Enhancing Sweet Potato Cultivation in Papua New Guinea

Preamble

Sweet potato, scientifically known as Ipomea batatas, is native to Central and South America.

Nutritionally, 100g of sweet potato contains 86 calories, 20.1g grams of carbohydrates, 3g of fiber, 1.6g of protein, 0.1g of fat, and is a good source of vitamins A and C, and many other nutrients. The high nutritional value of sweet potato and its sweet taste makes it a valuable food crop.

The species was introduced from the Indonesian province of West Papua into the highlands of Papua New Guinea in the 1700s. Today, the crop is planted throughout the country, but the species is a staple food for the highlands region.

Sweet potato is traditionally planted in Papua New Guinea using dug-up mounts in the ground. The mounts are usually circular in shape or regular rows of long mounts in between trenches. These two practices of sweet potato cultivation have been used for some 300 years in this country.

The amount of work involved with planting sweet potatoes using the traditional method is cumbersome, involving clearing and burning vegetation for planting, mounding for planting of sweet potato slips, planting sweet potato slips, tending, and harvesting.

When sweet potato is planted using the traditional method of cultivation – planted directly in the soil - the crop struggles to find whatever nutrients and water that are available to nourish itself. Therefore, harvests may be bountiful in fertile soils, but not so in infertile soils, and during dry seasons and droughts.

Planting of sweet potatoes in sacks removes all the cumbersome involved with planting sweet potatoes the traditional way. All one has to do is regularly water and fertilize his sweet potatoes in the sacks until they are ready for harvest.

Today, due to the need to address the issues of climate change, environmental sustainability, chronic unemployment, food security, and poverty in Papua New Guinea, there is a need to adopt low-cost technologies to address these social, economic, and environmental issues. Therefore, planting of sweet potatoes in bags (sacks) is one way to address these social, economic, and environmental issues. Planting of sweet potatoes in bags can also be used as a livelihood activity for unemployed citizens living within rural and urban settings, providing self-employment and food for unemployed individuals and families.

 Soil for Cultivation of Sweet Potatoes

Sweet potato requires well-drained and fertile soils to thrive. Sandy or clay soils are not suitable for the cultivation of sweet potato.

To successfully cultivate sweet potato in sacks, one has to prepare loam soil, which should have the right amount of sand (fine or coarse sand is ok), clay, compost, and other ingredients like ash or charcoal. The consistency and texture of soil for successful cultivation of sweet potatoes in sacks will depend on what one has available to him. The easiest ingredients one can use to prepare soils for the cultivation of sweet potatoes is as follows: mix 40 percent compost, 40 percent sand, and 20 percent clay, to produce your planting soil.

 Preparation of Sacks for Cultivation of Sweet Potatoes

The following is required for cultivating sweet potatoes in sacks: a 50kg sack; a 1-Litre Coca Cola plastic bottle (or 1-Litre Fanta plastic bottle) that has been perforated on the sides to allow water to flow through, with the neck of the bottle slightly cut open to pour in water; fermented organic liquid fertilizer; and prepared loam soil.

The number of sacks to prepare for planting sweet potatoes is limitless, and depends on the land area one has. But for residences in towns and cities, 1- 4 sacks would be sufficient for houses with limited land areas.

Fill a 50kg sack with the loam soil one has prepared for cultivation of sweet potatoes. Once the sack is filled almost to the brim, dig a hole in the center of the soil at the top of the sack, place the perforated 1-Litre Coca Cola bottle in the hole and bury it (do not bury the whole bottle but leave half of it above ground), and tie the edges of the sack onto the 1-Litre Coca Cola bottle to cover the top of the sack (see Fig. 2).

 Procuring Vines (Slips) and Planting of Sweet Potatoes

Sweet potato slips can be procured in two ways: (a) collect slips from an existing sweet potato crop to plant; or (b) grow sweet potato tubers in water or soil to raise slips that can be harvested later and used to grow sweet potatoes in sacks.

Once sweet potato slips have been procured and the sacks of soils for cultivation are ready, make 12 holes in the sweet potato sack using a pocket knife or a sharp metal rod. How holes for planting of sweet potato slips are made in a 50kg bag are shown in the picture below.

The sack for planting of sweet potatoes must be stood upright as demonstrated in the picture below. This will allow for balanced flow of water and fertilizer throughout the bag to feed all the sweet potato slips.

Use a stick or metal rod to push the sweet potato slips into the holes made in the 50kg sack and allow the outer ends to dangle from the sack as shown in the picture below.

Water the sack of sweet potatoes thoroughly and leave for the night. Water will be poured through the perforated 1-Litre Coca Cola bottle buried at the top of the sack.

 Watering and Fertilizing Sweet Potato Sacks

There is a difference between pigs raised in a pen and those that are allowed to roam outside and feed on whatever they could find. The pigs raised in the pen would grow much faster and have healthier bodies due to them being sufficiently fed food and water, while the free ranging ones would be undernourished. The same is also true for chickens adequately fed inside a chicken house and chickens that are free ranging.

Plants are usually planted in the soil and allowed to fend for themselves. However, we can also grow plants in containers or the soil and adequately feed them water and nutrients to have better growth and bountiful harvests. We can also have better growth and bountiful harvests with sweet potatoes cultivated in sacks by manipulating their growing medium, water, and fertilizer. 

With the cultivation of sweet potatoes in sacks, use sufficient amounts of water and fertilizer to avoid wastage and excessive costs. A strict watering and fertilization regime would suffice.

For watering, 3 liters of water must be given to a sack of sweet potatoes daily. But if one is to water his sacks of sweet potatoes every 2 days, 4 – 6 liters of water must be administered every Monday and Wednesday of each week.

For fertilizer, 3 - 4 liters of liquid fertilizer must be given to one sack of sweet potatoes every Friday of each week. No watering is to be done when fertilizer is applied to the sacks of sweet potatoes every Friday of the week.

The production of liquid fertilizer is not covered here because it is a lengthy topic of its own. However, a picture of liquid fertilizer produced in a 150-liter container is given below to emphasize its importance for successful cultivation of sweet potatoes in sacks. The liquid fertilizer is made by fermenting kitchen waste, garden waste, grass clippings, and other vegetable matter with water in a sealed container (the lid of the container should be slightly opened to allow gases to escape).

When it rains the previous night, no watering or fertilizing is required for the following day. Watering and fertilizing sweet potato sacks after a rainy night would result in a wastage of water and fertilizer.

 Harvesting

Varieties of sweet potatoes vary in their times for harvest. Some sweet potatoes can be harvested 3 months after planting, others can be harvested after 4 months, others can be harvested at 5 months, and some can be harvested after 6 months.

One has to have some knowledge as to the sweet potato variety he has planted so that he can harvest them at the right time. Harvesting too early can result in small tubers, and harvesting too late can result in the loss of crops due to rotten sweet potatoes.

If one is not too sure of the sweet potato variety he has planted and is not sure of the right time to harvest, he can check the top of the sack to ascertain the size of his sweet potatoes. He can remove the top of the sack and dig around the top to see if his sweet potatoes are of optimal size and are ready to be harvested. If the sweet potato tubers are too small to harvest, he can cover the top of the sack and allow the tubers to grow to harvestable sizes before harvesting.

 Cost of Cultivating Sweet Potatoes in Sacks

With low-cost technologies for the cultivation of food crops, the idea is to minimize cost as much as possible. Therefore, with low-cost sweet potato cultivation, the materials used must cost as little as possible.

It cost nothing in terms of labour, sacks, water, and fertilizer used in cultivating the sweet potatoes shown in the pictures above.