Soil Moisture and Bulk Density Effects on Signal Intensity and Carbon Measurement Using the Inelastic Neutron Scattering Technology.

Accurate measurement of soil carbon (C) is important for soil nutrient management decisions and assessment of management effects on C sequestration.  However, rapid but accurate determination of soil C stock at relatively low cost and in real time, is considered a major component needed for successful verification of sequestered C and profitable trading of C credits the emerging global carbon market.  Current procedures that are commonly used to measure soil C, though considered analytically accurate, are destructive, labor- and cost-intensive, and C values obtained from very small sample volumes are projected to represent entire fields regardless of inherent spatial variability.

 The Inelastic Neutron Scattering (INS) technique is one of many emerging technologies being developed for soil C measurement with potentials to significantly reduce some of the problems associated with current soil C measurement techniques.  However, unlike most of the other emerging techniques the INS system is completely non-destructive, in-situ, and field deployable; it can be operated both in static and in continuous scanning modes.  In the static mode, the INS can assess soil C for individual measurement positions, and can also integrate across large areas to give a mean value for an entire field when operated in the dynamic scanning mode.

 Preliminary results from laboratory and field experiments indicate that the INS can be an accurate and rapid procedure to assess soil C.  The results further suggest that INS C measurement can be affected by soil moisture conditions and soil bulk density.  However, the direct relationship between soil moisture and bulk density to INS signal strength and soil C measurement are poorly understood.  Our objectives in this study were to further characterize INS system and determine the interactive effects of soil moisture and bulk density on INS signal intensity and total C counts under laboratory conditions.