Wednesday, 21 July 2021
Whether an old hand or a newcomer to spring barley, it is important to have reliable agronomy information to hand. AHDB’s Georgina Key reports on new research findings set to shape RB209’s nitrogen (N) recommendations for this increasingly popular crop.
In recent years, numerous pressures on winter crops have led to an explosion in spring barley plantings – rising from just under 700,000 to 1m ha between 2016 and 2020. Behind this statistic is a raft of new (or returning) farmers to the market. The expansion has also seen the crop march into new territories beyond the traditional light-textured soils, including those with a heavier texture.
With new spring barley varieties also hitting the AHDB Recommended Lists (RL) each year – altering nutrient-use efficiency dynamics – we commissioned ADAS to lead research to help the AHDB Nutrient management guide (RB209) keep pace with modern production systems.
The work featured an impressive array of trials, building on bespoke research experiments conducted as part of the project (2018–20), and a review of other recent experiments (2005–17). With rates, timings, yield and quality in the spotlight, the work represents one of the most significant investments in nutrient management for spring barley for quite some time.
Adjusting nitrogen for yield
When it comes to yield, RB209 recommendations are based on a ‘typical’ yield benchmark of 5.5 t/ha (spring feed barley). Going into the project, it was felt that this yield figure might be a little conservative. Certainly, when yields are pushed, the crop is capable of going far higher. For example, the five-year (2016–20) yield average in RL trials is 7.5 t/ha.
This project confirmed these suspicions. It followed RB209 recommendations and landed an impressive average yield (selected experiments) of 7.4 t/ha. Although many commercial yields will fall shy of this, it is clear that modern spring barley varieties use nitrogen more efficiently compared to their predecessors.
As RB209 suggests that the recommended N rate is increased by 20 kg for each additional expected tonne (up to 9 t/ha) above the 5.5 t/ha benchmark, it may actually overestimate fertiliser N requirements. In fact, across all experimental datasets, the average recommended N rate was 165 kg N/ha. However, the measured average economic optimum N rate was far lower – just 118 kg N/ha.
The researchers proposed two solutions to readjust RB209’s recommendations. Firstly, to change (increase) the yield adjustment. Secondly, to adopt a method that calculates fertiliser N requirement based on crop N demand and fertiliser recovery. The final report provides the details. However, each option results in similar N recommendations at expected yields of 7–8 t/ha.
Readjusting nitrogen for quality
Attention to detail is essential, especially when it comes to hitting the typical grain N content (N%) specifications required by malting markets – malt distilling (below 1.65%), brewing (1.60–1.85%) and grain distilling (above 1.85%). Hitting specs requires a mix of quality guidance and local experience to strike a balance between pushing yields and keeping grain N content within tight N% bands.
Across all experimental datasets, it was found that a reduction in the N rate of 29 kg N/ha brought down grain N% by 0.1%. These results are broadly in line with the current RB209 recommendation (reduction of 30 kg N/ha). The average grain N% at the N optimum was 1.7% (currently, RB209 is based on 1.9%), and around two thirds (67%) of crops achieved a grain N% of under 1.8%. Ultimately, historic field grain N% and yield data will help guide decisions on the potential to reduce fertiliser rates.
Results from 11 N-timing experiments largely confirmed RB209’s recommendations, with all N applied between drilling and early stem extension (with large timing flexibility in this window). The work also concluded that application of at least 40 kg N/ha in the seedbed is often beneficial – but should be capped at 40 kg N/ha, where nitrate-leaching risks are high (e.g. sown before March, grown on a light-sand soil or where high rainfall occurs soon after drilling).
The research also investigated sulphur (S) rates and found that current RB209 recommendations were sufficiently accurate. The research findings will now be reviewed by the UK Partnership for Crop Nutrition – the body responsible for revising RB209.
The Updating nitrogen and sulphur fertiliser recommendations for spring barley project involved researchers from ADAS and SRUC.
Three nitrogen-rate plots in spring barley.