Australia: Nitrogen application and soil mineralisation in growing malting barley

Applying enough nitrogen to malting barley crops so they yield well, yet meet the protein grade, is a tricky balance.

And much research is needed to "open up this black box", according to Foundation for Arable Research Australia managing director Nick Poole, Weekly Times Now reported on October 28.

Nick Poole explained to growers the progress of nitrogen management trials and the influence of mineralisation at Southern Farming Systems' AgriFocus field day at Westmere, near Lake Bolac.

"When growing malt barley you are trying to produce grain for a specific market, that has a very specific protein range," he said.

"And therefore, trying to determine how much nutrition, or in this case, how much nitrogen you need to apply to that crop is critically important."

Poole said one of the ways to be more accurate was to prepare a nitrogen budget.

This takes into account how much nitrogen is already in the soil at the start of spring, how much nitrogen is in the crop and how much, typically, malting barley crops yield on that farm.

"These key components enable you to make a better estimation of what nitrogen you should put on," he said.

But the risk that could upset even the best laid plans was a wet period that allowed nitrogen to mineralise in the soil.

If this happened and the nitrogen was taken up by the plant late in the season, the barley's protein levels could shoot up.

"At present, the big black box is nitrogen mineralisation," Poole said.

"Particularly in this region, where soils remain wetter later into the season.

"Further north where soils get drier, they don't mineralise as much nitrogen as we suspect they do in soils down south.

"Therefore it is quite difficult to specifically say how much N is going to mineralise, depending on the season.

"Overall we have to take N mineralisation into account more so here than elsewhere."

Poole said farmers could get a handle on how likely it was that their crops would be subject to excessive nitrogen mineralisation by knowing their farm.

"They will know which paddocks produce excessive amounts of vegetation, even though they have not had much nitrogen applied to them," he said.

"A good way to spot paddocks that have high mineralisation capacity is think back through previous seasons to recall which crops appear particularly pumped up, thick, vegetative crops.

"When you have paddocks that have excessive amounts of N mineralisation capacity it makes it much more difficult to grow malting barley because that nitrogen can come out of the system very late on and go straight into the grain."

Excessive nitrogen mineralisation with other crops could be an advantage as protein levels would be raised.

30 October, 2013