Managing Alfalfa and Berseem Clover for Forage and Plowdown Nitrogen in Barley Rotations

Abstract

Annual legume plowdown systems, which utilize fall regrowth for N contributions to rotational crops, have not been adapted to irrigated, intermountain areas of the Northern Rockies. Our objective was to evaluate plowdown systems using ‘Nitro’ alfalfa (Medicago sativa L.) and ‘Bigbee’ berseem clover (Trifolium alexandrinum L.). These two legumes were grown under five harvest management systems (zero to three forage harvests prior to fall plowdown of regrowth, or a standard three harvest system with no herbage plowdown) at two sites in western MT differing in soil characteristics. They were assayed for forage and plowdown production and for N benefits to ‘Clark’ barley (Hordeum vulgare L.; syn. H. distichon L.) for two subsequent years. Maximum herbage plowdown N was 125 to over 200 kg N ha−1 for berseem clover and 87 kg N ha−1 for alfalfa. A two‐harvest system resulted in 3.6 to 6.6 Mg ha−1 forage and 45 to 78 kg N ha−1 in herbage plowdown. Effects of plowdown were measured directly in increased soil N availability and correlated increases in N uptake in subsequent barley; benefits were expressed in increased grain yields and/or grain N concentrations and were apparent for two successive years at the site of lower native fertility. Alfalfa N benefits were superior to berseem clover, though disproportionate to herbage plowdown N quantities, possibly due to greater root and crown N in alfalfa. Where the management goal is primarily forage production with moderate benefit of plowdown N, berseem clover works well in a two‐harvest system; Nitro alfalfa is preferred where greater benefits of plowdown N are desired.

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

“…Similarly, Westcott et al (1995) concluded that green manure effects on subsequent spring soil nitrate levels were a determining factor in barley N uptake and yield responses to treatments.…”

“…Net N mineralization has been shown to correlate with C:N ratios of clover green manures . In a study comparing plough-down of berseem clover and alfalfa (Medicago sativa L.), soil N availability was consistently greater for alfalfa, although above-ground biomass N was higher for berseem clover than alfalfa (Westcott et al 1995). It was suggested that the higher soil N availability with alfalfa may have been due to greater N contributions from roots and crowns.…”

“…They suggested that the amount of green manure N available to subsequent barley may not have been large enough to affect barley yields. Treatment effects from legume plough-down can be difficult to detect against high background levels of soil N (Westcott et al 1995), as at Edmonton. Westcott et al aÁf Within columns, means followed by the same letter are not significantly different at P B0.05.…”

“…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.…”