The experiment was conducted at the experimental field of IWM Division, BARI, Gazipur and at farmer’s field of Godagari, Barind, Rajshahi during 2015-2016, 2016-2017 and 2017-2018. The soils were silty clay loam with field capacity (28.5-29%), and bulk density (1.44-1.48) gm/cc at both locations. The recommended dose of fertilizers was applied: P20K20S14Zn5B1 kg/ha and CD: 5 t/ha. Full doses of P, K, S, Zn, B, and cowdung were applied at the time of final land preparation. The experiment was laid out in an RCBD design with four replications. The unit plot size was 6 m × 6 m. The treatments were selected based on irrigation application at different growth stages as stated below:
Treatments
T1= Rainfed
T2= One irrigation (light irrigation of 1.0-1.5 cm) at post-sowing
T3= One irrigation (light irrigation of 2-3 cm) at pod development (80-85 DAS) stage
T4= Two irrigations given each at post-sowing and pod development (80-85 DAS) stages
Seeds were sown on 19, 16 and 15 November in the year 2015, 2016 and 2017 at Gazipur and 27 October 2015, 22 and 02 November 2016 and 2017 at Godagari, Barind, Rajshahi at a spacing of 20 cm plant to plant and 40 cm line to line. Soil moisture at every 10 days interval was measured. The measured amount of water was applied to each plot as per treatment to maintain the soil moisture content in the root zone depth. Ten plants from each plot were selected randomly for collecting growth data including root length, shoot length, canopy coverage and biomass. Canopy coverage was calculated using the following equation:
Canopy coverage = To obtain biomass data and plant samples were collected from the field and oven-dried at 650C temperature until fixed weight come. Biomass data were collected five times. Undesirable plants were rouged out. After physiological maturity, pods were harvested from the plants and then dried. After 4-5 days, sun drying, seeds were separated from the pod and again dried for 2-3 days and preserved for future use. The crop was harvested on 15, 16 and14 March in 2015-2016, 2016-2017 and 2017-2018 at Gazipur and 9, 20, and 5 March 2015-2016, 2016-2017 and 2017-2018 at Rajshahi. After harvest, yield and yield contributing data were collected.
Estimation of irrigation water: Irrigation water was applied to bring the soil moisture content at the root zone to field capacity taking into account the effective root zone depth. Irrigation water was calculated using the following equation (Michael, 1985):
Where d = Depth of water applied (cm))
Fc = Field capacity of soil (%)
Mci = Moisture content of the soil at the time of irrigation (%)
As = Apparent specific gravity of the soil
D = Depth of root zone (cm)