The effect of temperature on the growth and development of five white clover (Trifolium repens L.) populations : a thesis presented in partial fulfilment of the requirements for the degree of Master in Science at Massey University

The Role of White Clover (Trifolium repens L) in Pastoral Agriculture White clover is widely distributed throughout the temperate regions of the world where it is of major agronomic importance (Erith 1924; Martin 1960; Williams 1970; Levy 1970). The most important function of legumes in a pasture is their ability to fix atmospheric nitrogen through symbiosis with root nodule bacteria called Rhizobium (Martin 1960) and thus increase the potential pool of nitrogen for the pasture. Sears et al. (1953, 1965) estimated that approximately 410 kg/ha/year of nitrogen can be fixed by white clover under initial pasture development conditions in New Zealand. This nitrogen becomes available for associated grass growth through transfer of breakdown products of the clover shoot and root parts and transfer of nitrogen compounds through the grazing animal (Butler and Bathurst, 1956). White clover is also important because of its high quality feed for grazing animals (Williams 1970). Compared with grass herbage, white clover has higher levels of protein, and minerals such as calcium and magnesium (Johns 1966). A low supply of these elements is frequently associated with metabolic disorders of animals. White clover herbage is also of high digestibility and acceptability by animals (Ulyatt et al. 1976). Although white clover has become the most important pasture legume in New Zealand, its effective use is dependent on an adequate supply of nutrients in the soil (Sears 1953), effective symbiosis with R. trifolii (Munro and Hughes, 1966) and optimum climatic conditions (Mitchell, 1956). The environmental influences, particularly the limitations of cold temperature on clover growth, are the main interest in this study.