SOIL CARBON POOLS IN CENTRAL TEXAS: PRAIRIES, RESTORED GRASSLANDS, AND CROPLANDS

Authors: Potter, Kenneth; Derner, Justin

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2006
Publication Date: 5/15/2006
Citation: Potter, K.N., Derner, J.D. 2006. Soil carbon pools in Central Texas: prairies, restored grasslands, and croplands. Journal of Soil and Water Conservation. 61(3):124-128.

Interpretive Summary: Soil quality depends to a large extent upon the amount of organic matter present in the soil. Organic matter is a source of plant nutrients, helps to hold plant available water in the soil, and helps bind soil into aggregates that can improve soil water infiltration and gas exchange with the atmosphere. Organic matter is often measured by the amount of carbon it contains. Losses or gains of organic matter often depend upon the size of the particles. Larger particles decompose faster while the smaller particles are more resistant to decomposition. We measured the amount of carbon in three groups of soils with different histories. One group had never been tilled and is referred to as the native grassland. The second group had a long history of tillage and was referred to as the agricultural soil. The third group had previously been tilled and then restored to grass and was referred to as the restored grassland. The native grassland had the largest amount of large and small particles of organic matter throughout the surface 40 cm. The agricultural soils had between 40 to 60 % as much organic matter as the native grassland. More of the agricultural soil organic matter was in the smallest size fraction. The restored grassland had about the same amount of organic matter in the profile as the agricultural soil, but more was in the larger size fraction in the surface 10 cm of the soil. The carbon size fraction pools is changing, but has not resulted in a larger total amount of carbon in the soil.

Technical Abstract: Establishment of perennial grasses on degraded soils has been suggested as a means to improve soil quality and sequester carbon in the soil. Particulate organic carbon (POC) may be an important component in the increased soil carbon content. We measured POC (defined as organic carbon in the 53 to 2000 µm size fraction) and mineral associated organic carbon (MAC) (defined as the less than 53 µm size fraction) at tree locations in central Texas. Each location had an untilled native grassland, a long-term agricultural site and a restored grassland. Organic carbon pool sizes varied in the surface 40 cm of native grassland, restored grasslands and agricultural soils. The native grasslands contained the largest amounts of total organic carbon (TOC), while the restored grasslands and agricultural soils contained similar amounts of TOC. Both POC and MAC pools were reduced in the restored grass and agricultural soils compared to the native grassland soils, even beyond the depth of tillage. The restored grassland soils had a larger POC content than the agricultural soils, but the increase in POC was limited to the surface 10 cm of soil. Trends in POC accumulation over time from 9 to 30 years were not significant in this study. [GRACEnet Publication]