Effects of Mulching with Polyethylene Film and Weather on Agronomic Characters of Sweetpotato Varieties for Steamed and Cured Slices Processing

Abstract

Steamed and dried sweet potato slices so-called “hoshi-imo” is an important agricultural product in Ibaraki and other prefectures in Japan. Using two cultivars ”Tamayutaka” and ”Izumi-13”, which have been cultivated for hoshi-imo production, we investigated the agronomic characters, root yield, rate of ”Shirota” which is a white-opaque defect, dry matter content and starch content from 2000 to 2008. Then we analyzed the influences of film mulching and weather condition on these agronomic characters. Soil temperature was raised 0.3–0.7°C during the cultivation period, but the Shirota defect was not significantly influenced by film mulching. Root yield and starch content were increased by film mulching. These results indicate the benefit of mulching on root production for hoshi-imo. A negative correlation was observed between the precipitation in the latter half of the growing period and the rate of Shirota defect. A low soil moisture was suggested to increase the occurrence of Shirota defect.