Comparative plowdown value of red clover strains

Cultivars and common seedlots of double- and single-cut red clover (Trifolium pratense L.) were direct seeded at the Elora Research Station in 1982 and 1983, fall plowed, and followed by 3 yr of corn (Zea mays L.) harvested for grain yield. The 1982 and 1983 sites differed in background soil N status. Common seedlots produced subsequent corn yields equal to those following certified cultivars, indicating no advantage to the use of certified seed for plowdown purposes. Although double-cut strains produced more aboveground biomass, both in midseason and at plowdown, single-cut strains produced more fall root biomass (1 yr only) and a higher percent root N, but in the end, corn yield did not differ between double- and single-cut strains. The ranges of performance of double- and single-cut strains did not overlap for aboveground biomass, but overlapped substantially for both root and percent shoot N and for root biomass. First-year corn yield varied significantly with red clover strain, in both the double- and single-cut groups, although no strain differences were apparent by the second and third years. Compared to continuous corn with no N fertilizer, red clover increased corn yield by 1.5–1.8 t ha−1 in Year 1, by 0.4–0.9 t ha−1 in Year 2, and by 0–0.7 t ha−1 in Year 3. First-year corn yield was not significantly correlated with red clover parameters measured the preceding year, including aboveground biomass and nitrogen content at plowdown. However, observed patterns of response were consistent with a nitrogen-based plowdown benefit. Breeding to improve plowdown value will depend on identification of those specific plant attributes which confer legume plowdown benefit.Key words: Plowdown, green manure, red clover, nitrogen, corn