More nitrogen could benefit wheat
A fear of applying too much nitrogen (N) and falling foul of cross-compliance rules could be one reason why wheat yields have remained largely unchanged in recent years, prompting calls for a rethink on rates.
Data analysis carried out as part of the HGCA yield plateau project suggest that modern elite varieties of wheat need an extra 20kg of N/ha for every extra 1t of yield, says HGCA research and knowledge transfer manager Paul Gosling.
“We are almost certainly starving some of our wheat crops of nitrogen,” he says.
Over the period 1983 to 2009, the average national use of nitrogen fertiliser on wheat has remained static, while requirements have increased.
Speaking to Farmers Weekly, Yara’s head of agronomy Mark Tucker agrees, adding that combined with the trend of falling phosphate applications with growers increasingly taking “phosphate holidays”, they are not fully exploiting modern varieties.
“It does raise the question are farmers applying the optimum nitrogen rate to exploit these newer varieties? Average use is not in line with average requirement for arable cropping or grassland.”
However, Mr Tucker highlights that the revised DEFRA Fertiliser Manual (best practice guidelines) published in 2011was an improvement on the previous version for nitrogen. “Maybe we haven’t started to see the changes filter through from the new manual.
“This might be one element of the shortfall in nitrogen application.” But he also believes another element is the fear of compliance, with growers concerned about application limits.
Growers in Nitrate Vulnerable Zones (NVZs) cannot exceed the N-max, but those outside can tweak rates if they show it is needed to meet higher crop requirements.
“But the fear is perhaps confining growers from achieving high yields outside NVZs,” says Mr Tucker.
However, ADAS principal scientist Roger Sylvester-Bradley doesn’t believe nitrogen is a major factor behind the wheat yield plateau.
“We would be seeing a real reduction in proteins. Generally, all the evidence suggests that the protein [content] has to come down a lot with high yielding crops before you see any significant impact on yields.”
With Group 1 and 2 wheats, growers should be achieving 12% protein, while feed wheat should be at 11%. “If you are not seeing this, then you may be under doing nitrogen for high yields.”
It’s not just a case of overall nitrogen supply, it also about efficiency of N use, says Susannah Bolton, head of research and knowledge transfer at HGCA. There is a long way to go, but growers are getting better on nitrogen timing and using precision tools to get it where it is needed.
HGCA is putting together a new programme of research projects following a call for expressions of interest at the end of last year. With a budget of £700,000, the research will look at improving the efficiency of nutrient use on UK farms.
Mr Tucker agrees there needs to be an increased efficiency in nitrogen use. “We need to increase yields for each kg/ha applied.”
In conclusion, Mr Tucker believes there is a need to relook at nitrogen and phosphate, but growers will need to consider the economic optimum, taking the price of fertiliser and wheat prices into account. “But you will still end up finding that growers are generally applying 10% below the optimum for nitrogen.”
