Water Use Efficiency and Yield of Sweetpotato as Affected by Nitrogen and Potassium Application

The effect of nitrogen and potassium on the yield and water use efficiency of sweetpotato (Ipomoea batatas L.) was studied under water stress condition. The treatments consisted of two soil water regimes (30% and 80% of the soil field capacity) and nitrogen and potassium treatments (20, 100, and 200 kg of N ha-1, with a non-limiting potassium supply (160 kg of K ha-1) and 16, 80, and 160 kg of K ha-1, with a non-limiting nitrogen supply (200 kg of N ha-1). The experiment was carried out in complete randomized design with 4 replications. The supply of nitrogen and potassium at 100 kg N ha-1 and 160 kg K ha-1 produced the highest tuber yields under both well watered and water stressed conditions. A higher nitrogen supply in the soil produced greater leaf area, but increasing soil nitrogen beyond 100 kg N ha-1 reduced tuber yields. Leaf area and yields of Lole cultivar were less affected by water stress than were those of Wanmun cultivar. Under water stress conditions, Wanmun cultivar produced lower tuber yields than did Lole cultivar. Plant water use efficiency increased as the potassium supply increased under adequate and water-stressed conditions in both Lole and Wanmun cultivars.