Completed project
Improving citrus quality with regulated deficit irrigation (CT17000)
Publication date: December 3, 2018
Delivery Partner: NSW Department of Primary Industries
This project, which ran from 2018 to 2022, used irrigation trials to investigate a practical irrigation deficit method and provided citrus growers with new information to assist quality management in the orchard.
International research indicates that a regulated deficit irrigation approach can be applied during citrus maturation and ripening stages to enhance fruit sugar content, while saving irrigation water. However, there were previously no practical recommendations for its implementation in improving fruit quality on-farm.
The insights produced by this project will help inform Australian growers to adopt smart, innovative agronomic practices that can deliver improved fruit quality – with a particular focus on enhancing sugar content for fruit to be exported to Asian markets, where there is a preference for sweeter citrus.
This large-scale trial was held over four years at the Dareton Primary Industries Institute near the Sunraysia district, with trials using the three main commercial navel varieties and rootstocks.
The research found that successfully using deficit irrigation techniques requires optimising irrigation scheduling, understanding the stage at which to apply deficit irrigation stress, and investigating potential adverse effects on fruit quality and long-term tree health.
The study assessed the fruit responses to different deficit irrigation treatments. Fruit yield, number and fruit size distribution data were collected each experimental year using a commercial grading machine.
The researchers noted that responses may vary due to different soil types, rootstocks, tree health, crop management practices and climatic conditions. During the four-year trial, different climatic conditions (rainfall) occurred, allowing extra information to be collected.
A range of regulated deficit irrigation treatments was applied over the four years, with increased sugar levels achieved. The results clearly showed that there are some fruit size losses to enhance sugar levels and that there are different rootstock responses.
The trial results provide citrus growers with new information to assist quality management in the orchard. Research results have been shared at field days and via articles to raise industry awareness of the technique.
The final report for this project outlines a series of recommendations for citrus growers that are intended as general guidelines developed from the four seasons of regulated deficit irrigation trial results on navel oranges.
It is suggested that growers test regulated deficit irrigation on a small scale of approximately 2–5 rows, including a control row, before it is extended to a full block of trees. The responses might vary due to different soil types, rootstocks, tree health, crop management practices and climatic conditions.
This project was a strategic levy investment in the Hort Innovation Citrus Fund
© 2026 Horticulture Innovation Australia Limited.
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