Winter vetch as a cover crop can boost protein content in the first crop

Find out more about planting clover grass in late summer here: Planting clover grass in late summer (landbrugsinfo.dk)

What we have tested

Mixture Ø44 was sown in pure stands in the trials and compared with sowing the same amount of Ø44 in 10 kg cover crop of winter vetch of the 2 varieties Villana and Ostsaat Dr Baumanns. For clover grass sown in winter vetch, there are two sowing times in late summer, while clover grass in pure stand is only sown at the first sowing time. The first cut was harvested at 3 times at one-week intervals from early May to late May. The second cut was harvested 4 weeks after the first cut.

The yield effect of winter vetch is limited

The effect of winter vetch on yield is very limited compared to mix Ø44. The biggest difference of 554 feed units per hectare is between early sown Ostsaat Dr Baumanns cover crop and late sown Villana.

Table 1. Effect of winter vetch cover crop on yield in feed units, crude protein content in per cent of dry matter and FC organic matter in the first cut. Across 8 trials and three harvest times for the 1st cut. Results are preliminary. (2023- 2025)

Crude protein content increases when using winter vetch cover crop

Crude protein content increases when using winter vetch cover crop, mostly for the Ostsaat Dr Baumanns variety, where there is 3.1 percentage points more protein than in the Ø44 mix. There was a large variation in protein content between the trials, see figure 1. The time of sowing had no effect on the protein content.

Digestibility decreases in the 1st cut

The effect on digestibility (FC organic matter) is the opposite of crude protein. Planting in winter vetch, especially Ostsaat Dr Baumanns, has resulted in lower FC organic matter. There was no difference between the two sowing times.

Planting clover grass in winter vetch gives a lower sugar content in the first cut, which can be an advantage in years with a high sugar content in the grass (data not shown).

Time of 1st cut

With 3 harvest times, it is possible to see the development of the different stages over 3 weeks. In general, early harvest results in lower yields and later harvest results in lower digestibility.

The harvest times have been different in the trials. In the 8 trials, the first crop was harvested between 5 May and 29 May. In order to show a more nuanced result, we have chosen to look at data for two harvest times.

Harvesting the first cut in the middle of May (12-14 May) shows the same trend as the average of all harvest dates. There was no difference in yields, but there was a higher protein content with winter vetch, especially the Ostsaat Dr Baumanns variety. The effect on protein content was lower at the late sowing time. In the second crop, there was no difference in yield and crude protein content. See figure 2.

The FC organic matter at this time of sowing was in the range 81.6 to 84.0, highest in clover grass and lowest in the late sowing with Ostsaat Dr Baumanns.

Harvesting a week later (19-21 May) was carried out in 7 of the 8 trials. Even at this harvest time, there is not much difference in yield between the treatments. The protein content is again higher in winter vetch, especially Ostsaat Dr Baumanns, while digestibility decreases. At this time of sowing, the FC organic matter has been between 81.1 and 68.4.

Significance of sowing time

It was planned to sow the first time between 5 and 10 August and the second time about 14 days later. This was only done in 3 of the 8 trials and the second sowing time was 20 to 24 August. In the other trials, the first sowing took place between 14 August and 1 September, with the second sowing time between 1 and 21 September. The late sowing is due to the challenges farmers face with late harvest and excessive rainfall. But in an experimental context, it requires more data analysis before reliable figures can be established. So the results below are based on data without statistical calculation.

Older trials show that clover grass in pure stands must be sown before mid-August, otherwise the yield in the first cut and the proportion of clover will suffer. However, in this series of trials, there are no two sowing times for clover grass in pure stands.

Trends in the effect of sowing time (Preliminary results without statistical analysis):

• Yield in the first cut in clover grass with winter vetch cover crop seems to decrease with later sowing. Especially the Ostsaat Dr Baumanns variety. See table 1.
• Sowing time does not seem to affect the crude protein content and digestibility in the first cut. See table 1.
• The effect on clover share and 2nd cut has not yet been analysed.

Alternatives to winter vetch - balancing and blood clover

In 2025, Balansa and blood clover were trialled as alternatives to winter vetch. Like winter vetch, they were sown at two different times in the autumn, and first cuts were taken at three different times, one week apart.

The preliminary results for the first ploughing show that the effect of balansa and blood clover is very close to the results for the winter vetch variety Villana. However, none of these species match the protein improvement achieved with Ostsaat Dr Baumanns. At this time, there is no evidence in favour of balancing or blood clover over winter vetch.