THE INOCULATION OF WHITE CLOVER WITH MYCORRHIZAL FUNGI IN UNSTERILE HILL SOILS

SUMMARYThe response of two cultivars of white clover (Aberystwyth S184 and New Zealand Grasslands Huia), grown under laboratory and field conditions, to inoculation with two endophytes (Glomus mosseae L1 and Glomus etunicatus) was investigated in two hill soils with various amounts of added phosphate.In the experiment with the deep peat soil in the laboratory, inoculation with either endophyte increased infection from 2% to up to 70%, the increase being less the higher the amount of added P. Shoot growth of white clover was significantly increased (P≤ 0.05) by inoculation at the 0 and 20 kg P ha−1 level and decreased at the highest level of added P (200 kg P ha−1). Both endophytes produced similar effects. With the brown earth soil, total infection of roots with indigenous endophytes ranged from 30 to 50 % and this was significantly (P≤ 0.05) increased by inoculation only at 40 kg P ha−1. However, the introduced coarse endophytes had replaced between a quarter and a half of the predominantly fine indigenous endophyte at each level of added P. This change of endophyte was without significant effect on dry wt of shoots and roots although there was a general trend for inoculation, and with Glomus etunicatus more than with Glomus mosseae LI, to increase shoot and root dry wt. Inoculation also tended to increase the P content of shoots and roots but this was statistically significant only at 40 kg P ha−1.In the field experiment with the deep peat soil, inoculation with Giomus mosseae L1 doubled the amount of infected root from 18 to 42% but there was no effect on shoot growth or the concentration of P. With the brown earth soil, although the amount of infection was not increased, the introduced coarse endophytes had become established in the roots but no effect on shoot growth was observed in the year of sowing. However, in the first harvest year, in the presence of 40 kg P ha−1, clover inoculated with Glomus etunicatus produced double the amount of dry shoot per hectare produced by uninoculated plants and 75% greater than that produced with Glomus mosseae L1.These observations encourage the view that inoculation with mycorrhizal fungi of white clover for improved hill pastures might have a practical role if the responses could be made more predictable. It is concluded that further work is justified to understand the ecology of mycorrhizal fungi in hill pastures and how the symbiosis functions, to select suitable endophytes and to develop methods of inoculation appropriate for use in routine field practice.