Underseeded clover as a nitrogen source for spring wheat on a Gleysol

Although there is a potential to substantially reduce N fertiliser inputs b y cropping spring cereals with an interseeded legume, the agronomic value a nd the nitrate catch-crop effect associated with this practice are not docu mented under the conditions of eastern Canada. This 3-yr study estimated N credits and non-N nutritional effects for interseeded clover (Trifolium pra tense L. 'Arlington') in spring wheat production (Triticum aestivum L. 'Alg ot') and assessed fall and spring nitrate (NO3-) in soil. The soil is a St. Urbain clay (Orthic Gleysol) located in the St. Lawrence lowlands. Ammoniu m nitrate (NH4NO3) was applied at 0, 40, 80, 120 and 160 kg N ha(-1) with o r without red clover as a companion crop. Clover was incorporated as a gree n manure crop in mid-November Clover significantly (P less than or equal to 0.05) influenced wheat yield response to N fertilisation for 2 of the 3 yr . Clover did not reduce wheat grain yield through competition between the t wo plant species. Higher wheat yields with clover were attributed to N supp lied by clover through mineralisation of residues incorporated in the soil the previous fall. Nitrogen fertiliser replacement value of clover was appr oximately 80 kg N ha(-1) for 1994 and 1995. Clover occasionally increased N O3--N measured in the soil profile in late fall and in spring. Interseeded red clover may provide most of the N needs of a companion spring wheat crop in fine-textured gleysolic soils, but is an inefficient N catch-crop.