While small changes in management can have a significant impact on production and profit when it comes to improving water use efficiency, the only way to maximise these efficiencies is to measure them.

NSW Department of Primary Industries (DPI) is already proving this in the Advancing Water Management in NSW project which aims to lift water use efficiency for primarily surface irrigation systems.

“A measuring technology known as Irrimate was used to monitor irrigation performance in the Gwydir Valley during the 2006-07 cotton season and the results indicate that gains can be made,” DPI water use efficiency officer at Moree, Janelle Montgomery, said.

“Water use efficiencies are commonly measured at the whole farm level but Irrimate provides growers with simple tools to assess their irrigation performance on individual fields.”

Optimum irrigation performance is achieved when both application efficiency and distribution uniformity are high.

Thirty irrigation events were monitored in the Gwydir Valley during the season, with application efficiency ranging between 40 and 94 per cent.

“A number of irrigation events were already optimised – water was evenly applied down the field, meeting the deficit with little deep drainage or runoff losses,” Ms Montgomery said.

“Other events were improved simply by pulling siphons earlier or increasing the flow rate by maintaining a high level of head in the head ditch.”

Improving irrigation performance resulted in reduced application of water by up to 0.35 megalitres per hectare per irrigation, with an average reduction of 0.13 ML/Ha/irrigation.

Spread over 400ha and seven irrigations, this would amount to 364ML which could grow an extra 50 ha cotton or be traded.

Not all events resulted in reduced water application; irrigation performance was also improved by achieving higher distribution uniformity through better application of water.

Irrimate determines the infiltration characteristic of the soil – for some soil types this can change significantly over the season.

On a cracking clay soil at one trial site, infiltration had halved by the end of the season, the reasons being a combination of soil structure, soil moisture and/or lack of cracking.

The way this field is irrigated would therefore change over the season to ensure water is applied efficiently.

Rob Holmes from Holmes and McDouall Agronomy believes it is important that this work be carried out across a whole season to get a good handle on the information.

“With the aim to produce more bales of cotton for every megalitre we use, the irrigation evaluations carried out this season enabled us to gain an important insight into what was actually happening at a field level,” Mr Holmes said.

“The soils infiltration characteristics provided useful information that will help us to match our irrigation management to soil type.”

Growers want to achieve greater yields per megalitre of water used, which can only be achieved once their irrigation performance is optimised by irrigation application efficiency and distribution uniformity.

By measuring, growers can be sure they are using their water most productively.

Advancing Water Management in NSW is a collaborative project involving NSW DPI, Cotton Catchment Communities Co-operative Research Centre, Cotton Research and Development Corporation, and the Border Rivers-Gwydir and Namoi Catchment Management Authorities.

Contact Dr Janelle Montgomery, Moree, (02) 6752 5111.