Chapters 5.43
5.43 -Adoption of Sweet Potato as a Crop for Smallholder Farmers Challenged with Climate Change
Kate Elizabeth Maggiacomo, University of Guelph, Canada
Suggested citation for this chapter.
Maggiacomo,Kate E. (2022) Adoption of Sweet Potato as a Crop for Smallholder Farmers Challenged with Climate Change, In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org
An Introduction to Climate Change
Agricultural practices play a crucial role in the development, economy, and food security throughout the developing world, all of which are at risk due to the detrimental impacts of climate change on crop production and sustainability (Müller et al., 2011). Strategies must be implemented to create greater resiliency for farmers and enable them to maintain productivity (Morton, 2007). The adoption of sweet potato (Ipomoea batatas) as a secure and sustainable crop represents an opportunity for smallholder farmers to combat agricultural deprivation (Motsa et al., 2015).
Background to Sweet Potato
Sweet potato, or Ipomoea batatas from the Convolvulaceae family, originated in tropical South America (Karyeija et al., 2007). Sweet potato varieties were introduced to Asia, Africa, and India from Portugal (Srisuwan et al., 2006). Asia currently produces the largest amount of sweet potatoes, with Africa being the world’s second greatest producer, specifically in Uganda and Rwanda (Glato et al., 2017; Rose & Vasanthakaalam, 2011). Following the introduction of sweet potato into African agriculture, sweet potato became an indigenised crop as a result of its quick adaptation to the tropical and subtopical environments (Motsa et al., 2015). Sweet potato cultivation is a significant part of African agriculture as it represents a crop that promotes food security and nutrition((Karyeija et al., 2007). Production throughout Africa averages over 7 million tonnes, representing 5% of global production, which is estimated to increase substantially (Ewell, 2010). Most production throughout Africa is by smallholder farmers as a form of subsistence agriculture, with only 20% being traded or used for income (Andrade et al., 2009). Sweet potato represents a promising crop in the context of climate change, as it grows with 750-1000 mm of rainfall, but some varieties can tolerate as little as 500 mm of rainfall (Woolfe, 1992).
Hundreds of sweet potato varieties have been identified with over 200 varieties being cultivated in Rwanda alone (Rose & Vasanthakaalam, 2011). Sweet potato varieties and their traits are impacted by genetics and environmental influences (Ochieng, 2019; Andrade et al., 2009). The varietal diversity includes variation in the flesh, skin, root, shape, and size (Ochieng, 2019). Sweet potato flesh can vary from yellow, orange or white, and the skin can vary from yellow, orange, red, white, or purple (Rose & Vasanthakaalam, 2011). Other agro-morphological characteristics used in distinguishing varieties include vine growth, stem length and diameter, leaf size, storage root thickness and diameter, and root yield (Ochieng, 2019). The improvement of crop yield relies on access to successful, high-yielding varieties adapted to the local growing environment and needs (Ochieng, 2019).
Nutrients
While peoples in Africa and the global subtropics face significant rates of malnutrition, vitamin A deficiency, and other various health disorders, sweet potatoes are seen as a medicinal, nutrient rich crop that can help improve food resources and nutritional access (Kwak, 2019). Sweet potatoes are a source of carbohydrates, significant macronutrients and micronutrients, vitamin C, B complex, A, E, and folic acid (Motsa et al., 2015). Per 100 grams, sweet potatoes contain 114 kilocalories, 2.4 grams of dietary fibre, 26.3 grams of carbohydrates, 0.4 grams of fat, and 1.7 grams of protein. Sweet potatoes provide considerable amounts of vitamin A through Beta-carotene, making it an affordable and nutrient rich crop that can contribute to reducing the occurrence of vitamin A deficiency which contributes to immune system weakness in humans (Motsa et al., 2015; Andrade et al., 2009). The leaves and roots of the sweet potato can be a modest source of protein with 2.99 grams per 100 grams (Bovell-Benjamin, 2007; Sun et al., 2014). Two important storage proteins identified in sweet potato roots are Sporamins A and B which are rich in lysine and methionine, respectively (Maeshima et al.,1985). However, while significant amounts of lysine and methionine can be found in sweet potato roots, they are not significant in the other organs of the sweet potato (Maeshima et al.,1985). The nutritional content of the leaves includes up to 26.4% iron, 1.2% calcium, 15.8% vitamin E, and 34.7% carotenoid per 100 grams. Consumption of sweet potato can also be associated with health benefits including chemo preventive activities in which enzymes found in sweet potatoes can help to suppress cancer cells, along with anti-inflammatory, increased eyesight, and anti-diabetic properties (Bovell-Benjamin, 2007; Rabah et al., 2004).
