Sun shield reduces water needed to grow vegetables: southern NSW trial

Tony Catazariti and John and Anthony Vitucci
Tony Catazariti and John and Anthony Vitucci with loads of the mini capsicums grown under shade cloth, ready to send to market.

A new means of shielding broadacre vegetable crops from the sun could massively reduce the quantity of water required to grow vegetables in some of the driest parts of the Murray Darling Basin.

Preliminary trials by growers in Griffith, supported by the NSW Department of Primary Industries (DPI), indicate that a new Israeli technique using ‘screenhouses’ could see water used for growing vegetables cut by more than a third.

An Israeli research trial, reported last year in the journal Irrigation Science, found 38 per cent less water was required for ‘screenhouse’ crops compared with crops grown in open fields.

Griffith vegetable growers, Tony and Frank Catazariti and John and Anthony Vitucci, are in their second year of production using a shadecloth structure that covers one hectare to protect what are essentially field-grown vegetable crops.

Several years of research by the cloth suppliers, Queensland based-Envirotech, was required to determine the best combination of colour and density of shade cloth on the roof to modify sunlight penetration, and on the sides to moderate wind speed.

DPI District Horticulturist, Mr Mark Hickey, says the Australian trial is supporting overseas findings that sunlight intensity, windspeed and evaporative losses from the plant and soil surface were all lower and provided a more favourable environment for plant growth.

In the first year melons were grown in the structure, and this year mini capsicums – a high value crop not normally grown in southern NSW – were successfully grown using the new system.

Mr Hickey said in the first year of operation there was a dramatic difference in amount of moisture extracted from the soil by melons grown inside and outside the ‘screenhouse’.

Two different methods were used to determine soil moisture levels in the root zone of the crop, and studies of the root systems of the protected crops were undertaken.

Initial estimates from the growers are that 30 per cent less water was used to grow the melons under the shade cloth, compared with outside conditions.

“A crucial factor is an estimated 40 per cent reduction in ‘global radiation’, which means that evapo-transpiration is reduced.

“This is a significant benefit in terms of reducing water use but makes water management crucial, as excess water can lead to root diseases such as pythium and phytophthora.”

Mr Hickey said the shadecloth structure also creates a more conducive environment for pests, which means crops have to be carefully monitored to check for the spread of viruses.

Trials of the new system are to be extended in the next two years in a collaborative effort by NSW DPI and CSIRO Land and Water, under a new research project into water use efficiency in horticulture funded by the Cooperative Research Centre for Irrigation Futures (CRC IF).

Mr Hickey said further research needs to be undertaken into the impact of the new growing system on evapo-transpiration, through monitoring of daily changes in moisture levels, as well as on pests and diseases.

“One advantage of this system is that it does not overheat crops, as happens in greenhouses.”

The Griffith growers believe the screenhouse is economically viable, but the cost benefit of the system for other growers still needs to be assessed. This will be examined as part of the CRC project.

As with vegetable growing regions in the Murray-Darling Basin, Israel’s semi-arid and arid regions require irrigation to survive. Growers in Israel have limited access to freshwater and between1980 and 2002 and the amount of freshwater available for agriculture in that country fell by more than half.