“…In fact, the benefit of legumes to the growth of associated grass varies depending on both legume and grass species (Ta and Fails, 1987a). On the other hand, environmental variations, which are also known to affect NF (Feigenbaum and Mengel, 1979;Harding and Sheeley, 1980;Schweitzer and Harper, 1980;Wahua and Miller, 1978), N assimilation (Duke et al, 1979, Duke andDoehlert, 1981) and N excretion (Taet al, 1986;Virtanen et al, 1937) by legumes, would therefore also affect NT. Wyss and Wilson (1937) suggested that the relationship between photosynthesis and NF as affected by environmental conditions may be the dominant factor controlling N excretion.…”