Tipping the odds to grow grass when an El Niño looms
Author: Lee Menhenett, Senior Technical Agronomist, Incitec Pivot
Key messages
- El Niño has formed in the Pacific Ocean and threatens to be strong.
- Soil moisture levels are excellent going into spring.
- Start nitrogen fertiliser applications in late winter/early spring utilising stored soil moisture.
- Carefully consider the requirements of companion nutrients (phosphorus, potassium, sulphur) in Boosta® products.
- Potentially less rain events make Green Urea NV® and Green Boosta® product selection important.
The season
Late summer rain, a timely autumn break, and good winter rainfall have set up pasture paddocks with a good level of soil moisture. Figure 1 shows rainfall across Australia from 1 April to 31 July. This provides the basis for pasture growth into the spring. The unknown is spring rainfall. This year has an additional question mark with a “super El Niño” forming in the Pacific Ocean.
Figure 1: Map of rainfall across Australia 1 April to 31 July 2026. Source: BOM, 2026.
The BOM’s latest long-range rainfall forecast casts a dry outlook for spring. Figure 2 shows there is a <25% chance of exceeding median rainfall between August to October for most of the southern Australia pasture areas. While this forecast does not guarantee a drier period, there needs to be careful consideration when planning spring fertiliser programs.
Figure 2: Chance of exceeding median rainfall map of Australia between August to October. Source: BOM, 2026.
Start nitrogen programs early
Pasture growth and physiological development are governed by sunlight, temperatures, and plant available moisture. If any of these environmental factors are limiting then pasture growth slows. With a drier outlook for spring it is important to maximise growth rates while soil moisture is not limiting.
Nitrogen (N) extends the size of grasses, adding additional growth rates above base rates. N responses are described as kgDM/kgN, with typical spring responses ranging from 10-30kgDM/kgN. Plant species and type vary in seasonal responses to nitrogen.
Targeting N on the most responsive pasture types will grow more grass at a cheaper price. Below is a useful link to a feed cost calculator. Rates of N should be a minimum of 20kg/ha to a maximum of 60kg/ha. Lower rates are used in short grazing rotations (20 days), while higher rates are used for longer fodder lock up periods or where the first silage cut has been harvested. Urea is volatile, therefore, if there is not a rainfall event of >10mm within three days of application then Green Urea NV® should be used to retain more N in the system for grass growth. Green Urea NV® can also be included in Boosta® products. A minimum lock up period of four weeks is required from N applications to fodder cut. This allows enough time for pasture growth to respond to N and importantly, increase water soluble carbohydrates and dry matter content and reduce the buffer capacity of the silage.
Nitrogen and companion nutrients – Boosta® products
N responses are also correlated to paddock fertility – particularly phosphorus and potassium. Understanding soil test levels across paddocks will allow different nutrient strategies to be applied.
Nutrient strategies for different soil test values:
- Soil test values Above critical range – N only.
- Soil test values Equal critical range – consider full/partial fodder nutrient removal replacement*.
- Soil test values Below critical range – consider maintenance (replacement) rates plus capital application. This may not represent full capital recovery, however, may assist in closing partial nutrient deficiency to gain a dry matter benefit.
*As a general guide 1t/ha dry matter will typically remove 25kg nitrogen: 2kg phosphorus: 25kg potassium: 2kg sulphur.
Rates of Boosta® products will be primarily decided on getting the correct N rate and secondly on phosphorus, potassium and sulphur replacement and/or capital requirements.
Summary
Soil moisture levels are excellent, however, there is a forecast for a drier spring – which may or may not eventuate. Management strategies are in our control to bring forward our spring fertiliser programs to increase dry matter production while soil moisture levels can sustain growth.
If the spring is drier there will also be less effective rainfall events to move N into the soil.
Take advantage of any late winter early spring rainfall events to apply fertiliser. Green Urea NV® and Green Boosta® are cost effective products that will reduce N loss, retaining more N in the system for pasture growth.
Further information
For more information on spring pasture production, contact Lee Menhenett at lee.menhenett@incitecpivot.com.au
References
Bureau of Meteorology 2026
