Crop species and tillage effects on carbon sequestration in subsurface soil
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Crop species and conservation tillage may enhance carbon (C) and nitrogen (N) sequestration potential in subsurface soils. The objectives of this study were to determine the effects of crop species and tillage on soil organic C (SOC) and total N distribution in six soil depth intervals from 0 to 105 cm after 20 years of treatment imposition. Tillage had the most influence on soil C and N at 0 to 5 cm, and impacts extended to the 15- to 30-cm depth for wheat and sorghum. Overall, SOC and total N for wheat were 18 and 15% higher than sorghum and soybean. Dissolved organic C (DOC) depth distribution was similar to SOC and total N. The proportion of SOC as DOC ranged from 1.3 to 3.3% and increased with soil depth. The highest soil C and N levels occurred for wheat under no tillage. The depth of soil impacted by crop species was shallower for conventional tillage than no tillage, and the depth distribution exhibited a logarithmic pattern. Soil organic C, total N, and DOC decreased 404, 507, and 205%, respectively from 0-5 to 80-105 cm. The maximum depth interval below which no further decreases in SOC and total N occurred was 30 to 55 cm for soybean, 55 to 80 cm for wheat, and 80 to 105 cm for sorghum, demonstrating the importance of subsurface soils for C sequestration. Crop management impacts below the depth of tillage demonstrate the importance of crop rooting and belowground biomass, or translocation of dissolved organic matter, to subsoil C sequestration. Copyright 2007 by Lippincott Williams & Wilkins Inc.
