Author: Courtney Bills & Reily Menhenett. IPF Technical Agronomists, Broadacre

This season, Australian growers are facing a challenge – and an opportunity. Smart fertiliser management and precise crop timing will be the key to strong winter crop results.

Seasonal availability of key fertilisers such as urea and ammonium sulphate may shift grain growers into considering topdressing winter crops instead of applying fertilisers pre-plant as is the traditional approach in northern cropping regions (QLD/NSW).

For southern cropping regions (VIC/SA), excellent subsoil moisture in most growing areas will provide confidence for pre-spread and early in-crop nitrogen (N). Understanding individual crop demand and matching supply of N accordingly will ensure crops are set up for success and high returns.

Matching crop growth with N demand

Maximising yield starts with getting N on the crop at the right time. Fertility management isn’t just about how much N is in the soil – it’s about making sure it’s available when the crop needs it most. Every season, region, and farm is different.

Even for paddocks which have received some fertiliser pre-plant, holding back some N for an in season topdress will allow a flexible, responsive approach. The opportunity to incorporate N into the crop root zone and allow uptake is dependant on receiving sufficient timely rainfall or irrigation.

Optimal N rate can be a moving target, with crop requirements often fluctuating based on factors such as:

  • early season rainfall and stored soil moisture,
  • crop establishment and biomass (canopy size),
  • realistic yield potential
  • target protein
  • current grain prices, and
  • predicted in-crop rainfall.

Shifting from a fixed N program to a responsive strategy is increasingly important for maintaining profitability when faced with increasing variability.

Best timing for N = best results

Wheat and barley follow the Zadoks scale to measure key growth stages, and getting N timing right is critical to maximise yield and grain quality.

While their reproductive timing differs slightly in cereals, most N should be applied before flowering, when crops can use it most efficiently.

Three key N topdressing windows

1. Pre-Sowing – end of tillering (GS 0–30)

Early applied N is critical for establishment and tillering and ensures there is an adequate supply in the soil for the periods of peak uptake (Figure 1).

During this period, biomass builds rapidly and the number of fertile tillers are set. During peak uptake, N demand rises sharply to support tiller survival, spikelet formation, and canopy development. Adequate N at this stage is essential to maximise yield potential.

Figure 1: Nitrogen uptake pattern in wheat. Source: Adapted from Lemon, J 2007.

2. Stem Elongation (GS 31–39)

From first node to flag leaf emergence, N plays a key role in developing grain yield. Crop N uptake needs to satisfy the crop’s requirements for yield during this period, with a corresponding increase in grain protein between to 11.5-12.5% when N and moisture availability are matched. Higher N rates only increase grain protein once yield requirements have been met (Figure 2).

If targeting malting barley specifications, understanding soil N status before planting is critical, as excess N can push grain protein above malting thresholds and lead to downgrades. Pre-plant soil testing – especially to depth – helps match N supply to yield potential, protecting malting premiums while improving fertiliser efficiency.

3. Late Applications (GS 43–65)

From head emergence to flowering, late N can help lift grain protein, reduce screenings, maintain yield in favourable or irrigated conditions, and may also extend green leaf retention. However, apparent N use efficiency (ANUE) declines, so decisions should be driven by seasonal outlook and economics (Figure 2).

Figure 2: Typical grain yield and protein responses to nitrogen in wheat. Source: Incitec Pivot Fertilisers Internal.

Bottom line:

  • Early N drives yield potential
  • Mid-season N aids in yield and grain quality (protein)
  • Late N is a tactical tool, with higher risk and lower efficiency
  • Getting the balance right between timing, season, and crop demand is key to maximising return on nitrogen investment.

When to apply in canola?

For cereals and canola, the key challenge for growers is to balance vegetative growth to promote sufficient dry matter for optimal yield, without allowing excessive growth that can cause issues later in the season.

Similar to cereals, the most rapid period of N uptake in canola is between stem elongation and flowering (Figure 3). Deficiency of N early in season, particularly when coupled with other stresses such as pest or disease pressure, can result in premature stem elongation and flowering, thus resulting in yield penalties.

Figure 3: Nitrogen uptake pattern in canola. Source: Adapted from Norton R, 1992.

Importance of soil testing

Understanding where N is located in the soil profile is crucial when developing an N application plan.

For northern areas that generally apply a greater proportion of N pre-plant or during planting, segmented deep soil sampling is not only useful for N budgeting but is also useful for assessing subsoil moisture.

For southern areas, ensuring a crop has sufficient N to last until the main topdress is crucial – allowing a crop to enter N deficiency will impact yield, even in the early stages of growth. For this reason, pre-season deep N testing is crucial to understand mineral N available for plant growth.

Providing some N in starter fertiliser at sowing can also help to get the crop ‘up and going’.

Summary

Timing and placement are two imperatives when operating under constraints with N this season.

Staying flexible with application timing will help to manage risk in crop, leaving time and creating flexibility to match N to periods of crop demand.

Keeping a top dress ‘up the sleeve’ fits in well from both a logistical and agronomic perspective, maximising NUE to keep crops balanced all season long.

Further Information

For more information, contact IPF Technical Agronomist Courtney Bills on 0447 635 653 or Reily Menhenett on 0474093167 or via email courtney.bills@incitecpivot.com.au reily.menhenett@incitecpivot.com.au

References

Gourley CJP and Weaver DM (2019) A guide for fit for purpose soil sampling, Fertilizer Australia, Canberra, Australia.

Lemon, J. (2007), Nitrogen management for wheat protein and yield in the Esperance port zone. Department of Primary Industries and Regional Development, Western Australia, Perth. Bulletin 4707. https://library.dpird.wa.gov.au/bulletins/78

Norton R 1992, Nitrogen is the key canola nutrient. In Casey M, Cooke P (eds) Canola Cache. The Farmer’s Handbook for Growing Canola. Kondinin Group, Perth