Organic and inorganic carbon stock in soils of Rajasthan

Total carbon stock has been estimated in soils of Rajasthan, based on soil family association map on 1:250,000 scale and results are described in tenns of great groups. Extent and characteristics of each great group were abstracted from database of 375 map units and 150 soil profiles. Total carbon stock was 2130 Tg (1 Tg=10¹² g) in 0–100 cm soils, of which organic and inorganic carbon stocks were 1231 and 899 Tg, respectively. Soil organic and inorganic carbon contributed 58.9 and 41.1%, respectively in the total stock. Surface horizons (0–25 cm) contributed 31% in total carbon stock. Torripsamments, Haplocambids and Haplustepts together held 80% of total carbon and 86.9% of soil organic carbon stock. Haplocambids, Petrocalcids and Haplustepts together housed 72% of soil inorganic carbon. Organic carbon density was higher in Haplustalfs, Haplusterts, Haplustepts and Torripsamments, ranging from 4 to 7 kg m⁻², while its inorganic counterpart was higher in Petrocalcids, Haplocalcids, Haplogypsids and Torrifluvents, varying from 10 to 19 kg m⁻² in 0–100 cm soils. Mean organic carbon density under scrub vegetation for 0–100 cm soils was 203 kg km⁻² in central highlands and 14.0 kg km⁻² in western plain. Cropland in western plain had higher organic carbon density than the soils under scrub vegetation, while reverse was true for central highland. Inorganic carbon density was higher in soils used for single cropping than their counterparts under scrub vegetation and double cropping. Rainfall has significant (n = 150, p < 0.05) positive and negative relationship with organic and inorganic carbon density, respectively. Significant (n = 150, p < 0.05) negative inter-relationship between the two forms of carbon indicated an increase of one at the expense of the other.