Forage legumes benefit pastures and hay crops by fixing N, improving seasonal distribution of growth, and enhancing animal performance, but their lack of persistence is viewed as a major limitation. Stand persistence depends largely on plant persistence in crown‐forming perennials that do not spread by stolons or rhizomes, but depends on seed production, timely germination, and seedling survival in annuals, biennials, and many short‐lived perennials. Stolon‐ and rhizome‐forming perennials can colonize unoccupied areas if management is favorable. Conversely, differentials in seed production, seed dispersal mechanisms, and seed survival allow reseeding annuals, biennials, and short‐lived perennials to colonize areas that are more widely dispersed. Several pathogens and insects invade the stand each year, but to different intensities depending on climatic and crop management conditions. Other pathogens and insects reside in production fields and pastures, gradually increasing in population while reducing plant persistence, the seed bank, and seedling survival. Environmental and management stresses weaken plants, which are subsequently killed by combined influences of environmental stresses, resident insects, and pathogens. Improving disease and insect resistance is a major breeding objective for crown formers, but these efforts have to be supplemented by physiological improvement in stress resistance. To improve stand persistence of annuals, management and genetic information is needed on seed production capacity, hard seed content, seed bank management, and optimizing conditions for seed germination and seedling survival. The long‐term goal is to improve cultivar persistence, and develop management systems to aid legume persistence in a wide range of grassland ecosystems. Educational programs are also essential. Research Question Most producers understand the importance of legumes in forage systems, but management decisions that enhance short‐term yields or quality of a grass‐legume association can reduce persistence of the legume component. Our objective was to review the biology of legume persistence and evaluate management strategies associated with enhanced plant persistence of crown‐forming perennial legumes and reseeding properties of annual legumes and short‐lived perennials. Interactions of legumes with biological pests, environmental stresses, and associated grasses were considered. Literature Summary Legumes enhance animal performance and reduce N needs for grass pastures, but legumes seldom dominate in agricultural or natural ecosystems. Thus, the association must be managed to enhance vigor and persistence of the legume. Legume breeders have emphasized temperature resistance, especially cold adaptation, and disease resistance for crown‐forming perennials like alfalfa, but enhanced disease resistance and improved productivity may be at the expense of winterhardiness. Conversely, annual legumes are generally improved by increasing seed production and seedling vigor. The role of hard seed and dynamics of t...

Previous research has implied that forage yield in released alfalfa (Medicago sativa L.) cultivars declined slightly between 1978 and 1996. Our objective was to compare alfalfa cultivars released during the past five decades side by side in replicated yield trials to test for any changes in forage yield across time. Ten cultivars, two from each of the five decades, four recently released cultivars, and two check cultivars were compared for forage yield, persistence, and nutritive value at four locations. Cultivars were established in May 1999 at Iowa, Wisconsin, Ohio, and Minnesota. Forage was harvested three to four times in each of four production years depending on location. Plots were subsampled for nutritive value analyses for the first and third harvests in 2000 and 2001. Year × location × cultivar‐release date interactions demonstrated that forage yield and final stand densities differed among the cultivars in each year of the experiment at each location. Nutritive value traits were similar among all cultivars. Evidence for changes in forage yield for cultivars released between 1940 and 1995 was environmentally dependent. In environments where conditions lead to plant stand losses, recently released cultivars with multiple disease resistance had a yield advantage over older cultivars, but in environments where no differences in plant density occurred across time, older cultivars yielded the same as recent cultivars.

SUMMARY Mycorrhizal and non‐mycorrhizal onion seedlings were grown in individual soil chambers in which roots were confined to one side of a barrier. External hyphae of Glomus fasciculatus arising from mycorrhizal roots grew into an adjacent volume of soil. 32P was injected into soil at 1‐cm intervals up to a distance of 8 cm from the confined roots. Relatively high levels of radioactivity were subsequently detected in root segments of mycorrhizal plants at all distances from tracer injection. High levels of radioactivity were detected also in leaf segments of mycorrhizal plants. Radioactivity of root or leaf segments of non‐mycorrhizal plants did not exceed background level at any distance from tracer injection. 32P did not move more than 7.5 mm from the point of injection as indicated by gross autoradiography. Absorption of phosphate and its trans‐location to the host by hyphae of G. fasciculatus can extend the phosphate uptake zone of mycorrhizal onions to at least 7 cm from the root surface.

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