COMBINABLE CROP growers might be able to cut nitrogen use this spring, according to ADAS senior research soil scientist Peter Dampney.
Soil nitrogen levels could be above average this spring, apart from in western areas, based on rainfall figures to mid-January, he says. “Rainfall so far has been below average.”
That means, barring a deluge in February and March, soil nitrogen levels over most of eastern and central England are likely to be above average again, as in 2004.
Crops following break crops or where autumn or winter organic manures have been applied are likely to have retained the highest soil nitrogen levels, he suggests. “The dry winter will have less effect on sandy or shallow soils, where soil N is easily leached.”
With many oilseed rape, winter barley and winter wheat crops well-tillered after the mild conditions, growers have the chance to reduce fertiliser use, as last season, he notes. “Many did last year, but others regretted not doing so, which resulted in lush crops.
“Growers should omit or delay any February or early March N in cereals, and put less on oilseed rape where crops have sufficient shoot numbers,” he advises.
High N costs and a low grain price should also encourage growers to reduce total fertiliser this spring. “Economic optimum rates are becoming lower.
“Current RB209 recommendations for winter cereals are based on a break-even ratio of producing 3kg grain from each 1kg of N, while for oilseed rape the ratio is 2.5:1.
“This year, many cereal growers will be judging N use where the break-even ratio is between 5 and 6.” That means growers should reduce N rates by 15-30kg/ha for the whole season. “But reductions in N use may not be appropriate for milling wheats, where achieving 13% grain protein is important,” he stresses.