Effect of rate of application of superphosphate on populations of vesicular arbuscular endophytes

Abstract

The effect of altering the rate of superphosphate application on the population of vesicular arbuscular endophytes in a pasture soil was studied during 1976. Between 1950 and 1965 the pasture near Bakers Hill, Western Australia, had received an average of 150 kg superphosphate ha-1 year-1. For the ten years prior to 1976, five rates of superphosphate were applied to plots within the pasture. Varying the rate of superphosphate affected the number of VA endophyte spores. Adding 56 kg superphosphate ha-1 year-1 increased spore numbers by 40 per cent compared with the unfertilized plots. Spore numbers in plots receiving higher rates of superphosphate than 56 kg ha-1 were similar to those in unfertilized plots. The relative abundance of spores of the four endophyte species found (Glomus monosporus, Acaulospora laevis, Gigaspora sp. and 'White reticulate') was unaffected by superphosphate applications. In a glasshouse experiment vesicular arbuscular endophytes from plots that had received the highest rate of superphosphate (224 kg ha-1 year-1) did not differ from those which had received no superphosphate in their ability to infect and increase the phosphorus uptake and growth of clover. It was concluded that altering the rate of superphosphate application on an old, adequately fertilized pasture does not affect the infectivity or effectiveness of the vesicular arbuscular endophyte population.