Field experiment was conducted in Rabi season of 2015-16 and 2016-17 in the research field of Pulses Research Sub-Station, Bangladesh Agricultural Research Institute (BARI), Gazipur (24° 0′ 13″ N latitude and 90° 25′ 0″ E longitude). Gazipur is medium high land with fine-textured (clay loam) terrace soils. It belongs to Chhiata series (Soil taxonomy: Udic Rhodustalf) under the agroecological zone - Madhupur Tract (AEZ-28). The Gazipur area received average rainfall from 1.40 to 118 mm during October to March. The mean minimum and maximum air temperatures during October to March of the experiment were 12.2 & 33.1°C during 2015-16 and 13.6 & 33.1°C, respectively during 2016-17. The average minimum and maximum humidity (%) were 51 and 88 during October to March. Before starting the experiment, initial soil (0-15 cm) sample was analyzed as outlined by Page et al. (1982) and standard method. The land was firstly opened by a tractor operated chisel plough and then prepared thoroughly by ploughing with a power tiller followed by laddering and leveling. There were 5 treatments consisting of different levels of potassium (0, 30, 40, 50 & 60 kg K ha-1) including control such as T1 = Control, T2 = 30 kg K ha-1, T3= 40 kg K ha-1, T4= 50 kg K ha-1, T5= 60 kg K ha-1 along with the blanket dose of other nutrients N, P, S, Zn and B @ 15, 20, 10, 2 and 1.5 kg ha-1, respectively.The experiment was laid out in randomized complete block design (RCBD) with three replications. The unit plot size was 12 m2 (4 m x 3 m). Nutrients N, P, K, S, Zn and B were applied as urea, TSP, MoP, gypsum, zinc sulphate and boric acid, respectively during final plot preparation. Seeds of lentil (cv. BARI Masur-7) were treated using the fungicide Provex 200 (at 2.5 g kg-1 seeds) before sowing for controlling of root rot disease. Treated seeds (@ 30 kg ha-1) were sown on 09 November, 2015 and 16 November, 2016. Seeds were sown continuously in rows (10 rows/plot) maintaining row to row spacing of 30 cm. Hand weeding as well as thinning of seedlings were done at 25 days after sowing (DAS) maintaining the distance of plant to plant 05 cm by making a total of 800 plants per plot (12 m2). Again, hand weeding was done at 50 DAS. Three sprays were done with fungicide of Rovral starting from 55 DAS to control Stemphylium disease and two times insecticide (Karate @ 2 ml L-1 of water) sprayed at 10 days interval starting from 60 DAS to overcome insect infestation. The crop was harvested at maturity. Data on seed yield (kg ha-1) at around 10% moisture basis were recorded from the whole plot technique. For stover yield (kg ha-1), mature plants were collected from two 1m2 quadrates in each plot at harvest time. The yield contributing characters namely: plant height and number of pods plant-1 were recorded from ten plants selected randomly from each unit plot. Pods were detached from every plant and the number of pods per plant was counted and averaged. Thousand seed weight (g) was determined by the counting of 500 seeds randomly from each plot and weighing through electronic balance and converting it into 1000-seed weight. For nodule counting per plant, 5 plants from each plot were selected randomly at seedling, vegetative, flowering and podding stages. Plants were smoothly uprooted and the soil from roots was removed carefully using tap water. Separated nodules were sliced into two pieces to observe the inside color for nodules activity. The light-pink or red coloured nodules were considered as active. Stover and seed samples were digested with di-acid mixture (HNO3-HClO4) (5: 1) as described by Piper (1966) for determination of P (spectrophotometer method), K (atomic absorption spectrophotometer method), S (turbidity method using BaCl2 by spectrophotometer), Zn (atomic absorption spectrophotometer method, VARIAN SpectrAA 55B, Australia) and B (spectrophotometer following azomethine-H method) concentration. The N concentration was determined by Micro-Kjeldahl method. Protein content was calculated multiplying the N value by 6.25 (Hiller et al., 1948). Data on yield attributes, number of nodules per plant, protein content and N, P, K, S, Zn, B content were computed on average of two study years. Data of all parameters were statistically analyzed by ANOVA procedure. Then, multiple comparisons were done by LSD at 5% level (Statistix 10., 1985).