Closed: Nitrogen Prediction Response Evaluation (NPRE)

Timescale: 3 year project. Finished 2018
Project Lead: Dr. Simon Brown
Project Sponsor: BBRO

Project Summary

The fertiliser recommendations for sugar beet as laid out by DEFRA in RB209 assume a yield of 60t/ha. Whilst there is no evidence that higher yielding crops require more nitrogen, it remains important in the light of continuing pressure on the use of N fertiliser and the greenhouse gas levels associated with its production and use, that the industry maintains a long-term data set of crop yield responses to nitrogen fertiliser to maintain and defend its use in future review of publications such as RB209. Of course, such a database will also allow the identification of any changing trends in nitrogen requirements due to factors such as climate change or variety development.

Main Objectives (2014 - 2016)

Nitrogen application technologies that minimise losses and maximise N uptake have been linked to improved fresh weight and sugar yields, Stevens at al (1995). These authors attributed this in part to earlier canopy establishment and improved nitrogen use efficiency. Work by the Nordic Beet Research (NBR) Institute has also indicated small but consistent responses in terms of crop yield and sugar content to the use of placed nitrogen and phosphate fertiliser. The table below shows the range of relative yield increases due to N placement across a series of NBR trials between 1979 & 1994.

























In the USA, the use of placed N fertilisers and placed phosphate as a starter fertiliser to encourage early plant establishment is widely recommended by advisors and practiced by growers. Pilot work has been undertaken in plot work at Nottingham University and commercial farms trials in Norfolk 2016. Interestingly, this work showed some improvement in early season canopy development but the effects diminished over time and by final harvest there were no significant effects on yield. At the commercial site, turkey manure and a cover crops was used prior to the beet and the higher soil N levels may have reduced the impact of placed fertilisers.  At the experimental site at Nottingham, plots were affected by Aphanomyces and it not clear to what extent this may have affected results.


However, the published data indicates placement of N fertiliser and the use of starter P is worthy of further investigation. For the UK, it will be important to understand in more detail the interaction between fertiliser placement, soil texture, soil mineral N content and emergence, canopy expansion to assess in what circumstances yield benefit is seen as well as opportunities for improved N use efficiency and reduced N inputs. 


It is proposed to build extend the work started in 2016 to more sites over a further two years, allowing us to make a full assessment of both the efficiency of nutrient utilisation and the practical and financial aspects of fertiliser placement. This will provide a total of 3 years of data (including 2016 trials) on which to base informed advice to growers. It will also support any specific recommendations in the next planned edition of RB209 (The Nutrient Management Guide) in 2019.

The project aims to show whether, by placing N, can we improve N uptake efficiency and improve the performance of crops and to what extent it may be possible to reduce nitrogen inputs. It will also show whether this is further influenced by placing P with N. 

Outcomes / Key Message For Growers And Industry

  • The results indicate that across the range of soil types tested that there is no evidence of the need to increase the rates of nitrogen applied.
  • The trials support the existing nitrogen recommendations.
  • Further testing of nitrogen rates in soils especially with low soil mineral nitrogen levels is warranted to access the need to any adjustment in these situations.
  • The series of trials did not test nitrogen requirements at different harvest dates (length of growing season) and this may warrant assessment.
  • There were data which highlighted the potential depression of root sugar content at higher fertiliser nitrogen rates.  This may also apply in situations where organic manure/amendments are applied and/or cover crops, especially legume cover crops, are grown over winter prior to sugar beet.
  • The higher than expected soil nitrogen levels on the sites reinforce the need for careful assessment when deciding on nitrogen rates.  Using the Field Assessment method which relies on soil type, previous cropping and rainfall can be inaccurate and should be supplemented with SMN testing.
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