Download Integrated Approaches for Increasing Water Productivity in Irrigated

Integrated Approaches for
Increasing Water
Productivity in Irrigated
Rice-Based Systems in Asia
T.P.Tuong
International Rice Research Institute
We all agree
Premises
• The looming water
crisis is threatening
food security in Asia
• Need to develop novel
technologies and
production systems that
• increase or maintain
rice production
• reduce the
expensive/scarce
irrigation water
This presentation will
• Describe the framework & principles
for developing water saving and WPenhancing technologies
• Review the technologies at field level
• Discuss trade-off and challenges of
the technologies
Field water balance lowland rice
I + R = (E + T) + (S+P) + ∆S
Principles
1. Increase yield per unit
transpiration (WPT)
2. Reducing non-beneficial
depletions
3. Effectively using rain and
other (non-irrigation) inflows
4. Effectively using water from
the storage
5. Reducing outflows
Plant
level
Field
level
x
x
x
x
x
x
x
Strategies & Technologies at
field level
1. Enhancing WPT
•
Adjusting cropping calendar, especially to
avoid late season abiotic stresses
2. Reducing non-beneficial depletion
–
–
–
–
Shorten land preparation period
Healthy canopy (nutrient, density..)
Good weed management
Mulching
Field level – cont’d
3. Effectively using rain and other (nonirrigation) inflows
• Dry direct seeding
Field level – cont’d
3. Effectively using rain and other (nonirrigation) inflows
• Dry direct seeding
• Use marginal quality water, non conventional
water source
4. Use stored water
•
•
Increase rooting depth
Increase ponding depth
5. Reduce ouflows
Reducing outflows:
1. Increasing hydraulic resistance of soil
• Puddling
• Shallow tillage to
close cracks
400
P e r c o la tio n
O th e r c o m p o n e n t
350
• Soil compaction
W a te r u s e ( m m )
• Bund management
300
250
200
150
100
50
0
C o n tr o l
S h a llo w T illa g e
Reducing outflows:
2. Reducing pressure head of ponding water
• Reducing water depth
• Reducing ponding duration
vegetative
AWD
Field water depth (mm)
Saturated soil culture
60
(SSC)
0
14
reproductive
28
42
56
ripening
70
84
96
Days after transplanting
50
40
2 - 5 cm
terminal
drainage
1-2 cm
30
WR1
20
2 - 5 cm
10
1-2 cm
terminal
drainage
saturated
WR2
0
0
10
20
1-2 cm
Transp
. Early
WR3
recovery tillering
30
Late
tillering
40
50
saturated
60
PI to
flowering
70
80
Days after Transplanting
90
100
terminal Matu
Grain filling
drainage
4500
Amount of water (kg)
4000
3500
3000
2500
2000
1500
1000
Continuous
Flooding
Saturated
soil
Alternate wetting
and drying
Source: Tabbal et al. 1992
Amount of water applied to the field to produce
1 kg of rice under different irrigation regimes
Reducing outflows:
3. Aerobic rice system
Treat rice like any other (irrigated) crop:
No puddling, no standing water, aerobic soil
Trade offs and challenges
1. Interactions among scales
Water productivity trends over different spatial scales
Water productivity (kg/m3)
0.25
0.20
0.15
0.10
0.05
0.00
0
5000
10000
15000
20000
Scales (ha)
WP water input
WP irrigation
Source: Hafeez, 2003
Water saving principles
Translate to savings at
higher scales?
1. Increase yield per unit
transpiration (WPT)
Yes, always
2. Reducing nonbeneficial depletions
3. Effectively using rain
and other inflows
4. Effectively using water
from the storage
5. Reducing outflows
Yes, always
Depending on whether
excessive rainfall, other
inflows, storage water can
be used downstream
Depending on how outflows
are used downstreams
Trade offs and challenges
1. Interactions among scales
2. Nutrients
Phosphorus and nitrogen are less available in
aerobic conditions
SSC and AWD: same N mgt as flooded
Aerobic requires more N
Micronutrient deficiencies in raised beds
and aerobic rice systems
Trade-offs and Challenges
3. Weeds
Higher weed infestation
Weed species shift
4. Sustainability
Flooded rice: a sustainable system
Indications that SSC, AWD are sustainable,
But not aerobic rice systems
1.0
Yield Aerobic
Yield Flooded
0.8
0.6
0.4
0.2
0.0
DS01
WS01
DS02
Season
WS02
DS03
Source: Peng and Bouman, 2003
Trade-offs and Challenges
5. Environmental effects of WSIs
• Greenhouse gas: reduce methane but
increase N2O emission
• May increase nitrate and herbicide
pollution in ground and surface water
• Affect ecological functions of rice fields
Source: Molden, 2003
Conclusions
• There exist water-efficient technologies
• But “efficiency” is not enough, these
technologies also have to
– Be economically viable
– Sustain
– Be environment friendly
– Protect ecological functions of rice fields
Challenges for Rice Science
….and…….. beyond