Conventional and low-input Zea mays L./Glycine max (L.) Merr./Triticum aestivum L. rotations were established in 1988 with tillage treatments ranging from no-till to moldboard plowing. Sampling for vesicular-arbuscular mycorrhizal (VAM) fungi was conducted in October, 1992, after a soybean crop, and in May, 1993 during winter wheat reproductive development. Soil cores were removed to a depth of 27 cm and divided into 9 cm sections. Spores were isolated from this soil, characterized, and quantified. Field soil was used for an infectivity assay in the greenhouse using Paspalum notatum Flugge as host plant. Farming system significantly affected populations of VAM fungi. Soil in low-input agriculture had greater populations of Glomus occultum type group spores and other Glomus spp., whereas the conventionally farmed soil had greater populations of Glomus etunicatum type group spores. Tillage regime affected populations. The G. occultum group was more numerous under no-till, while the Glomus spp. and G. etunicatum groups were more numerous in soils under cultivation. The G. occultum group also was more numerous in the deepest soil section, whereas other groups were more numerous in the top and middle sections. Soil from low input plots produced greater colonization in the greenhouse assay than soil from conventionally farmed plots.
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