The experiment was conducted at the research field of Irrigation and Water Management Division, BARI, Gazipur, and ARS, Benerpota, Shatkhira during the rabi season of 2013-2014 with BARI Surjomukhi-2. It was a warm dry climate with the maximum, minimum and average temperatures of 26.94, 14.46 and 20.70°C, for Gazipur and 27.80, 16.04 and 21.92°C for Satkhira, respectively. The average relative humidity, sunshine hour and evaporation were 74.12 %, 5.42, and 2.96 mm for Gazipur and 69.38 %, 6.58, and 3.60 mm for Satkhira, respectively. The effective rainfall was about 41 and 32.2 mm for Gazipur and Satkhira respectively. The soil characteristics of experimental field was sandy clay loam in texture and pH = 6.03. Each treatment was replicated thrice with one additional spare plot. The experimental design was randomized complete block (RCB) with nine treatments i.e.
T1 = FI up to 100% FC at vegetative, pre-flowering, and heading stage
T2 = DI up to 80% FC at vegetative, pre-flowering, and heading stage
T3 = DI up to 60% FC at vegetative, pre-flowering, and heading stage
T4 = FI up to 100% FC at vegetative and pre-flowering stage
T5 = DI up to 80% FC at vegetative + pre-flowering stage
T6 = DI up to 60% FC at vegetative + pre-flowering stage
T7 = FI up to 100% FC at vegetative + heading stage
T8 = DI up to 80% FC at vegetative + heading stage and
T9 = DI up to 60% FC at vegetative + heading stage.
Where, FI indicates Full Irrigation and DI indicates Deficit Irrigation.
Land preparation was done by using tractor, power tiller, power leader etc. Before sowing seeds were soaked under water for easy germination. Fertilizers were applied at the rate of N90, P34, K80, Zn2, S30, B2.0 kg/ha and cow dung 5.0 t/ha for Gazipur and N108, P37, K30, Zn1.5, S11, Mg1.5, B2.0kg/ha and cow dung 5.0 t/ha for Satkhira. One third of N and total amount of other fertilizers were applied at the time of final land preparation and the rest two third was applied in two splits, one third will be applied after 20 – 25 DAS and the rest one third will be applied before flowering i.e., after 40 –45 DAS. Seeds were planted in line on 25 Nov and 15 Dec, 2013 at the rate of 8-10 kg/ha. The unit plot size and spacing were 4 m × 2 m and 50 cm × 25 cm, respectively. A processing irrigation of 15.57 mm water was applied in the field for ensuring good emergence. Intercultural operations, such as weeding, and pesticide application were done as when necessary. The soil water content was monitored in each plot by using the gravimetric method at 30 cm intervals down to 60 cm. Then, irrigation water amount of each plot was converted to time (min) and applied. The amount of applied water was measured by time-volume technique. Irrigation water was applied by furrow method to bring the soil moisture up to field capacity (29.5%) considering the effective root zone depths (50 cm). Soil moisture at every 10 days intervals was measured by using the crop period. At 60 DAP, some growth data, such as, plant population, plant height, root depth, canopy coverage, biomass etc were recorded. The crop was harvested on 18-19 March, and 20-27 March, 2014 in Gazipur and Satkhira, respectively. Ten plants were randomly selected from each plot for recording yield and yield contributing data during and after harvest. Then, those data were analyzed statistically. Seed oil content of nine treatments was determined according to A.O.A.C. (1990) using soxhlet apparatus and diethyl ether as a solvent.