The experiment was conducted at the research field of Irrigation and Water Management Division, Bangladesh Agricultural Research Institute, Gazipur during the winter season of 2012 to 2013 with the variety of BARI Sarisha-14. The average annual rainfall was about 1897.63 mm (BBS 2013). The soil characteristic of experimental field was sandy clay in texture, with a bulk density of 1.49-1.50 g/cm3 and volumetric water content at permanent wilting point and field capacity (FC) was 14.1 and 29.0%, respectively. The average pH of the soil was 6.45. It was a warm dry climate with the maximum temperature of 32 and 32.20C, minimum temperature of 18 and 21.40C, relative humidity of 93%, evaporation of 5.3 and 4.9 mm, sunshine of 9.7 and 9.49 hour, and wind speed of 71 and 107 km/hr during 2012 and 2013, respectively. Soil physiochemical properties were determined by following Graham et al. (2013), Bremner and Mulvaney (1982). The variety, BARI Sarisha-14 was sown in line on 17th and 15th November 2011 and 2012 at a rate of 6.5 kg/ha. The unit plot size and spacing were 3.9 m × 4.95 m and 30 cm ×15 cm, respectively. The experimental design was randomized complete block with three replications and six irrigation treatments viz. T1, T2, and T3 = Sprinkler irrigation at vegetative (V), pre-flowering (PF), and pod formation (P) stage, respectively (20, 35, and 55 days after sowing), T4 = Sprinkler irrigation at V and P stages (20 and 55 days after sowing), T5 = Sprinkler irrigation at PF and P stages (35 and 55 days after sowing), and T6 = Basin irrigation at V, PF and P stage (20, 35 and 55 days after sowing). Fertilizers were applied at the rate of N 104 kg/ha as urea, P32 kg/ha as TSP, K39 kg/ha as MP, S24 kg/ha as gupsum, Zn1.2 kg/ha as zinc sulphate and B1.0 kg/ha as boric acid, respectively (FRG 2012). Two-third of N and total amount of other fertilizers were applied at the time of final land preparation and remaining N was applied as top dress after first irrigation. A common irrigation of 10 mm was applied after sowing for ensuring proper emergence. Intercultural operations, such as weeding, thinning and pesticide (Diazinon 60 EC) application were done whenever necessary. After 20 to 25 days of pod formation, it reached its physiological maturity and harvesting was done on 12th and 8th February 2012 and 2013, respectively. At the time of harvesting, middle nine (09) rows out of 13 were selected randomly to collect 10 plants from each replication to avoid border effect. The data on plant height, number of branch per plant, and pod number per plant were collected after harvest. After threshing and cleaning, data on grain yields (12% moisture content) and yield contributing characters were recorded. The measured data were analyzed statistically by using R software (Version 3.1.1). Mean separation was done by least significant difference (LSD) test at 5% level of probability. Crop evapotranspiration (ET) was calculated by the following water balance equation (Karam et al. 2014).
ET = I + P ± ΔS – R – D
where, ET is evapotranspiration (mm), I is the depth of irrigation water (mm), P is the precipitation (mm), ΔS is the change in soil water storage (mm), R is the runoff, and D is the drainage below the root zone. In the equation, time-volume technique (Grimes et al. 1987) was used to irrigate (I) the crop. Soil water content was monitored in each plot by using the gravimetric method. Then, irrigation water amount of each plot was converted to time (min) and applied. The source of water was fresh underground and carried out by using plastic hose pipe of 30 mm in diameter. Irrigation water was applied to bring the soil moisture up to field capacity. Soil moisture was measured from different layers at every 10 days intervals. Precipitation was observed at the agro-meteorological station which was very close to the experimental field, ΔS obtained from gravimetric moisture observations in the soil profile to a depth of 60 cm. There was no surface runoff and drainage as measured quantity of water was applied to fill the gap between FC and soil moisture at the time of irrigation. The following formula was used to irrigate the crop (Michael 2014a),
I = (FC – MCi/100)× As × D .
where, I = Depth of water applied, cm, FC = Field capacity moisture content, % vol. Mci = Moisture content of the soil at the time of irrigation, % vol. As = Apparent specific gravity of the soil (g/cc3). D = Depth of root zone, cm. The establishment of sprinkler irrigation method needs some initial investment cost (fixed cost) which include lateral pipe, sprinkler head and tripod stand. Land use cost was also considered as a fixed cost in a seasonal basis. For basin irrigation, lateral pipe and land use cost was considered as an initial investment cost.