Changes to nitrogen recommendations, where appropriate, and soil N supply indices head possible amendments to DEFRA‘s fertiliser recommendations, RB209.

Draft sections of the new book, likely to be renamed The Fertiliser Manual, should be ready for review by the end of this month, says project leader Keith Goulding of Rothamsted Research.

Considerable attention during the review has been given to soil N supply indices and nitrogen recommendations after farmers and consultants said that improvement was needed in those areas.

A huge amount of data has been analysed on soil N supply, Prof Goulding says. “It’s looking likely that we will retain the seven indices currently used, but the emphasis will be changed to make it clear that these are not precise estimates.”

Part of the problem is the difficulty in determining how much N has been released into the soil by mineralisation of soil organic matter. “It is the biggest unknown when making recommendations.”

New research funded by HGCA and led by ADAS, TAG and SAC, will address some problems in estimating SNS.

Both current means of determining SNS – tables and soil analyses – will be kept. “However, the methods will be clarified. The allocation of previous crop, soil type and winter rainfall to indices will be re-examined and interpretations of the indices will vary with the crop.”

The revised system should be easier to use, Prof Goulding believes. The end result will be a considered index, not a number from a table, and will allow adjustments for previous manure use and cropping history.

Not surprisingly, more than 1000 data sets on nitrogen response curves for winter wheat were submitted for review by interested parties. Results to date suggest new varieties respond to around 50kg/ha more nitrogen than older types, although an assessment of the effect of variety and soil type is still awaited.

“Clearly, this will have implications for NVZ rules, which are out for consultation at the moment. The proposal is for a nitrogen maximum in NVZs, based on the current version of RB209, but augmented with new data. The team is working to ensure that it fits with the revision.

“The other important thing is the price of N compared with the price of grain. As these change, so too does the economic benefit of an increased recommendation,” he points out. “So we will be highlighting the importance of economics.”

All the N recommendations in the new manual will be based on ammonium nitrate. But information will be given for other forms of N, including urea, on efficiency of use and spreading.

“And there will be information on emissions of nitrous oxide to add to that on nitrate leaching and ammonia loss in sections on environmental impact and N losses.”

While no major revisions of the indices or the methods of analysis are thought to be needed for P, K, Mg and lime, there will be stronger emphasis on the need for sulphur due to its relevance to N use efficiency, with recent HGCA funded research playing a major part.

Soil N supply indices and N recommendations: Areas pinpointed by farmers and consultants for review in Keith Goulding’s (right) Cereals 2007 survey.

DEFRA’s preference for the name is Fertiliser Manual, but with some mention of RB209 to maintain continuity. The format is likely to be a hard copy, in similar style to the 7th edition, but with a recommendation for a full revision taking place every four years rather than small revisions each year.

Other adjustments:

• Small changes to P&K on sugar beet
  
• N recommendations for beet and potatoes being debated
  
• Slightly higher N rates for veg
  
• Nutrient contents of manures updated