Abstract

A trial on potato (Solanum tuberosum L.) response to three doses of potassium (K) under deficit irrigation was conducted under dry sub-humid conditions in Bekaa plain, Lebanon, between 8 April 2015 and 31 July 2015. Grown on clay, neutral pH, Eutric Fluvisol, table potato crop (cv. Spunta) was fertilized at three levels of K: 120 (K₁), 240 (K₂) and 360 kg K₂O ha^-1 (K₃), tested against a zero-K treatment (K₀). All treatments received equal amounts of nitrogen (150 kg N ha^-1) and phosphorus (150 kg P₂O₅ ha^-1). The crop, subjected to mild deficit irrigation (85% of evapotranspiration) starting from the shoot development stage, was irrigated with a drip system. Soil moisture was monitored throughout the season by moisture sensors inserted at 25 cm and 50 cm soil depth to schedule the irrigation. The crop performance was assessed by measuring canopy temperature and chlorophyll content as a function of the different K applications. The K₃, treatment exhibited higher chlorophyll contents during flowering, tuber initiation and bulking stages. At midday, the K₃ canopy temperature was the lowest (29.6 °C), compared to K₀ (31.0 °C), indicating facilitated stomatal aperture, and consequent carbon exchange rate. These results demonstrate the important role of K in establishing and maintaining carbon translocation from source leaves to sink organs, thus enhancing potato productivity. The final tuber yield increased significantly from 2.3 in K₀ to 3.3 kg m^-2, in K₃. The average tuber weight and commercial tuber weight were significantly greater in the K₃ treatment while the tuber dry matter content was unaffected by the application of potassium. Further increase in potato tuber yields should be sought through the distribution of K applications during the season, particularly during the crucial stage of tuber bulking, when K requirements rise. Potassium role in regulating plant water relations in potato should be further examined in order to cope with extreme weather conditions that often occur in semiarid and dry subhumid regions.