Author: Reily Menhenett, Technical Agronomist, Incitec Pivot 

Global supply challenges have placed pressure on nitrogen availability this season, with urea impacted most severely. With the highest concentration of nitrogen by weight in a solid fertiliser, it is no surprise urea is the world’s most traded nitrogen fertiliser.  

To help support Australian farmers, Incitec Pivot proactively sourced additional cargos of both of urea and ammonium sulphate (GranAm®), shoring up nitrogen availability and supply.  

Growers have the option to incorporate GranAm®, or GranAm® in a blend with urea, into their topdress program this season. There are a few key points to consider when using GranAm®.  

Nutrient content 

GranAm® is Incitec Pivot’s granulated ammonium sulphate fertiliser, which has superior blending compatibility and spreadability compared to crystalline forms.  

As the name suggests, ammonium sulphate ((NH4)2SO4) contains both nitrogen and sulphur in the same granule. GranAm® contains 21% nitrogen and 24% sulphur by weight. In comparison, urea (CO(NH2)2) contains 46% nitrogen by weight.  

Because of this, GranAm® requires a higher spreading rate to achieve the same nitrogen application. If a low nitrogen rate is required (for example 20kg/ha of N), this can be an advantage, as spreading 100kg/ha of GranAm® will achieve a more even physical distribution compared to 45kg/ha of urea –an unrealistically low application rate for effective spreading.  

One of the key advantages of applying GranAm® is that it also supplies sulphur. In cropping systems that rely predominately on ammonium phosphates and urea, sulphur is often neglected and can become deficient.  

Table 1 shows sulphur removal rates for some common crops. In cropping systems which grow a lot of canola, sulphur can quickly become limiting.  

Table 1: Sulphur removal from common grain crops (Source Incitec Pivot AiP notes). 

Crop Type S Removal (kg/t) 
Wheat 1.4 
Barley 1.1 
Oats 1.5 
Canola 9.8 
Lupins 3.1 
Chickpeas 1.8 
Faba Beans 1.4 
Field Peas 2.0 
Hay – cereal 1.0 

Handling 

Urea and GranAm® have slightly different physical characteristics, which have implications for storage and handling. Table 2 shows the critical relative humidity (CRH) of urea, GranAm®, and a Urea/ GranAm® blend. CRH of a product or blend is an important consideration where storage conditions may be a factor.  

Table 2: Critical relative humidity (at 30oC) and bulk density of urea, GranAm®, and a Urea/GranAm blend. 

Product Critical relative humidity (%) Bulk density (kg/m3) 
Urea 73 750 
GranAm® 79 900 
Blend 56 ~825 

Bulk density is another important factor that influences product spreadability. It describes the weight per volume of each product and how ‘heavy’ granules might be.  

The differences in density (Table 2) need to be accounted for when setting effective spread width and flow rate through the spreader. When changing products, it is recommended that spreaders are recalibrated, to ensure the targeted application rate matches up with the actual application rate.  

Loss of nitrogen through volatilisation 

Under most conditions, volatilisation potential is reduced with GranAm® compared to urea. The pH in the fertiliser granule zone is acidic for GranAm®, whereas it becomes alkaline for urea. In addition, the nitrogen in GranAm® is already present in the ammonium form, rather than having to be hydrolysed from urea, through the unstable ammonium carbonate intermediatory.  

Figure 1 shows the difference in volatilisation potential for urea and GranAm®, averaged across Incitec Pivot trials conducted in Southern Australia during 2024 and 2025.  

Figure 1: Average nitrogen loss (kg/ha) by volatilisation for urea vs GranAm®. Source: Incitec Pivot trials.  

One important exception is when calcium carbonate (CaCo3, free limestone) is above 10% on the soil surface. This can happen on calcareous soils or where there has been a recent incorporation of lime. In these instances, the volatilisation risk from GranAm® is higher than that of urea. An example of this is shown in Figure 2 from a trial conducted at Ungarra in 2024.  

Figure 2: Increased volatilisation potential of GranAm® on calcareous soil at Ungarra. 

Soil acidity 

Another key difference between these two products is their acidification potential. This has two components – the acidification potential has two aspects – the acidity (hydrogen ions) released during mineralisation and nitrification, and the impact of nitrate leaching.  

For urea, there is first hydrolysis (consumption of H+), followed by nitrification (release of 4H+) and then uptake of nitrate (consumption of 2H+), resulting in a net of 1H+ generated. If nitrate is leached however, there is a net of 3H+ generated by this process.  

For GranAm®, the nitrogen is already in the ammonium form, and so it only undergoes nitrification (release of 4H+) before being taken up (consumption of 2H+) for a net of 2H+ generated. If all nitrate is leached, there is a net of 4H+ generated.  

Table 3 outlines the approximate quantity of lime required to neutralise the acidity released from these products under different circumstances.  

Table 3: Quantity of lime required to neutralise acidity generated through application of nutrient.  

Product kg lime to neutralise acidity per kg N applied 
All nitrate taken up All nitrate leached 
Urea 0 3.6 
GranAm® 3.6 7.1 

Summary 

GranAm® offers an excellent opportunity for growers who are looking to build out their nitrogen programs this season.  

GranAm® offers benefits with added sulphur and lower volatilisation potential, as well as logistical advantages in some circumstances.  

Where urea availability is limited, GranAm® offers a high-quality alternative for growers looking to maintain productive and efficient nitrogen programs.  

Further information 

For further information contact Reily Menhenett on 0474 093 167 or by email: reily.menhenett@incitecpivot.com.au.