Winter-killed oats (Avena sativa) may have potential for use to suppress weeds in early seeded crops such as pea (Pisum sativum). Residue biomass and surface coverage are generally correlated with weed suppression. Oat residues also contain allelochemicals. Our objective was to determine if oat cultivars vary in residue production and allelopathy. Differences between oat cultivars were observed in residue production, and for effects on emergence of common lambsquarters (Chenopodium album) and shepherd's-purse (Capsella bursa-pastoris) in the greenhouse, and germination of pea and common lambsquarters in an infusion assay. Two of the oat cultivars producing the greatest biomass, `Blaze' (in the field) and `Classic' (in the greenhouse), interfered minimally with pea germination and were among the best cultivars in inhibiting common lambsquarters and shepherd's-purse. `Blaze' also greatly inhibited common lambsquarters germination in the infusion assay that measured allelopathy. Thus, `Blaze' and `Classic' possess suitable characteristics for use as a cover crop preceding peas.
Winter-killed cover crops may protect the soil surface from erosion and reduce herbicide use in an early planted crop such as pea (Pisum sativum). Our objective was to determine the potential of winter-killed cover crops in a snap pea production system. White mustard (Brassica hirta) produced the most residue in the fall but retained only 37% of that residue into the spring. Barley (Hordeum vulgare) and oats (Avena sativa) produced less fall residue but had more residue and ground cover in the spring. Greater ground cover in the spring facilitated higher soil moisture, contributing to higher weed numbers and weight and lower pea yields for oat and barley compared with a bare ground treatment. White mustard had weed populations and pea yields similar to the bare ground treatment. Within the weed-free subplot, no differences in pea yields existed among cover crop treatments, indicating no direct interference with pea growth by the residues. In greenhouse experiments, field-grown oat and barley residue suppressed greater than 50% of the germination of common lambsquarters (Chenopodium album) and shepherd's-purse (Capsella bursapastoris), while in the field none of the cover crop provided better weed control than the fallow.