Soil C Assessment and Mapping in the Central Sands of Wisconsin.

There is a need for rapid and accurate assessments of soil organic carbon. The central sands of Wisconsin are intensively cultivated with high levels of inorganic fertilizers and irrigation. The soils are sandy (>85% sand) and mostly classified as Psamments. We have collected 300 pedon and topsoil samples using random, grid and Latin hypercube  sampling designs to assess soil C contents and stocks.  A range of maps were available including fine resolution EMI (dualem) and 1.5 m  LiDAR images.  Topsoil thickness varied 17 to 72 cm (mean 28 cm) and C contents ranged from 0.6 to 1.1%. Maximum stocks were over 60 Mg/ha after 30 years of intensive cultivation and appear higher than in similar soils under grassland or pine forest. The implications of the sampling design in relation to the mapping of SOC in these sandy soils will be discussed.