Secondarily-treated sewage effluent was sprayed onto a 50-year old hardwood stand in Harbor Springs, Michigan. Effluent was applied at rates of 0.0, 3.8, and 7.6 cm per week onto thinned and unthinned experimental plots during the growing seasons of 1978 and 1979. Each spray level and density combination was replicated 4 times. Mycorrhizal development of Acer sp. roots was examined during 6 months over a two year period in these irrigation and control plots. Soil pH, soil organic carbon, and soil water content were also measured. Mycorrhizal development was significantly greater on the sprayed than on the unsprayed plots (p<0.05), but it did not vary significantly (p<0.05) with season or thinning. The soil pH was increased from an average of 3.7 to 5.1 with 3.8 cm/wk irrigation and to 6.2 with 7.6 cm/wk irrigation. Percent organic carbon was significantly (p<0.05) greater in 1979 than in 1978 in the control plots. In the 3.8 cm/wk irrigation plots organic carbon in the A1 horizon was significantly (p<0.05) less than in either the 7.6 cm/wk irrigation plots or in the control plots.