Use of legume intercropping to establish organic timothy seed crops

Timothy (Phleum pratense L.) is a perennial grass widely grown for livestock feed in temperate regions of the world. It is one of the primary forage grasses grown for seed in Scandinavia due to good cold tolerance and high-quality feed characteristics. Changes to European Union requirements for use of organic seed in organic forage and livestock production are expected and will soon increase demand for organic timothy seed in the region. Inadequate nitrogen (N) supply is a key yield-limiting challenge on many arable farms in Norway’s main seed growing region. In this study, we investigated methods to produce organic timothy seed with limited access to manure, by intercropping seven legume species sown with timothy in the same row or in alternate rows. Timothy seed was harvested for two seed production years in three field experiments in southeastern Norway. Sowing annual legumes with timothy increased seed yield by 10 to 25% in first-year stands. Berseem clover (Trifolium alexandrinum L.) and subterranean clover (Trifolium subterraneum L.) sown in the same row with timothy provided the most consistent seed yield increases. Perennial legume intercrops decreased seed yield by 10 to 36% in fist-year stands but black medic (Medicago lupulina L.) provided 21 to 64% seed yield increases in second-year stands. Seed yield increases in response to legume intercrops were attributable to panicle number and seed number but not seed weight. International seed purity standards can be met if the legume has a seed size and shape that can be removed during seed cleaning.