Drip irrigation/fertigation (“advanced fertigation”, “open hydroponics”) is being adopted by

the Australian citrus industry. Hardware sophistication and the complexity of management

regimes being used vary enormously; from old paradigms applied using modern equipment,

through to approaches used overseas, but untested under Australian conditions. Generally,

these technologies are being adopted without support. This project aimed to address

knowledge gaps and test assumptions regarding the application of modern approaches to the

delivery of water and dissolved mineral fertilisers to citrus trees under Australian conditions.

Seedling rootstocks growing in sand culture were used to investigate the impact of variations

in nutrient solution composition. Relative vigour of the rootstocks was maintained

irrespective of nutritional treatment. The rootstock genotypes differed in their rate of

response to increasing N supply and the efficiency with which N was used in the shoots. The

most vigorous rootstock responded to small increments in N supply and achieved maximum

growth with lower tissue N than less vigorous rootstocks. Across all rootstocks, more than 45

mg N/L in the nutrient solution conferred no additional advantage. Further, optimum

potassium concentration appeared to be around 23 mg/L. Neither shoot biomass production

nor macronutrient accumulation were advantaged by acidification of the nutrient solution.

Some aspects of modern irrigation/fertigation practices were compared using young navel

oranges at Dareton. Similar amounts of water and fertiliser were supplied in either a “best

practice” approach or an “open hydroponics” approach. The strongest influence on tree

behaviour was season. Neither irrigation nor fertiliser management influenced tree behaviour

to any great extent. The composition of soil solutions was extremely variable. Despite best

practice ETo scheduling, high concentrations of N in the irrigation water resulted in a gradual

movement of NO3

- down the soil profile. In a fertigation program based on reduced and

oxidised forms of N, nitrate-N greater than ~34-45 mg/L was clearly in excess of the roots’

ability to take up NO3

- Water and solute movement in lysimeters was quantified and compared to field

measurements. Various scenarios were explored using a 2D/3D water and solute

movement model (“Hydrus”) that evaluated NO3

- movement under different fertigation application patterns, involving pulsed and non-pulsed irrigation, and variable timing of fertigation applications across the daily irrigation pattern. The simulations suggested that injection of NO3

- into the irrigation water in the early or middle pulses of daily irrigation resulted in less NO3

- being retained in the rootzone for uptake by tree roots, and concomitant greater leaching losses than application of fertigation in the later part of irrigation pulses, or at a low level across the whole day.

The application of modern fertigation strategies is unsupported by objective public-domain

data, and the long term impact of such strategies under Australian conditions is unknown. A

field site was established to quantify the long term responses of three selections of navel

oranges on five different rootstocks to fertiliser delivered using modern delivery technology.

The site will serve as a research and technology transfer resource well into the future, and is

probably unique in the world. Industry support in the future will be needed to take full

advantage of the potential benefits of this site.

Two Excel spreadsheet-based decision support tools were developed to assist irrigators to

make more informed decisions regarding irrigation scheduling and fertilisers use. One of

these, E-Schedule, an irrigation scheduling decision support tool, was developed to make it

simpler to bring together all the disparate pieces of information, including weather

predictions, needed to make informed irrigation scheduling decisions. E-Schedule has

nationwide applicability.