Sweet Potato Cultivation on NTT Rooftop to Reduce Urban Heat

NTT Urban Development Corp. and NTT Facilities, Inc. have been jointly testing mitigation effects on the urban heat island effect by installing a sweet-potato hydroponics system on the rooftop of an office building, it was announced on August 29, 2006. The system grows sweet potatoes without soil by circulating water mixed with soluble fertilizer, containing minerals and other nutrients, through the growing unit.

When sweet potatoes give off water vapor through leaves, they absorb large amounts of heat, lowering the surrounding temperature. To obtain quantitative data to verify this effect, a measuring device was set up on the rooftop. The resulting data show that sweet potato leaves release 50 percent more water compared to grass, which is commonly used for rooftop gardens.

The results also show that when the temperature of an area without greenery rose to 55 degrees Celsius, the area shaded by sweet potato leaves was not higher than 30 degrees Celsius, indicating a maximum temperature difference of 25 degrees Celsius. This proves that the system also has a great insulating effect.

The final test results will be made public after November when the harvest of the sweet potatoes is completed. The two companies will continue to make efforts to improve the system and reduce costs, with a view to creating market acceptance of this type of cultivation as an effective measure to combat the heat island effect.

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Posted: 2006/11/25 11:41:26 AM
Japanese version