THE INFLUENCE OF VESICULAR ARBUSCULAR MYCORRHIZAE (VAM) ON SUGARCANE GROWTH IN THE FIELD

THE role of a species of vesicular arbuscular mycorrhiza (VAM), Glomus clarum, in yield decline of sugarcane was examined in a small plot field experiment in the Tully district of northern Queensland. A source of phosphorus was used to create a range of soil P levels at a site naturally low in P. The whole site was fumigated with methyl bromide before planting to remove all endemic VAM species. A pure culture of Glomus clarum was cultivated in pots in a glasshouse and used to inoculate some of the pre-germinated sugarcane plantlets; others remained VAM-free. These pre-germinated plants were then transplanted to the field site, resulting in both VAM and non-VAM plants growing in a similar range of P-amended soils. Sugarcane was grown at the site to maturity (257 days after planting) and the weight and number of millable cane stalks recorded. Sugarcane was able to achieve maximum yield with lower levels of P in the soil when VAM were present, suggesting VAM does indeed aid P uptake in low P soils. High soil P levels appeared to decrease VAM colonisation of sugarcane roots. Importantly, VAM did not contribute to a depression in growth of sugarcane at high soil P levels.