Nitrogen fertilisers — improving efficiency and saving money
Nitrogen is critical to plant growth and reproduction. Pasture and crop growth will often respond to an increased availability of soil nitrogen. This situation is often managed through the addition of nitrogen fertilisers.
Nitrous oxide is a powerful greenhouse gas and accounts for 5 per cent to 7 per cent of global greenhouse emissions with 90 percent of these derived from agricultural practices. Nitrogen based fertilisers and livestock manure (urine and dung) are the key sources of nitrous oxide emissions on farms.
Greater efficiency in the capture of nitrogen in products has the greatest impact on reducing nitrous oxide losses, as well as reducing ammonia volatilisation to the atmosphere and nitrate leaching and runoff to groundwater and waterways. Improved nitrogen use efficiency (NUE) has both productivity and profitability benefits.
Nitrous oxide is most likely released from warm, waterlogged soils where there is excess nitrogen in the form of nitrate. Volatilisation of nitrogen as ammonia can also lead to indirect nitrous oxide emissions through redeposition contributing to excess nitrate elsewhere in the landscape.
Farmers can save money, boost pasture and crop production and reduce nitrous oxide losses by carefully planning and implementing best management practices with regards to the 4 Rs — the ‘right’ rate, source, timing and placement of nitrogen fertilisers to match plant needs.
Follow the 4 Rs:
- Right product
- Right rate
- Right time
- Right place
Research has estimated that usually 40 percent to 60 percent of nitrogen inputs into cropping and grazing systems, respectively, is lost to the environment. By improving agricultural practices we can reduce these losses, improve productivity and save money.
Match nitrogen supply to crop/pasture demand by:
- using soil or plant testing to assess plant available nitrogen supply. Apply nitrogen fertiliser rate based on target yield and crop or pasture nitrogen requirement over the growing season.
- accounting for soil moisture availability and seasonal forecasts for more timely and calibrated fertiliser decisions support.
- using industry-relevant decision support tools (such as Yield Prophet in Grains, Dairy nitrogen fertiliser Advisor, GrazFert for beef and sheep).
- avoiding high application rates of nitrogen in any single application (never exceed recommended rates, split applications may be more effective and adjust rates according to rainfall and temperature).
Time fertiliser application to minimise nitrogen loss:
- Where possible, align nitrogen fertiliser applications with crop and pasture demand. Crop/pasture demand is highest when growth rates are highest.
- Avoid applying nitrogen fertiliser to warm (>10°C) waterlogged soils.
- Avoid tillage under wet conditions.
- Consult a 7-day weather forecast to identify risks of soil saturation and if likely delay nitrogen fertiliser application.
- In summer, avoid applying urea fertiliser after irrigation as this is likely to increase volatilisation losses.
- Minimise the length of fallow when converting long-term pasture to crops, especially in high rainfall zones and irrigated crops.
Determine and improve plant access to nitrogen by improving soil health and nutrient status — see next section on Soils. Adding nitrogen to soils that have inherent limitations to plant growth is unlikely to result in higher productivity and financial gain.
Choose the best type of nitrogen:
- Avoid Nitrate based fertilisers which are more prone to losses.
- Enhanced Efficiency Fertilisers, for example coated for slow release, or with nitrification inhibitors may better match the fertiliser supply and plant demand for soil nitrogen.
- Chemicals can be added to fertiliser (inhibitors) which can reduce nitrate leaching and ammonium volatilisation. However, it is recommended to seek expert advice when choosing inhibitors.
Incorporate fertiliser at the top of raised beds or ridges to avoid concentration and losses in furrows and wet areas.
Estimate the methane and nitrous oxide emissions on your farm using a greenhouse gas accounting tool (go to the links to appropriate tools for your type of enterprise).
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 that indicates that significant amounts of applied N fertiliser remains unaccounted for under certain cropping systems and conditions. Unfortunately, this N is often 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 per cent 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 while 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 per cent; it varied from 63 per cent in the HRZ to 76 per cent 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 to:
- increase crop utilisation of soil N ('soaking up' excessive N)
- reduce 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 before 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 following attachments and YouTube video:
What if only a third of added nitrogen fertiliser was ending up in our crop? Where does the rest go?
New insights are being gained from a collaborative 3-year research project called 'Action on the Ground — Reducing on-farm nitrous oxide emissions through improved nitrogen use efficiency in grains'.
With the cooperation of 7 farming families and 3 Catchment Management Authorities, Agriculture Victoria research scientists established nine trial sites within low, medium, high rainfall and irrigated cropping zones across Victoria.
