Author: Incitec Pivot’s Technical Agronomist, Reily Menhenett


With sowing time fast approaching, many conversations will start to turn to nitrogen (N) budgeting and the winter topdress window.

Why this matters?

Although the dry summer was recently broken by significant rainfall activity across most of South Eastern Australia, climate models continue to point to below-average rainfall across key growing regions in South Australia, Victoria, and southern New South Wales.

Coupled with supply chain issues challenging supply of urea, ensuring applied fertiliser is kept in the system is the key to maximising return on investment from an application of nitrogen.

When it comes to N programs, unreliable weather forecasts can result in urea being spread ahead of a rain front that doesn’t eventuate. For growers with large spreading programs in particular, logistics often dictate spreading well in advance of a front, which can lead to significant N losses through volatilisation.

Incorporating Green Urea NV into topdress programs can help balance agronomy and logistics – getting N out in a timely fashion while reducing costly losses.

How much rainfall is needed?

To limit volatilisation losses, urea requires either rainfall or physical incorporation into the soil. The amount needed depends on:

  • Soil texture: Light soils generally require 5–10 mm, heavy soils 15–20 mm
  • Soil Cation Exchange Capacity (CEC): Light soils have lower buffering capacity for ammonium, while heavy soils buffer more effectively
  • Rainfall distribution: Steady rainfall is more effective at washing granules in than intermittent showers or heavy dews.

Incitec Pivot has developed the Green Urea Calculator which accounts for soil type and rainfall to help growers to estimate volatilisation risk for specific situations.

How many opportunities do I have to spread?

Using CliMate data, it’s possible to determine how frequently key regions receive an ‘effective’ rainfall event. Data is categorised as:

  • Events >15 mm in a 3-day period
  • Events >15 mm in a 14-day period.

Here, 15 mm is used as a comparative benchmark for a significant rainfall event; actual rainfall requirements may vary. Numbers are averages for 1980–2025 during the main topdress window of May to August.

  • 3 days represents the window for effective incorporation before significant losses occur with conventional urea.
  • 14 days represents the protection window when using Green Urea NV.

Figure 1 demonstrates that using Green Urea NV to extend the incorporation window out to 14 days increases spreading opportunities by 5 to 10 times compared to a 3-day window.

Figure 1: Number of rainfall events >15mm at various locations in South Eastern Australia. Source: CliMate.

Key takeaways

Green Urea NV:

  • Allows growers to start spreading earlier than conventional urea, without risking volatilisation losses
  • Provides significant logistical advantage, especially in seasons or locations with limited effective rainfall
  • Offers flexibility to commence programs early, then switch to conventional urea just before rainfall events if preferred.
  • Ensures that fertiliser application provides a real return on investment, by retaining more applied nitrogen in the system

Further information

For more on Green Urea NV and spreading window flexibility, contact: Reily Menhenett – Technical Agronomist, Incitec Pivot on 0474 093 167 or by email: reily.menhenett@incitecpivot.com.au.

Resources

CliMate: How Often? Historical rainfall analysis tool (1980–2025)