Optimum nitrogen requirements in new spring barley and wheat varieties are no different to their varietal predecessors from the 1980’s, Scottish trials suggest.

But there was a grain nitrogen dilution effect in the newer varieties, which growers would have to take into account or exploit, said the Scottish Agricultural College’s Alex Sinclair.

“In the spring barley trials the yield difference between old and new varieties was 2t/ha across the whole range of nitrogen rates used. But the response curves were parallel and gave an identical nitrogen requirement for yield.”

It was a similar story in wheat, he said. “I don’t think it’s that much of a surprise. New varieties get through the variety trialling system by being high yielding given the same nitrogen applications.”

But high-yielding wheat crops did contain 0.2% less grain nitrogen at the optimum nitrogen rate than the older varieties, he said.

“Regaining that extra 0.2% needed another 60kgN/ha. So if you are growing for an end market [requiring certain protein levels] you are going to need a higher rate of nitrogen for crops where grain nitrogen has been diluted.”

In spring barley the grain dilution factor could be used to maximise yields while still maintaining malting barley specification, he said.

“There could be a trade-off where growers say lets not reduce N by 20-30kgN/ha to get malting quality if he knows he can get high yields [to dilute the grain N].”

The research is part of an on-going HGCA-funded project in England and Scotland to optimise nitrogen rates, which will feed into the new RB209 fertiliser revision.