Abstract. Links between erosion/sedimentation history and soil carbon cycling were examined in a highly erosive setting in Mississippi loess soils. We sampled soils on (relatively) undisturbed and cropped hillslopes and measured C, N, 14C, and CO2 flux to characterize carbon storage and dynamics and to parameterize Century and spreadsheet •4C models for different erosion and tillage histories. For this site, where 100 years of intensive cotton cropping were followed by fertilization and contour plowing, there was an initial and dramatic decline in soil carbon content from 1870 to 1950, followed by a dramatic increase in soil carbon. Soil erosion amplifies C loss and recovery: About 100% of the original, prehistoric soil carbon was likely lost over 127 years of intensive land use, but about 30% of that carbon was replaced after 1950. The eroded cropland was therefore a local sink for CO2 since the 1950s. However, a net CO2 sink requires a full accounting of eroded carbon, which in turn requires that decomposition rates in lower slopes or wetlands be reduced to about 20% of the upland value. As a result, erosion may induce unaccounted sinks or sources of CO2, depending on the fate of eroded carbon and its protection from decomposition.For erosion rates typical of the United States, the sink terms may be large enough (1 Gt yr -l, backof-the-envelope) to warrant a careful accounting of site management, cropping, and fertilization histories, as well as burial rates, for a more meaningful global assessment.
The objective of this study was to parameterize and implement the Century ecosystem model for an eroding, cultivated site near Senatobia, in Panola County, Mississippi, in order to understand the loss and replacement of soil organic carbon on an eroding cropland. The sites chosen for this study are located on highly eroded loess soils where USDA has conducted studies on rates of soil erosion. We used USDA sediment data from the study site and historical erosion estimates from the nearby area as model input for soil loss; in addition, inputs for parametization include particle-size data, climate data, and rainfall/runoff data that were collected and reported in companion papers. A cropping scenario was implemented to simulate a research site at the USDA watershed 2 at the Nelson Farm. Model output was compiled for comparison with data collected and reported in companion reports; interpretive comparisons are reported in b Harden et al, in press.
Conversion Factors Multiply by to obtain Length Centimeter, cm 2.54 inch Meter, m 3.281 foot Kilometer, km 0.6214 mile Area Hectare, ha 2.471 Acre Square meter, m 2 10.76 Square foot, ft 2 Mass Milligram, mg 3.52 X 10-5 Ounce (avdp), oz Gram, g 3.52 X 10-2 Ounce kilogram 2.205 Pound Megagram, Mg, metric ton 1.102 Ton (US, 2000 lb), ton Yield and Rate Milligrams per square meter 3.27 X 10-6 ounces per square foot Kilogram per hectare, kg ha-1 0.893 Pound per acre, lb acre-1 kilogram per hectare, kg ha-1 1.86 X 10-2 Bushel per acre, 48 lb, bu acre-1 Megagrams per hectare, Mg ha-1 2.24 Tons per acre, tons acre-1 Pressure Megapascal, Mpa (10
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