Carbon stock and organic carbon dynamics in soils of Rajasthan, India

Abstract

Soil carbon stock (CS), was estimated in the 0–25 and 0–100 cm soil depths of arid and semi-arid regions of Rajasthan. Carbon stock was 2.13 Pg in the 0–100 cm soil depth, of which 1.23 Pg was soil organic carbon and 0.90 Pg was soil inorganic carbon. The surface horizon (0–25 cm) stored 31% of the soil carbon stock. Soil carbon stocks were higher in Entisols (0.72 Pg or 33.6% of CS on 43.6% of the land area) and Aridisols (0.70 Pg or 32.7% of CS on 28.9% of the land area) than in Inceptisols (0.61 Pg or 28.6% of CS on 24.01% of the land area), Alfisols (0.015 Pg or 0.007% of CS on 0.76% of the land area) and Verisols (0.105 Pg or 0.005% of the CS on the 3.2% of the land area). Torripsamments, Haplocambids and Haplustepts together held 80% of CS and 86.9% of soil organic carbon stock, whereas Haplocambids, Petrocalcids and Haplustepts comprised 72% inorganic carbon stock. Soil organic carbon density (SOC) ranged from 4000 to 7000 kg/km2 in Haplustalfs, Haplusterts, Haplustepts and Torripsamments, while its inorganic counterpart (SIC) was of higher range (10,000–19,000 kg/km2) in Petrocalcids, Haplocalcids, Halpogypsids and Torrifluents. Under scrub vegetation of semi-arid Rajasthan the mean SOC in the 0–25 cm and 0–100 cm depths were 170 and 203.9 kg/km2, respectively. In the arid region with similar situation the mean SOC was 5.5 and 14.0 kg/km2, respectively. Excessive tillage and intensive cultivation in semi-arid region reduced soil organic carbon density from 60 kg/km2 under single cropping to 10.5 kg/km2 under double cropping. Subsistence farming in the arid region maintained 47 kg/km2 SOC under croplands. SOC declined regularly from 1975 to 2002 in the arid region. A multiple linear regression model that includes rainfall together with tillage, silt, clay, available water capacity (AWC) and period of canopy cover accounted for 97% of the variation in soil organic carbon density for arid regions. The regression model further pointed out that a 4200–4600 kg/km2/year SOC could be sequestered in untilled soils of the arid region, which have year-round canopy cover.