Annual legumes as green manure and forage crops in winter canola (Brassica napus L.) rotations

Abstract

. 1999. Annual legumes as green manure and forage crops in winter canola (Brassica napus L.) rotations. Can. J. Plant Sci. 79: 19-25. Cropping systems that reduce chemical fertilizer N requirements in winter canola (Brassica napus L.) need further study. Studies were conducted in 1994/1995 and 1995/1996 at two locations in Michigan i) to quantify the N accumulated at plowdown by berseem clover (Trifolium alexandrinum L.), alfalfa (Medicago sativa L.) and three annual medic species (Medicago truncatula Gaertn., M. polymorpha L., and M. scutellata L.) when they were managed as green manure or managed as forage; ii) to compare N response of the winter canola crop following the legumes; and iii) to estimate the N fertilizer replacement value (FRV) of the legumes. The legumes were seeded in early May in both years. Winter canola was planted after legume plowdown 90 d after planting (DAP). Four N rates (0, 50, 100, and 150 kg N ha -1 ) were applied to the winter canola in early spring. Herbage N yield at plowdown was highest (103.9 kg N ha -1 ) in berseem clover managed as green manure and this treatment resulted in the highest winter canola yield in 1995, but treatment differences were not significant in 1996. A supplementary effect of some treatments on winter canola yield was observed in 1995. Fertilizer N had a similar effect on winter canola yield across all treatments, and resulted in a quadratic response in 1995 and a linear response in 1996. Winter canola grain yield following annual legumes managed as green manure or as forage were similar. Winter canola yield following berseem clover was higher than when following annual medics. No FRV of legumes on winter canola was observed.

Grain yield and N benefits to sequential wheat and barley crops from single-year alfalfa, berseem and red clover, chickling vetch and lentil

“…In western Montana, berseem clover produced greater herbage plowdown N than an annual alfalfa, however, N uptake in the following barley (Hordeum vulgare L.) crop was less (Westcott et al 1995). Shrestha et al (1999) reported that berseem clover managed as forage had a similar amount of plowdown N compared to alfalfa managed as a forage.…”

“…Legume harvest management has been shown to have a major effect on the ability of legumes to contribute N to the soil (Sheaffer et al 1989;Shrestha et al 1999). Hesterman et al (1986Hesterman et al ( , 1987 determined that the biologically fixed N contribution of a one-cut system incorporated in the fall resulted in 37% greater N than a three-cut system.…”

“…Similar N yields of barley were observed following early-and late-season incorporated green manure lentil and flatpea . Shrestha et al (1999) determined that higher amounts of incorporated N from legumes managed as green manure crops compared to legumes managed as forage had no effect on the following winter canola (Brassica napus L.) grain yield.…”

The green manure value of seven clover species grown as annual crops on low and high fertility temperate soils

“…In areas with adequate rainfall, such as the Parkland and Boreal regions of Alberta, forage legumes offer potential to provide both forage yield and green manure benefits. Berseem clover provided similar benefit to a subsequent crop when managed solely as a green manure or when harvested once for forage and regrowth was ploughed down (Westcott et al 1995;Shrestha et al 1999).…”

“…(Blackshaw et al 2001). A few green manure studies in Canada and northern USA have included annual clover species (Westcott et al 1995;Shrestha et al 1999;Bullied et al 2002), but further research is needed.…”