Experiment site: The field experiment was conducted at the Horticultural Research Farm, BSMRAU, Gazipur during winter season of 2007-08. The location of the experimental site is at the center of Madhupur Tract (24.09 0 N latitude and 90.26 0 longitudes) at 8.5 m above the sea level (Anon., 1998). Soil The soil of the experimental field was silty clay of Shallow Red Brown Terrace type under Salna Series of Modhupur Tract in Agro ecological zone (AEZ) 28. The soil containing a pH of 6.4 (Anon., 1998; Haider et al., 1991). Climate The experimental site is situated in a sub-tropical climate zone and characterized by no rainfall during December to March and plenty during the rest of the year. Mean weekly data on relative humidity, rainfall and maximum and minimum temperature during the study period were noted from the meteorological station of BSMRAU from September 2007 to April 2008 as reported by Yasmin et al. (2019).
Planting material Top shoot cuttings of standard potato variety Diamant was used in the experiment. The seed was collected from the Tuber Crop Research Center (TCRC). Treatments of the experiment Combination of planting time (P1 = 25, November; P2 = 5, December; P3 = 15, December) and plant density /spacing S1 = (96 plants /m2 or 50 cm X 10 cm); S2 = (64 plants / m2 or 50 cm X 15 cm) and S3 = (48 plants / m2 or 50 cm X 20 cm) resulted in nine treatment combinations (P1S1, P1S2, P1S3, P2S1, P2S2, P2S3, P3S1, P3S2, P3S3). The control was whole tuber with 60 cm X 25 cm spacing.
Preparation of planting material The land was properly ploughed and fertilizer were applied @ cowdung 10 tons / ha, urea 350 kg / ha, TSP 220 kg / ha and MP 270 kg / ha. Full dose of TSP and Mp and 1/3 rd urea were applied at final land preparation and rest 2/3 rd urea were applied in two splits at 10 days interval from emergence for better vegetative growth. Well sprouted seed tubers of Diamant variety were planted at 25, October to produce top shoot cuttings. When the plants reached at 20-25 cm height first top shoot cuttings were taken and planted them after treating with hormone (15 ppm IBA and 10 ppm IAA) in a well prepared seed bed containing sand and well rotten cowdung at the ratio of 1: 1 at 10, November 2007 for rooting. Another two top shoot cuttings were taken at 20, November and 30, November and planted them in well prepared seed bed for rooting. Thus, rooted top shoot cuttings were prepared for planting at 25, November, 05 December and 15, December.
Economic analysis Partial economic analysis was done in order to find out the benefits of using different treatments compare to control. For this purpose cost for seed sowing, cuttings of top shoot, fertilizer / pesticide application, harvesting costs etc. were recorded in per hectare. Partial analysis was done by calculating non-material (labour) and material cost (Seed, fertilizer etc.) for computing the cost of production. The price of the potato tubers was determined on market price basis. Benefit cost ratio was calculated by using the following formula: Benefit cost ratio = Net returns (tk / ha) / Total variable cost (tk / ha). Design and layout, land preparation, intercultural operations and harvesting were performed according to the method described by Yasmin et al. (2019).
Data collection Data on different morphological, physiological and tuber characters were recorded on the following parameters from the sample plants of each plot during the course of experiment. The sampling was done randomly. The plants in the outer row were excluded during randomization. Five plants were randomly selected from each plot to record the data on rate of plant, survivability (%), plant vigor, plant height (cm), foliage coverage (%), number of branches per plant, number of tubers per plant, weight of tubers per plant, yield of tubers (kg / plot and tons / ha), tuber grade by number (%), tuber grade by weight (%) and economic analysis: BCR calculation according to the method applied by Yasmin et al. (2019).