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Rooting characteristics of forage legumes have not been investigated extensively. Little is known about how or if rate of root elongation, rooting depth, root distribution and density, number of rooting points, and root/shoot ratio may influence legume persistence across different soils and environments. Genera, species and cultivars of temperate and tropical legumes show marked variability in rooting characteristics. Variation in soil temperature influence root growth and development, and N2 fixation. Water stress, low soil pH and aluminum toxicity, high soil bulk-density and strain of rhizobia also are reported to affect root development. Variability among legumes may offer opportunities for breeding and selecting more persistent legumes for specific soil and climatic conditions, and for particular uses under grazing and cutting. Improved methods for conducting long-term research on legume roots are needed. Future research should focus on how rooting characteristics affect legume persistence.
Competition of white (Trifolium repens L.) and red clover (T. pratense L.) with associated species is reviewed. White clover is emphasized, as it is the most important legume in grassland farming in New Zealand. Grazing management strategies exist which increase both white and red clover content in swards, and genotype differences can confer considerable additional competitive advantages. Both clovers have superior light interception, different growth rhythms, and N2-fixing capability compared with grasses. These features allow them to compete successfully in vigorous grass dominated swards. However, the guerilla habit of white clover, bestowed on it through its stoloniferous character, ensures that this species persists in a wide range of grazed pasture.