On-farm trials at Corrigin, WA, exploring wheat protein responses to nitrogen applications
at different rates and times.
PHOTO: Steve Milroy
A three-year project at Corrigin, Western Australia, may prompt a rethink of risk-management strategies. These strategies are used to avoid pinched grain and low returns in poor seasons, but also have the effect of lowering protein and yield gains.
The aim is to improve the competitiveness and profitability of the WA wheat industry by lifting protein levels. WA can produce up to three million tonnes of low-protein grain and marketers have trouble selling that much at satisfactory prices.
The project is aiming to identify more clearly the in-crop nitrogen management able to lift wheat protein from 8 per cent to over 10 per cent; a gain potentially worth an extra $100 million a year to the industry in WA.
Corrigin was chosen as the trial site because it is a district known for producing low-protein grain as a consequence of a generally cautious use of nitrogen.
However, the project leader, CSIRO research agronomist Dr Steve Milroy, found he could lift protein levels by up to 3.5 per cent with “anything like a decent rate of nitrogen”.
This was repeated over three seasons, on several different soil types on different farms.
However, because of some unique climatic challenges in the region, it is not a straightforward case of simply increasing nitrogen applications.
Rising temperatures and low and unpredictable rainfall in spring mean soil moisture runs out just as the grain is filling, resulting in pinched grain.
Consequently, risk-averse growers tend to be conservative in their use of nitrogen.
Dr Milroy says the first worry is the risk of a dry spring and not earning a return on the inputs.
“Secondly, there is a concern not to push a crop too hard with applied nitrogen in case a large canopy causes the crop to use water too fast, increasing the risk of finishing with pinched grain.”
So the question is how much nitrogen is needed to achieve 10 per cent grain protein. Dr Milroy says that for a crop of 3.5 tonnes per hectare, 10 per cent protein means the crop needs to take up about 90 to 100 kilograms of nitrogen per hectare. A crop of 2.5t/ha needs to take up 60 to 70kg. “Some of this will come from nitrogen already in the soil, but when you take into account our low fertiliser recovery rates, this presents an economic challenge if growers want good protein and reasonable yields.”
The challenge for WA growers wanting to improve the yield/protein balance is to determine on a farm-by-farm basis just how much nitrogen will lift grain quality without compromising risk management strategies.
Dr Milroy says the first thing that happens when low rates of nitrogen are applied to soils that are rundown, is a response in yield, but not in grain protein.
“It has been shown through hundreds of experiments across WA that this is the case in very-low nitrogen status situations. Grain protein doesn’t respond until a bit more nitrogen is available. So if you are getting a yield response but not a protein response to applied nitrogen, it probably means that you don’t yet have enough nitrogen.”
Timing also affects the response. Early applications get a yield response, but later applications are more likely to increase grain protein.
“Split application improves the recovery of applied nitrogen, and if some of your nitrogen is applied after the beginning of stem elongation you are more likely to get a response in protein than if all the nitrogen is applied at sowing,” Dr Milroy says.
Most growers already split their nitrogen applications, so Dr Milroy emphasises the importance of adequate nitrogen at sowing. “If you don’t put enough in at sowing and you have inherently low nitrogen, you can limit tillering and that starts to penalise yield, which can’t be made up through later nitrogen applications.”
To improve nitrogen management it gets down to knowing, first, how much nitrogen is already in the soil prior to seeding. Dr Milroy then suggests planting a test strip with additional nitrogen. “I think a lot of growers would be surprised at how much yield they could be sacrificing because of the risk management practised to minimise pinched grain or low returns in poor years.”
He says a test strip would help quantify the differential between the cost of nitrogen and the extra income earned from higher yield and protein grain.
Another part of the equation is legumes, which can make a significant nitrogen contribution. However, Dr Milroy says the economics need studying on a case-by-case basis. “Our experiments suggest that if nitrogen is the sole reason for growing legumes, the crop probably isn’t going to deliver much of an economic benefit because of the lower profit from legume crops.”
Dr Steve Milroy,
08 9333 6000,
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