Effect of soil temperature on growth and yield of sweet potato (Ipomoea batatas L.) under cool climate

In cool climates, low temperature is critical for growth and yield of sweet potato ( Ipomoea batatas L. ) . Despite its negative effects, few studies have quantified the impact. We evaluated effects of soil temperature ( T s ) on growth and yield in sweet potato from 2-year field trials in northern Japan. T s was controlled by three steps using plastic mulch at different colors ( green, black and white ) with different T s ranged in 21~24 ° C especially at early growth before the surface of the mulch covered by plant canopy. Higher T s significantly increased vine elongation, branching, and leaf appearance, and the magnitude of increased by higher T s decreased with proceeding growth stages. Increasing T s significantly increased leaf chlorophyll content and stomatal conductance. Across treatments and years, aboveground biomass was linearly and positively correlated with T s , and 58 g m -2 increased in aboveground biomass was observed per 1 ° C increase in T s . However, final storage root fresh yield was not significantly affected by high T s over years. Increased individual storage root weight at high T s was offset by decreased storage root number. The present quantitative study tested in northern Japan showed that, the enhanced aboveground growth in sweet potato at higher T s especially during early growth did not contribute to increase of storage root yields in cool climates.