The nutrient availability of composts has to be known for their safe use in crop production. A field study was carried out to assess the effect of a spring application of composts and inorganic fertilizers on spring wheat (Triticum aestivum L. 'Messier') growth and N uptake in eastern Québec (Canada). The experiment was conducted in 1994 and 1995 on two different soils: a Kamouraska clay (Orthic Humic Gleysol) and a Saint-André sandy loam (Fragic Humo-Ferric Podzol). Four composts were applied at rates of 0, 90, 180 and 360 kg total N ha−1. Inorganic fertilizers were applied at rates of 0, 50, 100 and 200% of wheat N, P or K requirements. Treatments in which inorganic fertilizers (IN) were added to composts were also included. Grain yield was increased by N rates whereas composts alone at 90 kg total N ha–1 resulted in lower yields than the control in the first year on the sandy loam. Commercial composts resulted in higher yields than dairy manure composts. Wheat showed no significant response to P and K fertilizers on either soil. Compost rates had no effect on grain N content but commercial composts increased straw N by 36 to 63%. Addition of IN to composts increased grain yield by 0.1 to 1.5 Mg ha−1 and N uptake by 4 to 55 kg N ha−1, depending on soil and weather conditions. Apparent recovery efficiency of added N for composts was −14 to 15% whereas it ranged from 24 to 56% for IN. In spring wheat production, composts should be considered more as organic matter amendments because of their limited N efficiency. Key words: Composted dairy manure, shrimp wastes, peat moss, apparent N recovery

The addition of compost may mitigate soil degradation and contribute to the soil nutrient supply in spring cereal monoculture. A field study was carried out in eastern Quebec, Canada, to assess the impact of composts from four sources and ammonium nitrate (AN) applied at different rates in spring on soil moisture and inorganic N in spring wheat production (Triticum aestivum L. 'Messier'). The experiment was conducted in 1994 and 1995 on two different soils: a Kamouraska clay (Orthic Humic Gleysol) and a Saint-André sandy loam (Fragic Humo-Ferric Podzol). Composts were applied at rates of 0, 90, 180 and 360 kg total N ha−1. Ammonium nitrate was applied at 0, 45, 90 and 180 kg N ha–1. Treatments in which AN was added to composts were also included. Thirty days after N application, profile soil inorganic N increased linearly with rates of commercial composts and AN but not with farm composts, whereas at harvest, residual soil N was not affected by composts but was increased by AN. The relative contribution of the compost organic fraction was negligible in the first year of application. Soil inorganic N at 30 d after fertilizer applications was significantly related to plant N uptake at harvest (r2 = 0.74), suggesting useful index of compost N availability. Large amounts of compost raised soil moisture content of the sandy loam by 3–5%, particularly under dry climatic conditions. Commercial composts have a small N fertilizer value, whereas composted dairy manure should be considered preferable as a soil amendment. Key words: Dairy manure compost, shrimp wastes, peat moss, wheat

Manure management and composting methods may greatly affect compost characteristics. An experiment was conducted to characterize 23 on-farm and 6 industrial composts in Québec (Canada). Cluster analysis identified two major groups characterized by their chemical composition, source materials, management intensity and degree of decomposition. Electrical conductivity, total N and K, water-soluble NH4+, PO4, K, Al and organic C, and a cress test were the best chemical and biological parameters for grouping composts. These groups were strongly associated with bedding rate, turning frequency, composting duration, profile windrow appearance, material aggregation and odor. When restricted to dairy manure composts, no clear relationship could be established by cluster analysis between material grouping and their farm management. Statistical analysis on single chemical parameters of dairy manure composts, however, identified five farm management factors: type and amount of bedding, system of manure handling and storage, compost windrow turning, composting length and milk production intensity. These factors affected one or several major parameters: pH, dry matter, electrical conductivity, total and water-soluble C, N, P and K, and humic components characteristics. This study demonstrated the importance of leaching losses in the on-farm composting operations in humid cold regions and the need for more environmentally sustainable composting methods. Key words: Farm manure management, composting, chemical composition