The effect of different concentrations of Potassium Humate organic matter was investigated on yield and yield components of five potato varieties as a second crop after barley harvest in Ardabil region, northwest Iran. Experiment was carried out as split plot based on a randomized complete block design with three replications during 2010 and 2011 growing seasons. Potassium Humate was considered as the main factor at three levels (0, 250 and 300 mL.ha-1 in 300 liter water) and six potato varieties including Agria, Savalan, Kaizer, Markiz and Lota were allocated to subplots. Traits including plant height, number of stems, number and weight of tubers per plant, total tuber yield and marketable tuber yield were measured during growing season and after harvesting. Results revealed significant effect of potassium Humate, variety and interaction of potassium Humate and variety on the studied traits. Savalan and Agria produced the most stem numbers per plant when 300 mL.ha-1 Potassium Humate was used. Kaizer and Agria also produced higher plants, whereas the shortest ones were observed in Markiz. Application of 250 and 300 mL.ha-1 Potassium Humate increased plant height significantly. It also led to an increment of 24.8 g tuber weight per plant in average. The highest tuber number per plant was produced by Lota and Savalan at 250 and 300 mL.ha-1 Potassium Humate application rate. Lota produced the highest tuber weight per plant, total yield and marketable tuber yield when 250 mL.ha-1 Potassium Humate was applied. In conclution, planting Lota as a second crop after barley harvest with application of 250 mL.ha-1 Potassium Humate could be recommended in Ardabil region climatic condition.
