Abstract
Two 6-year-old grass–alfalfa mixtures were compared when fertilized with 0, 84 and 168 kg nitrogen per hectare and grazed by yearling Hereford steers. The effect of stocking rate, fertilization, forage mixture and year on the cumulative liveweight gain per hectare was also determined. The bromegrass (Bromus inermis L.) and alfalfa (Medicago sativa L.) mixture showed a linear increase in dry matter yield, but the nitrogen requirement of the intermediate wheatgrass (Agropyron intermedium L.) and alfalfa mixture was fully met by the 84-kg/ha N treatment. In 1960, the addition of 84 and 168 kg/ha N to the bromegrass–alfalfa increased animal production by 61 and 98% respectively. Corresponding increases of 53 and 56% were obtained from the fertilized intermediate wheatgrass–alfalfa mixture. Similar percentage increases were obtained in 1961. The 84-kg/ha N treatment reduced the alfalfa content of both mixtures by more than 40%. The 168-kg/ha N treatment practically eliminated the alfalfa from the stands. Nitrogen recovery by the bromegrass–alfalfa was similar at both fertility levels and amounted to 62% in 1960, and 24% in 1961. Recovery of nitrogen by intermediate wheatgrass–alfalfa was 62 and 36% from the 84- and 168-kg/ha N treatments in 1960, and 23 and 12% respectively in 1961.
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