Effects of Seeding Rate, Oat Companion Crop and Planting Date on Organic Establishment of Birdsfoot Trefoil (Lotus corniculatus).

The non-bloating perennial legume birdsfoot trefoil (BFT, Lotus corniculatus L.) is well suited to ruminant production in pastures, supporting greater levels of liveweight gain and milk production than other forages. However, BFT can be slow to establish, competing poorly with weeds. This study assessed BFT establishment strategies available to organic producers for annual herbage dry matter (DM) production and BFT cover at the third year after planting. We evaluated the effects of autumn vs. spring planting, use of an oat (Avena sativa) companion crop, and seeding rates of 3, 7, 20, and 34 kg pure live seed (PLS) ha^-1 at an irrigated site in northern Utah. For the three years following planting, mean annual DM production was greater than 5000 kg DM ha^-1 for all treatment combinations. Establishment method affected DM production in the first year after planting, with the greatest yield (6113 kg DM ha^-1) achieved at 20 kg ha^-1 PLS in autumn without a companion crop. In the second and third years after planting, dry matter production was greater than in the first year after planting and was not affected by seeding rate or establishment method. However, percent BFT cover assessed in the early spring of the third year after planting was greater for the highest seeding rate when spring-seeded with an oat companion crop than without because unseeded species were suppressed, while at the highest seeding rate BFT cover of autumn plantings was greater without a companion crop and cover of unseeded plant species was less for autumn plantings without a companion crop. Presence or absence of a companion crop had no effect on mean 3-yr DM production of spring-planted BFT, but BFT DM production of autumn plantings at 7 and 20 kg PLS ha^-1 was reduced by a seeding year companion crop.