RELATIVE EFFECTIVENESS OF PHOSPHORUS ON NARROW-LEAF AND BROADLEAF BIRDSFOOT-TREFOIL GROWTH AND THE EFFECT OF ADDED PHOSPHORUS ON VESICULAR-ARBUSCULAR MYCORRHIZAL INFECTION

The relative effectiveness of phosphorus (P) applications on growth an d the effect of added P on the extent of infection of roots of narrowl eaf birsfoot trefoil (Lotus tenuis) and of broadleaf birdsfoot trefoil (Lotus corniculatus) by an indigenous VAM fungi (Glomus sp.) was stud ied on a P-deficient soil (Typic Natraquoll). In terms of rate of incr ease of shoot growth per unit of added P, broadleaf was more efficient than narrowleaf birsdfoot trefoil but they did not differ in the rela tive effectiveness of P for growth. For the two Lotus species, when in creasing the level of added P there was an initial increase in the per centage of root length infected, and then with further additions, ther e was a consistent decrease of the infection. For narrowleaf, the maxi mum percentage of root length infected was when plants reached 11% of their maximum shoot growth. Whereas for broafleaf, the maximum percent age of root infected was when plants reached the 66% of their maximum shoot growth. Despite differences in both, the shape of the response c urve of shoot growth to P and the extent of infection between Lotus sp ecies, they did not differ in their ability to utilize the P that had reacted with the soil for a period of time.