Key messages
Soil, yield and protein maps, plus satellite imagery, helps identify paddock variability.
Variable rate applications of nitrogen can improve the return on investment by targeting nitrogen to zones where the greatest response can be achieved.
Protein maps are reflective of plant available nitrogen and can be used to identify areas of over/under nitrogen supply.
Where yield or protein maps aren’t available, NDVI imagery offers an easy way to generate your own prescription maps and begin variable rate applications.
Nitrogen is one of the biggest input costs for grain growers, and with ongoing concerns around urea prices and supply, making every kilogram count has never been more important.
That was the key message from Riverine Plains' recent Nitrogen Strategies webinar, which brought together seasonal insights, digital tools and practical nitrogen management approaches to help growers improve nitrogen use efficiency and target investment where it delivers the greatest return.
The webinar opened with an overview of rainfall deciles and soil moisture conditions across the region (learn more by reading our latest rainfall, decile, soil moisture and yield potential update). While conditions vary considerably across the Riverine Plains footprint, the key takeaway was that nitrogen decisions should always be considered alongside available soil moisture and seasonal outlooks.
As Riverine Plains Senior Communications Manager Michelle Pardy explained, growers are working with probabilities rather than certainties. Seasonal conditions and timing remain critical factors when making nitrogen decisions.
Tim Neale from DataFarming showed how satellite imagery can help identify crop variability and support nitrogen decision-making.
Indexes such as Normalised Difference Vegetation Index (NDVI) can provide a useful snapshot of crop health, while Normalised Difference Red Edge Index (NDRE) was highlighted as one of the better indexes for detecting nitrogen-related variation within crops.
While imagery can identify areas of high and low biomass, it’s still important to understand what is driving those differences. For example, nitrogen deficiency may be part of the story, but weeds, disease, sulfur deficiency, subsoil constraints and other factors can create similar effects within a paddock.
To illustrate, Tim presented a NDVI image showing a significant amount of paddock striping, which was traced back to poor set-up on a new spreader. The uneven nitrogen fertiliser distribution was able to be addressed, highlighting how this technology can be used to quickly respond to issues seen in the paddock.
Because NDVI imagery has been captured routinely every few days for several years, there’s already a considerable archive of data available for your farm. Tim explained how farmers can access this data for free via the Data Farming platform, as well as how to generate prescription application maps using their software (by subscription).
The importance of understanding variability also extends to on-farm trials. Tim noted that trial placement should account for variation within paddocks, as poorly positioned trials can unintentionally bias results.
Tim also encouraged growers to check imagery for cloud interference and use imagery as a decision-support tool alongside paddock observations and agronomic advice.
Ed Scott from Field Systems introduced in-paddock variability as an opportunity for farmers to extract more yield and improve input efficiency by targeting inputs to where they are most needed.
Ed spoke about the yield gap—the difference between water-limited yield potential and actual yield—which in the Riverine Plains can be as high as 1–2 t/ha, or more. Because nitrogen is the leading factor contributing to the yield gap (soil moisture and other constraints also figure), tweaking nitrogen management can offer opportunities to improve yield across variable paddocks.
Using data layers helps provide insights into variability across a paddock. For example, EM data, yield and protein data, soil tests and satellite imagery can variously help explain moisture availability, nutrition status, biomass and yield potential etc. Once different zones within a paddock are understood and ground-truthed, inputs such as nitrogen can be tailored across zones for a better response.
A strong message from the webinar was that growers should not chase perfectly even yield maps. Instead, decisions should focus on where nitrogen is most likely to generate a return. According to Ed, almost any targeted nitrogen strategy is likely to outperform blanket applications where significant variability exists across a paddock. Where farmers don’t have access to yield or protein data, Ed recommended a NDVI map as simple and easy-to-access way to start targeting nitrogen applications.
Protein data can show how much nitrogen was available to the plant, relative to moisture. This means protein mapping is becoming an increasingly valuable tool to support nitrogen decisions.
For example, areas of low protein in wheat (i.e 8–10%) suggest an undersupply of nitrogen to the crop, limiting yield. The protein target for the Riverine Plains region is 11–12%, and protein over 13–14% often indicates a nitrogen oversupply. Variable rate applications can help address this imbalance across a paddock by allocating more nitrogen to the under-supplied areas, and less to the over-supplied areas. This simple adjustment can help spread your nitrogen supply further, boosting yield in lower nitrogen status areas (by 1 t/ha or so) without compromising yield in the high nitrogen status areas. An even protein map indicates that the crop has optimised available nitrogen use, relative to the moisture available.
Ed noted that tweaking the medium-high performing soils is more likely to give a nitrogen management response than lower performing soils.
For growers considering variable-rate nitrogen, the presenters recommended starting with paddocks that have been historically low in protein, or that show the greatest variation in yield and protein, as those likely to give the biggest gains. Strip trials can provide valuable insights and help build confidence in adjusting management practices.
Several questions focused on the cost of adopting variable-rate nitrogen management. The presenters agreed that growers do not need expensive technology to get started. Existing yield maps, satellite imagery, soil differences and readily available digital platforms can all provide useful information. The key message was that some data is better than no data.
The webinar concluded with a reminder that timing remains critical. Variable-rate top-dressing can be used successfully after an initial blanket application, but adequate soil moisture and follow-up rainfall are still required to move nitrogen into the root zone and make it available to the crop.
The presenters also encouraged growers to think beyond urea alone. Nitrogen formulation, sulfur nutrition and other constraints can all influence crop performance and should be considered when diagnosing variability in the paddock.
Ultimately, the message was clear: understanding variability, using available data and matching nitrogen investment to seasonal conditions can help growers improve nitrogen use efficiency and maximise returns from every kilogram applied.
Watch the full recording of the webinar: Nitrogen strategies for the Riverine Plains
GRDC Grains Research Update, online – Spreading your fertiliser budget further
GRDC Groundcover | Variable-rate technology adds input efficiency to cropping
GRDC Society of Precision Agriculture (SPAA) Livestream – Variable Rate Technology
Link to Riverine Plains project - Fostering the adoption of VRT