Analysis of Primary Spring Growth of Four Pasture Legume Species1

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Abstract
Alfalfa (Medicago sativa L.) is the most‐used forage legume in the northern USA; however, it has several shortcomings, especially as a pasture species. Among northern‐adapted forage legume species that are potential alternatives in grazing situations are birdsfoot trefoil (Lotus corniculatus L.) sainfoin (Onobrychis viciifolia Scop.), and cicer milkvetch (Astragalus cicer L.). We conducted an analysis of primary spring growth of these four legumes to determine patterns of dry matter, crude protein (CP), and in vitro digestible dry matter (IVDDM) accumulation. The legumes were established on a Waukegan silt loam (Typic Hapludoll) in late July 1981. Beginning on 10 May 1982 and 1983, total forage was harvested weekly until 28 June when total forage accumulation had decreased. Near infrared reflectance spectroscopy was used to determine CP and IVDDM for leaves, stems, and reproductive parts for each species. All four species reached maximum dry matter accumulation on 21 June. Sainfoin produced the greatest forage dry matter (8.51 Mg ha−1); however, it also had the lowest IVDDM and CP concentration on 21 June. Thus, sainfoin had IVDDM and CP accumulations similar to those of other species. Cicer milkvetch had the greatest IVDDM concentration (67.6 dag kg−1) on 21 June, but its relatively low forage dry matter yield during primary spring growth reduced its IVDDM accumulation to an amount similar to that of the other species. Alfalfa had the greatest CP concentration on 21 June, but its CP yield exceeded only that of cicer milkvetch. None of the four species was definitely superior under these growth conditions. However, birdsfoot trefoil, sainfoin, and cicer milkvetch all showed potential as pasture substitutes for alfalfa, especially in that they did not reach a leaf‐to‐stem ratio of 1.0 or less until considerably later than alfalfa.