Soil organic matter and carbon fractions within aggregates and in soil profile in double- and cover cropping systems

Understanding the distribution of soil organic matter, carbon (C) and nitrogen (N) within aggregates and across soil profiles is critical for improving soil fertility, nutrient cycling, and long-term sustainability in agricultural systems. This study evaluates the short-term effects of various crop rotations and cover cropping systems on soil organic matter (SOM), aggregate-associated C and N fractions, and their vertical distribution in the soil profile. A three-year field experiment was conducted at the Agronomy Research Farm, Southern Illinois University Carbondale, with treatments including: (1) corn (Zea mays L.)-soybean (Glycine max L.) rotation without cover crop (CNSN), (2) corn-soybean rotation with rye cover crop (CRSR), (3) corn-wheat (Triticum aestivum L.)-soybean rotation without cover crop, and (4) corn-wheat-soybean rotation with a cereal rye (Secale cereale L.) cover crop (CWSR). Soil aggregates were collected from 0-5 and 5-15 cm depth and used for assessing aggregate size distribution, aggregate stability, SOM, soil C and N. Bulk density and soil C and N along with soil organic matter was measured from samples collected from 0-90 cm depth. CRSR and CWSN, significantly increased medium-sized aggregates (1-2 mm and 0.5-1 mm) as compared to the CNSN treatment. Including cereal rye into double cropping systems (CWSR) improved soil’s aggregate stability. Cropping systems, particularly those with winter wheat and cereal rye, increased soil organic matter in 2-4.75 mm aggregate fraction as compared the CNSN control. Soil organic matter concentration decreased with depth, with the highest values at 0-5 cm across all cropping systems. Soil bulk density by depths, soil C and N within aggregate and by depth will also be presented at the meeting. Our current findings indicate that utilizing CWSR could provide economic and soil benefits to growers in Illinois.