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Composition of Leaf Protein Concentrate and Deproteinized Juice from Alfalfa, Red Clover, and Birdsfoot Trefoil1

Losses during field wilting of silage and curing of hay reduce both yield and quality. Direct harvest and mechanical dewatering avoid these losses and produce a protein concentrate. A 2-year field experiment was conducted to evaluate legume species and harvest date effects on the yield and composition of the protein concentrate and deproteinized juice fractions from spring growth legume herbage. The soil was a Plano silt loam (fine-silty, mixed, mesic Typic Argiudoll). Alfalfa (Medicago sativa L.) protein concentrate averaged 201 g dry matter (DM) kg⁻¹ total mass, slightly higher than red clover (Trifolium pratense L.) and birdsfoot trefoil (Lotus corniculatus L.). Harvest date effects on DM concentration in both the protein concentrate and the deproteinized juice were significant but showed little relationship to shoot maturation stage. Alfalfa protein concentrate averaged 102 g N kg⁻¹ DM, which was more N than the protein concentrate from red clover and birdsfoot trefoil in 1981 but not in 1980. Harvest date effects were small for alfalfa protein concentrate N concentration but red clover and birdsfoot trefoil had less of that constituent on the last harvest date. Total nonstructural carbohydrate (TNC) was highest in the deproteinized juice from red clover, which had 327 g TNC kg⁻¹ DM, followed by birdsfoot trefoil and alfalfa with the lowest concentrations. Harvest date effects on TNC differed among species, but these differences were not large enough to be of practical importance. Alfalfa and red clover whole crops differed in the concentrations of several amino acids, but they differed less than the whole crop differed from the pressed forage and protein concentrate fractions within each species. Red clover protein concentrate had more threonine and valine than alfalfa protein concentrate but only 85% as much methionine, 52% as much cystine and less isoleucine. Results of this 2-yr experiment indicate that N and DM concentrations differ in protein concentrates from different perennial legumes. Amino acid concentrations in protein concentrate were generally less affected by species and maturation than the same constituents in the whole crops. Species differences in deproteinized juice TNC concentrations were substantial and should be considered in the development of mechanical dewatering systems.