Growth and Reproduction
Sweet potatoes grow in tropical and subtropical environments, able to adapt to temperate climates (Paneque-Ramirez, 1992). They should ideally be grown in a climate of 20-25°C during the day and 15-20°C during the night, however any temperature below 15°C is not favourable (Paneque-Ramirez, 1992). Sweet potato can be planted and harvested anytime throughout the year, under the right conditions (Motsa et al., 2015). The growing season ranges from 3.5-7 months, going through stages of planting to tuber formation, tuber formation to leaf development, and leaf development to final tuber development (Paneque-Ramirez, 1992). Sweet potato propagation is commonly asexual, requiring planting the tuber and stems (not seeds), ideally within 4 days of their cutting (Paneque-Ramirez, 1992). Planting should be done in rows at a depth of about 10 cm, and can be intercropped. Sweet potatoes can be grown in diverse soils, with the best being friable and humic soil, and with a depth greater than 25 cm, with good drainage. The ideal pH ranges from 5.5-6.5, hence a slightly acidic or neutral soil. The soil should remain moist through the growing season, at intervals of 7-10 days. As already noted, sweet potato prefers 750-1000 mm of rainfall but some varieties can tolerate as little as 500 mm of rainfall (Woolfe, 1992). CIP, also known as the International Potato Centre in Peru, is invested in improving global sweet potatoes to enhance climate change adaptation (International Potato Center, 2020). Their scientists have been able to produce more productive agronomic approaches, climate smart varieties and accelerate breeding efforts. To improve drought tolerance, they have developed the Triple S technique wherein sweet potatoes can be stored in sand and used to develop vines for when the rain starts again and the sweet potatoes are able to be planted. Additionally, CIP has bred sweet potato varieties, termed climate smart varieties, that have climate resilient traits and against severe drought and heat (International Potato Center, 2020). Sweet potatoes should be fertilized with phosphorus and potassium to improve yield. Weeding should be done after seed cutting and repeated every 60 days, and can be done either manually, mechanically, or chemically (Paneque-Ramirez, 1992).
Following the growth and development of the sweet potato, the harvesting time differs between varieties, but ranges from 3-6 months after planting (Paneque-Ramirez, 1992). Harvesting can be performed manually, semi-manually, or mechanically, with the most common method being manually by smallholder farmers. Once harvested, sweet potatoes can be stored if kept in the proper conditions. Damaged sweet potatoes, insects, and fungus should be removed, and then can be stored in a dark area that is cool with low humidity (Paneque-Ramirez, 1992). Post-harvest loses are often influenced by damage, cracks, and other physical traits that are seen as negative (FAO, 2020). In order to improve the production and value addition of sweet potatoes, a greater understanding of production and post-harvest methods should be shared (FAO, 2020)
How the Sweet Potato Can Help Combat Climate Change
Sweet potatoes can play a significant role throughout developing countries, representing a crop that is tolerant and adaptive to environmental conditions (Motsa et al., 2015). Sweet potato requires low input and technology to have a fast yield and to increase production capacity (Woolfe, 1992). This crop has a high water efficiency, needs less pesticides and fertilizers than many other crops, and can be used as a cover crop to suppress weeds and prevent water/soil loss (Kwak, 2019). It can provide security, as the roots can be left planted and used when needed, increasing access to a potential food supply (Motsa et al., 2015). Sweet potatoes can help combat malnutrition through their micro and macronutrient supply. They can be completely utilized as the entire sweet potato and roots can be eaten raw or cooked; the leaves can be eaten as a leafy vegetable, or they can be used in animal feed (Kwak, 2019; Motsa et al., 2015).
How Sweet Potato Can Be Adopted by Smallholder Farmers
As opposed to other crops, sweet potato crops have improved heat and drought tolerance (International Potato Centre, 2020). In order to improve the adoption of sweet potatoes for smallholder farmers, increased access and information of where to obtain seeds should be provided as well as improved guides for growing and maintaining sweet potato crops. Fortunately, the International Potato Centre (CIP, Peru) is able to work with farmers to produce research and sustainable practices for greater crop development (Wheatley & Loechl, 2008). Smallholder farmer organizations can obtain materials through seed exchange programs and CIP. Manuals produced and provided by CIP explain varietal information, helping farmers understand which varieties they should crop and how to do so (Stathers et al., 2018).
