Monday, November 5, 2007
90-11

Non-Destructive Carbon Measurement in Soil over Large Fields.

Lucian Wielopolski1, David J. Brown2, Cesar R. Izaurralde3, Sudeep Mitra1, Rex Omonode4, and H. Allen Torbert5. (1) Bldg 490-D, Brookhaven National Laboratory, Brookhaven National Laboratory, Environmental Sciences Department, Upton, NY 11973, (2) Washington State University, Department of Crop and Soil Sciences, PO Box 646420, Pullman, WA 99164, (3) Joint Global Change Research Institute, 8400 Baltimore Avenue, Suite 201, Collage Park, MD 20740, (4) AgCert Services (USA) Inc., 1901 S Harbor City Blvd., Suite 400, Melbourne, FL 32901,, (5) USDA-ARS, National Soil Dynamics Lab., 411 South Donahue Drive, Auburn, AL 36832

Carbon in soil plays a critical role in soil quality and productivity. Changes in soil management practices, as for example switching from conventional till (CT) to no till (NT), precision agriculture, carbon sequestration, and soil carbon stocks required in modeling global warming necessitate extensive quantification of soil carbon burdens on local, regional and global levels. These emerging needs supersede today’s throughput capabilities of the dry combustion (DC) chemical method, which at present is the standard analytical procedure for belowground carbon determination. The DC method is labor intensive, time consuming, provides point information, and requires intensive post-analysis for field predictions. There are three new technologies that, with various degrees of success, overcome the conventional limitations of the DC method. Here we present results obtained with the Inelastic Neutron Scattering (INS) method a new modality that differs fundamentally from the other two in that; 1) It is truly non-destructive, it is mounted about 30 cm above the ground and no soil samples are taken. 2) It has multi-elemental capability with high elemental specificity. 3) It probes large volumes from hundreds of kilograms and up, and 4) it enables stationary and scanning capabilities providing a true mean value for the field carbon content. The last characteristic is possible because of the fast, 10-9 to 10-18 s, processes involved between neutron emission, penetration into the soil, interaction with soil elements stimulating gamma emissions, and detection of gamma rays.  It is shown that when fields are fairly homogeneous the scanned values for a field are fairly close to the mean value of the static measurements obtained at various speeds. However, cases are reported in which these values disagree posing the question which one is correct. Is it possible that we missed some low areas during our static sampling?