Abstract: Field trials were conducted with spring-sown rye and field pea cover crops to determine the effect of five rye–pea proportions and three seeding rates (high, medium, and low) on weed suppression during cover crop growth. Measurements on weed and cover crop growth were taken approximately 2 mo after seeding when cover crops were killed. Cover crops were killed by mowing in 1996 and by undercutting in 1997 and 1998. Cover crop biomass, averaged over rye–pea proportion, was highest in 1998 at 4.3 million tons (MT)/ha (high seeding rate) and lowest in 1997 at 1.5 MT/ha (low seeding rate). Cover crops of pure rye or rye–pea mixes suppressed weeds more effectively than did pure pea. Dominant weeds were ladysthumb, smooth pigweed, smallflower galinsoga, and common lambsquarters. Ground cover by weeds ranged from a low of 2% (rye–pea mixes) to a maximum of 73% (pure pea). Cover crop mixes of 50% or more rye seeded at the high rate gave the best weed suppression.
Nomenclature: Ladysthumb, Polygonum persicaria L. #3 POLPE; smooth pigweed, Amaranthus hybridus L. # AMACH; smallflower galinsoga, Galinsoga parviflora Cav. # GASPA; common lambsquarters, Chenopodium album L. # CHEAL; field pea, Pisum sativum L.; rye, Secale cereale L. ‘Wheeler’.
Additional index words: Allelopathy, mixed cropping, undercutting, AMACH, CHEAL, GASPA, POLPE.
Abbreviations: DAS, days after seeding.