Lucerne is a high-yielding legume that can produce high quality, high protein silage. Like all legumes it fixes its own N and thus does not need artificial N fertiliser. It is extremely drought tolerant thanks to a deep taproot and thrives in light, free-draining soil with high pH. Lucerne represents another option for home-grown protein for Irish farmers, especially in the South and East of the country where summers are becoming drier.

In June 2021 a trial was established to see how different varieties of lucerne performed in monoculture (LC), in a 2-way mixture with perennial ryegrass (LC-PRG) and in a 3-way mixture with perennial ryegrass and red clover (LC-PRG-RC). Although it is too early to draw conclusions on the best performing lucerne variety, results after the first full harvest year (4 silage cuts) make for interesting reading, especially given the current prolonged spell of dry weather.

The average annual DM yield in 2022 was greatest for LC at 12.66t DM/ha, followed by LC-PRG-RC (11.98t DM/ha) and LC-PRG (8.90t DM/ha). The ~30% lower annual yield of LC-PRG compared to LC may be due to a couple of factors.

Firstly, no chemical N was applied to any of the treatments as it was assumed that sufficient N would be supplied by the large proportion of legume in each of mixture. It is possible that the large difference in root depths between lucerne and perennial ryegrass meant that most of the N fixed by the lucerne was out of reach of the ryegrass.

Secondly, and more significantly, is the difference in the seasonal DM yields of each treatment across harvests – especially the yields recorded for the second cut at the end of June. The graph below shows a significant yield reduction of 43% for LC-PRG at the June harvest with LC production remaining steady. It is noteworthy that this harvest took place at the end of a prolonged dry spell with many of the LC-PRG plots showing signs of water stress where perennial ryegrass made up over 70% of herbage composition. Even the 3-way mixture, which contained 40% red clover on average, suffered a yield reduction during this dry spell.