The yield plateau in oilseed rape

Since the early 1980s, there has been relatively little increase in commercial oilseed rape yields in the UK. Learn about the potential causes of the yield plateau, including what is inside and outside of your control.

The stagnation in commercial yields does not reflect the pace set by new varieties. In AHDB Recommended Lists (RL) trials*, yields have increased by about 0.05 t/ha each year. This has resulted in an increasing gap between farm yields and potential yields.

*Note: RL trials now have a greater emphasis on light leaf spot resistance than yield.

With potential UK yield estimated at more than 6.5 t/ha, research has looked to identify yield constraints in commercial situations.

In 2011, average farm yield was 0.8 t/ha above the long-term average of 3.1 t/ha. Analysis of crop-production data from this year found that the relatively high yields were mainly a result of good weather, rather than good management. The key factors in 2011 can be summarised as follows:

• Good weather after drilling that favoured consistent plant establishment
• A dry spring that restricted crop growth and promoted optimum canopy size
• A sunny spring that resulted in more seeds per pod and increased the rate of early seed fill
• A cool summer that prolonged the seed-filling period
• Favourable weather that limited disease and allowed good control with fungicides

 In 2012, AHDB published an analysis of national yield trends and farm-specific data (from over the last 30 years). The research aimed to identify the agronomic factors, rather than the meteorological ones, that constrain oilseed rape yields. The work found no single factor was responsible. However, it identified some major constraints:

• Increases in cropping frequency, leading to greater amounts of soilborne disease
• Poor selection and management of varieties
• Relatively low nitrogen- and sulphur-use efficiency

Oilseed rape yields for farm (blue line) and AHDB Recommended Lists trials (green line)