Tropical Grasslands (1992) Volume 26, 120129
Inoculation of Vigna parkeri with mycorrhizal fungi in an acid Florida spodosol
J.J. O'DONNELL1, D.M. SYLVIA1, W.D. PITMAN2 and J.E. RECHCIGL2
1Department of Soil and Water Science, University of Florida, Gainesville, USA.
Vigna parkeri is a promising forage legume, but problems have been encountered with stand establishment and low tolerance to water stress. Vesicular-arbuscular mycorrhizal (VAM) fungi have been reported to ameliorate these problems. Our objectives were to (i) evaluate the effect of VAM inoculation on establishment and growth of V. parkeri in a spodosol under amended soil conditions, (ii) assess the effectiveness of introduced versus indigenous VAM fungi, (iii) compare VAM colonisation of V. parkeri grown alone with that of V. parkeri grown in combination with Paspalum notatum, and (iv) assess the effect of soil type and VAM isolate on colonisation of V. parkeri. Field and greenhouse studies were conducted in Pomona fine sand (sandy, siliceous, hyperthermic, Ultic Haplaquod) with low initial P status (Mehlich I-extractable P = 5 mg/kg) that was limed and amended with various rates of P. An attempt was made to equalise VAM inoculum densities in these studies, but the time required to conduct most-probable-number assays was sufficient for significant changes in propagule density to occur. The VAM fungi generally failed to adequately colonise V. parkeri in limed Pomona fine sand and shoot-P contents were found to be above the critical level for maximum biomass production in all treatments. Nonetheless, some differences were found in plant cover suggesting that selected stains of VAM fungi may be important in establishment. In the study where soil type was evaluated, colonisation was obtained even at shoot-P concentrations > 5 g/kg, indicating that shoot-P concentration was not the only factor inhibiting colonisation in the Pomona soil. We suggest that pH may have also limited colonisation in these studies and that future work with this plant should include VAM isolates tolerant of acid soil environments.