Nitrogen Fertilisers - Improving Efficiency and Saving Money
These pages provide information, tools, contacts and links to other useful websites that can help farmers save money, boost production and reduce nitrous oxide losses by implementing best management practices with regard to the rate, source, timing and placement of nitrogen fertilisers.
- Nitrogen and Nitrogen fertiliser
- Improving Nitrogen fertiliser use efficiency
- Nitrogen fertiliser and nitrous oxide
- Best management practices to reduce nitrous oxide emissions and improve Nitrogen use efficiency the four R's
- Useful links
Nitrogen and Nitrogen fertiliser
Nitrogen (N) is critical to crop growth and grain production. The demands of modern agriculture require higher levels of N than are normally found in native soils. As cropping systems transition from the use of pasture-ley legume rotations, increasing rates of fertilisers are used to meet crop demand for N.
Becoming more efficient in the application of N fertilisers on farms and avoiding N losses has direct financial benefits for farmers, and will likely lead to reduced nitrous oxide (N2O) emissions and nitrate runoff into waterways.Fig. 1. Summarised version of a Nitrogen cycle in a grazing/cropping system. The Victorian Resources Online website includes a detailed animation explaining the N cycle.
Improving Nitrogen fertiliser use efficiency
There is a growing body of evidence indicating that significant amounts of applied N fertiliser (and potentially mineralised soil N*) remains unaccounted for, under certain cropping systems and conditions. Unfortunately, this N is often being irretrievably lost from the cropping system; representing both a significant cost to growers and the environment.
Agriculture Victoria research scientists have been at the forefront of research into N fertiliser management and N2O emissions in Victoria's cropping industry for over a decade. A variety of field experiments have been established on farms across Victoria's cropping zones to help better understand the issue. In the high rainfall zone (HRZ) of south western Victoria, Agriculture Victoria researchers, have recorded losses of up to 85% of the N applied in situations where large amounts of N fertiliser were applied at sowing. In some trials around Hamilton, applying N at sowing to soils already naturally high in N, gave no significant increases in crop yield response. Effectively, what this means is that applying N fertiliser in these situations was both a waste of time and money!
In 2017, Agriculture Victoria researchers completed a collaborative, three year research project into N use efficiency in key Victorian cropping zones.
Lead researcher, Professor Roger Armstrong stated that "A real standout result of the project was the high number of instances where N fertiliser response was limited. Reducing current rates of fertiliser N input, particularly in the HRZ, where paddocks have experienced a long history of legume pastures, can have minimal impact on productivity whilst saving growers money. However, of real concern to growers is the large losses of N fertiliser that we recorded. Fertiliser N recovery in the crop, plus that remaining in the soil at harvest, averaged only 71%; it varied from 63% in the HRZ to 76% in the low/medium rainfall regions."
This research indicates that the best strategies to reduce both fertiliser costs and N2O emissions in these systems are through:
- Increasing crop utilisation of soil N ('soaking up' excessive N)
- Reducing fertiliser inputs, via better predictions of current soil N status using deep soil sampling prior to sowing.
Currently, growers and their advisers can only guess the likely amount of In-Crop Mineralisation* (ICM) that is occurring in these soils when making predictions about likely amounts of fertiliser that will need to be applied to meet predicted crop demand. However, simple and rapid soil tests are being developed that will allow an accurate assessment of potential N mineralisation rates prior to sowing. Two soil tests (Hot KCl and Solvita) show promise as predictors of ICM, both of which can perform better than some of the current 'rules of thumb' used by advisers across the regions but are not currently available commercially.
The project design and key findings from this collaborative three year research project are summarised in the below attachments and YouTube video:
and the YouTube video: 'Long term nitrous oxide and N fertiliser use efficiency research findings'
A good explanation of the Nitrogen cycle and how N2O emissions can be reduced can be found at the Fertcare Nitrogen Use Efficiency webpages.
Nitrous oxide (N2O) is emitted from soils, N fertilisers, as well as from stock effluent. Sometimes called 'laughing gas', N2O is no laughing matter. Nitrous oxide can have significant impacts on our environment. It's a powerful greenhouse gas; that's around 300 times more effective in trapping heat than carbon dioxide and it persists in our atmosphere for up to 114 years. Nitrous oxide also has the added downside of being an ozone layer destroying gas.
