VA Mycorrhizal Colonization and Spore Populations in an Abandoned Agricultural Field after Five Years of Sludge Application

Abstract

The effects of five years of sewage sludge application on vesicular-arbuscular mycorrhizal (VAM) fungi were studied. The commercially produced sludge, Milorganite, has been applied to plots monthly during growing seasons since 1978. Urea-phosphate fertilizer was applied to other plots, with still others containing no nutrient amendment. The VAM spore counts, along with root colonization percentages of Cirsium arvense and Barbarea vulgarus grown in field plots and bioassay plants (corn and geranium) grown in a glasshouse, all showed little or no difference between the sludge-amended and unamended plots. Depressed VAM spore populations and colonization occurred in urea-phosphate fertilizer. Non-VAM fungal populations were higher in the sludge-amended plots than in the other treatments. The VAM colonization levels of the test plants were not hindered by the toxic metals in the sludge-amended soils after five years of Milorganite addition.