Carbon storage after long-term grass establishment on degraded soils

Recent concern about global warming has led to attempts to estimate the effects of management on carbon sequestration in soil. The objective of this study is to determine the amount of soil organic carbon (SOC) degraded by agricultural practices and the rate of carbon sequestration in soils after restoration of grass for various periods of time. The SOC contents of previously cultivated clay soils (Udic Haplusterts) in central Texas returned to grass 6, 26, and 60 years ago are compared with those of soils in continuous agriculture for more than 100 years and those of prairie soils that have never been tilled. Surface (0 to 5 cm) SOC concentration ranged from 4.44 to 5.95% In the prairie to 1.53 to 1.88% in the agricultural sites. Carbon concentration in restored grasslands was generally intermediate to that reported for the native prairie and agricultural sites. The SOC mass in the surface 120 cm of the agricultural soils was 25 to 43% less than that of native prairie sites. After the establishment of grasses, SOC mass in the grass sites was greater than at the agricultural sites. A linear relationship between the length of time in grass and the amount of SOC sequestered in the surface 60 cm Gt well for time periods from 6 to 60 years. The slope of this function provided an estimate of the carbon sequestration rate, in this case 447 kg C ha(-1) yr(-1), At this rate, it would require nearly an additional century (98 years) for the 60-year grass site to reach a carbon pool equivalent to that of the prairie.