
- Several maps of more specific classifications — for example by soil types, agro-ecological zones, and land use — are available from the European Digital Archive of Soil Maps, China. Most images are digitized from paper maps, of variable clarity.
- A map of sweetpotato distribution in China is included on the Maps Page.
Northern (Spring Crop)
This region includes Liaoning, Jilin, Beijing, south and central Heilongjiang, northern Hebai and Shaanxi, southern Shanxi and Ningxia, and southeastern Gansu. It is possible to grow sweetpotato as far north as approximately 45º N, although the short growing season (typically 130 to 140 days) limits production to one crop, planted in middle or late May and harvested in late September or early October. Given this constraint, some areas are well suited to sweetpotato cultivation, with maximum temperatures above 20º C for about three months, adequate summer rain, and high solar radiation. Seedling beds heated with plastic sheeting are sometimes used to allow for earlier planting. Overall, however, sweetpotato is a minor crop in this region.
Huang-Huai Basin (Spring and Summer Crops)
The northern border of this region is defined by mountains, extending along the southern face of the Qinling Mountains, then the eastern face of the Taihang Mountains to a line bisecting Baoding, Tianjin, and Luda. The southern boundary crosses Henan Province and is then defined by the Huai River to the North Jiangsu Central Irrigation Canal. The predominate climate is temperate and semi-humid with many dry sunny days and significant day and night temperature differences, all well suited to sweetpotato. Sweetpotato cultivation, and agriculture in general, has benefited from control of the Huang and Huai river basins, primarily through terrace dams, without which the area is subject to recurrent drought and flooding. Soils are generally fertile, but in some areas production is limited by salinization. The spring crop is planted in late April or early May and harvested in October. The summer crop is planted between mid June and early July and harvested not much later than the spring crop.
This historically has been an area of high production, especially Shandong Province, but the decline of sweetpotato is also most apparent here. Cropping area in Shandong declined from about one million hectares in the early 1980s to less than 500,000 hectares in the late 1990s, although average yields increased in the late 1990s, possibly due to the rapid adoption of improved production technologies, such as virus-reduced planting materials (Fuglie et. al. 1999, cited in Huang et. al. 2003). Several hypotheses have been suggested for this paradox (given the favorable natural conditions), including declining profitability of sweetpotato relative to other crops and a change in the scale of pig production which might in turn reduce the linkage with sweetpotato as feed (Huang et. al. 2003). (This topic is covered further in the "Consumption, Storage, and Marketing" section.)
Yangzi Basin (Summer Crop)
This region (also referred to as the Changjiang Basin) includes all of the Yangzi Basin other than Qinghai, by province: Jiangsu; Anhui; Henan south of the Huai River; southern Shaanxi; most of Guizhou; northern Hunan, Jiangxi, and Yunan; all of Sichuan except for the northwestern plateau. Located amidst several river basins, the climate in this region is distinguished by persistent cloud cover and fog, hence low solar radiation. The growing season lasts about 140 to 170 days (Huang et. al. 2003). Most cultivation takes place above 500 meters above sea level (masl) on loess and red soils. A summer crop is planted from late April to June and harvested from October through mid November. Sweetpotato production in this region has been increasing (again paradoxically, given the less than ideal physical conditions), such that as of the late 1990s, the region accounted for approximately 60 percent of total national production.
Southern (Summer and Autumn Crops)
This region is formed by a long narrow east-west band north of the Tropic of Cancer, including southern areas of Fujian, Jiangxi, Hunan, northern Guangdon and Guangxi, central Yunnan, and a small area of southern Guizhou. Summer sweetpotatoes are sown in May and harvested between August and October, while an autumn crop can be sown in July or August for harvest in November or December. Monthly precipitation declines to less than 100 millimeters in September and October, when temperatures and evaporation rates are high and crops are more dependent on irrigation. Sweetpotato is sometimes intercropped in this region, either with paddy rice (sweetpotato sown in autumn) or following the wheat harvest in May or June.
Southern (Autumn and Winter Crops)
Consisting of the southern coast and islands south of the Tropic of Cancer, this region includes the southern areas of Guangdong, Guangxi and Yunnan, and islands in the South China Sea. With China's hottest climate, this area experiences little or no frost, allowing for cultivation year-round. However, the main seasons are autumn and winter, when day and night temperature differences are greatest and daily photoperiod is shortest. Autumn sweetpotatoes are grown either in paddies or in upland areas, sown in July through August and harvested in November or December.
