Carbon storage after long-term grass establishment on degraded soils

Recent concern about global warming has led to attempts to estimate the eff ects of management on carbon sequestration in soil. The objective of this s tudy is to determine the amount of soil organic carbon (SOC) degraded by ag ricultural practices and the rate of carbon sequestration in soils after re storation of grass for various periods of time. The SOC contents of previou sly cultivated clay soils (Udic Haplusterts) in central Texas returned to g rass 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 n ever 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 co ncentration in restored grasslands was generally intermediate to that repor ted for the native prairie and agricultural sites. The SOC mass in the surf ace 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 s ites was greater than at the agricultural sites. A linear relationship betw een the length of time in grass and the amount of SOC sequestered in the su rface 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 cas e 447 kg C ha(-1) yr(-1), At this rate, it would require nearly an addition al century (98 years) for the 60-year grass site to reach a carbon pool equ ivalent to that of the prairie.