Impact of tillage practices on organic carbon and nitrogen storage in cool, humid soils of eastern Canada

Soil organic matter storage capacity in agroecosystems varies with soil type, climate and agricultural management practices. The effects of different tillage systems on organic C and N storage were determined for a range of soils of eastern Canada mainly under continuous corn and small grain cereal production. Soil profiles from eight sites on which comparative tillage experiments had been performed for up to 11 years 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 determined for each sampling depth. Bulk density measurements showed that the total soil mass in the soil profiles was not influenced by the tillage systems. No significant differences were found between tillage treatments in the total organic C and N storage down to 60 cm depth; the soil profiles under no-till (NT) and chisel plowing (CP) generally did not contain more C and N than those under conventional moldboard plowing (MP). However, the depth distribution of soil C and N varied with 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 trend 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 soil organic matter in the entire soil profile at least in a 5-10 year period. Placement of the residues would be a major factor influencing the C and N distribution at specific depths.