Date of Award


Degree Name

Master of Science (Thesis) (Arts & Sciences)

Schools and Centres

Arts & Sciences

First Supervisor

Dr Timothy D Meagher


The sustainability of sprinkler-irrigated vegetable crops in the Binningup–Myalup area of south-western Australia was investigated. The main crops are carrots, potatoes and onions. The crops are grown throughout the year in sandy soils and require large volumes of sprinkler irrigation during the summer growing period and little during winter. The irrigation water is extracted from the underlying superficial aquifer.

The combination of water with a relatively high salt content, evaporation between the sprinkler and the ground, and subsequent high evapotranspiration, leads to escalating soil water salinity during summer. At Binningup, the necessary horticultural practice of daily watering in summer to maintain soil moisture accumulates salts in the root zone of the crops at levels that inhibit yield and occasionally results in crop failure.

This investigation confirms the hypothesis that short-duration, high-volume winter rainfall events are sufficient to rinse accumulated salts from the soil profile each year and sustain current horticultural practice. Occasional high-volume rainfall in summer similarly rinses salt from the root zone. Thus, it is not the average volume of winter rainfall that ensures sustainability but the fortuitous occurrence of summer storms and high-volume rainfall in winter. It is shown that, even in a year of 50 per cent of average rainfall, the soil was rinsed and the aquifer replenished. It is also shown that after 10 years of production, the irrigation water supply monitored at the surface three to four metres, is stable in salinity and thus sustainable.

This research also investigated the effect of daily variation in both soil moisture and soil salinity on crop yield for vegetable crops, grown in identical soil structure during both the summer and winter periods. Alternative irrigation strategies were considered to evaluate whether sprinkler irrigation regimes can be modified to manage effective reduction of soil water salinity during the summer period to avoid loss of production or crop failure.

Data-logging equipment used to record soil moisture in the profile and water from rainfall and sprinkler irrigation provided indicative results. These records are supported by an adjacent online, real-time agricultural weather station and in situ tipping bucket rain gauges.

The results could modify reticulation and enhance sustainability of both vegetable crops and the underlying aquifer resource.

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