Field trials assessing the effect of inoculating agricultural soils with endomycorrhizal fungi

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Abstract
Summary: Four field experiments were established to gauge the effect of inoculating white clover with selected strains of vesicular-arbuscular mycorrhizal (VAM) fungi. The four sites chosen ranged in fertility from undeveloped, phosphorus-impoverished tussock grassland to high fertility alluvial flats. As far as practicable conventional agronomic practices were followed prior to and during sowing. The soils were otherwise untreated and contained the normal complement of indigenous VAM fungi. Infested soil pellets were used to introduce the fungi into the soils as this was considered more appropriate to pastoral farming than for example transplanting infected seedlings.Initially the introduced fungi tended to have little or no effect on dry-matter yields but by the end of the first season there were significant responses to Gigaspora margarita, Glomus mosseae, Glomus macrocarpum or a mixed inoculum of Glomus pallidum and Glomus tenue. In the second season, dry-matter yields were increased on the two tussock grassland sites by up to 760 kg D.M./ha (ca. 30%), 825 kg D.M./ha on the moderately fertile site (14%) and 640 kg D.M./ha (5%) on the high fertility site. The growth responses tended to decrease with time probably owing to the spread of fungi from the inoculated to the control plots though growth responses were still present at the end of the 3rd year on two of the sites. Within each experiment the application of up to 50 kg P/ha per year did not reduce the size of the responses to inoculation. This and herbage chemical analyses suggested that a more efficient use of phosphatic fertilizers may have been only part of the reason for the responses to inoculation.