Influence of alfalfa in bromegrass-alfalfa mixtures on forage yield, protein yield, fertilizer N requirements, net returns, and energy performance
Field experiments were conducted at Lacombe and Eckville in central Alberta from 1993 to 1995 to determine the influence of alfalfa in bromegrass-alfalfa mixtures on forage yield, protein yield, fertilizer N requirements, net returns and energy performance. Ammonium nitrate was applied at 0, 50, 100, 150 and 200 kg N ha1 rates to five smooth bromegrass (Bromus inermis Leyss.)-alfalfa (medicago sativa Leyss.) compositions (pure bromegrass; 2:1, 1 :l and 1:2 ratio of bromegrass: alfalfa; and pure alfalfa). In the zero-N treatment, dry matter yield (DMY) and protein yield (PY) were lowest in pure bromegrass stands. The DMY and PY increased substantially when alfalfa was grown in association with bromegrass. There was a marked increased in DMY and PY from N applied in pure bromegrass stands, but the increases were much less in the mixed stands. The net returns above fertilizer and forage harvesting costs were much greater from mixed stands than from pure bromegrass. In pure bromegrass stands, the net returns increased with increasing N rates up to 200 kg N ha1 but equivalent net returns were usually attained without fertilizer N in bromegrass-alfalfa mixtures as low as 2:l. The amount of hay produced per unit of energy input and energy output/energy input ratio were greater for bromegrass-alfalfa mixture than for pure bromegrass or for alfalfa alone. In conclusion the results indicate that seeding of alfalfa in mixed stands with bromegrass can reduce the use of N fertilizer by more than 100 kg N ha-1 without any detrimental effect on forage yields, forage quality, and net returns to producers. However, the short-lived nature of alfalfa may be a serious limitation to bromegrass-alfalfa mixtures. Therefore, producers must also adopt management practices that increase the longevity of the alfalfa stands.
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