Growing environments

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Sweetpotato is grown in a wide range of environments under a range of farming systems, from the humid tropics to mild temperate zones, and from sea level to 2700 m altitude. Like cassava, it can be grown in semi-arid conditions, but it has greater tolerance than cassava to the low temperatures encountered at high altitude, and to heavy soils. However, it is intolerant of waterlogging, and is usually grown on ridges or mounds. Under favourable conditions, the vines grow quickly to cover the soil, eliminating weeds and hence minimising the labour required after planting. A number of factors have been identified as contributing to the rapid rise of sweetpotato to dominance in the agriculture of PNG, supplanting the traditional taro and yam. Importantly, sweetpotato has a wider tolerance of soil conditions, allowing extended rotations and cultivation of previously marginal areas, and it requires less labour, produces yield earlier, can be harvested over an extended period as required for consumption, and does not require cooking before feeding to animals. Increasing population pressure, and the use of land and labour for cash cropping, continue to promote the shift to sweetpotato production. Many of these factors play a role in other countries which have adopted sweetpotato as a subsistence crop.

Sweetpotato is seen as a poor man's food, with low market value and low consumer preference hence, it is rarely grown in prime lands and is relegated to marginal lands. It is often grown in less fertile soils such as sandy coastal areas, mine tailings, lahar, acidic soils of hillsides, drought prone areas and peat soils. When grown in good lands, they are usually planted after cash crops or before a fallow period. In paddy farms, they are grown during dry season when there is not enough water for the rice crop. The popularity of sweetpotato stems from its ability to tolerate harsh conditions. While yield on marginal lands may not be high, they are reliable source of food s and an alternative source of small amount of cash for subsistence farmers. Sweetpotato's dominance is strong in the cool tropical highlands from Uganda to Burundi and Papua New Guinea.

The recent trend to diversify the uses of sweetpotato, however, has increased the use of better and more productive lands for sweetpotato. In the Philippines, more irrigated fields of Central Luzon are now used for the crop as a postrice commodity and in the more productive lowlands of Samar and Leyte, as alternative to corn, a recognition of its potential as a cash crop. However, the expansion of sweetpotato in these better environments still depend on the market for the new products.

Contributors: Vilma Amante and Jane O'Sullivan

Origin

Botany and morphology

Importance

Nutritional value

Utilisation