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

Addition of compost from various sources and of different maturity may affe ct the soil biochemical properties. A field study was conducted to evaluate the effect of different composts, spring-applied alone or in combination w ith ammonium nitrate (AN), on microbial biomass C (MBC) and alkaline phosph atase activity (APA) in two soils cropped with spring wheat (Triticum aesti vum L. 'Messier') in eastern Quebec, Canada. The experiment was conducted i n 1994 and 1995 at different sites on a Kamouraska clay (Orthic Humic Gleys ol) and a Saint-Andre sandy loam (Fragic Humo-Ferric Podzol). Treatments in cluded 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 A PA were measured 30 d after compost application and at wheat harvest. Addit ional sampling was made the following spring. Generally, larger MBC and APA values were found at wheat harvest in soils treated with composts alone th an with AN alone or unfertilized. These effects were related to soil C cont ent and climatic conditions. Compost type affected soil biochemical propert ies 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.