Three nitrogen treatments were applied at each site, based on industry standard practice relevant to each region and the seasonal conditions.
Sites received a small rate of nitrogen fertiliser across all plots at sowing (with 0 to 20 kilograms of Nitrogen per hectare), typically in the form of MAP or DAP depending on farmer management.
- Plot 1 — a standard practice with urea fertiliser top dressed at mid-tillering.
- Plot 2 — where urea was applied at double the standard practice, and
- Plot 3 — a Control which received no additional nitrogen during the season.
Data collected at each site included:
- Recent land use history
- Soil testing, both pre- and post-harvest to a depth of 1.2 metres
- Measurement of nitrous oxide emissions and soil samples at key times during the growing season
- Recovery of nitrogen, applied as urea fertiliser, by the crop as well as residue nitrogen in the soil post harvest, and
- Crop measurements including establishment, biomass at flowering, grain yield at maturity, nitrogen uptake and key grain quality indicators.
Building on previous Victorian studies, Agriculture Victoria research scientist and project leader, Professor Roger Armstrong, explains some of the key project findings…
[Professor Roger Armstrong, Senior Scientist, Agriculture Victoria:]
'A real stand in our project results was the general lack of nitrogen fertiliser response. This was a function of both the poor seasonal conditions and also the large background levels of mineral nitrogen that we have found.
'Reducing current rates of fertiliser nitrogen input, particularly in some irrigated cropping areas, and also in the high rainfall zone where paddocks have experienced a long history of legume pastures, can have minimal impacts on productivity while saving growers money.
'As part of his role in the project Agriculture Victoria research scientist Ash Wallace found that the amount of fertiliser nitrogen used by the target crops ranged from less than 5% to a maximum of more 60% of the nitrogen applied. This big variation mainly reflected differences in growing season rainfall and irrigation.
'Average recovery of fertiliser nitrogen by the crop ranged from a high of 42% in irrigated crops, to 32% in low and medium rainfall dryland systems, to a low of 30% in high rainfall systems. These values are considerably lower than the figure of 50% currently used as rule of thumb by many in the industry.
'Of real concern to growers is the large losses of nitrogen fertiliser that we recorded. Fertiliser nitrogen recovery in the crop, plus that remaining in the soil at harvest, averaged only 71%. It varied from 63% in the High Rainfall Zone to 76% in the low and medium rainfall regions. This represented an average loss to the crop soil system of over a quarter of the fertiliser nitrogen applied.
'In-crop nitrogen mineralisation, where mineral nitrogen is produced from organic nitrogen in the soil, was found to be a potential major source of nitrogen to the crops in this study — constituting up to 63% of the total nitrogen in the crop.
'The relative importance of this source of nitrogen to crop nitrogen uptake appeared to vary predominantly with the in-season rainfall, rather than soil type or region. Currently, in-crop nitrogen mineralisation isn't very accurately accounted for in best management practices so it's really important that it is, if we are to have accurate nitrogen fertiliser predictions.
'The best strategy to reduce both costs and nitrous oxide emissions in these systems appeared to be through increased crop utilisation of soil nitrogen, i.e. 'soaking up' excessive nitrogen and reducing fertiliser inputs accordingly.
'Findings from similar trials in the High Rainfall Zone also indicate that, avoiding nitrogen application at sowing, (if pre-sowing assessments of soil mineral nitrogen levels show high background levels of N), and delaying fertiliser application until between tillering and early booting growth stages, improves both nitrogen utilisation and increases crop yield and grain protein levels.
'A key output of the project will be the development of both localised crop utilisation coefficients, as well as a methodology for predicting in-crop N mineralisation. Having both of these tools will help growers and advisers better predict how much fertiliser nitrogen is required as well as having greater confidence in their decision-making processes.
'The most important practice that growers can adopt is to measure the amount of mineral nitrogen in the profile prior to sowing using deep soil testing.
'Research undertaken by PhD student Katherine Dunsford in the project assessed new soil testing methods for measuring potential rates of nitrogen mineralisation. Both the Hot KCI and Solvita tests, performed better than the current 'rules of thumb' which are widely used by advisers. These tests look promising for rapid, in-field use by croppers — once they have been calibrated for Australian conditions.
