Effects of harvesting systems on yield, persistence, and nutritive value of alfalfa

Abstract

The number of annual harvests and the interval between harvests affect DM yield, persistence, and nutritive value of alfalfa (Medicago sativa L.). The effects of harvesting alfalfa three times annually, with the intervals between harvests varied and with the third harvest taken prior to, during, or after the critical fall rest period, were investigated from 1985 to 1988 on a field of alfalfa established in 1984. Seven harvesting systems, comprising three harvests with varied regrowth intervals and a two-harvest system, were studied along with two rates of potassium fertilization. Harvesting alfalfa three times a year, with the third harvest taken during or after the critical fall rest period, produced the largest yields of DM, digestible DM, and crude protein. Dry matter yield was not reduced in three-harvest systems when the third harvest was taken during the critical fall rest period, provided there was an interval of approximately 500 growing degree-days between second and third harvests. Taking the first harvest at the early bud stage of development instead of the early bloom stage reduced annual DM yields. Increasing annual potassium fertilization from 200 to 400 kg K ha−1 did not affect DM yield or persistence under any harvesting system. Harvesting management of alfalfa in the fall should be based on the duration of the growth period between the second and third harvests instead of a critical fall rest period based on calendar dates.Key words: Medicago sativa L., yield, nutritive value, persistence, harvest management, K fertilization