Project Background
RiskWi$e is a National Risk Management Initiative (NRMI), seeking to understand and improve the risk-reward outcomes for Australian grain growers by supporting grower on-farm decision-making. Grains Research and Development Corporation (GRDC) have invested $30 miliion to support this 5-year national initiative, running from 2023 -2028.
Grain growers face increasing levels of risk: The two main risks faced by grain growers that affect the success of their business are yield (impacted by weather changes) and price volatility – both are expected to become more unpredictable in the future.
Improved understanding of risks empowers growers:Â With a better knowledge of risks, grain growers will be able to make decisions about on-farm management that maximise the rewards and minimise negative outcomes.
RiskWi$e is designed to help growers manage risk:Â RiskWi$e will use participatory action research that engages growers in the conception to implementation process to help build trust and understanding of new knowledge on risk-reward that better informs decision making on-farm
Focus
- Involve grain growers in the identification of on-farm decisions that have unknown components of risk-reward that will be studied to elucidate new insights.
- Develop an improved understanding of the risk-reward relationships for on-farm management decisions.
- Inform growers and their advisers of new insights into optimising rewards and managing risk.
- Challenge grower decision-making so future management decisions are evaluated in terms of the probability of upside returns offset against the associated downside risks.
Deep N Testing
Deep N testing lets you know what N there is in the crop’s rootzone so you can make decisions about the amount of N to apply or adjust sowing rates to reflect starting N.
It is convenient to measure soil N now while the paddocks are dry and trafficable but there is one major downside to testing now – how much mineralisation will we get with pre-irrigation?
Mineralisation is the conversion of organic nitrogen contained in stubbles or pasture residues to plant available N thanks to microbial breakdown. Microbial activity is brought to life by warm temperatures and moisture (summer rainfall or irrigation). So, when we get lots of summer rainfall, we tend to see higher starting soil N levels. Pre-irrigation can also result in rapid increases in soil N particularly on legume/pulse residues.
If you do have high soil N, and rotations are locked in, then reducing sowing rates may be a tool in reducing the risk of lodging, particularly in barley. IFN barley population trials demonstrated that lower sowing rates (down to 90 plants/m2 or about 50 kg/ha) reduced lodging without affecting grain yield where soil N was high (>120kg N/ha) but where soil N was more typically around 65kg N/ha, sowing rates that resulted in at least 120 plants/m2 were required to maintain yield. Simply put – lots of early N encourages tillering that either can compensate for lower plant numbers or causes excessive vegetative growth that increases the risk of lodging in the cereals. Our barley trial plant target is still 160 plants/m2 (which ranged from as the extra seeds allows for a margin if establishment is poor or improves seedling weed competition.
So, the testing for N can happen in early autumn while it is reasonably easy or can be delayed until June (so you have the figures to work out your topdressing rates taking in to consideration what N is in the crop) and then be able to assess what N was mineralised by pre-irrigation.
Benefits to soil N testing
Making assumptions about N requirements can result in unnecessary fertiliser expenses.
In 2023, post the flooding of late 2022, the assumption that soil N would be low was based on observations post the 2011 flooding. However, soil N was quite high and several of our trials showed that N topdressing rates could be cut back quite significantly (our ‘0’ treatments yielded as well as our 150kg N/ha treatments in wheat, although there was a difference in protein) and the barley trials all suffered from excessive early vegetative growth and harvest lodging that could have been reduced by lowering our sowing rates.
Base N on target yields
When the amount of N applied was based on target yields rather than ‘typical’ rates, we saw the best returns per hectare and per megalitre thanks to (a) achieving high yield by supplying enough N to get there and (b) not spend money on unnecessary fertiliser.
Summary
Deep N testing gives you an idea of how much N is in your soil and allows for better N topdressing rate decisions. Testing now is easy and gives you an idea of what soil N you have, but waiting until winter does give a more accurate assessment but less time to act/order and it could be more difficult to take samples.
Maize Nitrogen Use Efficiency Trial
The trial was sown into a prepared seed bed (350 kg MAP/ha spread and multi-disced into maize residue), targeting an establishment of 85,000 plants/ha. The trial was sown dry on 8 November and watered up on 11 November. The site did crust following irrigation but establishment was satisfactory and reasonably uniform across the trial. Average plant population achieved was 83,500 plants/ha.
The trial tested 4 N rates (80, 160, 240 and 320 kg N/ha) in addition to the base rate of 210 kg N/ha and either split between two applications (sowing and 8 leaf) or three applications (sowing, 6 leaf and tasselling).
Soil testing at prior to sowing showed 151kg N/ha in the soil to 60cm.
The base rate was applied as water-run UAN on 12 December (150 kg N/ha) and 2 January (60 kg N/ha). The total N available for the base treatment was 396 kg N/ha (soil N + MAP + UAN), with no consideration of the mineralisation that may have occurred through the season. The base N rate was selected to reflect the Optimising Irrigated Grain findings, where the total N content of the crop at harvest averaged around 400 kg N/ha.
The trial was watered-up using approximately 1.2 Ml/ha and subsequent irrigations were based on evapotranspiration data. Total water use for the season was 8.1 Ml/ha.
The trial was harvested on 1 May
The yield results are presented below and have been corrected for moisture. Trial mean (average) was 16.5 t/ha.
Table 1: IFN Riskwise Maize NUE Trial yield summary
| Treatment | Yield t/ha | |||
|---|---|---|---|---|
| 210kg N/ha (base rate) | 17.25 | |||
| 290kg N/ha (210 + 80 split @Sowing & 8 leaf) | 15.88 | |||
| 370kg N/ha (210 + 160 split @ sowing & 8 leaf) | 16.13 | |||
| 450kg N/ha (210 + 240 split @ sowing & 8 leaf) | 16.70 | |||
| 530kg N/ha (210 + 320 split @ sowing & 8 leaf) | 16.35 | |||
| 290kg N/ha (210 + 80 split @ sowing, 6 leaf & tasselling) | 16.09 | |||
| 370kg N/ha (210 + 160 split @ sowing, 6 leaf & tasselling) | 17.25 | |||
| 450kg N/ha (210 + 240 split @ sowing, 6 leaf & tasselling) | 17.36 | |||
| 530kg N/ha (210 + 320 split @ sowing, 6 leaf & tasselling) | 15.71 | |||
| p | 0.564 | |||
| lsd | NS (2.006) | |||
| cv% | 8.3 | |||
| GM | 16.52 |
N rate or timing had no influence on yield. Simply adding more N to the crop did not result in additional yield. A relatively low rate of 210 kg N/ha (plus 151 kg N/ha in the soil left over from last season’s crop + MAP + mineralisation) was sufficient to reach the site’s yield potential.
This trial continues the Optimising Irrigated Grains learnings, demonstrated over 6 trials, that showed no yield response to applied N rates above 250 kg N/ha.
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