IMPROVING LEGUME PERSISTENCE IN FORAGE CROP SYSTEMS

Forage legumes benefit pastures and hay crops by fixing N, improving s easonal distribution of growth, and enhancing animal performance, but their lack of persistence is viewed as a major limitation. Stand persi stence depends largely on plant persistence in crown-forming perennial s that do not spread by stolons or rhizomes, but depends on seed produ ction, timely germination, and seedling survival in annuals, biennials , and many short-lived perennials. Stolon- and rhizome-forming perenni als can colonize unoccupied areas if management is favorable. Converse ly, differentials in seed production, seed dispersal mechanisms, and s eed survival allow reseeding annuals, biennials, and short-lived peren nials to colonize areas that are more widely dispersed. Several pathog ens and insects invade the stand each year, but to different intensiti es depending on climatic and crop management conditions. Other pathoge ns and insects reside in production fields and pastures, gradually inc reasing in population while reducing plant persistence, the seed bank, and seedling survival. Environmental and management stresses weaken p lants, which are subsequently killed by combined influences of environ mental stresses, resident insects, and pathogens. Improving disease an d insect resistance is a major breeding objective for crown formers, b ut these efforts have to be supplemented by physiological improvement in stress resistance. To improve stand persistence of annuals, managem ent and genetic information is needed on seed production capacity, har d seed content, seed bank management, and optimizing conditions for se ed germination and seedling survival. The long-term goal is to improve cultivar persistence, and develop management systems to aid legume pe rsistence in a wide range of grassland ecosystems. Educational program s are also essential.