Timing lifts irrigated yields

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Two light blue water drops on a darker blue backgroundIrrigating at both booting and grain fill increased predicted WUE by 12 per cent above rain-fed conditions while irrigating in response to soil water deficit lifted WUE by 23 per cent compared with rain-fed conditions.

Tasmania may be Australia’s wettest state, but research into water use efficiency benchmarks has found that irrigation, particularly in combination with additional nitrogen applications, has the potential to significantly lift yields

With high-value crops such as poppies and potatoes competing for irrigation water, strategic irrigation of cereals is a necessary practice in Tasmania.

However, recent research indicates there is room for significant improvement in the water use efficiency (WUE) of cereal crops. Field trials of barley between 2008 and 2011 report WUEs ranging from a low of seven through to 24 kilograms per hectare per millimetre of water.

Tasmanian Institute of Agriculture researcher Dr Tina Acuña says deciding when to irrigate is the key to increasing cereal WUE.

Research conducted as part of the GRDC Water Use Efficiency Initiative indicated small gains in predicted grain yield and WUE could be achieved in most years by additional strategic irrigation. For example, irrigating at both booting and grain fill increased predicted WUE by 12 per cent compared with rainfed conditions, and 10 per cent compared with irrigating at either stage alone.

Irrigation based on soil water deficit and crop water use further improved predicted WUE by 23 per cent compared with rainfed conditions.

These results indicate that investing in soil moisture monitoring equipment would help growers make more objective and profitable decisions in scheduling irrigation of cereals.

cereal crop in TasmaniaDr Tina Acuña at the Tasmanian Institute of Agriculture

Research into water use efficiency benchmarks has found that properly timed irrigation has the potential to lift cereal yields in Tasmania.

Dr Tina Acuña (right) at the Tasmanian Institute of Agriculture.

Controlled-release fertiliser

The use of controlled-release nitrogen fertiliser to better match nitrogen supply to crop demand and lift water use efficiency (WUE) has potential, but further research is needed to understand the fit of these controlled-release products in Australian cropping systems.

Controlled-release fertilisers are coated with a polymer blend, the composition and thickness of which determines when and how fast the fertiliser is released into the soil. They are typically applied only once at sowing – offering logistical advantages in wetter areas where applying fertiliser during the season can be problematic.

CSIRO crop simulation studies as part of the GRDC-funded Water Use Efficiency Initiative examined the potential of controlled-release nitrogen fertilisers to lift wheat yields in high-rainfall cropping areas of Tasmania and the Lower Eyre Peninsula.

In the Tasmanian modelling work, the controlled-release fertilisers were predicted to have limited yield benefits due to the lack of large leaching losses at the particular site simulated. Controlled-release fertilisers are only likely to provide yield benefits in situations where nitrogen supply to crops becomes inadequate because of losses of added nitrogen through leaching or nitrous oxide emissions.

A local grower group in the Lower Eyre Peninsula was keen to test controlled-release fertiliser as growers were finding it difficult to deliver enough nitrogen to their high-rainfall cropping system. The simulation study predicted that in this case the use of the controlled-release fertiliser would significantly reduce leaching and that nitrogen rate could be halved while maintaining the same wheat yield.

This study highlighted the importance of understanding the water-holding capacity of cropping soils, which in the case of the study site was very low. Water and not nitrogen was the main factor limiting further increases in yield, although controlled-release fertiliser could allow reductions in nitrogen application and reduce the need for top-dressing.

More information:

Dr Tina Acuña, Tasmanian Institute of Agriculture,
03 6226 7507,

Dr Kirsten Verburg, CSIRO Land and Water,
02 6246 5954,

Dr Therese McBeath, CSIRO Ecosystem Sciences,
08 8303 8455,

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GRDC Project Code UT00016, CSP00111, LEA001

Region South, North, West