Yam in Sacks on Terrace Walls
3.1 - Yam in sacks on terrace walls
Emma Desilets, University of Guelph, Canada
Related video(s): Yam sac (English subtitles) (Source: Access Agriculture)
Suggested citation for this chapter.
Desilets, E. (2022) Yam in sacks on terrace walls. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. farmpedia.org
Introduction
A staple crop in many parts of Africa and Southeast Asia (Opara, 2003), yams (Dioscorea sp., not to be confused with sweet potato) are an important source of carbohydrates, contain good amounts of fibre and vitamin C (Wanasundera and Ravindran, 1994), and can provide a family with a new source of income and nutrition. Unfortunately, many smallholder farmers in hilly regions lack enough cultivated land area to grow more crops and support their families (Chapagain et al., 2019). To overcome this, farmers use terrace farming, which creates step-like patterns on sloping hillsides where the flat surfaces are cultivated; however, the vertical walls are typically unused (Chapagain et al., 2019). For smallholder farmers, every inch of land counts, so taking advantage of these unused walls by vertically growing yam in sacks is an option to consider, as shown in Figure 1. Yams can also be grown in sacks on flatlands, to save labour at harvest and on fertilizer/manure, and to conserve water.
It is important to note that this practice is not reserved for hillsides; yams can be grown in sacks against any wall, such as the side of a house, or even leaning against one another. Growing yams in sacks not only utilizes unused space and provides yams with adequate sunlight, but also prevents leaching of critical fertilizers and water, and critically, helps cut down on labour, especially at harvest time — the bag can simply be opened rather than having to dig out a large and very heavy tuber (Chapagain et al., 2019). The practice appears to have started in Nepal in 2014 (Chapagain et al., 2019), but has since spread to West Africa, where some farmers grow up to 5000 yams in sacks.
Implementation of Yam in Sacks
This section explains how to grow yam in sacks. According to the Food and Agriculture Organization (FAO), yams are not typically grown from seeds and are instead grown by planting cut pieces of adult yam (Henderson, 1977).
How to Plant:
While seeds can produce yam, propagation from cuttings is preferred to maintain high yields and similar traits to the parent tuber. To start, cuttings from the tuber are taken, preferably from the crown, which is the top section containing stems, or a small whole tuber weighing 250-400 grams each can be used (Henderson, 1977). A sack or bag to grow the yam in is also needed. Appropriate sacks should be long enough to contain the average fully grown tuber; a good option is an empty seed sack or fertilizer bag. The sack is filled about halfway, or enough so that it can be lifted, and then transported to rest against a wall, terrace, or other bags, where it will remain for the duration. The bag should not contain any large stones, as this will impede the growth of the yam. In addition, the area should be exposed to the sun, as yams are light-loving, shade-sensitive plants that require warm temperatures after planting (Lebot, 2020). The remainder of the sack should then be filled with soil, leaving some space at the top for fertilizer or manure. The soil must be light, sandy, well-drained, and crumbly, as the tuber penetrates the soil while expanding during growth (Lebot, 2020). About five inches (12 cm) of soil near the back of the sack, as opposed to the centre, should then be dug out to plant the yam. According to a video documenting this process, the yam should be placed horizontally so that the crown is in the centre of the soil, but the cut end of the yam is against the side of the sack. This is done because growth comes from the crown; if it were not central, the yam could break through the bag (1/3 TV, 2021). The tuber should then be covered with soil, and dry, dead leaves and grass should be placed on top of the soil to protect the yam.
How to Fertilize:
The last step in planting the yams is to fertilize the soil, which could be the key to healthy yams and a good harvest. One option is to simply scatter compost, manure, or fertilizer on top of each bag in addition to the dry leaves. Fertilizing yams in sacks differs from fertilizing in the ground, as the yam roots cannot travel when confined to the sack; when growing yams in a sack, the roots are near the top of the bag. As shown in the video referenced above, spreading fertilizer over the top of the soil or at the bottom of the bag is an ineffective method, since the concentration of fertilizer is too strong if applied directly, which is why fertilizing in batches is suggested (1/3 TV, 2021). Five to six weeks after planting, only seven or eight balls of fertilizer should be scattered on top of the dry leaves. Rain should dissolve the fertilizer, or the sacks can be watered at least three times a week. This fertilizing process should be repeated weekly for one month (1/3 TV, 2021).