PRODUCTION SYSTEMS AND CONSTRAINTS
The sweetpotato crop of China, in spite of its enormous volume, has not been the topic of much research regarding common cultivation practices, very briefly described in the "Geography and Production Zones" section. (This section of the Vietnam chapter is also of some relevance, at least to southern China.)
Viral Infections are a major constraint of sweetpotato production, often transferred via the vine cuttings used to establish a crop. A technique to produce plants which are free of viral infection was introduced to China by the International Potato Center (CIP) in 1988, initially in Shandong and Anhui provinces with potential to be very widely applied across the country. The process involves the extraction of very small quantities of disease-free plant material which are grown under sterile conditions and regenerated in greenhouses. The technique can produce a crop yielding 30 to 40 tons per hectare without additional chemical inputs or genetic improvement (Future Harvest). Although planting material produced in this way might not be perfectly "virus free," possibly due to improper testing and/or reinfection during field multiplication, the reduction of viral infection has contributed to higher potential yields (Kreuze 2004).
Nematodes are widespread and can pose a serious problem. CIP is working with two Chinese research facilities, the China Agricultural University and the Xuzhou Sweet Potato Research Center, toward developing a transgenic cultivar containing a gene, OCI-1, for cystein proteinase inhibition in nematodes. Expression of the gene is reportedly low, but pending field trials (Kreuze 2004).
Weevil Damage (Cylas spp.) is a constraint of sweetpotato production in tropical and sub-tropical regions, hence more of a problem in the warmer southern regions of China. Since no sweetpotato varieties exhibiting effective weevil resistance have been found, another approach being developed is the introduction via genetic transformation of traits conferring resistance, a current focus of cooperation between CIP and China.
VARIETIES AND SEED SYSTEMS
Many varieties of sweetpotato are utilized in China, but most growers are using varieties developed since around 1980. China's national program has been successful at developing and disseminating improved varieties, for example Xushou 18, currently grown on several hundred thousand hectares (Fuglie et. al. 2002). Collaboration between China and CIP on sweetpotato varietal development is fairly recent, but offers further potential for growth in the production and value of the crop.
Jiang et. al. have reported that in the Sichuan area, new varieties of sweetpotato have proven very high yield potentials, even though the development of new sweetpotato varieties has lagged behind rice, wheat and maize. Typical yields of 16 to 17 tons per hectare, which have not increased much over 20 years, are only about 40 percent of the potential of new varieties (although these estimates do not specify management practices).
Since animal feed is the primary utilization of sweetpotato in China, improved nutritional quality for animals (especially pigs) is a major concern of varietal development. Sweetpotato root contains relatively little protein, and protein digestibility is further reduced by trypsin inhibitors. These traits, and others affecting sweetpotato's protein and energy digestibility, are also being considered as candidates for transgenic developments.
CONSUMPTION, STORAGE, AND MARKETING
Consumption
General Trends. Since sweetpotato, and root and tuber crops in general, are usually neither imported nor exported in significant quantities, average per capita supply over a given country or region can be fairly well estimated by production. For 2003, China's total sweetpotato production of almost 104 million tons (fresh weight), for a population of slightly over one billion three hundred million, averages out to 79 kilograms per capita. This is very high by world standards, though below the highest rates of production, for example around 100 kilograms per capita in some areas of Papua New Guinea and Central Africa. In China, however, this comparison is of little relevance since relatively little of the sweetpotato crop is directly consumed by people.
Consumption of sweetpotato as a direct staple food crop has dramatically declined in recent decades, from an estimated 50 percent of total production in the 1970s to less than 15 percent by the end of the 1990s (Huang et. al. 2003, p. 16). Other studies have provided varied estimates of this transition, but agree that a structural change is taking place, with strong regional variations. Generally, with rising incomes, demand has grown for wheat in northern China and rice in the south. However, since sweetpotato can be utilized in several ways, local attributes are important. For example, in Sichuan Province (in the Yangzi Basin summer crop region), livestock production has rapidly grown, while maize production (the other major component of animal feed) has not kept pace, providing a strong regional market for sweetpotato as feed. In Shandong, conversely, the rapidly developing food processing industry has created some demand for sweetpotato (for products such as noodles, starch, and alcohol), but since maize is more readily available for animal feed, production of sweetpotato has diminished over the past few decades (Huang et. al. 2003, p. 19).
Sweetpotato as Pig Feed. A survey conducted with households in Sichuan and Shandong provinces found that the vast majority (roughly three quarters) raise pigs, but in most cases very few (typically two or three). Feed is derived from various sources, usually including both sweetpotato and maize, most of which is home-produced. Compound feed is commercially available, but not yet widely used. Sweetpotato production was found to be positively correlated with pigs up to three, beyond which production declined, possibly due to the constraints of small land holdings and the relatively high labor demand of sweetpotato.
