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Title: Changes in Alfalfa Yield and Nutritive Value Within Individual Harvest Periods

item Brink, Geoffrey
item Hall, Marvin
item Shewmaker, Glenn
item Martin, Neal
item Undersander, Dan
item Walgenbach, Richard

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2010
Publication Date: 6/2/2010
Citation: Brink, G.E., Hall, M.H., Shewmaker, G.E., Martin, N.P., Undersander, D.J., Walgenbach, R.P. 2010. Changes in Alfalfa Yield and Nutritive Value Within Individual Harvest Periods. Agronomy Journal. 102:1274–1282.

Interpretive Summary: Extensive research has documented how annual yield of alfalfa increases and quality decreases as the time period between harvests lengthens. However, producers need to know how yield and quality change within each of time periods in which alfalfa is typically harvested during the growing season. This research determined how rapidly alfalfa yield changes relative to quality in the spring, early summer, late summer, and fall in Idaho, Pennsylvania, Wisconsin. We found that average yields were always greatest in the spring at all locations. In the eastern United States, alfalfa yield increased most rapidly in the spring while in the Midwest and West, alfalfa yield increased most rapidly in the early summer. At all locations forage quality declined most rapidly in the spring. Thus, decisions regarding the appropriate time to cut alfalfa are most important in the spring when a high portion of the annual yield is declining most rapidly in quality.

Technical Abstract: Harvest management investigations have demonstrated the effect of cutting date and frequency on the annual yield and quality of alfalfa (Medicago sativa L.), but not within individual harvest periods throughout the growing season. In spring, early summer, late summer, and fall, primary growth of three varieties was harvested at late vegetative stage (stem length > 30 cm; no buds, flowers, or seed pods) and every 5 d thereafter for 20 d in Idaho, Pennsylvania, and Wisconsin. Forage yield and neutral detergent fiber (NDF) were measured at each harvest. Plots not harvested for yield and quality analysis for a particular period were cut at first flower. Across all harvest periods and locations, yield was greatest in the spring; the rate of yield accumulation was greatest in the early summer in Idaho and Wisconsin (198 and 181 kg/ha/d, respectively) and in the spring in Pennsylvania (462 kg/ha/d). The rate of increase in NDF with maturity, however, was slower in the early and late summer than in the spring. Given that variable environmental conditions greatly impact alfalfa growth, our results suggest that tradeoffs between yield and quality are greatest in the spring when yield is greatest and forage quality is changing most rapidly, while quality of harvests made later in the growing season are impacted less by maturity.