Soil parameters and plant responses associated with arbuscular mycorrhizasfrom contrasting grassland management regimes

Increased interest in sustainable low-input forms of agriculture has focuse d attention on the role of beneficial soil microsymbionts, such as arbuscul ar mycorrhizal fungi (AMF), in plant productivity and health. Root colonisa tion by AMF and AMF spore density was significantly lower in grassland soil s with a history of high-input, conventional management than in soils with a low-input or organic management. Spores of AMF isolated from contrasting management regimes, taken from a total of 24 sites at 13 farms, were used i n a series of inoculation trials involving three host plants (Allium amelop rasum L., Trifolium repens L. and Lolium perenne L.). The mean yield respon se (measured as shoot dry weight) was significantly greater when host plant s were inoculated with spores taken from farms with organic rather than hig h-input management for both Allium and Trifolium hosts. Very low levels of root infection in Lolium hosts excluded these plants from further analysis. Not all organic farms had highly effective AMF associations however, and s ome highly effective AMF isolates were found in high-input systems. (C) 199 9 Elsevier Science B.V. All rights reserved.