Changes in Composition of Alfalfa, Red Clover, and Birdsfoot Trefoil during Autumn

Considerable research has been conducted to evaluate the influence of harvest management of alfalfa (Medicago sativa L.) during late summer and autumn on persistence and subsequent forage yields. These studies generally have not included data on changes in forage quality during autumn. The objective of this experiment was to measure changes in forage yield and composition of alfalfa, red clover (Trifolium pratense L.), and birdsfoot trefoil (Lotus corniculatus L.) in response to delay of harvest during autumn. Small plots of each species were seeded on Plano silt loam soil (fine-silty, mixed, mesic Typic Argiudoll) using chemical weed control. Regrowth was measured following a late August harvest each season. Separate plots of each species were harvested on the average dates of 7, 17, and 28 October and 8 and 19 November during 1979 and 1980. Dry matter yield of alfalfa increased by 16% between 7 and 17 October in 1979 and by 22% in 1980. Yield of all three species declined after the mid-October harvest in both years. Nitrogen concentration in forage of all species declined between 7 October and 8 November in 1979, and between 7 and 28 October in 1980. In vitro dry matter disappearance (IVDMD) did not change between 7 and 28 October but generally declined by 19 November. Total nonstructural carbohydrate concentration increased between 7 and 28 October and declined thereafter. Neutral detergent fiber concentration in alfalfa did not increase between 7 and 28 October in 1979 but increased after that date. Red clover did not increase in neutral detergent fiber concentration during autumn in 1979. In 1980 forage of all species increased in neutral detergent fiber after 8 November. The concentrations of P, K, and S in the forage of all three species declined during autumn. Red clover was lower in S concentration (0.21 %) than alfalfa (0.32 %) or birdsfoot trefoil (0.29 %). Calcium concentration increased significantly during autumn. The concentration of Mg in all three species remained unchanged or increased during autumn. These results indicate that significant yields of high quality forage were produced following harvest in late August. The three legumes differed in yield but were generally similar in IVDMD and N concentration on a particular harvest date. Forage yield declined more rapidly between 7 October and 17 November than did forage IVDMD or N concentration.