IMPACT OF TILLAGE PRACTICES ON ORGANIC-CARBON AND NITROGEN STORAGE INCOOL, HUMID SOILS OF EASTERN CANADA

Soil organic matter storage capacity in agroecosystems varies with soi l type, climate and agricultural management practices. The effects of different tillage systems on organic C and N storage were determined f or a range of soils of eastern Canada mainly under continuous corn and small grain cereal production. Soil profiles from eight sites on whic h comparative tillage experiments had been performed for up to 11 year s were sampled to a 60 cm depth in four increments (0-10, 10-20, 20-40 and 40-60 cm). Organic C and N contents and dry bulk density were det ermined for each sampling depth. Bulk density measurements showed that the total soil mass in the soil profiles was not influenced by the ti llage systems. No significant differences were found between tillage t reatments in the total organic C and N storage down to 60 cm depth; th e soil profiles under no-till (NT) and chisel plowing (CP) generally d id not contain more C and N than those under conventional moldboard pl owing (MP). However, the depth distribution of soil C and N varied wit h tillage. In the surface 0-10 cm, C and N contents were higher under NT than under MP, whereas at deeper levels (20-40 cm) the reverse tren d was observed. It is concluded that under eastern Canadian conditions , where crop production and residue inputs are not affected by tillage , reduced tillage systems would not, result in the storage of more soi l organic matter in the entire soil profile at least in a 5-10 year pe riod. Placement of the residues would be a major factor influencing th e C and N distribution at specific depths.