Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 30, 1999
Publication Date: October 20, 1999
Citation: Potter, K.N., Torbert, H.A., Johnson, H.B., Tischler, C.R. Carbon storage after long-term grass establishment on degraded soils. Soil Science. 1999. v. 164. p. 718-725. Interpretive Summary: Soil organic carbon content is important for agricultural production, water quality, and atmospheric carbon dioxide balance. Soils have been degraded by many years of tillage for agricultural production and by erosion. One potential method of increasing soil carbon is planting degraded soils to grass, but the rate of carbon accumulation is not known. Knowing the rate of carbon storage is particularly important if landowners are to be paid to store carbon. In this study, we measured the amount of organic carbon in soils at three sites in central Texas that have never been tilled, soils which have been tilled for over 100 years, and soils that had previously been tilled for long periods, but which have since been planted to grass. The length of time in grass was 6 years, 26 years, and 60 years. The cultivated soils contained 30 to 40% less carbon in the surface 60 cm than the never tilled prairie soils. Returning the soils to grass increased the soil organic carbon content at an average rate of 447 kg C ha**-1 yr**-1. At this rate, there is potential carbon storage for nearly a century before the oldest grass site contains as much carbon as the native prairie.
Technical Abstract: Recent concern about global warming has led to attempts to estimate the the effects of management on carbon sequestration in soil. The objective of our 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 to those of soils in continuous agriculture for more than 100 years and to those of prairie soils which have never been tilled. Surface (0.05 m) 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 those reported for the native prairie and agricultural sites. The SOC mass in the surface 1.2 m of the agricultural soils was 25% to 43% less than that of native priaire sites. After the establishment of grasses, SOC mass in the grass sites were greater than those at the agricultural sites. A linear relationship between the length of time in grass and the amount of SOC sequestered in the surface 0.6 m fit 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.