Vesicular-arbuscular mycorrhiza infection in cut grassland following long-term slurry application

Abstract

Herbage root samples from a long-term field experiment in which pig and cow slurries had been applied to cut grassland for 19 yr were examined for vesicular-arbuscular (VA) mycorrhiza.There were fertilized and unfertilized controls and three application rates (50,100 and 200 m 3 ha −1 yr −1) of both types of slurry, with six replicate plots in randomized blocks.Soil samples were analysed for pH (in water), “total” Cu and Zn, EDTA-extractable Cu and Zn and NaHC0 3-extractable P.The proportions of Lolium perenne, Agrostis stolonifera and Poa spp in the herbage dry matter at the first cut of 1989 were also determined. Despite contrasting long-term effects of the two types of slurry on soil pH, increasing application rate of both pig and cow slurries produced a marked decrease in overall mycorrhizal infection of plant roots in the sward with a corresponding increase in infection by the fine endophyte, Glomus tenue.Calculated correlation coefficients showed that mycorrhizal infection was related to soil extraetable P,Cu, Zn and pH and also to differences in sward botanical composition,especially the proportion of L. perenne. Furthermore, stepwise multiple regression analysis identified soil chemical properties, especially total Zn and pH, as the more important explanatory variables in preference to botanical composition.