Nitrous oxide emissions represent a loss of valuable N from soils which would otherwise be available for plant growth. Nitrogen is critical to plant growth and reproduction. Production agriculture requires higher levels of N than are normally found in native soils. Hence, the addition of N fertilisers.
Although some N2O production is a natural part of the N cycle, levels of N2O emissions are greatly affected by the way we manage our soils and fertiliser input. High levels of N2O emissions usually indicate overuse of N fertiliser. Unfortunately, there is increasing evidence that the relationship between N2O emissions and increasing N input is an exponential, rather than a lineal relationship for most crop types.
Excessive levels of N can also result in leaching of nitrates into water systems, both above and below-ground. Nitrogen rich leachates are a key culprit in algal blooms and dissolved oxygen depletion which is toxic to wildlife.
Nitrogen-based fertilisers and livestock waste (urine and dung) are the key sources of N2O emissions on farms. In 2007, Australian N2O emissions from agricultural soils were estimated at 20.2 million tonnes of "carbon dioxide equivalent" or 85.9% of all anthropogenic N2O emissions. Between 1990 and 2007, N2O emissions in Australia rose by 24% (source: NANORP website) and this increase is largely attributable to the increased application of nitrogenous fertilisers. That's why the race is on to better understand how nitrogen fertiliser can be better managed whilst finding cost effective ways to reduce N2O emissions.
Agriculture Victoria Researcher, Professor Roger Armstrong, explains some of the key Victorian N2O research findings : "Overall we have found that N2O emissions are quite low in low and medium rainfall areas, particularly if N isn't applied during periods of temporary waterlogging. The key thing is to remember that N2O emissions are closely tied to anaerobic soils that occur during waterlogging events".
High levels of N2O emissions in cropping soils indicate excessive fertiliser use (especially nitrate-based fertilisers) which is amplified on waterlogged sites with high levels of organic labile soil carbon, clay soils and warm clay soils (with temperatures above 150C.
Soil texture also influences N2O production since pore size influences drainage and N2O emissions peak when water filled pore space of soils is around 70%.
Not surprisingly, the 'perfect storm' of conditions suited to high N2O emissions are most often found on irrigated and HRZ sites.
Thanks to the wealth of research undertaken in Victoria and other major cropping areas in Australia and overseas, we now have some pretty solid 'rules of thumb' around Best Management Practices for N fertilisers. A handy way to remember these is to think about the Four R's: Using the Right Product, the Right Amount, Getting the Right Timing and the Right Placement".The 'Four R's' are summarised in the video 'Long term nitrous oxide and N fertiliser use efficiency research findings'
Less N2O is emitted where ammonium (NH4+) is the main form of N and/or where the rate of NH4+ conversion to nitrate (NO3- ) in the soil is slowed. Try to use fertilisers that don't supply N in the form of nitrates e.g. N supplied as ammonium or urea will result in a slower rate of nitrate production, especially in water logged soils, and therefore less N2O emissions.
Consider using Nitrification inhibitors which slow the conversion of ammonium to nitrate) but the price and logistics need to be considered for your situation.
Slow release products, where the release pattern matches plant demand for N, are not currently cost-effective in many croppin situations but may become more viable as the technology develops.
Aim to provide N from organic matter sources e.g. manure, compost and pasture legume / pulse crop residues. However, adding high rates of organic matter adds significant amounts of readily mineralisable N as well as lots of labile carbon (C) and can exacerbate N loss. In cropping, the more realistic option is to utilise more legume residues for N supply this will provide a more moderate rate of N and C. If you're using manures, obtain a nutrient analysis to determine both organic and total N and make allowances in your fertiliser budget.
The higher the rate, the greater the likelihood of emissions, so make sure you test your soils to determine both the existing mineral N content and then allow for the amount of soil N that could be mineralised during the growing season. Once you have estimated the crops' N demand, subtract the measured N supply from the soil via your soil test and the estimated N supply from mineralisation to determine the N fertiliser rate you need to apply.
