The experiment was conducted at two locations of BARI, Gazipur, and farmer’s field, Shympur, Rajshahi, during the rabi season of 2015-2016 with a Mustard crop of variety, BARI Sarisha-14. The weather conditions, especially the temperature, humidity, and rainfall are recorded. The soil texture of the experimental field was sandy clay loam in both locations. The soil pH was 6.45 in Gazipur, 7.80 in Rajshahi. Five irrigation treatments were replicated thrice with a randomized complete block (RCB) design. The treatments were as follows:
T1 = Full irrigation at pre-flowering (25-30 DAS) and pod formation (50-55 DAS) stages
T2 = DI80%up to FC at pre-flowering (25-30 DAS) and pod formation (50-55 DAS) stage
T3 = DI60%up to FC at pre-flowering (25-30 DAS) and pod formation (50-55 DAS) stage
T4 = DI80% at pre-flowering (25-30 DAS) stage
T5 = DI80% at pod formation (50-55 DAS) stage
Land preparation was done by using the tractor, power tiller, etc. Fertilizers were applied at the rate of N75, P20, K45, S15, Zn1.25, B0.5 kg ha-1, and cowdung 5.0 t/ha for Gazipur, while for Rajshahi it was N104, P29, K75, S24, Zn2.1, B0.85 kg ha-1 and cowdung 5.0 t/ha. Two-thirds of N and the total amount of other fertilizers and cowdung were applied at the time of final land preparation and the remaining N was applied as top-dresses after first irrigation. Seeds were planted in line on 1 and 5 November 2015 at the rate of 7 kg/ha. The unit plot size and spacing were 4.8 m × 3.9 m and 30cm x 15cm, respectively. No watering was done at the time of sowing and after germination. Weeding and thinning were done at 10-12 DAS and 15-17 DAS. Insecticide (Sumethion 57 EC) was applied at 54 and 64 DAS. The soil water content was determined in each plot by gravimetric method at 30 cm intervals down to 60 cm soil depth. Then, the irrigation water amount was estimated for each plot and then the time required (in minute) to apply this amount was calculated and applied. The amount of applied water was measured by the time-volume technique. Soil moisture was collected before sowing, before each irrigation, and after harvest. Irrigation water was applied by the basin method to bring the soil moisture up to field capacity (29.5%) considering the effective root zone depth (60 cm). Soil moisture at every 10 days intervals was measured during the crop period. However, scheduled irrigation was applied at 25 and 56 DAS at Gazipur, while at 25 DAS and 47 DAS at Rajshahi. The vegetative stage, pre-flowering stage, flowering stage, and pod-formation stages appeared from 4 to 24 DAS, 25 to 31 DAS, 32 to 40 DAS, and 41 to 71 DAS, respectively. Physiological maturity was observed at 76 DAS and harvested on 20 to 23 January 2016 at Gazipur, while it was 28 January 2016 at Rajshahi, respectively.
Seasonal evapotranspiration was calculated by summing up applied water, effective rainfall (ER), and soil water contribution (SWC). Water productivity (WP) was calculated as the ratio of grain yield and water use (WU). Biomass and leaf area index (LAI) was monitored at times during the crop period. During harvest 1 sq. meter plot was selected from each replication to collect the yield and yield contributing data. Then, all the data were analyzed statistically by using R software, and mean separation was done by Duncan's multiple range test at a 5% level of significance. Financial analysis was done considering water-limiting situations (Ali et al., 2007, and English, 1990). Here the consideration was that by applying less water than the full requirement some amount of water was saved which was subsequently utilized to cover additional area. Total cost was calculated by adding total operating cost, interest on operating cost, and land-use cost.