Microbial biomass C and alkaline phosphatase activity in two compost amended soils

Addition of compost from various sources and of different maturity may affect the soil biochemical properties. A field study was conducted to evaluate the effect of different composts, spring-applied alone or in combination with ammonium nitrate (AN), on microbial biomass C (MBC) and alkaline phosphatase activity (APA) in two soils cropped with spring wheat (Triticum aestivum L. 'Messier') in eastern Quebec, Canada. The experiment was conducted in 1994 and 1995 at different sites on a Kamouraska clay (Orthic Humic Gleysol) and a Saint-André sandy loam (Fragic Humo-Ferric Podzol). Treatments included composts at 180 kg N ha−1, composts at 90 kg N ha−1 supplemented with AN, AN at 90 kg N ha−1, and an unfertilized control. Soil MBC and APA were measured 30 d after compost application and at wheat harvest. Additional sampling was made the following spring. Generally, larger MBC and APA values were found at wheat harvest in soils treated with composts alone than with AN alone or unfertilized. These effects were related to soil C content and climatic conditions. Compost type affected soil biochemical properties which could be attributed to the total C supply and material maturation state. Compost addition constitutes an efficient short-term way to promote soil microbial biomass and enzyme activity in cold climates. Key words: Compost, fertilizer, microbial biomass, soil enzyme, wheat