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 furrowRidgeHalf furrow

Fertilizer placement: 150 Kg N / ha mixed into the top few centimetres of soil P1P1 Fertiliser P2P2 P3P3 P5P5 P4P4

Soil surface management ScSc SnSn SpSp Normal Compacted Plastic cover “Water supply turned off when water level reaches a pre- determined depth in the furrow”

Time to ‘turn off’ and ‘water to infiltrate’ Pressure head at base of furrow (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 Water Saving (mm) % SnSn ScSc SpSp Initial water held in the profile was 180 mm in all treatments Water application rate = 900 L/hr

Application rate (L/h) SnSn ScSc SpSp Applied mm Applied mm Saved % Applied mm Saved % Effect of water application rate on water saved Initial water held in the profile was 180 mm in all treatments

Nitrogen concentration SnSn SpSp

Fertiliser Placement Normal soil (S n ) Compacted Soil (S c ) Plastic Covered Soil (S p ) kg N ha -1 P1P P2P P3P P4P4 P5P5 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