AHDB have recently published an updated version of the AHDB Nutrient Management Guide (RB209), with information provided on the updates here.

On the back of a three year AHDB and industry funded research project, which was led by ADAS with collaboration with SRUC, new updates to Nitrogen (N) recommendations for spring barley are included in the revised version. Read the final report for the project.

The updates include amendments to both recommended N rates and recommended N timing guidance.

Recommended N rate

The results from 11 trials performed across the UK between 2018 and 2020 indicated that previous RB209 recommendations over-estimated the N requirement. Breeding and agronomic progress appears to have increased yields without increasing N requirement as much. However, crops grown in higher yielding environments did have a greater N requirement, confirming the need to increase N in response to a higher expected yield.

Table 1 shows the updated recommendations for N rate, which are now based on a yield of 7t/ha, rather than 5.5t/ha in the previous version. N rate should be adjusted by +/- 20kg N/ha per tonne deviation from 7t/ha, up to a maximum of 9t/ha (see Table 2).

There is considerable variation in the grain N% achieved at the optimum N rates. Across the 11 experiments performed in the project, the average grain N% at the economic optimum N rate for yield was only 1.63%. The average optimum N rate for yield was 118 kg N/ha and the average yield at the optimum N rate was 7.4 t/ha. The experiments confirmed that reductions in N rate of 30kg N/ha to achieve a reduction of 0.1% grain N% are appropriate across a range of grain N% (1.5% to 1.8%).

However, when estimating the appropriate N rate to use for malting barley it is important to take account of historic grain N% data for your farm. This is because quite a few crops achieve a grain N% of less than 1.8% even when fertilised at the recommended rates for feed.

Table 1. Updated N rate recommendations

SNS Index
0 1 2 3 4 5 6
kg N/ha
Feed
All soils 160 140 110 70 30 0 0
Malting barley (1.8% grain N)a
All soils 130 110 80 40 0 0 0
  1. Estimate the nitrogen reduction needed for grain N of less than 1.8% based on 30 kg N/ha less for each 0.1% reduction in grain N%.

Table 2. Updated N rate recommendations in response to different expected yields.

SNS Index
Expected Yield (t/ha) 0 1 2 3 4 5 6
4 100 80 50 0 0 0 0
5 120 100 70 30 0 0 0
6 140 120 90 50 0 0 0
7 160 140 110 70 30 0 0
8 180 160 130 90 50 0 0
9 200 180 150 110 70 0 0

 

Recommended N timing

The results from the project confirmed the importance of applying some N in the seedbed, with absence of seedbed N in the experiments resulting in a 0.5 t/ha yield reduction on average. There was no consistent effect of N timing on grain N%, although there was some infrequent evidence that late applications of N (at GS 37 – 39) could result in increases in grain N%.

The new N timing guidance is as follows:

“Apply all N between the time of drilling and GS30, with at least 40 kg N/ha in the seedbed. Reduce the risk of nitrate leaching by limiting any seed bed N applications of more than 40kg N/ha if the crop is sown before March, or on a light sand soil, or if there is a likelihood of substantial rainfall soon after drilling”.

Contact Sarah Kendall sarah.kendall@adas.co.uk for more information