The AHDB’s Nutrient Management Guide RB209 handbook is a critical resource for agronomists and growers, allowing them to make the most of organic materials and enabling the economic and environmentally sustainable use of fertilisers. The latest revision, officially launched this month by AHDB, is the culmination of 10 years of research involving key stakeholders from across the crop nutrition industry.

The revision includes the first major change in phosphorus (P) recommendations in over four decades and details a shift from a ‘soil balance’ approach towards a ‘crop targeting’ approach.

Why the shift in focus to crop nutrition?

Crop nutrition is in need of serious attention. Evidence from a pilot Nutrient Benchmarking Scheme supported by AHDB and Yara in 2017 and 2018 indicated that 75% of grain samples from 53 different farms were deficient in one or more essential nutrients, correlating with the findings from the Yield Enhancement Network.

The data raise concerns about the appropriate use of nutrients and how much each crop can acquire. The lack of clarity about nutrient needs of crops could, on one hand, hurt the overall yield through critical nutrient levels not being met or, on the other hand, result in money wasted, and pollution risked, through applying more of some nutrients than will benefit the crop.

Our understanding of the role of Phosphorus

Phosphorus (P) is a critical macro-element for plants, essential to metabolic processes such as photosynthesis. However, the pilot Nutrient Benchmarking Scheme identified that 59% of samples taken were short when it came to P. It has been almost 50 years since P recommendations have had a major revision. In that time, our understanding has evolved concerning where P comes from, how it’s best applied and the rate and scale at which it is absorbed by the crop.

At the same time, questions have grown about the environmental impacts of P overuse, the cost-effectiveness of P management and the risks to yield when P levels reduce below the critical level. So the recent research has asked ‘At what point do P levels become critical?’ and ‘How long does it take for P to run down in the soil?’

Ten years of stakeholder engagement, four research reviews and six research reports later (all 766 pages can be found on the AHDB website!), the changes to the RB209 take a step towards answering these key questions and opens the door for further progress in crop nutrition.

What are the new amendments to RB209?

The main amendments to RB209 focus on two key areas, improving the quality of soil analysis and the inclusion of grain analysis as a new monitoring tool.

Carrying out soil analysis

RB209 will now include detailed advice on how to carefully carry out soil sampling, soil analysis and interpretation of results. The following guidance has been added:

  • By carrying out sampling in batches, it’s possible to compare the performance of one field with another and one year’s analysis with another.
  • You should always keep the sampling conditions the same and use the same lab.
  • Double-check the results against P balances (inputs minus the offtakes) and compare with adjacent samples, and with grain analyses.

Ultimately, soil analysis will have some discrepancies; even the weather can cause variation. If done well, its strengths are that it can be used to identify the average soil P index, along with the rate of P change which can vary between fields.

However, soil analysis is not a precise science and should no longer be relied upon as the sole guide for P management. The nutrition level in the soil is only the beginning of the story. To get an accurate evaluation of whether or not your nutrition application is correct, you also need to analyse the condition of the end product – the grain itself.

When it comes to P levels in grain, 0.32% is now considered the critical point. Lower than this and you need to start looking into why your crop is not getting enough P, it may be a low soil level, or could just as easily be due to topsoil dryness, or something wrong with rooting.

The need for grain nutrient benchmarking

The new amendments to RB209 recognise the valuable role of grain analysis along with soil analysis to assess P levels, as well as all other nutrients. Grain analysis is more precise and reliable at measuring P and phosphate offtake and checks for deficiencies. Also, for the same price as analysing for just P, results are provided for all 11 other plant nutrients.

For most nutrients, the grains store most of what the crop has managed to take up, so grain analysis surveys the whole crop over the whole season rather than gauging a specific point of time like leaf analysis. Then, by sharing the results with other farmers or ‘Grain nutrient benchmarking’, the relative performance of each crop can be gauged quickly for each nutrient, even those for which critical levels are uncertain e.g. iron.

A new direction for RB209

Overall the changes can be summed up in the need to ‘feed the crop, not the soil’. We need to set target indices according to rotation rather than crop by crop and manage soil phosphorus a lot more carefully.

By monitoring nutrient levels in the soil regularly, we can better understand the rate of build-up and run-down, save crops from reaching critical nutrient levels and ultimately save growers money.

About the author

Roger Sylvester-Bradley leads on research on crop performance with ADAS, is an honorary professor of temperate crop physiology with the University of Nottingham and a founder of the Yield Enhancement Network.

Roger works to inspire innovation in the cropping industry and in-field research, so as to enhance crop productivity and sustainability.