AHDB has published findings of an extensive review of the Fertiliser Manual RB209, which will form the basis of a new edition of the guide to be released next May.
For the first time, the review proposes an adjustment to take account of predicted yield is included in nitrogen (N) guidance for winter wheat. It says: “Research has shown that the economically optimal rate of N fertiliser increases with yield.
“Where previous experience of growing wheat indicates that yields above 8t/ha can be realistically expected, the recommended rate should be increased by 20kg N/ha for each t/ha additional yield, up to a maximum of 14t/ha. Similarly, for low yielding crops, the recommended rate should be reduced by 20kg N/ha for each t/ha reduction in expected yield.”
Mark Tucker, marketing and agronomy manager at Yara, has concerns about basing fertiliser applications on predicted yield. “Yara’s dataset shows a very poor correlation when you look at optimal N for a cereal crop against a yield expectation.
“In 2012 we had record low yields and in 2015, record high, neither of which could be forecast during the nitrogen recommendation process. What guidance is there on what yield to use? We prefer not to use yield.”
Mr Tucker’s concerns centre upon applying N levels in anticipation of a high yield which is not realised at harvest. “What guidance should there be to mitigate the environmental impact through exceeding the demand of the crop? For example, early drilling or a catch crop to trap nitrogen. Yara is producing its own guidance.”
For West Sussex-based David Jones of CCC Agronomy the nitrogen application rates for winter wheat fall short. “On certain soil types they are still not putting enough N on milling wheat. It needs to be over 300kg/ha for 13 per cent milling wheat.”
For feed barley, the review proposes raising recommended application levels by 20kg N/ha for sandy soils and 10kg N/ha for silty soils and a predicted yield adjustment, as for wheat. Mr Jones says it would have been useful to have more differentiation in barley recommendations between two-row and six-row hybrid varieties.
“With some of the six-row hybrid varieties we are getting responses up to 230-240kg N/ha.”
Barley data was analysed to examine the effects of nitrogen supply on grain %N response, to allow more detailed advice on how nitrogen rates should be adjusted to meet grain quality specifications.
New advice on timing winter barley N applications recommends that where total nitrogen rate is between 100 and 200kg N/ha or more, split the dressing, applying 50 per cent during late tillering in mid-February/early March and 50 per cent at growth stage 30/31. Where the total nitrogen rate is above 200kg N/ha, apply three splits with 40 per cent during late tillering, 40 per cent at GS30/31 and 20 per cent at GS32, says the review guidance.
Winter oat N recommendations have been increased by 40kg N/ha. “Winter oats need more N,” says Mr Jones. “They have stiffer straw and there are better growth regulators now so you can push them a bit harder.”
Nitrogen fertiliser timings for winter oilseed rape are recommended to change to reflect a ‘canopy management’ approach, where nitrogen is delayed for crops with large canopies following winter and a proportion of nitrogen for crops with high yield potential is delayed until yellow bud or early flowering.
George Lawrie, who chairs the UK Partnership for Crop Nutrient Management steering group, says: “We’ve left no stone unturned during the review; every aspect of nutrient management has been revisited and scrutinised.
“Advances in nutrient management have been incorporated and the new guide will provide evidence-based nutrient management recommendations that growers can trust.”
The £98,000 Fertiliser Manual RB209 review was overseen by the AHDB-led UK Partnership for Crop Nutrient Management and delivered by an ADAS-led consortium of experts from across the UK research community. It was supported by £200,000-worth of in-kind funding by industry.
Farmers, growers, agronomists, breeders, researchers, fertiliser companies and other industry experts were among those consulted on how existing RB209 recommendations could be improved to incorporate the latest scientific advances.
The review, which took account of the latest research developments since 2009, was split into six packages: principles of crop nutrient management; organic materials; grass and forage; cereals and oilseeds; potatoes and horticulture.
Find out more at: www.ahdb.org.uk