Hairy vetch (Vicia villosa Roth) preceding soybean suppresses nodulation and reduces grain yield in a low-fertility sandy soil

Hairy vetch ( Vicia villosa Roth) is increasingly used as a preceding cover crop for high nitrogen (N)-demand crops; however, its effects under different termination approaches intended to supply starter N to subsequent soybean remain unclear. A two-year field study in northeast Germany evaluated residual N following cover crop termination and its effects on soybean nodulation and grain yield. Irrespective of termination method, hairy vetch yielded significantly higher soil mineral N compared to fallow and winter rye, ranging 37.1 – 257.1 kg ha -1 in spring compared to 22.6 – 77.0 kg ha -1 in autumn. However, this residual N was associated with low soybean nodulation, grain yield, and grain N yield. Soybeans after winter rye produced on average 34 nodules plant -1 in contrast to 12 nodules plant -1 in those after hairy vetch. Average soybean grain yield ranged from 1591 kg ha -1 in winter rye to 1458 kg ha -1 in hairy vetch. Interactive effects between year, cover crop and termination method were significant for aboveground biomass and grain yield but not for nodulation and yield components. In particular, the conventional tillage (CT) of hairy vetch resulted in the lowest grain output, particularly in year I, but not in year II. Winter rye termination using the CT and reduced tillage (RT) significantly increased grain yield, whereas the specialized tillage (ST) was less effective. We conclude that full incorporation of hairy vetch residues exerts a negative effect on following soybean productivity, with the extent of the effect varying with termination method and year.