Rural Industries Research & Development Corporation

Research Compendium 1993 - 1994

Research Project

VEGETABLE PRODUCTION AND WATER POLLUTION ON THE SWAN COASTAL PLAIN

Objective

To develop improved management techniques to reduce the impact of phosphatic and nitrogenous fertilisers applied to vegetables grown on sands on the water systems of the Swan coastal plain.

Background

Western Australia is Australia's major exporter of carrots, cauliflowers, Chinese cabbage, lettuce, celery and cabbage as well as significant quantities of onions and potatoes. The value of vegetable exports from Western Australia in 1991-92 was $31.3m or 36.6% of total vegetable exports from Australia. Most of these export crops are grown on the sandy soils of the Swan coastal plain. These sands have low nutrient and water holding capacities. Leaching of fertilisers (especially nitrogen and phosphorus) applied to horticultural crops have been implicated as one of the contributors to the pollution of the ground and surface water bodies (lakes, rivers and estuaries) of the coastal plain.

The future of vegetable production on the coastal plain is under threat because of these environmental concerns. Relocation of vegetable production would increase freight costs and reduce grower returns. There is considerable benefits in maintaining these industries in their present location. Current fertiliser and irrigation practices are not efficient and have contributed to the problem. Improved fertiliser and irrigation practices should reduce environmental impact and reduce the risk of relocation.

Research

Experiments were conducted to determine phosphorus soil test standards for carrots, cauliflowers, lettuce and onions grown on Karrakatta sands. Other experiments compared the relative benefits of placement (broadcast versus banding) of phosphorus on vegetables. The interaction of irrigation (rate, method) with nitrogen fertiliser application was also examined to develop more efficient management techniques.

Outcome

Phosphorus soil test standards were developed and finalised for carrots and cauliflowers on the Karrakatta sands with preliminary information developed for lettuce and onions. This information showed that growers could reduce their current application of phosphorus substantially at high soil test levels.

The benefit-to-cost ratio of adopting phosphorus soil testing on the coastal plain was eight. By contrast there appeared little benefit in banding phosphorus to carrots, cauliflower or lettuce compared with broadcasting although, with onions, banding appears more efficient. Application of nitrogen in small quantities frequently using fertigation after planting rather than less frequent broadcasting demonstrated savings in nitrogen.

In particular, a substantial reduction - or possible elimination - in application of nitrogen preplanting could be achieved if fertigation of nitrogen was used. For example daily fertigation of nitrogen to lettuce was shown to be more profitable than broadcasting weekly because of yields and more efficient use of nitrogen.

Implications

The adoption of improved nitrogen, phosphorus fertiliser and irrigation practices resulting from this project has the possibility of enabling vegetable production to be carried on the Swan coastal plain with minimal environmental impact, whilst at the same time saving growers money. This should reduce the pressure on the vegetable industry to relocate further from the coastal plain with increased costs, such as freight and reduced grower profits.

RIRDC Project No: DAW-30A

RESEARCHER: Dr Ian R McPharlin

ORGANISATION: Horticultural Industries

PHONE: 09 368 3671

PUBLICATIONS:

McPharlin I R, Jeffery, R C and Weissberg R, 1994, Determination of the residual value of phosphate and soil test phosphorus calibration for carrots on a Karrakatta sand. Commun.Soil Sci.Plant Anal., 25(5&6), pp489-500.

Last updated: 10 October 1996
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