Nitrogen fertilisers - improving efficiency and saving money

[Narrator:]

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 9 trial sites within low, medium, high rainfall and irrigated cropping zones across Victoria.

3 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.

Treatments included:

• 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.'

[Narrator:]

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.'

[Narrator:]

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.

[Narrator:]

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.'

[Narrator:]

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% 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 4 R's: Getting the Right Product, the Right Amount, Getting the Right Timing and the Right Placement.'

[Narrator:]

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.