Effet du labour printanier et des cultures intercalaires de trèfle rouge sur le rendement du maïs-grain

Because corn (Zea mays L.) production may cause soil degradation, cultural systems to minimize this degradation are required. Intercropping of corn with legumes may reduce such degradation, but effects on corn yields must be evaluated. The objective of the study was to determine the effect of a red clover (Trifolium pratense L.) intercrop in conjunction with spring ploughing on the yield of grain corn on two soil types: a Chicot sandy loam and a Ste-Rosalie clay loam. A split-plot experimental design established on each soil consisted of three cultural practices as the main plots and three rates of N fertilizer as the split plots. Corn yields decreased significantly from 1987 to 1989 in conjunction with an increase in the biomass produced by the intercropped red clover and the weeds that it harboured. However, spring ploughing of this biomass rather than fall incorporation had no negative effects on the yield of corn. Although in the case of fall ploughing the presence of red clover did allow for the accumulation of additional inorganic nitrogen in the soil in the spring, the competitiveness of the red clover and especially of the weeds caused a decrease in the yield of grain corn. The use of intercropped red clover for soil conservation in Quebec may thus be limited if a tight control over weeds is not maintained. Key words: Intercropping, Zea mays, Trifolium pratense, nitrogen, spring ploughing