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Title: Soil carbon content after 55 years of management of a Vertisol in central Texas

item Potter, Kenneth

Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2006
Publication Date: 11/30/2006
Citation: Potter, K.N. 2006. Soil carbon content after 55 years of management of a Vertisol in central Texas. Journal of Soil and Water Conservation Society. 61(6):338-343.

Interpretive Summary: Agricultural practices have resulted in changes in the amount of carbon stored in the soil profile. The most intensive tillage practices such as moldboard plowing have been thought to decrease soil carbon storage while less intensive management practices maintained or even increased the amount of carbon stored in the soil. A problem in assessing management effects on soil carbon is that change occurs very slowly and varies with different soil and climatic conditions. It is often difficult to determine initial soil properties half a century after management has been in place, which is why most studies have compared soil properties with different management practices. We located soil samples preserved fifty five years after sampling on an experimental farm. The samples were labeled in a manner that allowed us to determine the sites of the original sampling. We re-sampled those locations and compared the amount of soil carbon stored in the soil. Having initial soil properties and recent samples allowed a better interpretation of the effect of agricultural practices on soil carbon. Early agriculture, prior to the initial sampling in 1949, had greatly depleted soil organic carbon. Agricultural practices since 1949 had slightly increased soil carbon contents. Planting grass had a greater effect than row and small grain crops.

Technical Abstract: Management effects on soil physical properties are often difficult to determine because there is often no fixed starting point. Soil organic carbon was determined for a central Texas Vertisol (Udic Pellusterts) from archived samples from 1949 and recent samples taken in 2004. Existing management records were also useful to interpret the data. Five fields were sampled, representing an untilled native pasture, two previously tilled soils which had been planted to Bermuda grass, and two fields which had been in nearly continuous crop production for the 55 year time interval. Soil organic carbon was determined for depth increments of 0 to 15, 15 to 30, 30 to 60, 60 to 90 and 90 to 105 cm. The 1949 samples showed that the tilled soils had been seriously degraded of organic carbon by agricultural activities prior to 1949. More modern agricultural practices since 1949 have increased soil carbon concentration in the surface 15 cm. Returning the soils to grass production increased soil surface carbon contents at a faster rate than the conventional agricultural practices. Having archived samples greatly aided in interpreting the effects on management on the soil. [GRACEnet Publication]