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Achieving High Wheat-protein Levels Using Late Nitrogen Applications

20 July 2014

GRDC

Growers in northern region farming systems must be cautious when trying to achieve high wheat-protein levels using late nitrogen applications recent GRDC trials suggest.

A recurring issue across the northern region in 2010 and 2011 was low to very low grain protein levels across a wide range of crop yield levels. As a consequence, many loads of grain were downgraded, reducing economic returns.

                                

GRDC-funded trials in 2012-13 to evaluate the effectiveness of nitrogen application to wheat crops from full flag-leaf emergence onwards were carried out by researchers from the Northern Grower Alliance (NGA).

“Growers apply nitrogen at these late timings solely to increase grain-protein levels,” says Richard Daniel, chief executive officer of NGA. “Increases in yield at this stage are highly unlikely.”

The project assessed the effect of nitrogen on protein accumulation, the likelihood of economic benefit, and whether there was an optimal method or timing for nitrogen application. The two wheat varieties evaluated were EGA Gregory and Suntop – both consistently high yielding, but with generally lower protein levels than other varieties.

Comparing Methods

The series of 11 trials, over the two seasons, compared all potential application methods. Urea was applied using a spread (by hand), streambar (in an aqueous solution using streamer bars), and foliar (aqueous solution using nozzles) at a rate of 40 kilograms of nitrogen per hectare.

This rate was higher than those used commercially to ensure measurable differences in protein levels between treatments.

NGA researchers were not surprised that both the spread and streambar methods were ineffective at increasing protein levels due to the generally low levels of rainfall in both years of the trials. Also, for these methods to provide a benefit, nitrogen must be successfully incorporated into the soil and reach a depth where roots are actively foraging.

The spread and streambar approaches are more suited to early-season application. The foliar application method resulted in significantly increased protein compared to spread and streambar. This strongly suggests that leaf uptake, in late-season application, is capable of significantly increasing grain-protein levels.

“Although it was clear we were able to get significant increases in protein from foliar application of urea, we just weren’t able to get enough benefit in any trial to make it actually pay,” Mr Daniel says.

On average, foliar application resulted in an extra 0.3 per cent protein compared with spread urea across all trials. However, the largest individual benefit of the foliar method was 1.2 per cent in 2012 and 0.7 per cent in 2013.

“In more than half of the trials we also compared the same rate of urea spread at planting, at jointing, or split between the two timings. These treatments resulted in the highest grain proteins in nearly all dryland trials,” Mr Daniel says.

The researchers found that applying nitrogen before or at planting, or as a top-up during early crop growth stages, was the more reliable and effective strategy. This strategy also added to crop yield potential.

Results at an irrigated site in southern Queensland in 2013 provided similar benefits to those achieved at the dryland sites, despite a total of 150 millimetres of irrigation (applied in five separate waterings) during the late nitrogen application timings.

“At the nitrogen recovery levels seen, wheat-grade price differentials of about $30 per tonne to $40/t would have been needed to achieve economic benefits,” Mr Daniel says.

“Unfortunately, we only experience these sorts of returns in two or three years out of every 10.

“The NGA trials show that late foliar application of nitrogen is likely to remain a niche practice unless we can improve the efficiency of nitrogen uptake, and also ensure more consistent grain grade price differentials,” he says.

Recent experiences in central and southern New South Wales have shown protein responses to applied nitrogen are more reliable when yield is already maximised. This means growers should aim to maximise their yield response first when budgeting for seasonal nitrogen.

Jim Laycock, a technical agronomist from Incitec Pivot Fertilisers, agrees with Mr Daniel. “As is often the case where yield potential is below average, it is difficult to justify the additional cost of nitrogen to move wheat quality to higher grades without a significant yield response as well,” Mr Laycock says.

Economics and Rainfall

Based on these results, growers are advised to look at both the economics and rainfall variability and build a picture of what they hope to achieve, Mr Daniel says.

Nitrogen requirement depends on a number of variables, including growers’ targets for water-limited yield potential and grain protein, management of disease factors, supply of other nutrients to crops, weed-control measures and sowing time.

When choosing varieties, growers should consider long-term yield and protein results for their specific region, disease resistance and/or tolerance packages and target grades.

July 2014

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