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

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

Richards’ Equation (RE) for water flow Convection Dispersion Equation (CDE) for solute transport

HYDRUS 2-D Model

Flow Domain

Half furrow Ridge Half furrow

Fertilizer placement:

150 Kg N / ha mixed into the top few centimetres of soil

P1 Fertiliser

Fertiliser

P2

P3

P5

P4

Soil surface management

Sc

Sn

Sp

Normal

Compacted

Plasticcover

“Water supply turned off when water level reaches a pre-determined depth in the furrow”

Time to ‘turn off’ and ‘water to infiltrate’Pr

essu

re h

ead

atba

se o

f fur

row

(cm

)

Drainage flux from base of root zone

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

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

Nitrogen concentration

Sn Sp

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

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

Soil water content at initiation of irrigation and 120 hours later

Flow Domain

Boundary conditions