IN VITRO DIGESTIBILITY OF FORAGE SPECIES AS AFFECTED BY FERTILIZER APPLICATION, STAGE OF DEVELOPMENT AND HARVEST DATES

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Abstract
In vitro digestibility (IVD) and yield of digestible dry matter (DDM) was determined on four forage species; Saratoga bromegrass (Bromus inermis L.), Frode orchardgrass (Dactylis glomerata L.), Climax timothy (Phleum pratense L.) and DuPuits alfalfa (Medicago sativa L.) grown as single species over a 2-year period. Nitrogen and potassium fertilizer in various combinations and rates were applied to these forage species. Two cuttings per season of the various species were harvested. Fertilization with nitrogen and potassium did not affect IVD of grasses at any of the rates applied. The IVD of alfalfa was increased by potassium fertilization, while DDM yield was increased by both nitrogen and potassium fertilization.Each forage species was also harvested at 4-day intervals throughout the season to determine effect of advancing maturity on digestibility. The IVD of the first harvest of forage early in June averaged 77% for the four species, but by late July it had dropped to 58%. Of the four species tested, the IVD of orchardgrass decreased most rapidly while that of bromegrass decreased most slowly.