The optimum N fertiliser rate depends on the type of crop, the soil type, farming system and the crops' growth stage. Aim to match the rate closely to a conservative and realistic estimate of your crops projected needs:
Sample soils to determine mineral N content wherever there is uncertainty around the quantity and location of N in the crop root zone. In annual crops, sample close to planting as feasible, or soon after crop emergence, especially where high levels of residual N exist, e.g. from previous N-fixing crops residues. Depending on crop root depth, sample soils at depths; 0-10 cm and 10-60 cm (and down to 60-90 cm if roots extend to that depth).
Also, check that other factors such as other nutrients, disease or soil constraints (such as acidic soils) aren't limiting your crop's growth and ability to utilise any extra N applied. This is where precision cropping techniques (such as variable rate technology, pH mapping) and disease assessments can help get more accurate fertiliser application and avoid wasting inputs that aren't needed.
Determine and improve plant access to N by improving soil health and nutrient status. Pouring additional N inputs onto soils that have inherent limitations to crop growth such as high salinity is unlikely to result in financial gain.
If available, using appropriate, industry-relevant decision support tools (e.g. Yield Prophet in Grains) and seasonal forecasts for more timely and calibrated fertiliser decision support; knowledge of moisture status and soil N reserves and supply need to be taken into account.
Consider all other non-fertiliser N sources, e.g. soil mineral N, organic N mineralisation from previous crop residues, manures, irrigation water etc.
Consider subsoil limitations such as salinity, acidity or high Boron that might restrict your crops ability to use N effectively.
Matching the timing of fertiliser application to coincide with your crops' changing demand will maximise crop N uptake and minimise your fertiliser costs. Always aim to avoid applying fertiliser when soils are waterlogged or likely to become so, e.g. prior to forecast heavy rain. Consider that:
- Crops usually only use small amounts of N in early growth stages so if you apply most of the crops projected N needs at or close to planting, N losses are more likely.
- Sample soils and, if you're able to, apply 'in-crop' N fertiliser rather than 'up-front' N to better match your crops demand. Supplying N fertiliser at crop development stages during high N uptake periods can increase N uptake by the crop, provided sufficient follow up rainfall occurs. Most crops require less than 20% of their total N requirement by first flowers2.
If you're converting long-term pasture to crops, minimise the length of fallow, especially in HRZ and irrigated crops. Long fallows lead to rapid build-up of N in the nitrate form and subsequently, much higher N2O losses compared to short fallows before cropping. Avoid conversion in high rainfall years e.g. when La Niña is forecast.
Use the best technique for placing N fertiliser in the right place that maximises crop N uptake. Apply fertiliser close to the active root zone or where rain will move fertiliser to the main root zone. Generally, it's best to place your N into the soil. This helps to ensure N is more accessible to the crop roots, because crops can't access N if it is stranded in dry topsoils. It also tends to reduce losses of N by ammonia volatilisation from some soils.
In soil types that are prone to erosion or volatilisation, such as soils with highly alkaline topsoils that can occur in parts of the Wimmera and most of the Mallee, apply fertiliser into subsoils and aim to place it as deep below the composting crop residue as possible, may help to improve crop uptake of applied N.
Use tillage practices and systems such as controlled traffic farming to maximise water and N uptake by crops, by avoiding compaction and waterlogging and maintain good drainage. Where waterlogging results from sealing or dispersive topsoils, practices such as retention of soil cover, maintaining soil organic matter, gypsum or lime application and reducing cultivation can be effective.
Remember too that improved surface drainage, minimising tillage and controlled traffic practices also help by improving soil structure (resulting in better grain yields) whilst reducing N losses occurring during waterlogging.
Don't forget to make sure you've checked and measured the accuracy of your fertiliser spreader and operator and avoid double-ups and drainage lines – unless you want to watch money go down the drain.
Other management techniques to improve N use efficiency and reduce N2O emissions include:
- Using deep-rooted follow up crops to 'mop up' residual N in high N situations with sufficient rainfall.
- Switching off fertiliser applicators at end rows and other turn around points.
