Effects of Sewage Treatment Water Supply on Leaf Development and Yield of Tuberous Roots in Multilayered Sweet Potato Cultivation

Abstract

To develop a way to mass-produce sweet potatoes (Ipomoea batatas (L.) Lam.) as an energy crop to replace fossil fuels, the effects of using a sewage supply as a fertilizer and heat source were investigated. When 25 pots planted with sweet potato vine seedlings were arranged in three layers and cultivated for 160 days from June to November by supplying treated sewage to the root zone, the yield of tuberous roots reached 19.5 kg m−2 due to the massive growth of leaves. In addition, when sweet potato seedlings were replanted in December and treated sewage was supplied to maintain the irrigation water temperature above 15 °C even in winter, overwintering cultivation was successful and 8.4 kg m−2 of tuberous roots were harvested in July. As a result, the annual production rate for 12 months increased to 25.3 kg m−2, about 10 times the national average of 2.4 kg m−2 for open-field cultivation. The results far exceed previously reported maximum production of resource crops, such as sugarcane and eucalyptus, suggesting that the mass production of sweet potatoes by supplying treated sewage could provide an alternative to fossil fuels on a large scale.