It is likely that the prospects for sweetpotato as pig feed will depend on the relative availability of alternate feed sources, and the future of small-scale household pig production in general (Huang et. al. 2003, p. 35). Where labor markets offer greater economic opportunity (generally in coastal areas), small-scale household pig production becomes a less attractive option as more people seek off-farm employment, and more efficient grain markets encourage pig production on a larger commercial scale. Demand for sweetpotato therefore falls relative to commercially available maize-based feeds (Chen and Rozelle 2003). A study suggests that trends in household pig production are regionally varied, generally declining in coastal provinces, but being maintained in some interior regions such as Sichuan and Hunan (Chen 2001, cited by Huang et al. 2003).
Starch Production. Another important utilization of China's sweetpotato crop is the production of starch, used in a wide variety of products, including food ([e.g] canned soups, desserts, processed meats) for many purposes, such as thickening, binding, taste and other culinary qualities, and conversion into sugar. Starch is also be used for non-food applications such as textiles, paper, adhesives, and pharmaceuticals (Fuglie and Oates 2004).
This application of sweetpotato could be especially important in China since demand for starch generally increases not only with population, but also with personal incomes. Also, in China and generally in Asia, processing is often done on a much smaller scale than in most of the industrial world, so that the industry has potential to grow further as a source of employment.
Storage
As sweetpotato is not primarily a staple crop, but rather is utilized primarily either for animal feed or other products, storage is not a major concern, at least not a topic of much available research.
Marketing
The Chinese government initiated reforms in the late 1970s to shift from a socialist to a more market-oriented economy, including the gradual elimination of production quotas, which had mandated the sale of agricultural products to government agencies at pre-determined prices. Sweetpotato was one of the first crops to be freed of quota restrictions, and its price has since been largely determined by local supply and demand conditions. The marketing of other major crops (rice, wheat, and maize) continues to be affected by commodity-specific policies, as well as imports and exports (Huang et. al. 2003, pp. 53-54). The organization of local markets has not been researched in depth, but sweetpotato prices are reported to be seasonally stable in Beijing, but locally variable with supply and demand conditions in the provinces (RIRDC).
Markets for sweetpotato products are providing a source of employment and income to some areas, for example in Sichuan, where some farmers are specializing in sweetpotato processing, collecting, wholesaling, and retailing, primarily of noodles and starch. As a newly developing enterprise, the market is still largely informal, lacking a standardized product grading system and publicly available market information. Official data pertaining to the scale of sweetpotato processing are not readily available, but some manufacturing enterprises have grown large by local standards, providing employment in areas where off-farm opportunities are relatively scarce (Zhang and Tilburg 2001).
Agricultural research facilities with online contacts include:
Other organizations with a more specific focus on sweetpotato include:
Xuzhou Sweetpotato Research Center
Xuzhou, Jiangsu 221121
Contact: Professor Ma Daifu
Tel. (86-516) 335-2147
FAX (86-516) 335-2147
Crop Research Institute, Sichuan Academy of Agricultural Sciences
No. 20 Jingsui Street, Chengdu, Sichuan 610066
Contact: Huang Gang.
Tel. (86-28) 8450-4080
FAX (86-28) 8451-2025
Crop Research Institute, Shandong Academy of Agricultural Sciences
28 Sangyuan Road, Jinan 250100
Contact: Dr. Zhang Liming
Tel. (86-531) 317-9093
FAX (86-531) 861-1148
The contact for CIP's office in China is available via CIP ESEAP (East, Southeast Asia and the Pacific).
CONTRIBUTORS
Kelly Theisen is the principal contributor to the initial (2006) China chapter of the Sweetpotato Atlas.
Keith Fuglie and Jan Kreuze provided information and advice via personal communication.
REFERENCES
Chen, Jing. 2001. The Economy of Backyard Hog Raising in China. Unpublished dissertation. University of California, Davis.
Chen, Jing and Scott Rozelle. 2003. Market Emergence and the Rise and Fall of Backyard Hog Production in China. Paper prepared for presentation at the American Agricultural Economics Association Annual Meeting, Montreal, Canada July 27-30, 2003.
Fuglie, K.; Liming Zhang; L. Salazar; T. Walker. 1999. Economic Impact of Virus-Free Sweet Potato Planting Material in Shandong Province, China. International Potato Center (CIP). Lima.
