Summer annual forage crops can be an important source of livestock feed in emergency situations when traditional crops are compromised or become unavailable. Functionally diverse forage crop mixtures can increase resource use efficiency and provide additional ecosystem services over forage crop monocultures, especially in low-input cropping systems.  The purpose of this research was to explore niche differentiation and facilitation in summer annual forage crops grown mid-summer in the northeastern United States. Four species with different nitrogen acquisition and plant architecture traits were tested: 1) sorghum sudangrass (Sorghum bicolor, grass, tall); 2) pearl millet (Pennisetum glaucum, grass, short); 3) sunn hemp (Crotolaria juncea, legume, tall); and 4) cowpea (Vigna unguiculata, legume, short). These crops were seeded at multiple rates in monocultures and in all possible combinations of two, three, and four species mixtures. Low-input conditions were simulated with a reduced seeding rate and by applying 896 kg/ha of poultry litter (5-4-3) prior to seeding crops; less than half of a typical rate for a crop of sorghum sudangrass. All forage crops were seeded with a cone seeder in 1.26 by 4 m plots. Light transmittance was measured weekly and biomass of each forage crop was sampled from 0.5 m² quadrats at 56 days after planting. Preliminary analysis of the biculture treatments shows that mixtures that contained both a grass and a legume were on average 33% more productive than mixtures that did not contain both functional groups. Mixtures with taller species also produced greater biomass than with shorter species, with the greatest biomass in the sorghum sudangrass and sunn hemp mixture (350 g m^-2) and the lowest biomass in the sorghum sudangrass and millet mixture (156 g m^-2). Initial results suggest that combining species with different nitrogen acquisition traits can be more beneficial than combining species with different plant statures.