Nitrogen levels: Are farmers getting the balance right?

Optimizing nitrogen levels in soil is not an exact science, and standard recommendations for winter wheat do not offer a ‘one size fits all’ solution. And in light of UK crop yields plateauing, curiosity over the role nitrogen has to play have heightened.

Dr Sarah Clarke, research scientist at sustainable crop management company, ADAS UK, said that while official recommendations on nitrogen levels from the UK’s Department for Environment, Food and Rural Affairs take into account soil type and location, there could be other factors involved in determining levels that are, so far, unknown.

“Current nitrogen fertilizer recommendations are correct, on average, but there are large variations and we have found around 50% of farmers are either under or over applying nitrogen by 50 kilos per hectare,” ​she told Milling & Grains.

Four-year research project on nitrogen application​

ADAS has teamed up with consultants NIAB TAG to run on-farm nitrogen trials at 18 farms across the UK to try to identify and rectify these discrepancies and help farmers make more informed decisions.

The four-year £350,000 ($583,870) ‘LearN’ project is part funded by the HGCA, with support from distributor Agrii and fertilizer group GrowHow.

Dr Clarke said: “There is a lot of evidence to support the need for this type of research. Field and soil mapping technology, like satellite imagery and canopy sensing, is a lot more accessible and easier to use these days but farmers do not always use it to their best advantage and could be missing out on an extra ton of winter wheat each season. Farmers need the ability to more accurately predict nitrogen application rates.”​

Of course, there are a lot of variables that affect winter wheat yields, but nitrogen levels have a huge impact on overall profitability, she said. Under-fertilizing results in lower yields, while over-fertilizing is an unnecessary expense, in many cases, she explained.

Clear evidence to show farmers are under-fertilizing​

For the last 30 years, average nitrogen rates have remained between 190 and 200kg/ha, but with grain protein declining and yields leveling out, there is clear evidence to show farmers are under-fertilizing, Clarke said. However, she said there is plenty of room to manoeuvre - even in nitrate vulnerable zones (NVZ).

“Approximately two-thirds of farms in England and Wales are situated in nitrogen vulnerable zones, or on land that drains into nitrate polluted waters and needs protecting, but there is even flexibility in these areas as long as the seasonal average of nitrogen application does not exceed 250kg/ha.” ​

The project includes detailed plot trials at six core farm sites in Eastern England and tramline trials at a further 12 farms. Three wheat fields per farm will be involved each year for the duration of the project, with different nitrogen rates applied to adjacent tramlines. The trials start in the Spring with initial findings set to be compiled in the Autumn.