How to Harvest:
Mature yams are distinguishable by the yellowing of leaves, and most edible yams reach maturity 8-11 months after planting (Opara, 2003). To harvest, the sacks should be torn down the side. A shovel can be used to remove some of the soil, but the actual yam should be dug out by hand, as it is possible to damage the tuber with a tool. The stem of the yam should then be cut and removed. It is possible to recycle the sacks by laying them on their sides and emptying the contents; the soil can be reused. The yams should be stored in a cool, dark area until ready for use. It is important to note that yams contain toxic substances when raw and must be sliced and soaked in water, or cooked, before consumption (Opara, 2003).
Critical Analysis
While harvesting yams in sacks requires much less labour than harvesting from the ground, planting is slightly more difficult and requires more resources. Growing yams is typically a highly laborious and tiresome process. Yams grown in the ground require standing, bending, and squatting for long periods, which is very intensive considering some yams can grow to weigh more than 100 lbs (45 kg) (Opara, 2003). Planting in sacks cuts down on intensive labour, but is more time-consuming, as each individual sack must be prepared. Since each tuber requires one sack, many sacks and pieces of tuber will need to be acquired. A farmer may already have some empty sacks or fertilizer bags, or they can be acquired at the market, but accessing these materials may also be difficult. Acquiring sacks large enough to accommodate the size of the growing yam may also be difficult, as smaller bags will limit the size of the tuber. In addition, the disposal of unusable sacks will create plastic waste, so consideration should be given to biodegradable bags. If the materials needed to grow yam in sacks are accessible, some benefits are that it cuts down on hard labour, especially at harvest time, utilizes unused space, and mitigates weeds, soil fertility decline via reduced leaching, and soilborne and leaf pests and diseases — all of which comprise the highest constraints to yam production (Wanasundera and Ravindran, 1994). It also permits yams to be grown in regions with otherwise heavier (clay) soil. Another aspect to consider when growing yams is their storage ability: a yam can lose 10-20 percent of its weight after three months of regular storage in a cool, dry area, a figure that includes an element of moisture loss along with a decrease in food value (Coursey, 1967). Yams cannot be stored in cold storage, as they will suffer chilling damage, and yams are susceptible to insects and plant pathogens (Coursey, 1967). There are also added costs for materials — purchasing yam tubers, sacks, and fertilizer — but these items may already be commonplace or easy to acquire from the market. The cost of yams ranges around $2 USD per plant. This added source of income can make a dramatic difference to a smallholder farm if this technique is successfully adopted.
Picture Based Lesson to Train Farmers
Sub-Saharan Africa/Caribbean version
Source: MN Raizada and LJ Smith (2016) A Picture Book of Best Practices for Subsistence Farmers: Edition (note geographic region). eBook, University of Guelph Sustainable Agriculture Kit (SAK) Project, June 2016, Guelph, Canada. Available online at www.sakbooks.com.
Links to Useful Resources
References
1. Chapagain, T., & Raizada, M.N. (2017). Agronomic challenges and opportunities for smallholder terrace agriculture in developing countries. Frontiers in Plant Science, 8, 331. DOI
2. Chapagain, T., Ghimire, B., Pudasaini, R., Gurung, K., Choi, K., Rai, L., Magar, S., Bishnu, B.K., & Raizada, M.N. (2019). The underutilized terrace wall can be intensified to improve farmer livelihoods. Agronomy for Sustainable Development, 39(3), 2-11. DOI
3. Coursey, D.G. (1967). Yam storage - I: A review of yam storage practices and of information on storage losses. Journal of Stored Products Research, 2(3), 229-244. DOI
4. Henderson, A. (1977). How to propagate yams. In Roots and Tubers (pp. 30-38). Food and Agriculture Organization of the United Nations, Rome, Italy.
5. Ghimire, B., Dhakal, R., Pudasaini, R., Devkota, R., & Chaudhary, P. (2016). Demonstration of yam cultivation in sacks at Laitak village [Photograph]. Leisa India. Link
6. Lebot, V. (2020). Yams: Agronomy. In V. Lebot, Tropical Root and Tuber Crops: Cassava, Sweet Potato, Yams and Aroids (pp. 273-292). CABI. DOI
7. Opara, L.U. (2003). Yams. Food and Agriculture Organization of the United Nations. Retrieved November 8, 2022. Link
8. 1/3 TV. (2021, May 17). Step by step process: How to plant yam in bags [Video]. YouTube. Link
9. Wanasundera, J.P., & Ravindran, G. (1994). Nutritional assessment of yam (Dioscorea alata) tubers. Plant Foods for Human Nutrition, 46(1), 33-39. DOI