Potassium promotes yield, quality and economic returns of two sweet potato varieties in acidic loamy sand soil

Potassium (K) deficiency can limit growth and yield of sweet potato, particularly in sandy soils with a low pH. Most previous studies that focused on investigating rate of K applied for sweet potato did not use strongly acidic sandy soil. Therefore, the objective of this study was to investigate the effects of K on growth parameters, storage root yield, quality, and economic return over fertilizer cost of two sweet potato varieties grown in a strongly acidic loamy sand soil in Kalasin province, Northeast Thailand. An experiment with a 2 × 4 split plot design and four replications was established. The factors consisted of two sweet potato varieties (Beni Haruka and Okinawa-Kugani-Imo) and four K rates, 0 (control), 30, 60 and 90 kg K ha-1. At the rate of 90 kg K ha-1, storage root yield, total soluble solids, and economic return of Okinawa-Kugani-Imo variety were better than those of Beni Haruka. Storage root yield and economic return of Okinawa-Kugani-Imo were significantly increased with increasing K application rate up to 90 kg K ha-1, while Beni Haruka had the same trend up to 60 kg K ha-1, but had no significant differences when increasing the rate to 90 kg K ha-1. Therefore, recommended K application rates for sweet potato variety Okinawa-Kugani-Imo and Beni Haruka, grown in the dry season after paddy rice harvest in the acidic loamy sand soil, were 90 and 60 kg K ha-1, respectively.