Presentation from the WCCA 2011 event held in Brisbane, Australia.

1. Effect of mulch on water use and productivity of
wheat in Punjab, India-Field and simulation studies
Balwinder Singh, IRRI, Philippines
Liz Humphreys, IRRI, Philippines
Don Gaydon, CSIRO, Australia
Phil Eberbach, CSU, Australia
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2. Methodology
•Field experiments (2006-07 and 2007-08)
•Crop model application
Ludhiana, Punjab
2

3. Treatments
Mulch treatments
• With mulch (8 t/ha)
• Without mulch
Irrigation management
-First irrigation at -40kPa SMP at 15-20 cm soil depth
- Subsequent irrigations at -40kPa SMP at 35-40 cm soil depth
3

4. Rainfall/irrigation- 2006-07
80
Rain- 160 mm
70
Mulch irrigation = 75 mm
60
Rain/irrigation (mm)
Non-mulch irrigation= 150 mm
50
40
30
20
10
0
1 16 31 46 61 76 91 106 121 136 151
Days after sowing
4

5. Rainfall/irrigation- 2007-08
80 Rain- 88 mm
70 Non-mulch irrigation= 225 mm
60 7 days Mulch irrigation = 150 mm
28 days
Rain/irrigation (mm)
50
40
30
20
10
0
1 16 31 46 61 76 91 106 121 136 151
Days after sowing
5

6. Grain yield (kg/ha)
5
Mulch Non mulch
4 NS
Grain yield (kg/ha)
3
2
1
0
2006-07 2007-08
14
Mulch Non mulch
Biomass production (t/ha)
12
10
8
Total biomass production (t/ha)
6
4
2
0
6
2006-07 2007-08

7. .
Evapotranspiration (ET)
Water balance equation
ET= R+I-D-R-Δ(θv)
R = Rainfall
I = irrigation (volume was measured with a Woltman helical turbine meter)
D= drainage below root zone (1.8 m) (zero) ( based soil matric potential gradients to 180
cm depth)
R= runoff, zero as the plots had small bunds
Δ(θv) = change in soil water content (0-180 cm) between sowing and harvesting
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8. .
Evapotranspiration (ET)
450
Mulch Non mulch
400
N/S
N/S
350
300
ET (mm)
250
200
150
100
50
0
2006-07 2007-08
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9. Water productivity
Grain WPET (kg/ha/mm)
14
Mulch Non mulch WPET = grain yield or biomass/ET
12
Units, kg/ha.mm
10
8
Grain water productivity
6
based on ET (kg/ha.mm)
4
2
0
2006-07 2007-08
40
Mulch Non mulch
Biomass WPET (kg/ha/mm)
35
30
Biomass water productivity
25
based on ET (kg/ha.mm)
20
15
10
5
0
2006-07 9 2007-08

10. APSIM application
APSIM validation
Balwinder-Singh, Gaydon DS, Humphreys E, Eberbach PL (2011). Evaluating the performance of APSIM for
irrigated wheat in Punjab, India. Field Crops Research, 124, 1-13.
Model attribute R2 (co-efficient of determination)
Grain yield 0.89
Biomass 0.95
ET 0.86
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11. Simulation set up
• Weather data at Ludhiana, Punjab (1970-2006) (36 years)
• Soil type-Sandy loam (290 mm PAWC, 0-180 cm)
Variables
• mulch ( 0, 8 t/ha)
• 8 irrigation schedules
(10%, 20%, 30%, 40%, 50%, 60% and 70%SWD of 0-60 cm soil layer, rainfed)
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12. •Wheat var. PBW 343 sown 10 November
• 150 plants/m2
•Initial soil water content at field capacity
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13. Grain yield - mulch and irrigation interactions
1.2
10%-NM
10%-M
~ 0.5 t/ha
1 40%-NM
40%-M
70%-NM
0.8 70%-M
Cumulative Probability
0-NM
0-M Yield ranged from 3
0.6
to 8 t/ha
0.4 In 60% years yield
< 7 t/ha
0.2
0
0 1 2 3 4 5 6 13 7 8 9
Grain yield (t ha-1)

14. Biomass production
1.2
40%-NM
1
Cumulative probability
40%-M
0.8
0-NM
0.6 0-M
0.4
0.2
0
0 5000 10000 15000 20000
Biomass production (kg/ha)
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15. Irrigation water input
1.2
10%-NM
10%-M
1
40%-NM
At 40% SWD, mulch 40%-M
reduced irrigations by Cumulative probability
0.8 70%-NM
1 in ~50% years 70%-M
Average reduction 0.6
~40 mm
0.4
0.2
0
0 100 200 300 400 500 600
Irrigation water (mm)
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16. Soil evaporation
1.2
10%-NM
Es reduced 1 10%-M
by ~ 40mm 40%-NM
Cumulative probability
In irrigated wheat 0.8
40%-M
by ~20 mm in rainfed 0-NM
0.6
wheat 0-NM
0.4
0.2
0
0 50 100 150 200
Soil Evaporation (mm)
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17. Transpiration
1.2
Followed the same trends as 10%-NM
by grain yield 10%-M
1
40%-NM
No effect in frequent irrigation
40%-M
treatments
Cumulative probability
0.8 70%-NM
70%-M
0-NM
0.6 0-M
0.4
0.2
0
0 100 200 300 400 500
Transpiration (mm)
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18. Evapotranspiration
1.2
10%-NM
10%-M
ET reduced by mulch 1 40%-NM
~ 40mm (same as Es)
40%-M
in frequent irrigation
70%-NM
treatments
Cumulative probability
0.8
70%-M
However, No 0-NM
difference for ET was 0.6 0-NM
observed in field study
0.4
No difference in
rainfed treatment
0.2
0
0 100 200 300 400 500 600
ET (mm)
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19. Grain water productivity (WPET)
1.2
Highest WP at 40%
SWD 10-NM
1
10-M
Cumulative probability)
40-NM
0.8
40-M
70-NM
0.6
70-M
0.4
0.2
0
5 7 9 11 13 15 17 19 21
Grain WPET (kg ha-1 mm-1)
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20. Conclusions
• Mulch reduced irrigation requirement when irrigated
according to soil water status
(by 1 irrigation in ~50% of years)
• Mulch reduced Es of well-irrigated wheat by ~40 mm
• No effect of mulch on grain yield of irrigated wheat
• APSIM Wheat predicted ET lowered by mulch
BUT field study showed no effect of mulch on ET (due to
increased T) – a worry!
Which is right? - needs further investigation.
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