Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/17/2006
Publication Date: 2/27/2006
Citation: Brink, G.E., Hall, M.P., Shewmaker, G.E., Martin, N.P., Undersander, D.J., Walgenbach, R.P. 2006. Rate of yield and quality change in alfalfa. Proceedings of Idaho Alfalfa and Forage Conference. p. 5-10. Interpretive Summary: Alfalfa growers must always contend with the negative relationship between yield and forage quality that occurs as the crop matures - maximizing yield or quality usually compromises the other. Growers need to know when they must pay particular attention to this relationship and when they can strive for greater yield without a large tradeoff in quality. This study was conducted to determine how quickly alfalfa forage quality declines as yield increases during the spring, summer, and fall. In May, June, July, and September, three alfalfa varieties were harvested initially at late vegetative stage in Idaho, Pennsylvania, and Wisconsin. Different plots were then harvested every 5 days up to to 20 days. We found that yield increased most rapidly during the first cutting (May; 100 lb/acre/day) and slowest during the fourth cutting (September; 20 lb/acre/day). However, forage quality declined most rapidly during the first cutting and slowest during the fourth cutting. These results provide producers with a management tool to decide when harvest should occur to obtain alfalfa having appropriate quality.
Technical Abstract: Cutting management investigations have documented the effects of harvest date and frequency on alfalfa (Medicago sativa L.) forage yield and quality during the production year; more frequent harvest generally reduces annual yield and increases quality. Information is needed on the change in forage quality relative to yield that occurs within individual harvest periods over the whole growing season. In spring, early summer, late summer, and fall, 'Standfast', 'WL 346', and 'Affinity' alfalfa were harvested at late vegetative stage in Idaho, Pennsylvania, and Wisconsin. Primary growth of each variety was harvested every 5 days thereafter to 20 days of maturity. At all sites, initial yield of the first cut was greatest for the first harvest period. In Idaho, yield increased 120 lb/acre/day during the first harvest period and 180 lb/acre/day during the second and third periods. In contrast, yield increased most rapidly during early harvest periods in Pennsylvania (first; 290 lb/acre/day) and Wisconsin (second; 250 lb/acre/day), but the rate of increase declined during the third (90 to 100 lb/acre/day) and fourth harvest (-20 to 40 lb/acre/day) periods. In Idaho and Pennsylvania, in vitro cell wall digestibility (NDFD) declined more slowly during the first harvest period than during later harvest periods, but in Wisconsin the rate of NDFD decline during the first harvest period was similar to or greater than later harvest periods. Our results suggest that because forage quality changes impact a larger proportion of the annual yield at first harvest, the decline in forage quality that occurs during the spring has a greater impact on feeding and cash value of hay than at any other time of the year.