Total and Active Soil Carbon Fractions in Row Crop Systems Under Organic and Conventional Management: Assessment for Adequate Sampling.

Agricultural soils have the potential to be significant sinks for sequestering atmospheric CO₂. Schemes for encouraging sequestration, such as farmer payments, need accurate, precise, and economical methods to monitor actual sequestration.  Protocols to assess C sequestration rates in agronomic fields are not yet well developed. In this study we compare the ability of organic, conventional tilled, and conventional no-tilled cropping systems to sequester soil organic C. In addition, we use our data to conduct a power analysis that will inform the development of protocols for monitoring sequestration in agricultural soils. In 2011, we sampled 24 row crop production fields from across Illinois.  Fields were grouped to contain a common sampled soil type with groups including organic, conventional tilled, and conventional no-tilled fields in both corn and soybean phases of their rotations. Twenty-four soil cores were collected in each field and split into three different sampling depths. Each sample-by-depth was analyzed separately for total organic C, particulate organic matter-C, potentially mineralizable N, and enzymatic activity. Our discussion will expand on issues of sampling intensity and expected minimum detectable differences.