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Montana State Univ., Western Agric. Res. Ctr., 580 Quast Ln., Corvallis, MT 59828
Montana State Univ., Northwest Agric. Res. Ctr., Kalispell, MT. Mont
Montana State Univ., Western Agric. Res. Ctr., 580 Quast Ln., Corvallis, MT 59828
Montana State Univ., Northwest Agric. Res. Ctr., Kalispell, MT. Mont
* Corresponding author.
Annual legume plowdown systems, which utilize fall regrowth for N contributions to rotational crops, have not been adapted to irrigated, inlermountain 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. disfichon L.) for two subsequent years. Maximum herbage plowdown N was I25 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.
Received for publication November 9, 1994.
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