Long-Term Tillage Impacts on Soil Aggregation and Carbon Dynamics under Wheat-Fallow in the Central Great Plains

Long-term conservation tillage improves soil quality by enhancing soil structure, improving water availability, and reducing soil erosion. We investigated the effect of tillage intensity on soil organic carbon (SOC), organic carbon fractions, particulate organic matter (POM), and wet aggregate-size distribution after 39 yr of management. The data reported here were taken from a long-term tillage study initiated in 1967 near Akron, CO. Treatments sampled were conventional tillage (CT), moldboard plow (MP), no-tillage (NT), and reduced tillage (RT). In 2006, soil samples were collected from the 0- to 5-, 5- to 10-, 10- to 20-, 20- to 30-, and 30- to 60-cm depths in winter wheat (Triticum aestivum L.)-summer fallow (WF). Soils were fractionated for aggregate mass and POM-mineral-associated carbon (C) to evaluate the form and stability of SOC. On a fixed-depth basis, NT and RT had 21% more SOC, at the 0- to 30-cm depth than CT and MP. However, on equivalent mass basis (ESM), SOC was greater with NT, MP, and RT by 11% compared with CT. Conservation practices, NT and RT, had more macroaggregation and consequently greater soil stability compared with CT and MP. Tillage practices significantly impacted whole SOC distribution between POM-C and mineral-associated organic matter C (MAOM-C). The POM-C vs. MAOM-C component of the whole SOC was 23 vs. 77% at 0 to 5 cm and 10 vs. 90% at 5- to 20-cm depth. The POM-C associated with NT and RT, accounted for 17% of SOC where POM-C accounted for 12% of SOC with CT and MP at 0- to 20-cm depth. Redistribution and stratification of SOC, POM, and POM-C were observed especially with MP. Over all, we found the application of conservation tillage practices to be crucial for maintaining soil quality and soil C stock in the WF systems of the central Great Plains.