Nitrogen (N) use can be reduced by up to 20% in a spring barley crop grown after spring beans compared with a continuous spring barley rotation, according to a new study from the Centre for Sustainable Cropping at the James Hutton Institute in Scotland, which included researchers from the Ryan Institute at the University of Galway.

This will come as no surprise to Irish bean growers and is the equivalent to a reduction of 22kg/ha N.

The study analysed data from a Scottish long-term field bean experimental platform from 2009 to 2023.

Results show that the spring barley after beans had an average reduction in its environmental impact of 25%.

While the reduced fertiliser usage played a key role in this reduction, it was also noted that pesticide applications were around 50% lower when beans were included in the crop rotation.

It was also found that the yield of spring barley after spring beans increased by 1.2t/ha (0.49t/ac) compared with a continuous spring barley rotation.

However, the continuous spring barley did yield higher in 2022 under drought conditions, as there was not enough soil moisture for the spring barley to make use of the residual N in the soil.

Residual N

The researchers also noted that the level of residual N depends on the growth and yield of the legume crop. Where a bean crop struggles or does not yield well, the following spring barley crop sees a lower benefit.

The researchers suggest that where spring bean yields are very low, the N applied to the following crop should not be reduced. However, this would require further research before being recommended to farmers.

While this study is based in Scotland, it shows the benefits that legume crops can have on a crop rotation, both economically and environmentally.