Established no-till systems present a challenging limitation because soil organic carbon (SOC) accumulates mostly in the top 5 cm and most of the soil quality improvement occurs in this surface soil layer. Occasional tillage for no-till systems is proposed as a single, one-time tillage, conducted once in 12 or more years, to invert the high SOC surface layer with less improved deeper soil. This also presents an opportunity to apply and incorporate lime or manure for further improvement of the soil. We hypothesize that occasional tillage will result in increased SOC in the long term, even though significant short-term C losses may occur following tillage. Two experiments in long-term NT fields were installed under rainfed corn or sorghum rotated with soybeans in Eastern Nebraska. Tillage treatments were done in spring or fall and include: continuous no-till, tandem disk, 10-cm wide twisted shank-chisel, moldboard plow and mini-moldboard plow. A portable infrared gas analyzer (Li-Cor 6200) with a 980-cm3 chamber was used to monitor carbon dioxide (CO2) efflux before and immediately after tillage and continuing up until planting. Profile distribution of SOC, particulate organic C (POC) and active C have been assessed on samples taken at planting time at the 0-2.5, 2.5-5.0, 5.0-10, 10-20, and 20-30 cm depths. Some tillage operations effectively redistributed total and labile organic C with negligible CO2 losses when compared to the undisturbed continuous no-till.
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