A nondormant alfalfa ( Medicago sativa L.) cultivar with increased root N production was developed to supply both N and forage in short‐term crop rotations. Our objective was to determine the effect of establishment treatments on seeding year herbage and N production of the nondormant cultivar, ‘Nitro’, and two check cultivars: nondormant ‘CUF101’ and moderately dormant ‘Saranac AR’ Field experiments were conducted for 2 yr on a Waukegan silt loam (Typic Haplaquoll). Establishment treatments included seeding alone (solo seeded) with and without herbicides, and companion crop seeding with non‐vernalized winter rye ( Secale cereale L.), nonvernalized winter wheat ( Triticum aestivum L.), and spring oats ( Avena sativa L.). Seeding year alfalfa herbage yields, root dry matter and N yields, and fall N yields of all cultivars were greater for solo‐seeding (with or without herbicides) than for companion‐crop seeding. Alfalfa herbage and root dry matter yields and root N yields were similar when nonvernalized winter rye or wheat, or spring oat (removed at boot) were the companion crops. Alfalfa cultivar differences in herbage and root dry matter and root N yields were greatest for solo‐seeding. When solo‐seeded with a herbicide, Nitro produced 20 and 30% greater root dry matter yields than CUF 101 and Saranac AR, respectively. Root N yields of Nitro were 25 and 36% greater than those of CUF 101 and Saranac AR, respectively, when a herbicide was used. With companion crop establishment, root dry matter and N yields of Nitro were often similar to those of CUF 101 or Saranac AR. We concluded that the enhanced root N production of Nitro alfalfa was agronomically significantly only when alfalfa was established without competition from weeds or small grain companion crops.
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Sheaffer et al. (1988) studied this question.