'Another key finding from this study was around nitrous oxide emissions. High nitrous oxide losses were recorded from the high rainfall zone sites, which appeared to be underpinned by high soil carbon and nitrogen levels. However, the real surprise was that highest nitrous oxide emissions occurred in irrigated cropping paddocks of north-central Victoria. These emissions seemed to be underpinned more by irrigation and poor drainage, than by soil carbon and nitrogen levels, which were relatively low at these sites.
'Very low levels of emissions were recorded in the low and medium rainfall cropping sites.'
So, what did farmers involved in the trial think about the findings?
[Keith Fischer, Farmer, Wimmera:]
'I got a lot of information out of the findings. I'd been informed that the losses from nitrogen application were of a high percentage but in our area we're not losing a lot.
'During the dry years a lot was going into the soil and staying there for the following year, whereas we were thinking we were losing it and having to apply more. So now I can reduce the amount of nitrogen I am applying, knowing that there's back up in the soil for the following year.
'Deep soil testing is important, in the past we were believing that we were losing the nitrogen, but now knowing with deep soil testing I can get a knowledge of how much nitrogen is in the soil, so that during the season I can apply the correct amount so I'm not wasting the amount of nitrogen I'm applying.
'This knowledge helps me to plan for the season, it reduces our costs, it reduces our effects on the environment and we get as good, if not better, yields each year so we win in many ways.'
So in summary this project indicates that, in many cases, there is actually sufficient soil nitrogen present in the soil profile, prior to sowing, to meet most of the crop demand.
By undertaking appropriate soil testing, grain growers could save the expense of applying nitrogen fertiliser that the crop simply doesn't need.
Losses of fertiliser nitrogen (and presumably background soil nitrogen) from the soil can be significant, representing both a major financial loss to grain growers and a negative environmental impact from nitrous oxide emissions.
For more information about this project and how you can access the results and tools, visit www.agriculture.vic.gov.au or contact one of our team members.
A good explanation of the Nitrogen cycle and how N2O emissions can be reduced can be found at the Fertcare Nitrogen Use Efficiency webpages.
Nitrogen fertilisers and nitrous oxide
Nitrous oxide (N2O) is emitted from soils, N fertilisers and 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 that 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 per cent of all anthropogenic N2O emissions. Between 1990 and 2007, N2O emissions in Australia rose by 24 per cent 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 while 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 15°C.
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 per cent.
Not surprisingly, the 'perfect storm' of conditions suited to high N2O emissions are most often found on irrigated and HRZ sites.
Best management practices to reduce emissions and improve efficiency
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 Rs, which are the:
- right product
- right amount
- right timing
- right placement.
The 'four Rs' are summarised in the following video.
Nitrous oxide may be an invisible gas but it can have significant impacts on our environment. Sometimes called 'laughing gas', nitrous oxide is no laughing matter.
It's a powerful greenhouse gas that's over 300 times stronger at trapping in heat than carbon dioxide, and it's a pollutant that damages our ozone layer.
Agriculture Victoria scientist and Project leader, Professor Roger Armstrong, explains:
[Professor Roger Armstrong, Senior Scientist, Agriculture Victoria:]
'Although nitrogen fertilisers are an essential part of most Australian grain production systems, our research has shown that nitrous oxide emissions are a function of both the rate of nitrogen fertiliser applied, as well as the background soil mineral N levels.
'In some situations, we're adding considerably more nitrogen than the crop needs. Unfortunately, there is increasing evidence that the relationship between nitrous oxide emissions and increasing Nitrogen input is an exponential, rather than a lineal relationship for most crop types.
'But the good news is that by having a better understanding of how much soil mineral nitrogen is present at sowing and by some fine tweaking of when we apply nitrogen fertiliser during the crop, we can both simultaneously reduce nitrous oxide emissions, improve grain yield and quality all while saving money on fertiliser.'
So that's why the race is on to better understand how nitrogen fertiliser can be better managed while finding cost effective ways to reduce nitrous oxide emissions.
Agriculture Victoria research scientists have been at the forefront of research into nitrogen fertiliser management and nitrous oxide 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.
Professor Roger Armstrong, explains some of the key Victorian research findings:
[Professor Roger Armstrong:]
'Overall we found that nitrous oxide emissions are quite low in low and medium rainfall areas, particularly if nitrogen isn't applied when there is periods of temporary waterlogging. The key thing is to remember that nitrous oxide emissions are closely tied to waterlogging events.
'Other key risk factors that result in higher emissions are:
- high levels of labile soil carbon,
- high levels of existing mineral nitrogen
- warm soils.
'In the High Rainfall Zone of South western Victoria we’ve found that larger amounts of nitrogen fertiliser applied at sowing result in losses of up to 85 per cent of the nitrogen applied.
