Soil Profile Investigations of Carbon Content and Other Properties Using a Sensor Probe.

In the discussions relating to the potential market for sequestered soil carbon, one of the key issues is measurement. Soil carbon can vary significantly within fields and within soil profiles. Detecting low rates of carbon change against a high background of variability is challenging, since the levels of soil carbon within a field often can vary more than the expected rate of change over a contract period.  Optical measurements, especially in the near infrared region, have been shown to correlate well with soil carbon levels.  Investigations of the soil profile were conducted using a soil sensor probe containing the following sensors: visible and near-infrared (VIS-NIR) spectroscopy from 400 to 2200 nm, soil electrical conductivity (EC), and insertion force. The measurements were calibrated to laboratory-measured soil carbon, nitrogen, moisture, bulk-density, and other properties, and cross-validated.