The experiment was conducted at Regional Agricultural Research station, BARI, Ishawardi, Pabna, during rabi seasons 2015-16 and 2016-2017. The experimental soil was a silty clay loam having field capacity of 28.5%, permanent wilting point at 13% and bulk density of 1.49 g/ cm3. Four irrigation treatments were assigned in a Randomize Complete Block Design with three replications. Seed of BARI Gom -28 was sown in unit plots of size was 7 × 7.5 m, on raised bed in 40cm base width, 20cm top width, 15 cm height and maintained 20cm distance between two beds by using the bed planter and was subjected to following irrigation treatments:
T1 = Irrigations up to 100% FC at CRI, botting and grain filling stage (flat land)
T2 = Irrigations up to 100% FC at CRI, botting and grain filling stage on raised bed
T3 = Irrigations up to 80% FC at CRI, botting and grain filling stage on raised bed
T4 = Irrigations up to 60% FC at CRI, botting and grain filling stage on raised bed
Seeds were sown on 24 November 2015 and 20 November 2016, harvested on 13 March 2016 and 10 March 2017 respectively. 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- 45 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 soil sampling core which were 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 as under:
Soil content moisture (%) = {(Fresh weight of the sample) / (Dry weight of the sample)} x 100. The following irrigations were applied according to the specified treatments and irrigation water was applied up to field capacity at each irrigation. 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 = {(F.C-M.C) × (B.D × D)} / 100.
Where,
d = Depth of water to be applied, cm
M.C = Moisture content (%) just before irrigation
F.C = Field capacity of soil
B.D. = Bulk density of the soil, gm/cm
D = Depth of root-zone to be irrigated, cm
The depth of rooting was considered to be 45 cm. It is reported that 70 % of total moisture is extracted from the 50 % effective root zone depth (Michael, 1996).