Optimizing Yield and Forage Quality of Summer Annual Grass-Legume Mixtures in the Northeast.

A summer annual intercropping experiment was conducted across the northeastern United States at three sites in 2013 and 2014. We compared four crop species that differed in stature and nitrogen acquisition traits: (i) pearl millet [Pennisetum glaucum (L.) R. Br.], (ii) sorghum sudangrass [Sorghum bicolor (L.) Moench × S. sudanense (Piper) Stapf], (iii) cowpea [Vigna unguiculata (L.) Walp], and (iv) sunn hemp (Crotalaria juncea L.). Crops were seeded in monoculture and in three- and four-species mixtures using a replacement design where monoculture seeding rates were divided by the number of species in the mixture. Crops were harvested at ~35 (2014 only), ~45, and ~90 days after planting (DAP) and analyzed for forage quality. In general, crop yield was greater at the Maryland site than at the Northern New York site, and crop yield increased and forage quality decreased with sampling date. Relative forage quality tended to be greater in cowpea than in pearl millet, sorghum sudangrass, and mixtures. Relative forage quality of sunn hemp changed dramatically with harvest date and tended to be better than pearl millet, sorghum sudangrass, and mixtures at 35 DAP, but worse than these treatments at 90 DAP. Milk production was estimated using the University of Wisconsin’s Alfalfa/Grass Evaluation System, Milk 2016. Preliminary results show that milk production was higher in grass monocultures and in mixtures compared to legume monocultures, which was largely driven by biomass production.