Storage of organic and inorganic carbon of biogenic origin in the soils of the parkland-prairie ecosystem

The objective of this study is to estimate the storage of biogenic C in the soils of the Weyburn-Virden map area, a 20,917 km2 parkland-prairie region in southeastern Saskatchewan between 49° and 50° N latitude, and 101$\sp\circ15\sp\prime$ and 104$\sp\circ00\sp\prime$ W longitude. The estimate includes both organic C and previously biogenic C stored in pedogenic carbonates. Quantitative data available on horizons, pedons and landscapes were scaled up to the regional level using soil survey data and maps. A soil organic C distribution map made from 186 catenas over the map area indicates Black soils in the northeastern of the study area have a high organic C storage, in the range of 15 to 24 kg m-2 gradually decreasing through a transitional area to a lower organic C in the range of 6 to 12 kg m-2 in the western part where Dark Brown and Solonetzic soils are dominant. Organic C stores in sandy and Solonetzic soils were less than medium and fine-textured Chernozemic soilsin the same general area. A total of 323 Tg organic C was estimated in soils to a 90-cm depth based on the organic C distribution map. About one third of this C was stored in the Ap horizons. To assess the effects of cultivation on organic C storage, four catenas that included Dark Brown Amulet and Solonetzic Brooking soils were studied. The native catena had a higher organic C store (129 Mg ha-1) compared to the cultivated catenas (114 Mg ha-1 for 90 y, 82 Mg ha-1 for 47 y and 69 Mg ha-1 for 27 y). The high organic C store in the catena with 90 y of cultivation appears to relate with the several periods of forage cropping in the recent past. X-ray diffraction analyses showed that pedogenic carbonates occur mainly as calcite, whereas lithogenic carbonates are mainly dolomite. The $\delta\sp{13}$3C values of $-$8.2 to $-$5.5% indicate that 70 to nearly 100% of the carbonates in the clay and fine silt fractions of Cca horizons is pedogenic, compared to 7 to 10% in the coarse silts, where the pedogenic carbonates mainly occur as surface coatings. A carbonate distribution map based on the CaCO3 contents of 67 pedons over the map area indicated that carbonate storage in Black soils in the northeast ranged from 330 to 410 kg m-2, compared to 80-250 kg m-2 in Dark Brown and Solonetzic soils of the western regions. (Abstract shortened by UMI.