Higher nitrogen rates for wheat are likely to be justified in any revision of DEFRA’s fertiliser bible RB209, the report reviewing last January’s consultation into whether the guide needed revising suggests.
A copy of the report obtained by Farmers Weekly says that a number of responses emphasised there was widespread concern about current N recommendations in wheat.
“The vast majority revolved around the fact wheat yields have increased significantly in recent years, and a large part of the research underpinning RB209 was old and outdated,” ADAS researcher and report author Peter Dampney, says.
Current RB209 recommendations are based on the results from over 282 experiments carried out between 1981 and 1994, using wheat varieties with significantly lower yield potential than current varieties.
Higher crop yields result in a theoretically higher crop N requirement, the report notes.
The problem is exacerbated for milling wheat producers, where growers need to apply more nitrogen not only to meet the higher yield potential, but also to overcome dilution of grain proteins to meet target protein specifications.
Potentially valuable datasets investigating nitrogen requirements of modern wheat varieties are available, the report acknowledges.
“Preliminary appraisal of the available data indicates an increase in N rates for wheat is likely to be justified.”
If adopted it should relieve concerns expressed by some responders of the possibility of reduced N rates being set as statutory maxima, which they believed would have an adverse effect on farm businesses and the competitiveness of UK agriculture.
There were also strong views that the recommendations should continue to allow flexibility in actual decision making, based on local information and experience.
Many farmers and advisers commented they were already careful with nutrient use decisions because of the costs involved, and they did not want RB209 to become an inflexible prescriptive recipe book, the report says.
The report also highlights unease over soil sampling methods and results, and cites recent coverage of the issue in Farmers Weekly and Crops magazine, particularly over the accuracy of soil mineral N data.
“The use, accuracy and methodology of sampling and laboratory analysis for SMN needs to be re-assessed, including methods for determining mineralisable N,” it says.
In addition, the report notes suggestions that RB209 is not detailed enough in covering the requirements for how to prepare and transport samples.
Specific technical revisions were also suggested by consultees, particularly regarding soil nitrogen supply indices, which were considered too high after set-aside, oilseed rape and peas.
The adjustment for SNS after a dry winter was also considered to overestimate the soil nitrogen supply.
A total of 79 responses were received during the consultation exercise, which finished at the end of last January.
DEFRA is now looking at issues raised and considering how to involve the industry during the revision process.