The experiment was conducted at the Regional Agricultural Research Station, BARI, Ishurdi, Pabna, during rabi season 2017-2018. The experimental site was a silty clay loam having a field capacity of 28.5%, a permanent wilting point of 13%, and a bulk density of 1.49 g cm-3. Four irrigation treatments were assigned like I1= Irrigation at CRI stage, I2= Irrigation at CRI and vegetative stages, I3= Irrigation at CRI and grain filling stages, and I4= Irrigation at CRI, vegetative and grain filling stages on four tillage methods like T1= Bed Planting, T2= PTOS, T3= Strip tillage, and T4= Zero tillage in a factorial Randomize Complete Block Design with three replications. Seed of BARI Gom -30 was sown in unit plots of size was 7 × 7.5 m. PTOS (Power tiller operated seeder), ST (strip tillage), and zero tillage system were maintained 20 cm row to row distance and in bed planting system maintained 40cm base width, 20cm top width, 15 cm height, and maintained 20cm distance between two beds and 20 cm row to raw distance. Seeds were sown on 22 November 2017, harvested on 15 March 2018, and maintained about 20-25 cm T-aman rice residue at sowing time. Post sowing irrigation was applied up to field capacity to ensure germination. SMD was determined by estimating soil moisture content. For this purpose soil samples were taken from the effective root zone of the wheat plant which is 0 – 90 cm. The root zone was divided into 3 sections viz., 0-15, 15-30 and 30-45cm. Soil samples were collected from these 3 sections with the help of an Augur. The fresh weight of the soil sampled was recorded immediately with the help of a portable weighing balance. After weighed, the samples were stored in a soil sampling core which was then placed in an electric oven for 24h at 100°C. The dry weight of the samples was recorded after oven dry. Soil moisture contents were then calculated.
Soil content moisture (%) = ×100
The following irrigations were applied according to the specified treatments and irrigation water was applied up to field capacity at each irrigation and calculated amount of water by using a flow meter. The amount of water applied to each treatment was calculated on the basis of the soil moisture contents at the time of irrigation by using the following expression.
d = M.C × B.D × D
Where,
d = depth of water to be applied
M.C = moisture content (%)
B.D. = bulk density of the soil
D = depth of root-zone to be irrigated
The Depth of rooting was considered 45 cm. It is reported that 70 % of total moisture is extracted from the 50 % effective root zone depth (Michael, 1996). The seasonal crop water use was calculated by the following relationship:
SWU = NIR + Rf +Σ × ASi X Di
Where, SWU = Seasonal water use, mm
NIR = Total irrigation water depth, mm
Rf = Seasonal rainfall, mm
Mbi = Moisture percentage at the beginning of the season in the ith layer of the soil
Mei = Moisture percentage at the end of the season in the ith layer of the soil
n = No. of soil layers in the root zone, D,
This was considered of three layers, 0-15, 15 –30, and 30 – 45 cm
Di = Depth of the ith layer of soil within the root zone, mm
Asi = Apparent specific gravity of ith layer of soil
All other agronomic practices were carried out uniformly. The grain yield was recorded after harvest. Water use efficiency was used in evaluating the yield performance and water management practices. The water utilized by the crop was calculated by the following relationship:
Water use efficiency (WUE) = , kg m-3
In addition, meteorological data on parameters like temperature, relative humidity, rainfall, etc., and daily pan evaporation were also recorded. Statistical analysis was done by using R software.