The experiment was conducted at RARS, Rahmatpur, Barishal during 01 December 2017 to 12 May 2018 to study the effects of deficit irrigation on yield and water productivity of different maize varieties. The test crop was a different high-yielding variety of maize: BARI hybrid Maize 9 (BHM−9), BARI Hybrid Maize 7 (BHM−7) and NK-40. These varieties are popular due to their high yield potential and stress-tolerant characteristics. The recommended doses of urea, triple superphosphate, muriate of potash, gypsum, zinc sulphate, borc acid, cowdung at the rate of 500, 240, 180, 240, 10, 5 kg/ha and 6 t/ha were applied. One-third of urea and the entire doses of other fertilizers were applied at the time of final land preparation. The rest two-thirds of urea was top-dressed in two equal splits at 30 and 50 DAS. The first weeding was done manually at 20 DAS and also the thinning was done on the same day keeping only one healthy plant per hill; the rest of the plants were uprooted carefully to avoid disturbance to the nearby plants. The next time, weeding was done only at 64 DAS during the growing season of the crop.
The experiment consisted of two factors: irrigation and variety. Irrigation and variety had five levels or treatments. Irrigation was scheduled based on the depth of water required. The irrigation treatments were allocated to the main plot and the varieties in the subplot. The irrigation and variety treatments were:
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Main plot: Irrigation (5)
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I1
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Full irrigation at initial, vegetative, silking and grain filling (20-25 DAS, 50-60 DAS, 75-80 DAS and 110-120 DAS) stages (Farmer Practice)
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I2
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Full irrigation at initial stage (20-25 DAS)
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I3
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50 % irrigation both at initial and vegetative (20-25 DAS and 50-60 DAS) stages
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I4
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75% irrigation at initial, vegetative stage and silking (20-25 DAS, 50-60 DAS and 75-80 DAS) stages
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I5
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50% irrigation at initial, vegetative, silking and grain filling (20-25 DAS, 50-60 DAS, 75-80 DAS and 110-120 DAS) stages
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Subplot: Variety (5)
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V1
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BARI Hybrid Maize- 9
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V2
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BARI Hybrid Maize- 7
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V3
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NK-40
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Irrigation was applied based on the depth of water required. The procedure of calculating irrigation water is summarized below
Here,
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dir
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Depth of irrigation water to be applied within the one irrigation cycle (mm),
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FC
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Mean soil moisture content at field capacity (%),
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RLi
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Residual soil moisture level before each irrigation in the ith layer of soil profile(%)
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Asi
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Apparent Specific Gravity of the ith layer of soil,
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Di
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Depth of the ith layer of the soil profile within the root zone to be irrigated (mm),
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Irrigation was applied by using a power sprayer and no excess water was applied in the plots. In this case, the volume of water was measured by the following equations.
V= a d (m3)
Here, V= Volume of water in m3
a= area of the plot in m2
d= depth of water applied (m)
The following data was collected from the sample plants
- Plant height
- Cob length
- Cob perimeter
- Number of grains per cob
- Grain yield
- Straw yield
- Hundred (100)-grains weight
Harvest index
Harvest index (HI) is the ratio of grain yield and biological / biomass yield. The biological yield is the sum of the grain and straw yields. The HI is expressed as
Harvest Index (HI) = (1)
Water productivity
The water use of a crop field is generally described in terms of water productivity (WP), which is the ratio of the crop yield to the total amount of water used in the field during the entire growing period of the crop. The WP demonstrates the productivity of water in producing crop yield. WP for maize was calculated by:
WP = (2)
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Where,
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WP
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Water Productivity, kg/m3
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Y
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Grain yield, kg/m2
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SWU
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Seasonal water use in the crop field, m
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The WU was calculated by summing up the water applied in irrigation (taking into account the rainfall) and soil moisture contribution.
Data analysis
The collected data were analyzed using MSTAT statistical package and the mean differences were adjusted by LSD.