Watts, Stuart Michael2019-12-092019-12-092020-05-01http://hdl.handle.net/2097/40325Agricultural practices such as added C inputs and adoption of no-till are known to increase soil organic C (SOC) near the soil surface; however, it is unclear if these effects persist at depth. A long-term experiment compared the effects of two tillage systems (no-till (NT) and conventional till (CT)) and N source on SOC in Mollisol planted with continuous corn (Zea mays L.) in central Kansas. The N sources included composted organic waste (OrgF), urea (MinF), and no N fertilizer addition (Ctrl). The soil profile to a depth of 120 cm was measured for soil organic C (SOC) and N, bulk density, dissolved organic C (DOC), and δ¹³C and δ¹⁵N. Soil organic C in the soil profile was expressed as equivalent soil mass. Soil organic C and N were higher in the surface 5 cm in NT compared to CT, but the reverse was true within the 5-15 cm soil layer. Dissolved organic carbon (DOC) and the δ¹³C and δ¹⁵N signatures reflected the effects of OrgF addition to a depth of 45 cm; however, effects on soil organic C stocks were only apparent in the surface 15 cm. Twenty-two years of OrgF increased SOC stocks in the 0-15 cm layer by 18.2 Mg C ha⁻¹ over Ctrl (-1.22 Mg C ha⁻¹) and MinF (2.24 Mg C ha⁻¹). In the profile (0-60 cm), all treatments lost SOC from the 1992 baseline except for NT OrgF (0.66 Mg C ha⁻¹). Conventionally tilled OrgF lost 7.49 Mg C ha⁻¹ suggesting that NT conserved the additional C inputs more than CT. Most of the losses were in the 30 to 60 cm layers where there was a buried A horizon. Within the 30-45 cm depth, NT OrgF decreased losses of SOC (-3.80 Mg C ha⁻¹) compared to CT OrgF (-12.9 Mg C ha⁻¹). In summary, surface management effects on soil C sequestration were confined to the surface 15 cm even with additional C inputs. Although DOC and δ¹³C was elevated with OrgF in the 15-45 cm depths, this did not result in sequestered C. In these annual cropping systems, considerations need to made for deep-rooted crops and rotations to deliver C inputs into the subsoil; however, this must include no-tillage as tillage loses the benefits of additional C inputs.en-US© the author. This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).http://rightsstatements.org/vocab/InC/1.0/Deep soil carbonTillageNitrogen fertilizerSoil carbon sequestrationNo-tillCompostThesis