Impact of Agronomic Management On Soil Organic Carbon Dynamics in Particle Size Fractions in a Brookston Clay Loam Soil.

In order to better understand the impact of management on contents and dynamics of soil organic carbon (SOC) in particle size fractions of fine-textured soil, we studied the size-separated SOC pools at the plowing layer in a Brookston clay loam soil (Orthic Humic Gleysol), under various management practices. In the plowing layer of long-term fertilization and rotation study, SOC contents were 29.8% greater in rotation (corn-oats-alfalfa-alfalfa) than in monoculture corn soils and were 22.5% greater in fertilization than non-fertilization treatments. Ten years after a single compost application (100 Mg/ha), SOC contents in the top 30 cm showed no difference between the food waste compost relative to the control; however, SOC contents were 13% and 15% greater for leaf compost and pig manure wheat straw, respectively, relative to the control. Two decades no-tillage practices did not lead to difference in SOC stock relative to conventional tillage; however, it resulted in significant stratification of SOC at the plowing layer, with 25% more SOC in the surface 0-5 cm and 15% less in the subsurface (5-20 cm) for no-tillage than mouldboard plough soils.  We observed that management induced changes in SOC mainly occur in top 10 cm soil and about 80–90% of the total SOC was accumulated in the clay+silt fraction (0.053 mm). We also discovered that management induced changes in SOC show different pattern in particle fractions, an exponential increase of SOC in sand fraction (>0.53 mm), a logarithmic change in clay fraction (<0.002 mm), and a linear increase in silt fraction (<0.053 mm and >0.002 mm) with increasing in total SOC. Changes in SOC stock and SOC contents in the fraction suggested that agronomic management not only alter SOC quantity but also SOC quality, and further SOC increasing would mainly occur in the sand and silt fractions for this soil.