Interaction Among Harvest Frequency, Fertilizer and Herbicide Use with Intensively Managed Alfalfa in the North-Central USA

This research evaluated effects of 2 alfalfa (Medicago sativa L,) cultivars (winter hardy and moderately winter hardy), 3 levels of fertiliser (none, medium, high), 3 levels of herbicide (none, medium, high), and 2 harvest systems ( 4 harvests and 5 harvests per year) on forage yield and quality, Five years (1987-1991) of an experiment in Michigan, USA, have been completed. During the first production year (1988). forage dry matter (DM) production was similar for the 5-harvest (15.2 Mg/ha) and the 4-harvest system (14.8 Mg/ha), During subsequent years, DM production was greater in the 4-harvest than in the 5-harvest system (13,4 v. 10,9, 12.6 v. 10.1, and 12.1 v. 9.7 Mg/ha for production years 2, 3 and 4, respectively). Forage quality, as measured by crude protein, acid detergent and neutral detergent fibre concentrations, was higher in the 5-harvest system during all years. The moderately winter-hardy cultivar produced more DM than did the winter hardy cultivar during production years 2, 3 and 4. Fertiliser use and DM production were positively correlated. Significant fertiliser x harvest management and fertiliser x herbicide interactions indicated that the beneficial effects of fertiliser were more pronounced under intensive harvest management and when weed pressure was controlled,