'Effectively what this mean was that applying nitrogen fertiliser in these situations was both a waste of time and money.
'The good news, however, is that we have some pretty solid rules of thumb for Best Management Practices for fertilisers.
'The best way to remember these rules of thumb are the four R's: Getting the Right Product, the Right Amount, Getting the Right Timing and the Right Placement.'
The Right Product:
First of all, non-fertiliser derived nitrogen, originating from sources such as via legume rotations and crop residues is an important source of N to crops and should be accounted for when planning fertiliser N applications.
Consider if nitrification inhibitors (which slow the conversion of ammonium to nitrate), are financially justifiable for your situation.
The Right Rate:
The higher the rate, the greater the likelihood of emissions, so make sure you test your soils to determine both the existing mineral nitrogen content and then allow for the amount of soil nitrogen that could be mineralised during the growing season.
Once you have estimated the crops nitrogen demand, subtract the measured nitrogen supply from the soil via your soil test and the estimated nitrogen supply from mineralisation to determine the nitrogen fertiliser rate you need to apply.
Also, check that other factors such as nutrients or disease aren’t limiting your crop's growth and ability to utilise any extra nitrogen applied. This is where precision cropping techniques (such as variable rate technology, pH mapping) and disease assessments such as PredictB can help get more accurate fertiliser application and avoid wasting inputs that aren’t needed.
The Right Timing:
Match your timing of fertiliser application to coincide with your crops' changing demand. Split applications improves crop nitrogen uptake, but always avoid applying fertiliser when soils are waterlogged. The greatest demand for nitrogen by your crop normally occurs around mid to late tillering so factor this into your fertiliser management program.
The Right Place:
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.
Use the best technique for placing nitrogen fertiliser in the right place that maximises crop nitrogen uptake. Generally, it's best to place your nitrogen into the soil. This helps to ensure nitrogen is more accessible to the crop roots, because crops can't access nitrogen if it is stranded in dry topsoils. It also tends to reduce losses of nitrogen from some soils.
There is a potential for even greater losses of nitrogen through volatilisation of topdressed urea, on highly alkaline soils such as soils in parts of the Wimmera and most of the Mallee.
Remember, too, that improved surface drainage, minimal-tillage and controlled traffic practices also help by improving soil structure (resulting in better grain yields) while reducing nitrogen losses occurring during waterlogging.
If you're converting pasture into a cropping phase, avoid long periods of fallow, especially in high rainfall areas and if irrigation is used. Short fallows reduce the risk of high nitrous oxide emissions that result from the build up of high background concentrations of labile soil carbon and mineral N that occur during the decomposition of pasture residues.
Future research into nitrogen use and management is continuing to ensure Victorian farmers can not only reduce greenhouse gas emissions but also ensure fertiliser costs are minimised.
Less N2O is emitted where ammonium (NH4+) is the main form of N 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 — for example, N supplied as ammonium or urea will result in a slower rate of nitrate production, especially in waterlogged soils, and therefore less N2O emissions.
Consider using nitrification inhibitors, which slow the conversion of ammonium to nitrate). But the price and logistics must be considered for your situation.
Slow release products, where the release pattern matches plant demand for N, are not currently cost-effective in many cropping situations but may become more viable as the technology develops.
Aim to provide N from organic matter sources, for example, manure, compost and pasture legume or 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, get 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, for example, from previous N-fixing crops residues. Depending on crop root depth, sample soils at depths 0 to 10 cm and 10 to 60 cm (and down to 60 to 90 cm if roots extend to that depth).
Watch the following video on soil sampling.
[Greg Bekker, Livestock and Land Management Extension Officer:]
Soil testing is a really important decision-making tool. We use it to determine soil nutrient levels and other soil characteristics.
The tools you will need are a soil corer, a clean plastic bucket, a plastic bag to put your samples in and a tray to do your subsampling. An aerial photo or mud map will assist with the planning of that soil sampling.
[Visual: Be sure your corer is the correct size.]
The other really important factor is to make sure your soil corer is 10 centimetres and take the time to measure it.
[Visual: Aerial photos are available at your local Agriculture Victoria office]
An aerial photo can be used in planning where to take your soil test.
Areas that we don't do are around water troughs, gateways, within four metres of a fence line and other clearly different areas within the paddock. So within this gully here, we are not going to take a sample, and also a stock camp at the top of the hill.
Once we have determined that, it is very easy to work out where we are going to put our transect.
