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Strategies to reduce deep drainage and nitrogen leaching from furrow irrigated systems: A simulation study
Keith L. Bristow, Altaf A. Siyal and Jirka Šimůnek
CSIRO LAND AND WATER / SUSTAINABLE AGRICULTURE
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Need to improve productivity and environmental performance of furrow irrigated systems
Think about potential changes / improvements within a systems context Consider developed and developing world context Consider environmental and social (eg labour) implications of potential changes Draw on experiences from Australia and especially China, Asia, Africa Improve water use efficiency (reduce evaporation and deep drainage) and
nutrient use efficiency (reduce runoff and leaching losses)
Furrow Irrigation
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Richards’ Equation (RE) for water flow
Convection Dispersion Equation (CDE) for solute transport
HYDRUS 2-D Model
Flow Domain
Half furrow Ridge Half furrow
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Fertilizer placement:
150 Kg N / ha mixed into the top few centimetres of soil
P1 Fertiliser
Fertiliser
P2
P3
P5
P4
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Soil surface management
Sc
Sn
Sp
Normal
Compacted
Plasticcover
“Water supply turned off when water level reaches a pre-determined depth in the furrow”
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Time to ‘turn off’ and ‘water to infiltrate’P
ress
ure
hea
d a
tb
ase
of
furr
ow
(cm
)
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Drainage flux from base of root zone
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Effect of soil surface treatment on water applied
Cumulative input
Cumulative output
Water held in
the flow domain
WaterSaving
(mm) (mm) (mm) %Sn 120 5.5 114.5 0Sc 100 0.6 99.4 17Sp 86 0.2 85.8 28
Initial water held in the profile was 180 mm in all treatmentsWater application rate = 900 L/hr
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Applicationrate (L/h)
Sn Sc Sp
Appliedmm
Appliedmm
Saved%
Appliedmm
Saved%
600 187 136 27 106 43
800 132 107 19 90 32
1000 112 95 15 84 25
Effect of water application rate on water saved
Initial water held in the profile was 180 mm in all treatments
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Nitrogen concentration
Sn Sp
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Fertiliser Placement
Normal soil
(Sn)
Compacted Soil
(Sc)
Plastic Covered
Soil (Sp)
kg N ha-1 kg N ha-1 kg N ha-1
P1 50.0 1.4 0.0P2 3.0 0.1 0.0P3 23.0 0.6 0.0P4 0.0 0.0 0.0P5 0.0 0.0 0.0
Effect of fertiliser placement on nitrogen leached from the root zone
Total nitrogen applied was 150 kg N / ha
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Can use ‘plastics’ to maximise the benefit of capillarity and minimise the impact of gravity in furrow irrigated systems
This analysis demonstrated water savings can exceed 40% and leaching losses can be reduced from 33% to zero
Projects to explore design and management of ‘smart’ plastics are now underway
Conclusions
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Soil water content at initiation of irrigation and 120 hours later
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Flow Domain
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Boundary conditions