- Protect stored fertiliser from moisture.
- Avoid/pick up fertiliser spills.
- Ensure your fertiliser operators are adequately trained/accredited in handling and spreading fertiliser.
- Use GPS enabled data loggers to identify high and low yielding zones and adjust your inputs for best N use efficiency.
- Use crop varieties that are able to make the most of available N.
Future research into N use and management is continuing to ensure Victorian farmers can not only reduce greenhouse gas emissions, but also ensure fertiliser costs are minimised.
Summaries and published research papers on N and N2O emissions relevant to Victorians can be found in a variety of formats on the websites listed below.
Agriculture Victoria links:
- Understanding carbon and emissions: Information of soil carbon and greenhouse gas emissions from Australian agriculture.
- Nitrogen monitoring tools: Provides useful information and tools to assess the risk of N loss and productive use of N fertiliser.
External website links:
Fertcare: In response to climate change issues, Fertcare® has brought together new information on N2O, N use efficiency and soil carbon, including extensive reports and best management practices, including:
- Nitrogen Use Efficiency And Nitrous Oxide
- Nitrogen Use Efficiency - Enhanced Efficiency Products
- N2O video - Nitrogen Use Efficiency And Nitrous Oxide
Primary Industries Climate Challenge Centre (PICCC): A collaborative venture between the University of Melbourne and Agriculture Victoria. PICCC combines the resources and activities of its partners to lead research, development and education related to climate change and the primary industries. Useful resources include:
- Enhanced Efficiency Fertilisers webpage - Best management practices for nitrogen on pastures.
- Nitrous oxide and fertilisers fact sheets
- Nitrous Oxide Research Program
- PICCC Director, Richard Eckard on Nitrous Oxide in crops and pastures - Video presentation
University of Melbourne - Greenhouse in Agriculture website:Research and development of cost-effective options for the abatement of methane and nitrous oxide from Victorian agriculture.
Grains Research Development Corporation (GRDC): Includes an extensive list of GRDC N fertiliser use and N2O reports and videos, fact sheets, as well as past and current GRDC projects under the 'More profit from crop nutrition 'program. Also, GRDC's Extension Hub Crop Nutrition Community of Practice, includes topical articles by leading industry experts who have a specific and applied focus on crop nutrition.
Dairy Australia (DA): The DA web pages have some really useful information and tools on how to optimise N fertiliser use in intensive pastures while minimising losses to the environment.
National Agricultural Nitrous Oxide Research Program (NANORP): NANORP is a national research network aimed at developing and delivering effective and practical strategies for reducing N2O emissions while maintaining productivity. The NANORP website provides access to farm greenhouse gas calculators and research reports on N2O.
Making Better Fertiliser Decisions (BFDC) for Cropping Systems In Australia: BFDC provides knowledge and resources to improve nutrient recommendations for optimising crop production.
EXtensionAUS: EXtensionAUS have produced a series of short YouTube video interviews with key soil scientists:
- Test first, then time Nitrogen fertiliser to reduce losses - Roger Armstrong https://www.youtube.com/watch?v=WTOjRMMwyC4
- Roger Armstrong, Mike Bell and Louise Barton discuss soil carbon and emissions https://www.youtube.com/watch?v=YQHsO_WauVk
- Dig deeper if you really want to know about Nitrogen - Charlie Walker https://www.youtube.com/watch?v=sbJLo2XgE2A
- Better fertiliser decisions for cropping webinar by Tony Cox, NSW DPI https://www.youtube.com/watch?v=X4kmf70ApQs
- A clearer picture for nitrogen in Australian soils - Louise Barton UWA https://www.youtube.com/watch?v=S6HMD_dxzhM
- Reducing Nitrogen losses in the High Rainfall Zone of Victoria - Rob Harris VIC DEDJTR https://www.youtube.com/watch?v=QSYt9etrK6w
- How to review Nitrogen nutrition at 3 timely points in the season with John Angus https://www.youtube.com/watch?v=gHwrwgyYszk
- Legumes & nitrogen for following crops, Mark Peoples, CSIRO https://www.youtube.com/watch?v=AzQkWQWdmRo