Fine-tuning nitrogen levels

Technical services manager at The Back Paddock Company Chris Dowling, Brisbane, Queensland, said a trend of lower protein levels in 2012 could mean economic losses for growers if nitrogen levels in soil weren’t monitored.

“In one season this might not be so bad, but over a number of seasons low protein levels – particularly in bread wheats – will result in quality issues and will affect the end use of the grain, pushing growers into markets that won’t give them the premiums they’re after,” Mr Dowling said.

Some of the long-term contributing factors to lower nitrogen levels included a decline in organic matter in paddocks and a lack of legumes within crop rotations, with more short-term factors including the recent wet summers and dry springs.

“In 2012 Moree had a very wet summer, which resulted in huge nitrogen losses – about 40 to 50 per cent of the nitrogen which would have been lost in a 12-month period was gone by February because of the waterlogged state of the soil,” he said.

Seasonal conditions were one of the main factors affecting nitrogen levels in the soil, Mr Dowling said, and while many farmers – if not all – would wish for the ability to control weather events for an optimum season, other factors such as crop rotation, nitrogen fertiliser applications and weed control, among others, were factors farmers could manipulate to help get the right amount of protein in their wheat.

Mr Dowling said following the recent rain events in northern NSW growers should now be revising the initial assessment of nitrogen levels conducted at the beginning of the season to ensure they still had enough nitrogen in their paddocks to meet the protein levels they want.

“This is especially important for growers who grow for particular markets, based around particular protein levels,” he said.

“There are a number of tools available for growers to help assess their nitrogen levels and by combining these tools growers can get a better impression of the nitrogen levels in their soil.

“One of the best tools at their disposal is the protein levels recorded in previous crops – having these records is a useful planning tool moving forward into the next season.”

But the balancing act between agronomic nitrogen response and economic returns can be difficult for any farmer growing any crop.

NSW Department of Primary Industries research agronomist Matthew Gardner, Tamworth, said results from three field trials of nitrogen fertiliser application on sorghum – conducted at Terry Hie Hie, Tamworth and Pine Ridge – showed returns of between $2 and $5 for every dollar per tonne spent on nitrogen application, which showed it was economical for a farmer to chase yield through the application of nitrogen fertilisers.

“During the trials – the first year of a five-year project – nitrogen application resulted in a greater number of protein responsive sites,” Mr Gardner said.

“It is generally thought maximum yield is achieved with grain protein at nine to 10pc, while at lower levels yield is being compromised by a lack of nitrogen.

“That said, we found there were limited yield responses to nitrogen application across the trials, with responses generally occurring where starting nitrogen was less than 70 kilograms a hectare.”

Mr Gardner said the greatest economic returns were achieved where grain yield was maximised, highlighting the importance of yield in driving profitability.

“Over the next four years we’re going to continue looking at the agronomic and economic responses to nitrogen nutrition in the northern grains region as part of the GRDC-funded project More Profit from Crop Nutrition,” he said.

“Specifically, we hope to better define some of those estimates required for budgets such as nitrogen mineralisation and further look into nitrogen use efficiency between varieties.”