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

ABSTRACT:

Management's effects on soil physical properties can be difficult to determine because there is often no fixed starting point. Soil organic carbon was determined for central Texas Vertisols (Udic Haplusterts) on archived samples from 1949 and samples taken in 2004. Management records were used to interpret the data. Five fields were sampled, representing an untilled native pasture, two previously tilled soils which had been planted to Bermuda grass (Cynodon dactylon (L.) Pers.) for 55 and 39 years before the 2004 sampling period, and two fields which had been continuously cropped for nearly the entire 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 (0 to 6, 6 to 12, 12 to 24, 24 to 36 and 36 to 42 in). The tilled soils had been seriously degraded of organic carbon by agricultural activities prior to 1949 compared to the native pasture soil. Soil carbon concentration in croplands had decreased from greater than five percent near the surface of native grasslands to less than one percent in croplands. Agricultural practices since 1949 have increased soil carbon concentration in the surface 15 cm (6 in) to 1.45 percent in croplands and 2.09 percent in restored grasslands. 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. It appears that previous estimates of carbon sequestration rates for the Vertisols may have been under estimated by comparative studies of no-till and conventional tillage practices.