[Visual: A transect is a designated line you will follow and take samples along.]
In this case we would look at a transect along there and also one back that way. That would give a truly representative soil sample of this paddock.
[Visual: Aerial photo with a Y-shaped transect that avoids all the areas that don't need sampling]
[Visual: You will need to take 20 to 30 samples.]
I've got that end tree as my end point, as a transect, so that is what I'm heading towards.
[Visual: Sample at the same time each year, ideally when your soil is not too dry.]
This corer has an internal taper, so it always taps out backwards and you must make sure it is totally cleared before you take the next sample.
[Visual: Your soil corer is tapered.]
[Visual: Calculate the distance between sampling points.]
This is a 300 metre transect that I have got from the aerial map, so that means I need to take a sample every 10 metres to get 30 samples.
We've got a urine patch and a cowpat there, so we're not going to test there.
[Visual: Divert around urine patches.]
Instead we just move off to the side along the same transect and take a sample.
[Visual: Preparing your samples for analysis.]
Once we have brought our 25 to 30 cores back, we put them in the bucket and need to mix them thoroughly. To do that we will pour them out into this tray and break up all of these cores.
[Visual: Remove vegetation and rocks.]
While we are doing this we remove any vegetation matter and rocks.
[Visual: Mix until your soil is a uniform size.]
Once we are happy that we have sampled that and have got a really consistent mix throughout we are going to subsample. We break that in half and then we will break this section in half again. You want to end up with about 200 to 300 grams of soil to put in the bag.
[Visual: Complete all paperwork accurately and send within 24 to 48 hours.]
Once you've got that sample it is really important that you have got your name, your address, paddock name and the date you took the sample.
Samples should be placed in the laboratory-supplied bags for postage.
The soil test results are going to come back to you in a range of different formats.
Use your local agronomists, landcare groups or departmental staff to assist you with the interpretation.
It's really important that we use this information to make informed decisions on what you're going to do with your soil and make sure that they align with your overall farm goals.
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 (for example, 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 must be taken into account.
Consider all other non-fertiliser N sources, for example, soil mineral N, organic N mineralisation from previous crop residues, manures and irrigation water.
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, for example, before 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 per cent 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 — for example, 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 the following can be effective:
- retention of soil cover
- maintaining soil organic matter
- gypsum or lime application
- reducing cultivation.
Remember, too, that improved surface drainage, minimising tillage and controlled traffic practices also help by improving soil structure (resulting in better grain yields) while 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:
- Use deep-rooted follow up crops to 'mop up' residual N in high N situations with sufficient rainfall.
- Switch 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 or accredited in handling and spreading fertiliser.
- Use GPS enabled dataloggers 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.
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:
- 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
Primary Industries Climate Challenge Centre (PICCC) is 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
- Nitrous oxide and fertilisers fact sheets
- Nitrous Oxide Research Program
- PICCC Director, Richard Eckard on Nitrous Oxide in crops and pastures (Video presentation)
Greenhouse in Agriculture
See the University of Melbourne — Greenhouse in Agriculture website for research and development of cost-effective options for the abatement of methane and nitrous oxide from Victorian agriculture.
Grains Research Development Corporation
Grains Research Development Corporation (GRDC) has an extensive list of GRDC N fertiliser use and N2O reports and videos on YouTube, 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.
The Dairy Australia (DA) website has 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
National Agricultural Nitrous Oxide Research Program (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.
Better Fertiliser Decisions
Making Better Fertiliser Decisions (BFDC) for Cropping Systems In Australia provides knowledge and resources to improve nutrient recommendations for optimising crop production.
EXtensionAUS have produced a series of short YouTube video interviews with key soil scientists:
- YouTube video: Test first, then time Nitrogen fertiliser to reduce losses — Roger Armstrong
- YouTube video: Roger Armstrong, Mike Bell and Louise Barton discuss soil carbon and emissions
- YouTube video: Dig deeper if you really want to know about Nitrogen - Charlie Walker
- YouTube video: Better fertiliser decisions for cropping webinar by Tony Cox, NSW DPI
- YouTube video: A clearer picture for nitrogen in Australian soils — Louise Barton UWA
- YouTube video: Reducing Nitrogen losses in the High Rainfall Zone of Victoria - Rob Harris VIC DJPR
- YouTube video: How to review Nitrogen nutrition at 3 timely points in the season with John Angus
- YouTube video: Legumes and nitrogen for following crops, Mark Peoples, CSIRO
See more pages in this series: