Functional Diversity in Summer Annual Grass and Legume Intercrops in the Northeastern United States

A warm-season annual intercropping experiment was conducted across the northeastern United States with four trials in 2013 and five trials in 2014 with four crop species selected based on differences in stature and N acquisition traits: (i) pearl millet [Pennisetum glaucum (L.) R. Br.], (ii) sorghum sudangrass [Sorghum bicolor (L.) Moench x 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 intercrop. Crop biomass was sampled at similar to 45 and 90 d after planting. When averaged across the nine site-years, biomass at the first and second sampling dates, respectively, of the monoculture treatments ranged from 1040 and 2500 kg ha(-1) (cowpea) to 3000 and 9300 kg ha(-1) (pearl millet). In general, biomass production of the legume monocultures was lower than the grass monocultures and intercrops at both sampling dates. All intercrops had land equivalent ratios (LERs) greater than one, indicating complementarity, likely a result of resource partitioning. Intercrops, particularly the four-species mixture, exhibited greater stability in yields across environments. The pearl millet-sorghum sudangrass-sunn hemp intercrop had the greatest evenness, suggesting that species selected for annual intercrops should have similar monoculture growth rates to minimize asymmetric competition.