SOIL-NITROGEN AND MOISTURE AS INFLUENCED BY COMPOSTS AND INORGANIC FERTILIZER RATE

The addition of compost may mitigate soil degradation and contribute t o the soil nutrient supply in spring cereal monoculture. A field study was carried out in eastern Quebec, Canada, to assess the impact of co mposts from four sources and ammonium nitrate (AN) applied at differen t rates in spring on soil moisture and inorganic N in spring wheat pro duction (Triticum aestivum L. 'Messier'). The experiment was conducted in 1994 and 1995 on two different soils: a Kamouraska clay (Orthic Hu mic Gleysol) and a Saint-Andre 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). Trea tments in which AN was added to composts were also included. Thirty da ys after N application, profile soil inorganic N increased linearly wi th rates of commercial composts and AN but not with farm composts, whe reas at harvest, residual soil N was not affected by composts but was increased by AN. The relative contribution of the compost organic frac tion was negligible in the first year of application. Soil inorganic N at 30 d after fertilizer applications was significantly related to pl ant N uptake at harvest (r(2) = 0.74), suggesting useful index of comp ost N availability. Large amounts of compost raised soil moisture cont ent of the sandy loam by 3-5%, particularly under dry climatic conditi ons. Commercial composts have a small N fertilizer value, whereas comp osted dairy manure should be considered preferable as a soil amendment .