Coal fly ash as a soil conditioner for field crops in southern Ontario

Sixty-eight percent of the 957 000 Mg of fly ash (FA) from coal-fired gener ating stations in Ontario was landfilled in 1998. Current restrictions by g overnment regulators prevent its use for agricultural purposes. Greenhouse and field experiments were therefore initiated to assess the effects of FA On plant growth. The objective of the greenhouse study was to evaluate vari ous rates of FA (0-80 Mg ha(-1) equivalent) on soil pH, soil and plant nutr ient le, eb, and plant growth using representative acidic clay and sandy so ils from Southern Ontario. After 90 d of soil incubation, the highest rates of FA. increased sail pH, but had no significant effect on hot-water extra ctable B. Dry-weights of plants grown in the same soil types were unaffecte d by FA rates. In a 3-yr field study, Fit was applied to acidic clay and sa ndy loam soils at rates ranging from 0 to 50 Mg ha(-1) (drg wt. basis). Lim e control treatments were also included. In Year 1, corn (Zen mays L) plant emergence, grain yield, percent moisture, and harvest index were not signi ficantly influenced by FA applications. However, soybean [Glycine mar (L)Me rr.] yields treated,with 50 Mg ha(-1) FA increased by as much as 35 and 31% in comparison with untreated and lime control treatments, respectively. Se lenium and boron, while presently the rate-limiting elements for maximum pe rmissible loading rates of FA for soil amendments in the province, did not accumulate in plants in quantities that would be of concern for plant healt h or animal and human consumption.