Vegetable production on sandy soils was under ongoing scrutiny by environmental regulators as a major contributor to nitrate pollution of groundwater. The project, ‘Developing guidelines for environmentally sustainable use of mineral fertilisers’ had shown that the 3Phase method for fertilising leafy vegetable crops was able to reduce leaching of nitrate to levels well below the current industry average, especially where those crops have a significant proportion of their nutrition supplied upfront, either in the form of animal manures or mineral fertiliser. The average nitrate leaching fraction the researcher achieved in their trials with broccoli, cabbage, celery and iceberg lettuce was in the range of 0.3-0.55 compared to levels frequently around 1.0 or higher among growers on the sandy soils of the Swan Coastal Plain. This represented a true, positive benefit to the environment from the 3Phase method. Rain caused most leaching over winter months while in summer, leaching could be minimised by timing nitrogen application to match crop growth and good irrigation scheduling practice.

The 3Phase method for sandy soils set benchmark rates of nitrogen, phosphorus and potassium for crops according to growth stage and included advice on placement, products and low-cost application methods. This project had now refined the 3Phase technique making it even simpler to adopt. A light dressing of granular NPK fertiliser at planting became fundamental to all crop programs. This was followed by the option of spraying a mixture of potassium nitrate and urea OR broadcasting granular NPK fertiliser, once or twice a week in the early establishment stage of crop growth (Phase 1). Banding of granular NPK fertiliser comprised Phase 2 until row closure and Phase 3 (which may have or may not have been needed depending on the crop and time of year) consisted of fertigation, often with urea only or perhaps with potassium nitrate added, again depending on the crop.

A survey of growers showed that several had already embraced elements of the 3Phase technique when this report was published as a means of reducing costs, improving crop quality and minimising their impact on the groundwater.

This project has been funded by Hort Innovation, using the research and development levies listed below and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

• Vegetable Fund