Selecting winter cover crop species for northern climatic conditions

The use of cover crops in crop rotations provides a wide range of ecosystem services including protection of the soil from nutrient loss. The objective of this study was to determine the suitability of winter cover crop species for Estonian conditions. Field trials with cover crop species winter rye (Secale cereale L), winter turnip rape (Brassica rapa spp. oleifera L.), forage radish (Raphanus sativus L. var. longipinnatus), hairy vetch (Vicia villosa Roth) and berseem clover (Trifolium alexandrinum L.) were carried out during the period 2016-2018 at the Estonian Crop Research Institute. Biomass production, nitrogen (N), phosphorous (P), potassium (K), calcium (Ca) and magnesium (Mg) accumulation were evaluated. The results under northern European conditions indicated that together with winter rye and winter turnip rape, hairy vetch survived the winters. By the spring, hairy vetch had produced the most biomass and accumulated the highest amount of N, compared with the other species. Winter turnip rape showed the greatest uptake of P, K and Ca in the spring. In both years, forage radish presented the highest biomass and nutrient accumulation in the autumn. After winterkill and decomposition in the spring, the forage radish left holes in the ground, which could be a beneficial characteristic, particularly in no-tillage farming systems. Berseem clover did not produce remarkable biomass in the autumn and was killed by the first frosts and was therefore considered unsuitable as an overwintering cover crop for northern latitudes.