Estimation of soil organic carbon stock in the Republic of Serbia

Spatial distribution of soil organic carbon (SOC) was investigated in the soils of the Republic of Serbia. Organic carbon stocks were estimated for soil layers 0-30 cm and 0-100 cm. The database included a total of 1,140 soil profiles. Soil map of the Republic of Serbia was adapted to the WRB classification and divided into 15,437 polygons (map units). We calculated the SOC stock values for each reference soil group based on mean values of SOC at 0-30 and 0-100 cm and their areas. Based on the size of the reference groups, total area of the Republic of Serbia, and the mean SOC values for each reference group, we calculated the total SOC stocks. Database was established in the period 2009-2011. Presently, the database includes a total of 1,140 soil profiles which involve 4,335 horizons. Data that comprise the database for analytical study were collected in the period 1962-2010. Using Soil Map of Serbia, areas of the main WRB reference soil groups were defined. Total values of organic carbon stocks for these reference groups were calculated on the basis of the mean values of organic carbon content at 0-30 cm and 0-100 cm and the area of each reference group. The database does not contain the results for organic carbon stocks in the following reference groups: Anthrosol, Calcisol, Histosol, Phaeozem, Podzol and Umbrisol. For the calculation of organic carbon stocks in these groups, we used values which represented the arithmetic means for all reference groups at 0-30 cm and 0-100 cm expressed in t ha-1. The calculated data indicated that there existed a great variability in the content of organic carbon among the reference soil groups. The largest SOC stocks for the soil layers 0-30 cm were found in Cambisol 194.76 x 1012 g and Leptosol 186.43 x 1012 g, and for the soil layers 0-100 cm in Cambisol 274.87 x 1012 g and Chermozem 230.43 x 1012 g. The highest mean values of organic carbon content were found in the reference group Leptosol - 151.33 t ha-1 and 178.95 t ha-1 for the depths of 0-30 cm and 0-100 cm, respectively. The analysis of the coefficients of variation indicated that the mean values were not sufficiently representative for that group (CV > 50%). The lowest mean values of organic carbon content were found in the reference group Arenosol - 41.78 t ha-1 and 96.03 t ha-1 for the depths of 0-30 cm and 0-100 cm, respectively. The analysis of the coefficients of variation showed that the mean values were sufficiently representative for this group (CV <50%). The research showed that the values of organic carbon content had highest variability in the reference groups Leptosol and Regosol. The result obtained on the basis of the compound area of the reference soil groups and the area of the Republic of Serbia (77,474 km2) indicated that the organic carbon stocks at 0-30 cm and 0-100 cm were 705.84 x 1012 g and 1,159.55 x 1012 g, respectively. The mean values for the main reference groups were 89.60 t ha-1 and 145.69 t ha-1 for the depths of 0-30 cm and 0-100 cm, respectively. The map of organic carbon distribution per soil type, at 0-30 cm, showed that largest organic carbon stocks were present in Central Serbia (southern part). In the north of the country, in Vojvodina Province, the region with the most intensive agricultural production, the organic carbon content at 30 cm was mostly low, amounting to 1.93%. The most common soil type in this part of the country is Chernozem, which covers 57.9% of the area. The values of organic carbon content for this reference group, at 30 cm, ranged from 7.89 to 133.51 t ha-1, with the mean value of 73.82 t ha-1. The organic carbon content at 100 cm ranged from 24.21 to 341.37 t ha-1, with the mean value of 168.20 t ha-1. The obtained values indicated that Chernozems have a greater depth of the humus horizon (Ah), which went up to 100 cm, then Cambisols with the humus horizon up to the depth of 60 cm. The compilation of data on organic carbon stocks and its distribution in the different soil reference groups is the first step in the evaluation and monitoring of changes of organic carbon stocks in the soils of Serbia.