Landscape Differences in Soil Aggregation Affects Carbon Saturation Deficit in An Iowa Agroecosystem.

Perennial bioenergy crops grown on agricultural lands have the potential to sequester C through increased SOC levels relative to annual crop production from increased C inputs and decreased C losses.  Recent work suggests soils have a maximum SOC storage level based on physiochemical properties, with the rate of C gain dependent on the difference in C input and output rates and the soil C satura­tion deficit, a measure of how far a soil is from it’s estimated saturation level. The objective of this study was to determine the C saturation deficit across landscape positions in an Iowa agroecosystem to determine the potential for SOC gains due to increased C inputs from conversion to perennial vegetation following many decades of annual rowcrop production.  C saturation deficit in soils was estimated on five landscape positions by determining the protective capacity of soils based on soil texture and quantification of the total organic C content.  Soil samples were fractionated according to aggregate size, and the C pools within aggregates determined.  Results show that landscape positions differ in the C saturation deficit, and the amount of C protected within aggregate fractions varies across positions.  These results suggest that 1) landscape level variation in C saturation deficits is a result of differences in both silt and clay contents and biologically mediated mechanisms for C protection, and 2) landscape position may be a major factor in determining the potential for soil C sequestration due to conversion of annual rowcrop production to perennial vegetation.