Investigation of Uncertainty in Organic Carbon Stock Estimates on a Field Scale

The uncertainty sources in the assessment of organic carbon stocks were studied in a layer of 0-30 cm within the sampling site (100 x 100 m) set on soddy-podzolic cultivated soil (Albic Glossic Retisol (Aric, Loamic, Ochric)). In the experiment, two sampling methods were used - the classic sampling in pits, by 10-cm layers, and sampling with an auger to a depth of 0-30 cm. The soil bulk density was determined by the Kachinsky method and the carbon content was analyzed by the Tyurin method. Some samples were additionally analyzed at the Bryansk State Agrarian University. The uncertainties associated with natural variation, sample preparation and the analytical process proper were estimated. The analytical uncertainty of bulk density measurement did not depend on the sampling depth under the experimental conditions and amounted to about 6%. The analytical error of Tyurin's method did not differ in two laboratories. Its contribution reached 5-9% of the total variation in soil organic carbon content at the test plot. The uncertainty of sample preparation ranged from 11 to 26%, natural variation-from 49 to 68% to the total variance, respectively. Determination of carbon content in the samples taken with an auger from the depth of 0-30 cm is preferable than layer-by-layer sampling as the number of intermediate operations is fewer, and the obtained results are comparable.