Assessment of Sampling Methods for Carbon Credit Monitoring.

Oklahoma legislature passed Oklahoma carbon sequestration enhancement act in 2001, and authorized Oklahoma Conservation Commission (OCC) to verify and certify carbon offsets, and a pilot project was initiated in 2008. The purpose of this research is to create a database, to evaluate the performance of the soil sampling probes which are alternatives to the tractor operated Hydraulic Probe having cutting edge diameter 3.98cm and can be used by Oklahoma conservation commission personnel to monitor carbon credits raised by the producers under no-till management in their fields, and to determine the minimum number of samples required to determine the expected rate of carbon sequestration in the soils of the region in a year per unit area. The database will provide a baseline (initial/ starting concentration of soil organic carbon) for the future use to determine amount of carbon sequestered in the fields under no-till and grasslands. The alternatives are 2.26cm cutting edge diameter Push Probe and 4.8cm cutting edge diameter Slide Hammer probe. The samples were taken up to 30cm depth and then divided into three segments 0-10, 10-20, 20-30cm. Soil moisture was measured gravimetrically using a sub sample and was used to determine bulk density, and carbon concentration was measured from a sub-sample through dry combustion using Leco analyzer. Preliminary results show that the bulk density measurements by push probe are significantly higher at the surface than the Slide hammer and the Hydraulic probe, and have significantly higher variation throughout the depth. Bulk density measurements of slide hammer and hydraulic probe are not significantly different. So far carbon concentration of the surface 0-10 and 10-20cm layers has been analyzed and the push probe gives significantly higher carbon mass at the surface layer due to elevated bulk density. Minimum number of soil samples will be determined to measure the expected rate of 0.28Mg/ha/yr in Oklahoma, determined by Chicago Climate Exchange program.