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Ongoing project

Improving citrus quality with regulated deficit irrigation (CT17000)

Key research provider: NSW Department of Primary Industries

What’s it all about?

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 are currently no practical recommendations for its implementation in improving fruit quality on-farm.

This project is using irrigation trials to develop a practical irrigation deficit method. It will ultimately produce guidelines allowing 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.

Initial project work has seen trial trees and rootstocks subjected to an irrigation deficit (50 per cent normal irrigation rates) for 60 days across three different parts of the growing season (Feb-April, March-May and April-June). The trees were ten-year-old navels of different varieties, including the early maturing M7 navel, mid maturing Houghton navel, and late maturing Lane late navel. Rootstocks involved were Poncirus trifoliata, Troyer citrange, Citrus volkameriana, Swingle citrumelo and Citrus marcophylla.

Soil moisture was monitored and measurements made of fruit sugar, sugar-acid ratio, fruit quality, juice, yield and fruit size distribution. The results were compared against control trees not subject to irrigation stress.

For some varieties, fruit subjected to deficit irrigation in February/March and March/April differed from fully irrigated controls, including increased sweetness and BrimA values (acid value) – but the regimen also reduced the size of fruit at harvest.

These initial findings suggest that lower levels of irrigation will increase sweetness of fruit, but more water is required to maintain yield. The next round of trials will repeat the experiment with drought stress set at 75 per cent of normal irrigation.

Growers in the Riverina and Perth heard about the trials from researchers at meetings during the year.   

Related levy funds

This project is a strategic levy investment in the Hort Innovation Citrus Fund