Fuglie, Keith O.; Sukendra Mahalaya; Fannia Suri. 2002. The Economics of Sweetpotato Genetic Resource Conservation and Varietal Improvement in Asia. In: R. Rao and D. Campilan, eds. Exploring the Complementarities of In Situ and Ex Situ Conservation Strategies for Asian Sweetpotato Genetic Resources: Proceedings of the Third International Workshop of the Asian Network for Sweetpotato Genetic Resources (ANSWER) held in Denpasar, Bali, Indonesia 2-4 October, 2001. pp. 79-122. International Plant Genetic Resources Institute Regional Office for Asia, the Pacific, and Oceania (IPGRI-APO). Serdang, Malaysia.
Fuglie, Keith O. and Christopher G. Oates. 2004. Starch Markets in Asia. Chapter 8 of: Fuglie, Keith O. and Michael Hermann (editors). 2004. Sweetpotato Post-Harvest Research and Development in China. Proceedings of an International Workshop held in Chengdu, Sichuan, PR China, Nov. 7-8, 2001. Bogor, Indonesia: International Potato Center (CIP).
Future Harvest. Researchers Boost Chinese Sweetpotato Production. (Website not accessible as of May, 2007.)
Gitomer, Charles. 1987. Sweet Potato and White Potato Development in China. Prepared for the International Potato Center (CIP). Lima. Peru International Food Policy Research Institute. Washington, [D.C]
Huang, Jikun; Scott Rozelle; Mark Rosegrant. 1999. China's Food Economy to the Twenty-first Century: Supply, Demand, and Trade. Economic Development and Cultural Change 47:737-766.
Huang, Jikun; Jun Song; Fanbian Qiao; Keith O. Fuglie. 2003. Sweetpotato in China: Economic Aspects and Utilization in Pig Production. International Potato Center (CIP) Bogor, Indonesia.
Jiang, Xie; Hu Jianjun; Wang Yi. 2004. Sweetpotato Processing and Product Research and Development at the Sichuan Academy of Agricultural Sciences. Chapter 9 of: Fuglie, Keith O. and Michael Hermann (editors). Sweetpotato Post-Harvest Research and Development in China. Proceedings of an International Workshop held in Chengdu, Sichuan, PR China, Nov. 7-8, 2001. Bogor, Indonesia: International Potato Center (CIP).
Kreuze, Jan. 2004. Trip Report from China, October 27 - November 7 (Shandong Agricultural University, Tai'an; Xuzhou Sweet Potato Research Center, Xuzhou; Sichuan University, Chengdu). International Potato Center (CIP), Lima.
Purseglove, [J.W] 1968. Tropical Crops: Dicotyledons. Longman Group Limited. Essex, England.
RIRDC (Rural Industries Research and Development Corporation, Government of Australia). 2003. Select Markets for Taro, Sweet Potato and Yam.
Wang, Shudian et. al. (eds.). 1984. Zhongguo ganshu zaipexixue (Chinese Sweet Potato Cultivation Studies. Shangai Kexue Chubanshe (Shanghai Science Press). Shanghai.
Yen, D. E. 1982. Sweetpotato in Historical Perspective. In: Villareal, [R.L] and Griggs, [T.D] (eds.). Sweet Potato: Proceedings of the First International Symposium. AVRDC Publication 82:172, pp. 17-30. Tainan, Taiwan.
Zhang, Dapeng; Genoveva Rossel; Albert Kriegner; Robert Hijmans. 2004. AFLP Assessment of Diversity in Sweetpotato from Latin America and Pacific Regions: Its Implications on the Dispersal of the Crop. Genetic Resources and Crop Evolution 51: 115-120. Kluwer Academic Publishers. The Netherlands.
Zhang, Dapeng and Li Xiu-Qing. 2004. Sweetpotato as Animal Feed: The Perspective of Crop Improvement for Nutrition Quality. Chapter 2 of: Fuglie, Keith O. and Michael Hermann (editors). Sweetpotato Post-Harvest Research and Development in China. Proceedings of an International Workshop held in Chengdu, Sichuan, PR China, Nov. 7-8, 2001. Bogor, Indonesia: International Potato Center (CIP).
Zhang, Xiaoyong and Aad van Tilburg. 2001. Adding Value to an Agricultural Product: An Effective Way of Improving Rural Livelihoods and Welfare. Paper prepared for the 74th EAAE Seminar "Livelihoods and Rural Poverty: Technology, Policy and Institutions" held in Wye, UK, September 12-15, 2001.