To improve the post-harvest yield and value of sweet potatoes, they should be sorted before storage and kept out of direct sunlight (Stathers et al., 2018). Harvested sweet potatoes should be stored in plastic or wooden crates with the heaviest at the bottom, making sure not to overpack the crate. The harvest should be sold from the market within 3-7 days to ensure rotting does not occur (Stathers et al., 2018).
The role of African women throughout sweet potato production is significant, as subsistence farming of this crop is often performed by the women. Needs assessments can be implemented to help smallholder women farmers growing sweet potatoes (Stathers et al., 2018; Andrade et al., 2009). These programs can also introduce them to community groups to understand the market and how to improve the value chain of sweet potatoes (Stathers et al., 2018). By increasing the supply and developing better marketable characteristics, contracts between farmers and processors can be created (Wolfe, 1992). The expected profit of sweet potato crops is $567 USD per hectare, with production costs being $268 USD per hectare, meaning that the net return would be $298 USD (Kassali, 2011). The total cost breakdown is 68% for labour costs including harvesting, weeding, cultivation, fertilization, and transportation (Kassali, 2011). Growing sweet potatoes is seen to have a profitable return and by using the methods mentioned above, the production of sweet potato products will have increased value and supply availability (Kwak, 2019).
Critical Analysis
Major pests and diseases impactful to sweet potato crops include whiteflies, feathery mottle virus, weevils, and chlorotic stunt virus. CIP sweet potato varieties can be used as they are bred for resistance, in addition to incorporating integrated pest management techniques and insecticides (Stathers et al., 2018; Paneque-Ramirez, 1992). In order to improve the adoption and cultivation of sweet potatoes, improved varieites with greater temperature and drought resistance can be accessed from CIP as well as extension manuals. Livelihoods can be improved by participatory approaches, educational provisions, a farm-to-market focus, and post harvest strategies.
Links to Useful Resources to Get Started and Further Reading
https://www.youtube.com/watch?v=Q4pLslnulDc → Describes the impact of improved cultivation practices on African women
https://www.youtube.com/watch?v=MNpKIVEwnp8 → Explains the basics of sweet potato production /p>
https://borgenproject.org/sweet-potatoes-africa/ → Introduces the Harvest Plus OFSP initiative /p>
https://www.npr.org/sections/thesalt/2012/08/15/158783117/saving-lives-in-africa-with-the-humble-sweet-potato → Explains biofortification and the impact they can have in Africa /p>
https://scinnovent.wordpress.com/2014/02/26/african-traditional-foods-and-nutrition-making-consumption-of-orange-fleshed-sweet-potatoes-a-big-deal/ → Interview with a Ghanaian researcher on the benefits of sweet potato for child nutrition /p>
https://www.cgiar.org/annual-report/performance-report-2019/biofortified-sweet-potato-fights-micronutrient-malnutrition-in-sub-saharan-africa/ → A report on the use of sweet potatoes to fight poverty and malnutrition/p>
https://www.usaid.gov/hy/news-information/videos/node/208971 → Three stories of African women using sweet potato to empower and support their families/p>
https://www.youtube.com/watch?v=5RBegs2jRlQ → OFSP production and market in Ghana/p>
https://www.almanac.com/plant/sweet-potatoes → This source gives an overview of sweet potatoes and step by step reccomendations for growth/p>
https://cdn-ext.agnet.tamu.edu/wp-content/uploads/2014/09/how-to-grow-sweet-potatoes.pdf → Manual explaining the steps of sweet potato cultivation/p>
http://cdn.newsproutfarms.com/downloads/New-Sprout-Sweet-Potato-Slip-Care-and-Planting-Guide.pdf → Sweet potato growing guide/p>
http://www.cardi.org/wp-content/uploads/2011/07/SweetPotato_TechnicalManual.pdf → A technical manual for sweet potato producers/p>
https://cgspace.cgiar.org/bitstream/handle/10568/98338/CIP_SP_T6_SweetpotatoProductionAndManagement_v40.pdf?sequence=10&isAllowed=y → CGIAR sweet potato guide to sweet potato production and management/p>
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