Sweet Potato Yield, Harvest, Curing, and Storage

How much do sweet potatoes yield per hectare and acre?

Sweet potatoes are generally tolerant to drought and have a light to moderate need for nutrients (fertilization). However, plants react very well when both water and nutrients are in sufficient quantities, maximizing development and production. For this reason, in a field where a farmer can adopt best practices (from soil preparation to pest control), the crop can yield 11,400-25,000 kg or even 40,000 kg per hectare (10,2-22,300 or even 35,700 lb per acre). This number varies depending on the sweet potato variety, the planting distances, the soil and cultivation practices, etc. Each plant may produce approximately 3-5 sweet potatoes. 

When and how to harvest sweet potatoes

Sweet potato’s maturity time varies depending mainly on the environmental conditions, the soil type, the cultivated variety, the age of the transplants, and the growing techniques. 

Generally, there is not a strictly defined moment for harvesting, and farmers must take into account the quality characteristics of the tubers and the risk of damage or disease (pathogens, pests, frost, etc.). Digging and harvesting some sample plants during the last development; stages of the plants may help the farmers make a more informed decision. Most growers use as indicators the followings:

• 80-130 days have passed from planting
• The tops of the plants become yellow and die back.
• A specific percentage of the tubers is larger than 3.5 inches (9 cm). Depending on the production country and the market requirements, this percentage may range from 30 to 75%. More specifically, in the USA, 65-75% of potatoes should be between 3.5-9 in (9-23 cm). Alternatively, the sweet potatoes may weigh 250 gr (0.55 lb) to 1 kg (2.2 lb). Moreover, sweet potatoes should be firm, fairly clean, well-shaped, healthy, and without damage. 
• The drop in soil temperature. Cool soil may reduce the quality and storability of sweet potatoes. As a result, harvesting them before the first frost is essential. 
• The juice from a cut of the sweet potato does not become black quickly.

Almost two weeks before harvesting, farmers stop the irrigation. Then, they remove the vines by using swinging pulverizers. They do this to thicken the skin of the potatoes and protect them during transportation.  

A week after, they remove or dig the upper part of the plants (vines) using mechanical measures. It is crucial to avoid chopping on the top of the raised mounds to prevent potato injuries. The foliar parts are used as animal feed. 

Harvesting sweet potatoes is usually a very laborious procedure. In many cases, flip plows or a tractor-drawn platform with a digger chain are used to flip or/and lift the sweet potatoes from the ground. Workers pass by to collect them manually from the ground. It is essential not to leave the sweet potatoes exposed to the sunlight for long periods (1.5 hours max to avoid sunburns). To avoid any damage, the roots must be treated with caution. 

How to cure and store sweet potatoes

After harvesting, producers transfer the potatoes directly to the market or store them. While it is not standard commercial practice, curing freshly harvested sweet potatoes can protect their quality (reduce storage losses), especially when the product will be stored for longer. This process usually lasts 4 to 7 days and involves controlling temperatures (air treatment, 26-32 °C or 79-90 °F), relative humidity (85-90%), and good ventilation. The reason is that under these conditions, wounds that may occur during the harvesting heal by developing a protective layer of cork and suberin deposits on their surface. Furthermore, data showed that curing might also improve sweet potatoes’ aroma, texture, and taste (by converting starch to sugars). 

After curing them, the producers store the potatoes in dark rooms, with temperatures between 10-15 °C (50-60 °F) and 80-90% relative humidity for several months until they transfer them to the market. More specifically, properly curred roots can be stored in such conditions for up to 1 year with 15-25% losses. When that time comes, and the sweet potatoes must be transferred to the market, producers clean them using special washing machines and dry them. Finally, they divide them into categories depending on their size and quality.  

References

•  https://agriculture.gov.tt/wp-content/uploads/2019/12/Sweet-Potato-Production.pdf
• https://ipm.missouri.edu/MPG/2020/9/sweetPotato-RA/
• https://www.uq.edu.au/_School_Science_Lessons/SPotProj.html
• https://hgic.clemson.edu/factsheet/sweet-potato/
• https://www.ams.usda.gov/
• https://www.nda.agric.za/docs/Brochures/PG_SweetPotato.pdf
• https://extension.uga.edu/publications/detail.html?number=C1014

Sweet Potato cultivation guide:

Fast Facts about Sweet Potatoes

Sweet Potato Plant Information and Variety Selection

Sweet Potato Nutrition and Health Benefits

How to Grow Sweet Potatoes in Your Backyard

How to Grow Sweet Potatoes for Profit

How to Produce Sweet Potato Slips

Sweet Potato Soil Requirements, Soil Preparation, and Planting

Sweet Potato Water Requirements and Irrigation Systems

Sweet Potato Fertilization Requirements

Sweet Potato Major Pests, Diseases and Weed Control

Sweet Potato Yield, Harvest, Curing, and Storage