Author: Dave McRae, Technical Agronomist, Incitec Pivot 

Limiting nitrogen (N) loss from agricultural production systems is not only important for grower profitability but also for reducing the negative effects on the environment. 

Fertiliser N can be supplied as urea, ammonia or nitrate, with some fertiliser products, such as EASY N, containing all three forms. Urea and nitrate-N are readily moved with water, while the movement of ammonium-N is influenced by the soil’s cation exchange capacity. 

Nitrate-N is highly mobile in soils, moving with water down the slope, along irrigation furrows, across beds and hills, and deeper into the soil profile. It also is the primary source of N losses through denitrification, resulting in the production of nitrous oxide (N2O) and dinitrogen (N2). 

One of the most effective ways to minimise N losses is to better synchronise nitrate-N availability with crop demand. Understanding how the 4 Rs (Right Rate, Right Time, Right Place and Right Product) influence Nitrogen Use Efficiency (NUE) is an important part of improving fertiliser performance in irrigated cotton and summer cropping systems. 

Rate 

Choosing an appropriate rate of fertiliser N based on expected crop yields and expected soil-N availability (mineral N + mineralised N) is the first step. Under-fertilising can reduce crop yields and run down soil fertility, while over-application can increase gaseous N losses (explained in Keeping pre-plant nitrogen below the ground but in the root zone).  

Developing a targeted N budget using NA Pro software will help determine an appropriate N rate. The “Right Time” principle can be broadly split into two application times: N applications to fallow or pre-plant, and in-crop. 

Pre-plant 

The placement of applied N has changed over the years, with less farmer labour available, increasing machinery and fuel costs, and larger areas to cover. Many growers are choosing to broadcast or spread their N fertiliser and incorporate it with tillage or rainfall/irrigation. 

If urea is not incorporated, volatilisation losses of up to 27% may occur. Switching to Green Urea NV® in this situation can reduce potential losses by 75-85%. 

The position of fertiliser N in the soil profile has a large influence on early season N losses. Deep banding of fertiliser N in position 2 or 3 (illustrated in Figure 1) has a low potential to lose N from early season irrigations. 

Figure 1: Nitrogen fertiliser position in the soil profile from various application techniques. Source: Incitec Pivot 2026 

Placing N fertiliser below the irrigation water level will assist in moving N into the root zone. N positioned above the irrigation water level (Figure 1, positions 1 or 4) in seasons with low rainfall or no overhead irrigation will likely result in N becoming stranded, reducing crop uptake. This can result in hundreds of kilograms of N per hectare not being available for crop uptake.  

Combining appropriate N positioning with your irrigation design with eNpower® treated pre-plant N can result in higher NUE and yields.  

Yield results from eNpower treated pre-plant are available in: Managing nitrogen in cotton wet vs dry season takeaways.   

In-crop 

Applying N in-crop to match increasing crop requirements from first squares can be very effective and limits potential N losses, although this depends on the application method and incorporation timing. For example, spreading urea and irrigating within 2 to 3 days minimises losses. For greater flexibility, Green Urea NV® can be used instead. Water running urea N (EASY Liquids N26) effectively moves N into the active root zone whilst minimising losses. 

The application method used distributes N differently, relative to water and nitrate movement (Figure 2). This can impact crop N uptake if N is not co-located with active plant roots and moist soil. Mobile forms of N, such as nitrate-N and urea, can be moved into the soil profile, towards the top of the hill/bed, across the hill/bed, or out of the field in the tail water. 

Schwenke et al. (2022) investigated the yield effects and the movement of N in a furrow irrigation system and found that all in-crop application methods – broadcast, side-dressed and water run – produced equivalent lint yields and similar NUE. The water-run treatment lost more N in tail water, particularly when large volumes of tail water exit the field. 

In subsequent two-year field trials, Schwenke found that tail water N losses were reduced by 40-43% when N injection was stopped as irrigation water reached the end of the field (personal communication, G. Schwenke). This reduced N losses to a similar level as the broadcast or side-dressed treatments.  

Figure 2: Irrigation water movement influencing nitrogen position in soil profile and plant availability. Source: Incitec Pivot 2026 

With effective irrigation management, selecting an appropriate N rate for the field, protecting pre-plant N applications with eNpower and matching the right product with application method to supply in-crop N, high yield cotton can be produced profitably whilst minimising N losses. 

Further information  

For further information on N management, fertiliser placement, and strategies to improve NUE, please contact:  

Reference 

Schwenke, G., Baird, J., Nachimuthu, G., MacDonald, B., McPherson, A., Mercer, C. & Hundt, A. (2022). Dressed for success. Are crop N uptake, N loss and lint yield of irrigated cotton affected by how in-crop N fertiliser is applied? Field Crops Research 287 108659.