Potato response to potassium fertilization rate and application timing under semi-arid conditions

A two-year experiment (2004-2005) was conducted at Tal Amara Research Station in the Bekaa Valley of Lebanon to evaluate the influence of progressive application of K rates and application timing on yield, yield components and tuber quality of potato (Solanum tuberosum L. cv. Agria). Four levels of potassium (0 (K0), 75 (K75), 150 (K150), and 225 (K225) kg K2O ha-1) and two application timings (tuber initiation and tuber bulking stages) were used in a split-plot design. The progressive application of potassium fertilizer from 0 to 225 kg K2O ha-1 significantly affected the yield and yield components of potato. In both years, small grade tubers and aggregate tuber yield increased quadratically with increasing K application rates up to 150 kg K2O ha-1, reaching a plateau thereafter, showing luxury consumption of the nutrient at 225 kg K2O ha-1. In 2004 when averaged over K application rates, large and medium grade tubers and aggregated tuber yield were 120%, 22%, and 12% greater, respectively, with K application at tuber bulking than at tuber initiation. A similar trend was also observed in 2005, when the small grade tubers and aggregate tuber yield were 20% and 12% higher, respectively, with K application at tuber bulking than at tuber initiation stage. Finally, no significant difference among treatments was observed for tuber dry matter (avg. 19.8%) and specific gravity (1.08 g cm-3)