Soils can be a source or sink for the atmospheric greenhouse gases (GHGs) depending on the land use management, which needs to be understood properly for devising management strategies to mitigate climate change. It is hypothesized that the aggregate size distribution under different land use management practices and the C and N concentration in these aggregates may influence GHG (CO 2, N 2O and CH 4) emissions from soil. To test this hypothesis, a laboratory incubation study was conducted using soils from a 16-year old tillage experiment on corn ( Zea mays L.) and the adjoining forest on a Crosby silt loam soil (Haplic Luvisols) at the Waterman Agricultural and Natural Resource Laboratory of the Ohio State University (OSU), Columbus, Ohio. It was observed that in forest soil, cumulative CO 2 and N 2O emissions were significantly higher than those from the cultivated soil by 81.2 and 100%, respectively. However, there was no significant difference between conventional tillage (CT) and no till (NT) with respect to the cumulative CO 2 and N 2O emissions. Emissions were significantly higher from the large macro-aggregates than from other aggregate size fractions. There was net CH 4 uptake by the soil during the incubation period. The cumulative CO 2 and N 2O emissions and CH 4 uptake from different aggregate size fractions accounted for 59, 56, and 47% of the emissions/uptake of these gases from the bulk soil, respectively. The contributions of the large macro-aggregates towards the bulk soil CO 2 (39%) and N 2O (37.9%) emissions and CH 4 uptake (49.7%) were significantly higher than those of the micro-aggregates and mineral fraction. Total soil carbon, nitrogen, particulate carbon and nitrogen, and mineral associated carbon and nitrogen accounted for 87, 87 and 66% variation in the cumulative CO 2 and N 2O emissions and CH 4 uptake, respectively.
