Potassium (K) is considered as key element for plant growth and physiology and improvement of productivity and quality of crops. The potassium (K) reduction from agricultural soils of Indo-Gangetic plain had been observed due to rapidly increasing intensive cropping systems, in combination with imbalanced fertilization. Now, burning issue is needed to better understand the role and dynamic of K in plants and K-use efficiency of crops. Hence, this study was undertaken during two consecutive years of 2015-16 and 2016-17 to know the effects of different levels of potassium on lentil productivity, nodulation, nutrient uptake and K use efficiency. The experiment was laid out in randomized complete block design considering five treatments with thrice replicates. The treatments were T1 (K Control), T2 (15 kg K ha-1), T3 (30 kg K ha-1), T4 (45 kg K ha-1) and T5 (60 kg K ha-1) along with the blanket dose of N18P20S10Zn2B1.5 kg ha-1 and cowdung 3 t ha-1. Yield and yield attributes of lentil responded significantly to K fertilizer. The highest mean seed yield (1684 kg ha-1) and maximum seed yield increase over control (31.9%) got from T5 treatment followed by T4 treatment. The highest total nutrient (N, P, K, S, Zn and B) uptake, maximum nodulation and the highest protein content (29.4%) in seed was, however, recorded from the plot receiving of 60 kg K ha-1. Apparent K recovery efficiency was recorded higher (17.8%) from T4 treatment. Apparent K recovery efficiency followed the order: T4>T5>T3>T2. From the economic point of view, T5 followed by T4 treatment is viable and sound. The results of the experiment suggest that 60 kg K ha-1 might be applied along with N18P20S10Zn2B1.5 kg ha-1 for lentil cultivation in calcareous soils of Bangladesh. The K rates for fertilizer recommendation in lentil need to be revised to take account for highest yield by higher increasing rate of K in soil

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