Rotation and tillage effects on soil organic carbon sequestration in a typic Hapludalf in Southern Ontario

Increased use of conservation tillage is being considered as a way to seque ster atmospheric C in the soil, However, little information exists on the e ffect of rotation and its interaction with tillage on soil organic carbon ( SOC), A research trial with combinations of rotations and tillage treatment s was sampled 20 years after its establishment to assess the effects on SOC sequestration in a typic Hapludalf in southern Ontario, Canada, The croppi ng treatments included continuous corn (zea mays L,), six rotations compris ed of 2 years of corn following 2 years of another crop or crop sequence, a nd continuous alfalfa (Medicago sativa L,), Each rotation was split into ei ther fall moldboard plow (MP) or fall chisel plow (CP) treatments, Continuo us alfalfa was plowed and replanted every 4 years. Soil samples were taken incrementally to a depth of 40 cm and SOC and bulk density determined, The average SOC concentration (0-40cm) was greatest in continuous alfalfa (18.0 g C kg(-1)). The treatments of soybean (Glycine max L. Merr.) + winter whe at (Triticum aestivum L.) or barley + barley (Trifolium pratense L,) (inter seeded with red clover) followed by 2 years of corn had higher SOC concentr ations (17.2-17.3 g C kg(-1)) than continuous corn and the treatments of 2 years of corn following 2 years of alfalfa or soybean (16.4-16.5 g C kg(-1) ). The rotation of 2 years of barley followed by 2 years of corn had the lo west SOC concentrations (15.2 g C kg(-1)). On an equivalent mass basis, the rotations of soybean + winter wheat or barley + barley (underseeded with r ed clover) followed by 2 years of corn, had 2-9 Mg ha(-1) more C than the o ther corn-based rotations. Including red clover in the winter wheat seemed to accelerate the rate of C mineralization compared to winter wheat without red clover; whereas interseeding red clover with barley increased SOC cont ents compared to excluding red clover in the barley rotation. More SOC was found in the top 10 cm and less in the 10-20 cm depth of the CP than in the MP soils. However, the CP did not increase the SOC content (0-20 cm) above that of MP indicating that this form of reduced tillage did not increase C sequestration in any of the rotations on this soil, (C) 2001 Elsevier Scie nce B.V. All rights reserved.